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Time-Resolved Resonance Raman Spectroscopy of Diphenylacetylene: Structures and Dynamics of the Lowest Excited Triplet State, Radical Cation, and Radical Anion
Abstract
Time-resolved resonance Raman spectra of the lowest excited triplet state, T{sub 1}, the radical cation, R{sup {sm_bullet}+}, and the radical anion, R{sup {sm_bullet}{minus}}, of diphenylacetylene (DPA) have been measured. Vibrational assignments of the Raman bands of these transients have been based on the frequency shifts on phenyl deuterations and {sup 13}C substitution of the C{triple_bond}C triple bond. The Raman spectra have shown that the C{triple_bond}C stretch exhibits large low-frequency shifts in the order, S{sub 0} (2217 cm{sup {minus}1}), R{sup {sm_bullet}+} (2142 cm{sup {minus}1}), R{sup {sm_bullet}{minus}} (2091 cm{sup {minus}1}), and T{sub 1} (1972 cm{sup {minus}1}), indicating that the C{triple_bond}C triple bond weakens dramatically in this sequence. The same trend, though not large, has been observed for phenyl skeletal vibrations as well. The dependence of the yield of R{sup {sm_bullet}+} on the pump laser power has revealed that the photoionization of DPA to produce R{sup {sm_bullet}+} is a biphotonic ionization can occur through the T{sub 1} state. 21 refs., 10 figs., 1 tab.
... Temperaturabhängige TA-Messungen [259] langlebigen Triplett-Zustands steht, geschlossen. [259] Struktursensitivere IR- [266,267] und Raman-Experimente [260,264,265,267] [250,252] womit zur Population des A u -aus dem B 1u -Zustand eine energetische Barriere überwunden werden muss. Dadurch kann sowohl die temperaturabhängige Lebensdauer des B 1u -Zustands, [259] als auch die bei höheren Anregungsenergien ausbleibende Fluoreszenz [262,263] [262,263] in denen niederfrequente Schwingungsmoden hohe Fluoreszenz-Quantenausbeuten und damit lange Lebensdauern zeigten, höher angeregte vibronische Zustände ebenso wie in mit ns-Laserpulsen durchgeführten REMPI-Experimenten [262] hingegen jedoch nicht detektiert werden konnten. ...
... sowie einen Quantendefekt von δ = 0.37 (für n = 3) offenbarten, unterstützt. Der A u -Zustand relaxiert schließlich in einen langlebigen B 1u -Triplett-Zustand [259,268] mit linearer D 2h -Geometrie, [260] dessen Nullpunktsenergie mittels Phosphoreszenz-Messungen auf 2.72 eV bestimmt wurde. [268] In den zeitaufgelösten Photoelektronen-Imaging-Experimenten wird bei langen Verzö- [269] /def2-TZVPP [275] ) ...
... konnten das postulierte Relaxationsmodell bestätigen und anhand der Schwingungsfrequenz der zentralen C-C-Bindung weitere Einblicke in die Struktur der involvierten Zustände liefern: Direkt nach Anregung des B 1u -Zustands liegt die C≡C-Schwingungsenergie bei 2099 cm −1 ,[264,265] bei langen Verzögerungszeiten (> 100 ns) hingegen bei 1970 cm −1 .[260] Damit ist die C≡C-Bindungsstärke sowohl im B 1u -, als auch im final populierten Triplett-Zustand im Vergleich zu Tolan-Molekülen ...
Das erste Ziel der vorliegenden Dissertation bestand darin, ein bereits bestehendes TOF-MS-Setup dahingehend zu erweitern, um damit Velocity Map Imaging-Experimente durchführen zu können. Dies erforderte zunächst die Konzipierung und Programmierung einiger für die Datenaufnahme, -verarbeitung und -analyse benötigter LabView-Anwendungen. Anschließend konnten erste Kalibrierexperimente an Methyliodid, in denen wichtige experimentelle Parameter identifiziert und optimiert wurden, durchgeführt werden. Außerdem gelang es dadurch, die Messgenauigkeit des Setups auf 0.7 % und dessen Auflösungsvermögen auf 4.4 % zu bestimmen, was im Bereich für VMI-Apparaturen typischer Werte liegt. Zur weiteren Überprüfung der Funktionstüchtigkeit des Setups wurde in ersten zeitaufgelösten Experimenten im Folgenden die Desaktivierung des S1-Zustands von Pyridin untersucht. Neben der Reproduktion einiger bereits literaturbekannter Resultate konnten dabei zusätzlich die im Multiphotonen-Ionisationsschritt populierten Rydberg-Zustände identifiziert werden. Anschließend wurde mit Experimenten an bisher weniger gut untersuchten organischen Aromaten und Heteroaromaten fortgefahren. Das Ziel dieser Studien lag in der Aufklärung der photoinduzierten Dynamiken der Verbindungen, wobei das zur Verfügung stehende ps-Lasersystem die Möglichkeit bot, die Desaktivierung elektronisch angeregter Zustände gezielt in Abhängigkeit von deren Schwingungsenergie zu untersuchen. Der darin bestehende Vorteil zeigte sich vor allem in Studien an Tolan und Phenanthridin, deren erste angeregte, optisch aktive Zustände am Origin Lebensdauern im ns-Bereich aufweisen, die sich mit zunehmender vibronischer Anregung jedoch auf bis zu 10 ps verringern. Als Grund dafür konnten nichtstrahlende Desaktivierungsprozesse, für deren Eintreten eine energetische Barriere überwunden werden muss, identifiziert werden. Während in Tolan nach Photoanregung ein Übergang in einen (πσ∗)-Zustand, der zur Ausbildung einer trans-bent-Struktur führt, erfolgt, ist im Falle von Phenanthridin vermutlich ein El-Sayed-erlaubter ISC-Übergang in einen 3(nπ∗)-Zustand für die drastische Verkürzung der S1-Lebensdauer verantwortlich. Ein solcher konnte weder im zu Phenanthridin isomerischen Benzo[h]quinolin, noch in dessen PAH-Muttermolekül Phenanthren beobachtet werden, was auf die höhere energetische Lage bzw. die Abwesenheit des mittels ISC populierten 3(nπ∗)-Zustands in diesen Molekülen zurückgeführt werden kann. In weiteren im Rahmen der vorliegenden Arbeit durchgeführten Experimente wurden zudem die aromatischen Moleküle Acenaphthylen und 4-(Dimethylamino)benzethin (DMABE) untersucht. Zeitaufgelöste Studien zeigten dabei, dass die Desaktivierung der S2-Zustände beider Moleküle auf der sub-ps-Zeitskala stattfindet und mit dem vorhandenen Lasersystem daher nicht aufgelöst werden kann. In Acenaphthylen erfolgt die S2-Relaxation größtenteils über einen sequentiellen IC-Mechanismus, innerhalb dem der S1-Zustand des Moleküls intermediär besetzt wird. Dessen Lebensdauer konnte am Origin auf 380 ps bestimmt werden, fällt mit steigender Schwingungsanregung jedoch auf bis zu 55 ps ab. Für die Desaktivierung des S2-Zustands von DMABE konnte hingegen ein paralleles Relaxationsmodell, in dem neben dem S1-Zustand ein weiterer elektronisch angeregter Zustand populiert wird, nachgewiesen werden. Bei diesem könnte es sich möglicherweise um einen (πσ∗)-Zustand, dessen Besetzung die Ausbildung einer trans-bent-Geometrie innerhalb der Acetylen-Einheit des Moleküls zur Folge hat, handeln. Einen weiteren großen Teil der vorliegenden Dissertation nahmen Experimente an van-der-Waals-gebundenen Clustersystemen ein. Im Fokus der Studien standen dabei Moleküle mit ausgedehnten aromatischen π-Systemen, da solche eine hohe Relevanz für verschiedene materialwissenschaftliche Forschungsgebiete besitzen. Ein Beispiel hierfür ist Tetracen, welches als Modellsystem für die Untersuchung von Singlet Fission-Prozessen angesehen wird. In Kombination mit nichtadiabatischen Surface-Hopping-Simulationen zeigten Experimente an Tetracen-Dimeren, dass nach deren S2-Anregung zunächst ein schneller S1←S2-Übergang (τ < 1 ps), gefolgt von der Ausbildung einer Excimerstruktur, stattfindet. Letztere erfolgt mit einer Zeitkonstante von 62 ps und führt zu einem Anstieg des transienten Ionensignals, wohingegen die Desaktivierung des Excimer-Zustands von einem abklingenden Signalbeitrag mit τ = 123 ps repräsentiert wird. Wenngleich über die weitere Relaxation der Excimerspezies zum gegenwärtigen Zeitpunkt keine Aussage getroffen werden kann, besteht damit die Möglichkeit, dass Excimer-Zustände als Zwischenstufe im SF-Mechanismus isolierter Tetracen-Dimere auftreten. In zeitaufgelösten Experimenten an Phenanthren-Dimeren konnte ebenfalls ein Anstieg des transienten Signals mit einer vergleichbaren Zeitkonstante von τ = 86 ps, der jedoch auf einem konstanten Signaloffset endet, gefunden werden. Dies deutet darauf hin, dass auch Phenanthren-Dimere in der Lage sind, Excimerstrukturen, die im Gegensatz zu denen des Tetracens jedoch deutlich langlebiger sind, auszubilden. Studien an den Dimerspezies der Azaphenanthrene Benzo[h]quinolin und Phenanthridin offenbarten hingegen etwas schnellere Relaxationen mit Zeitkonstanten von 15 bzw. 40 ps. Zudem zeigten beide Spezies eine stark ausgeprägte Fragmentation, sodass für deren Untersuchung auf die VMI-Detektionsmethode zurückgegriffen werden musste. Dadurch wurde deutlich, dass sich Photoionen-Imaging-Experimente hervorragend für Studien an schwach gebundenen Clustersystemen eignen, da diese die Separation verschiedener Signalbeiträge innerhalb eines betrachteten Massenkanals ermöglichen.
... Careful assignment of different crystal vibrational modes was identied according to the available references of diphenylacetylene in Fig. 1(c). [32][33][34][35][36] Before 10.1 GPa, all the peaks exhibit blue-shied under increasing pressure, indicating that the bond length becomes shorter and the vibration becomes stronger under high pressure. Aer 10.1 GPa, the peak of C^C vibration (2223 cm À1 at 1.2 GPa) splits into a new broader peak. ...
Organic solar cells have become an important development direction in solar cell materials because of their low cost, light weight, and good flexibility. However, the size of their bandgap is difficult to continuously regulate, resulting in a low power conversion efficiency. In this work, an organic molecule TPEPA was synthesized, and its luminescence performance and polymerization under high pressure were studied by performing in situ Raman, IR, fluorescence, and UV-vis spectroscopy. The Raman and IR spectroscopic results show that single bonds (C-H, C-Ph) and long chains (C-C[triple bond, length as m-dash]C-C) are more unstable and prone to amorphization under high pressure. At 10 GPa, the TPEPA molecule undergoes a transition of amorphization accompanied by a few polymerizations in the C[triple bond, length as m-dash]C bond structure. After holding pressure at 20 GPa for one day and releasing to ambient pressure, the other peaks almost disappeared, while the new peak of C(sp3)-H from the polymerization of the benzene ring was observed, indicating that the irreversible amorphization and polymerization did occur. UV-vis spectra results show that the bandgap is reduced from 2.9 eV to 1.3 eV, which is just in the maximum conversion efficiency bandgap range (1.3-1.4 eV) of p-n junction solar cell materials. This pressure is within the working pressure range of a large volume press, which is favorable in applications of large-scale synthesis. Our strategy may provide a method for the large-scale synthesis of novel organic solar cell materials.
Photo‐initiated intramolecular charge transfer (ICT) processes play a pivotal role in the excited state reaction dynamics in donor‐bridge‐acceptor systems. The efficacy of such a process can be improved by modifying the extent of π‐conjugation, relative orientation/twists of the donor/acceptor entities and polarity of the environment. Herein, 4‐dimethylamino‐4′‐cyanodiphenylacetylene (DACN‐DPA), a typical donor‐π‐bridge‐acceptor system, was chosen to unravel the role of various internal coordinates that govern the extent of photo‐initiated ICT dynamics. Transient absorption (TA) spectra of DACN‐DPA in n‐hexane exhibit a lifetime of >2 ns indicating the formation of a triplet state while, in acetonitrile, a short time‐constant of ∼2 ps indicates the formation of charge transferred species. Ultrafast Raman loss spectroscopy (URLS) measurements show distinct temporal and spectral dynamics of Raman bands associated with C≡C and C=C stretching vibrations. The appearance of a new band at ∼1492 cm⁻¹ in acetonitrile clearly indicates structural modification during the ultrafast ICT process. Furthermore, these observations are supported by TD‐DFT computations.
We present herein an in‐depth study of complexes in which a molecule containing a boron‐boron triple bond is bound to tellurate cations. The analysis allows the description of these salts as true π complexes between the B−B triple bond and the tellurium center. These complexes thus extend the well‐known Dewar‐Chatt‐Duncanson model of bonding to compounds made up solely of p block elements. Structural, spectroscopic and computational evidence is offered to argue that a set of recently reported heterocycles consisting of phenyltellurium cations complexed to diborynes bear all the hallmarks of π‐complexes in the π‐complex/metallacycle continuum envisioned by Joseph Chatt. Described as such, these compounds are unique in representing the extreme of a metal‐free continuum with conventional unsaturated three‐membered rings (cyclopropenes, azirenes, borirenes) occupying the opposite end.
Tolane (diphenylacetylene, C14H10) was studied by picosecond time-resolved photoionisation and photoelectron imaging in a supersonic jet. The low-energy part of the 1B1u <- S0 REMPI spectrum is very similar to an earlier LIF spectrum, however additional bands were observed at higher energies above the fluorescence cut-off. For a number of bands the dynamics were investigated via pump-probe photoionisation and photoelectron spectroscopy. Around the B1u origin the lifetimes are in the ns range, but they drop to some 10 ps at higher excitation energies. For the short-lived bands at higher energies a sequential two-step relaxation to a long-lived electronic state was observed that proceeds via an intermediately populated state with a lifetime of 100-200 ps. By comparison with previous quantum chemical calculations we assign this state as the biradicalic trans-bent 1Au state that is ionised in a two-photon process.
The initial studies of the dynamics of photoinduced charge separation conducted in our laboratories 20 years ago found strongly distance-dependent rate constants over short distances but failed to detect intermediates in the transport of positive charge (holes). These observations were consistent with the single-step superexchange or tunneling mechanism that had been observed for numerous donor–bridge–acceptor systems at that time. Subsequent studies found weak distance dependence for hole transport over longer distances in DNA, characteristic of incoherent hopping of either localized or delocalized holes. The introduction of synthetic DNA capped hairpin constructs possessing hole donor and acceptor chromophores (or purine bases) at opposite ends of a base-pair domain made it possible to determine the time required for transit of charge from one chromophore to the other and, in some cases, to distinguish between the transit time and the much faster initial charge injection time. These studies eliminated conventional tunneling as a viable mechanism for charge transport in DNA except at very short donor–acceptor separations; however, they did not establish the presence or nature of intermediates in the charge separation process.
Steady state spectroscopy, femtosecond transient absorption spectroscopy (fsTA), and femtosecond stimulated Raman spectroscopy (FSRS) of DNA mini-hairpins possessing a diphenylacetylenedicarboxamide (DPA) linker and 1-3 adenine-thymine (A-T) or guanine-cytosine (G-C) base pairs have been investigated. Ultraviolet and circular dichroism (UV and CD) spectra are consistent with ground state conformations that are predominantly base-paired and -stacked for conjugates possessing two or three base pairs; however, they offer no information concerning the conformation of conjugates possessing a single base pair. fsTA spectra are indicative of -stacked structures excepted in the case of the conjugate possessing a single G-C base pair. All of the conjugates display transient absorption bands characteristic of the DPA-. anion radical. Conjugates possessing two or three G-C base pairs display a transient absorption band characteristic of the short-lived G+. cation radical. The mini-hairpins with 1-3 A-T base pairs do not display the transient absorption band characteristic of the (An+.) polaron. This implies that an A-tract with three base pairs is too short to support polaron formation.
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The excited state behavior of DNA hairpins possessing a diphenylacetylenedicarboxamide (DPA) linker separated from a single guanine‒cytosine (G‒C) base pair by zero-to-six adenine‒thymine (A‒T) base pairs has been investigated by a combination of femtosecond and nanosecond transient absorption spectroscopy and femtosecond stimulated Raman spectroscopy. In the case of hairpins with zero or one A‒T base pair separating DPA and G, formation of both DPA anion radical (DPA-•) and G cation radical (G+•) are directly observed and characterized by their transient absorption and stimulated Raman spectra. For hairpins with two or more intervening A‒T base pairs, the transient absorption spectra of DPA-• and the adenine polaron (An+•) are observed. In addition to characterization of the hole carriers, the dynamics of each step in the charge separation and charge recombination process as well as the overall efficiency of charge separation have been determined, thus providing a complete account of the mechanism and dynamics of photoinduced charge transport in these DNA hairpins.
Developments of three new time-resolved vibrational spectroscopies and their applications to electronically excited states are reviewed. Transform-limited picosecond time-resolved Raman spectroscopy has been used to study the vibrational dynamics of trans-stilbene in the lowest excited singlet state. Picosecond time-frequency two-dimensional multiplex Coherent Antistokes Raman Scattering spectroscopy has been used to probe the structure of diphenylacetylene in the lowest and the second lowest excited singlet states. Nanosecond time-resolved dispersive infrared spectroscopy has detected the singlet and triplet intramolecular charge transfer states of 4-(di-nethylamino)benzonitrile. Strong evidence for a charge transfer structure has been obtained.
Recent spectroscopic as well as quantum-mechanical studies on the structure and dynamics of electronically excited diphenylacetylene are critically reviewed with an emphasis placed on the effect of the environment.
Slow crystallization and fast precipitation of a tetrazole-substituted diphenylacetylene derivative (MPT) led to formation of solids with significantly different photoluminescence efficiencies of 0.06 and 0.33, respectively. A detailed study of the photophysical properties of solutions of MPT as a function of concentration and temperature indicated that the extent of formation of J- and H-aggregates played a significant role in determining the luminescence properties of these materials. Time-resolved emission spectroscopy showed that the lifetime of emission arising from the aggregated species was significantly higher than that of the monomer species. The long-lived emission might be due to the formation of excimer arising from the excitation of ground state J- and H-aggregates. The higher quantum yield of fluorescence in the solids obtained by fast precipitation could be attributed to the presence of increased amounts of J-aggregates similar to that observed in highly concentrated solutions (>= 4.2 X 10(-4) M). The photophysical studies of MPT in various concentrations indicate that J-aggregates are significantly more fluorescent than the H-aggregates. Transient absorption spectra measured by nanosecond laser flash photolysis indicated the formation of a triplet excited state with an absorption maximum of similar to 490 nm and a quantum yield of 0.61.
The rotational motion of tolanes along their acetylene axis is not fully understood. What happens to the optical and electronic properties if the tolane backbone is forced into a twisted conformation? Several tethers were investigated to obtain tolanophanes, fixing the torsion angle of the two phenyl rings. X ray crystal structures revealed tether-specific torsion angles in the solid state. The absorption, emission and excitation spectra were recorded. Twisted tethered tolane conformers showed blue-shifted absorption; emission spectra were all torsionally independent and identical. The tethered tolanes were embedded in a rigid matrix by freezing to 77 K - well resolved emission spectra were recorded for planar tolanes but for twisted systems unexpectedly long-lived phosphorescence was observed. How is this triplet emission explained? Quantum chemical calculations (TDDFT/ cam-B3LYP/6-31G*) of the unsubstituted tolane showed that Intersystem Crossing (ISC) is favored with large spin-orbit coupling, which occurs when the molecular orbitals are orthogonal to each other - this is the case at the crossing of S1/T7. Also, a small energy difference between singlet and triplet states is required - we found that ISC can favorably take place at four crossings: S1/T6, S1/T7, S1/T8, S2/T9.
Vibrational Raman spectroscopy is now widely recognized as a useful technique for chemical analysis. It has become increasingly popular for the characterization of stable species since the technology which underpins Raman measurements has matured. Time-resolved Raman spectroscopy has also become established as an excellent method for the characterization of transient chemical species but it is not so widely applied. However, the technical advances which have reduced the cost and increased the reliability of conventional Raman systems can also be exploited in studies of transient species. In some cases it is just as straightforward to record the Raman spectra of a short-lived transient species as it is to monitor a more stable sample. This raises the possibility of routinely adding time-domain Raman measurements to more conventional Raman techniques, increasing the selectivity of the analysis while retaining its ability to provide spectral information which is characteristic of the species under investigation.
Structures and dynamics of excited electronic states and ionic radicals have been investigated for several compounds with photochemical interest. Picosecond and nanosecond time-resolved Raman spectroscopy was employed with the aid of laser flash photolysis and ab initio molecular orbital calculations. It was observed that the multiple bonds such as C≡C, C=C, C=O, C=N and phenyl rings were weakened in both the excited electronic states and ionic radicals; the weakening is much larger in the former than in the latter. Information on the dynamics of these transient species provided the basis for understanding photochemical reaction mechanisms.
Transient resonance Raman and absorption spectra of the lowest excited triplet states T1 and the cation radicals of phenothiazine and 2-chlorophenothiazine were measured. It was found that in the photoreaction of 2-chlorophenothiazine a transient exhibiting an absorption band at 556 nm was generated from the cation radical. The corresponding transient was not observed in the absorption spectrum of phenothiazine, a fact which suggests a possibility of phenothiazinyl radical generation for 2-chlorophenothiazine by photoinduced dechlorination. Vibrational assignments of the T1 states and the cation radicals of the both compounds were made based on the frequency shifts on isotopic substitutions. Unusually large low-frequency shifts of the phenyl 8a and 8b modes were observed in the T1 state but no appreciable shifts were detected in the cation radical, indicating that the phenyl rings are drastically weakened, and therefore, the phenyl C-C bonds are very much lengthened in the T1 state. This implies that the excitation is strongly localized on the phenyl rings and the T1 state has an n − π character.
Unusually large |D| values of zero-field splitting parameters were observed for 1,6-diphenylhexatriyne (|D|=0.396 cm−1) and 1,8-diphenyloctatetrayne (|D|=0.533 cm−1) by using time-resolved EPR (TREPR) spectroscopy. The lowest excited triplet (T1) states of these diphenylpolyynes were assigned to 3B1u(3πxπ∗x) in character from the degree of the polarization of phosphorescence. It has been concluded that the present diphenylpolyynes have a linear planar structure in the T1 states, although the TREPR and phosphorescence spectra indicate interactions between the T1(3πxπ∗x) and Tn(3πxπ∗y) states through spin–orbit and vibronic interactions.
The reaction of Cu2O with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (Hhfac) in the presence of alkynes results in the formation of (η2-alkyne) Cu(hfac). When using bis(trimethylsily)acetylene (BTMSA), both a mononuclear compound BTMSA Cu(hfac) (1) and a dinuclear complex BTMSA(Cu(hfac))2 (2) can be isolated; each complex was characterized by X-ray crystallography, IR, 1H and 13C NMR spectroscopies. In 1, the BTMSA ligand is η2 bonded parallel to the Cu (β-diketonate) plane, the trimethylsily groups are cis bent away from copper with small angles of deformation (θCCSi = 157 and 171°) and the CC bond distance is 1.17 Å. In 2, two BTMSACu(hfac) planes with a dihedral angle of 105.8° are observed. The intramolecular CuCu distance is only 2.800 Å and the central axis of BTMSA is situated perpendicular to the CuCu vector. A series of η2-alkyne Cu(hfac) were synthesized and characterized by NMR and IR spectroscopy.
The coherent Raman (CARS and CSRS) spectra for the excited (S1 and T1) states of bis(4-biphenylyl)acetylene (BBA) and also the spontaneous Raman spectrum for the ground (S0) state were observed. The assignments of vibrational bands were made tentatively by comparison with reported results for related compounds such as diphenylacetylene, biphenyl and trans-4,4′-diphenylstilbene in various electronic states. Characteristic features of the Raman shifts and intensities of the spectra in the S1 and T1 states are discussed in relation to the differences in electronic structures. The decrease of the C≡C stretching wavenumber in going from the S0 to the T1 state is ascribed to the localization of the triplet state inside the acetylene part as was described previously for the case of diphenylacetylene. A π-electronic conjugation over the biphenyl parts giving a more planar structure is deduced as being significant in the S1 state. © 1997 John Wiley & Sons, Ltd.
Photophysical and photochemical primary processes of diphenylacetylene (DPA) derivatives and related compounds have been reviewed. Curious photophysical properties of the low lying excited singlet states of DPA, such as an exceptionally slow S-2-->-S-1 internal conversion, a distinct temperature effect of the S-2 lifetime, and a strong excitation energy dependence of the fluorescence yield, were correlated with the S-2-S-1 energy gap. Contradictions of the assignments of the lowest excited singlet states of DPA were resolved and the mechanism of the S-2-->S-1 internal conversion was proposed from the comparison of the dynamic behavior of DPA with that of diphenylpolyenes. The small S-2-S-1 energy gap as well as the large displacement between the potential curves of the upper and lower electronic states can be a reason why the S-2 state of the DPA derivatives is exceptionally long-lived. The DPA derivatives of which the intramolecular charge-separated states are formed in polar solvents were used as probe molecules of the solvent-solute interaction. Significant enhancement of the charge recombination of aminophenyl(phenyl)acetylene in protic solvents should be due to the interaction between amino nitrogen atom of the solute molecule and the hydrogen-bonded solvent oligomer.
Picosecond transient CARS and picosecond transient infrared absorption spectra of three isotope-substituted diphenylacetylenes (DPA, DPA-13C, and DPA-d5) in solution have been recorded. The recorded CARS and infrared spectra of the S1 state have been interpreted in terms of a three-coordinate normal coordinate analysis. Existence of a center of symmetry has been indicated from the mutual exclusion relationship established for the CARS and infrared spectra, strongly supporting a trans-bent structure of the S1 state.
Linewidths of the isotropic Raman bands of diphenylacetylene for the CC stretching (2221 cm−1), C-phenyl stretching (1143 cm−1) and the skeleton phenyl ring vibrations ν1(999 cm−1) and ν8(1596 cm−1) were measured as a function of concentration in acetonitrile, methylcyclohexane and 2,5-dimethyltetrahydrofuran. Experimental results have been compared with those calculated on the basis of theoretical models of vibrational dephasing. The mechanisms of vibrational relaxation may provide some new insight into the primary photochemical process of diphenylacetylene.
Time-resolved resonance Raman spectra of the lowest excited triplet state T1, the radical cation R+ and the radical anion R− of 1,4-diphenylbutadiyne (DPB) have been measured. It has been shown that the CC symmetric stretch exhibits low-frequency shifts in the order, So (2219 cm−1), R+ (2156 cm−1), R− (2108 cm−1), and T1 (1999 cm−1), indicating that the CC triple bond weakens in this sequence. However, the frequency shifts are not as large as those observed for diphenylacetylene (DPA), suggesting that in the case of DPB the unpaired electron (spin density) is distributed over the two CC triple bonds of the conjugated system, which makes the weakening of the CC bonds of DPB much less than that of DPA. It has also been shown that like DPA, the ionization of DPB to generate R+ can occur biphotonically through the T1 state.
The lowest excited triplet (T1) states of diphenylacetylene and several α,ω-diphenylpolyynes (DPY) having two, three, four and six triple bonds were studied using continuous wave time-resolved electron paramagnetic resonance (CW-TREPR), pulsed EPR, and phosphorescence spectroscopy. Linear and planar molecular structures in the T1 states of DPY were suggested from the magnetophotoselection experiments and observation of a strong 0-0 band in the well-resolved phosphorescence spectra. The spin density distributions, which were obtained by electron spin echo envelope modulation measurements and semi-empirical molecular orbital calculations, and the phosphorescence polarization normal to the long axis of molecule for the 0-0 bands suggested that the T1 states of DPY have a 3B1u(πxπx∗) electronic configuration. DPY showed an abnormally large ∣D∣ value of the zero-field splitting parameters that increased with increasing molecular size. Such an unusual behavior of the D values is interpreted in terms of the spin-orbit interaction between the T1 and 3Au(πxπy∗) states mainly due to their energy proximity which is probably characteristic of the excited states for the polyynes. The estimated energy gap between the 3πxπy∗ and 3πxπx∗ states for DPY ranges from 2900 cm−1 to 1400 cm−1. There existed a good correlation between the acceleration of the nonradiative decay rate constant from the T1 state and appearance of a ring twisting vibronic band with b1g symmetry in the phosphorescence spectra for DPY. Therefore, we concluded that the vibronic interaction between the 3πxπy∗ and 3πxπx∗ states promoted by the b1g vibration leads to a broadening of the potential surface of the T1 state which results in the fast radiationless decay to the ground state. © 2001 American Institute of Physics.
A weak band at the tail of the known tolane (diphenylacetylene, DPA) fluorescence spectrum in several solvents is assigned to the forbidden 1(1)A(u) → 1(1)A(g) transition on the basis of its lifetime (∼200 ps) and its fluorescence excitation spectra. The 1(1)A(u) state, generally called the dark state, is not truly dark. We report the temperature (T) dependence of DPA fluorescence quantum yields (ϕ(f)) in methylcyclohexane (MCH) solution and the fluorescence and phosphorescence quantum yields of DPA in glassy MCH at 77 K. Significant differences between fluorescence and phosphorescence excitation spectra reveal that, in addition to the 1(1)B(1u) ← 1(1)A(g) transition, the first DPA absorption band includes a transition to another excited state, most probably the 1(1)B(2u) state, from which intersystem crossing is more efficient. The T dependence of ϕ(f) values in MCH solution is shown to be consistent with the previously reported T dependence of the lifetimes of transient DPA singlet excited state absorptions in the picosecond time scale. Transient absorption decay rate constants in hexane, methylcyclohexane and decalin as a function of T are retreated. Application of the medium enhanced barrier model shows that the medium is fully engaged with the molecular motion that is involved in the activated nonradiative decay path of the 1(1)B(1u) state. In accord with theoretical calculations and experimental observations, that process is assigned to the diabatic internal conversion of the short-lived linear fluorescent π,π* (1(1)B(1u)) state, over a low intrinsic energy barrier, to the longer lived weakly fluorescent trans-bent π,σ* (1(1)A(u)), which is the precursor of the DPA triplet state. Absorption and fluorescence measurements in several solvents show that the 1(1)B(1u)-1(1)A(g) energy gap decreases linearly with increasing medium polarizability. Our results allow a more definitive state order assignment for DPA.
Fluorenones substituted with cis- and trans-styryl and phenylethynyl groups at C-1, C-2, and C-4 were synthesized, as were the trans-2- and trans-4-(3,4-dimethoxystyryl) and β-methyl-2-styryl derivatives. The static absorption and fluorescence spectra of these compounds were measured, as were their redox potentials in acetonitrile. Transient spectra in a range of solvents were obtained on a microsecond time scale. The compounds showed marked solvent-dependent behavior. In solvents of low polarity, the principal photochemical process for the styryl derivatives is cis−trans isomerization via triplet intermediates. In polar solvents, singlet processes become more important, including photoionization from upper excited states. There are also significant regiochemical differences. The triplets from the 2-substituted fluorenones have microsecond lifetimes and λmax values in the 400−500-nm range, indicating that they have a trans configuration. By contrast, 1- and 4-substituted fluorenones give rise to triplets with much smaller lifetimes and λmax values, suggesting that their predominant configuration is perpendicular. There are analogous differences in the spectra of radical ions produced by photoionization. Those from the 2-derivatives have larger λmax values than those from the 1- and 4-derivatives. The photo- and electrochemical data support the thesis that the fluorenone/side-chain interactions are weaker in the 2- than in the 1- and 4-derivatives.
Raman and IR spectra of phenylacetylene dissolved in methylcyclohexane and acetonitrile have been recorded. The IR line widths and Raman isotropic line widths of totally symmetric A1 vibrations of phenylacetylenethe stretching mode of the ethynyl group CC (νS(CC)), the phenyl ring in-plane stretching (ν8a), the C-phenyl group stretching (νS(C−Ph)), and the phenyl ring breathing (mixed with trigonal vibration) (ν12)have been recorded. The spectra have been measured as a function of concentration at room temperature. Theoretical models of vibrational dephasing have been tested and compared with experiment.
Picosecond time-resolved CARS spectra of diphenylacetylene and its 13C-substituted analogue in cyclohexane are reported for the 2330−590 cm-1 wavenumber shift. The transient CARS bands of the S2 and S1 states are observed in addition to those of the cation radical, the anion radical, and the T1 state. It is found that the central CC stretch frequency of the S1 state is smaller than 1600 cm-1, indicating a marked decrease of the CC bond order in this state. The width of the central CC stretch band of the S2 state is found to be 40 cm-1 (hwhm). These spectral features are discussed in connection with the structure and dynamics in the two singlet excited states.
Stochastic modeling of the radiolysis of water and of aqueous solutions employing simulated track structures and the independent reaction times methodology is used to investigate the physical and chemical processes underlying observed radiation chemical kinetics. The calculations accurately reproduce both the time dependent yields of eaq- and the scavenging capacity dependence of the (scavenged) yields of eaq-, OH, H2, and H2O2 measured experimentally. The local spatial distribution of eaq- is described by a Gaussian of standard deviation 4.0 nm. This distribution reflects the “thermalization” of the subexcitation electron. The value matches recent experimental estimates but is somewhat wider than predicted in earlier (deterministic) studies. The Gaussian distribution used for H3O+, OH, H, and O has a standard deviation of 0.75 nm, which is of the same order obtained previously using deterministic methods. This distribution is due to the distance traveled between electronic collisions of low-energy (<25 eV) electrons and the fragmentation of the molecular cation, H2O+.
Ab initio complete active space self-consistent field (CASSCF) and second-order multireference Möller−Plesset (MRMP2) calculations have been performed to examine the photochemical behavior of diphenylacetylene (DPA) theoretically. The stable structure of DPA in S0 (S0-geometry) is optimized to be D2h. DPA at S0-geometry is mainly excited into the S3(B1u) state and then relaxes into the stable geometry in the B1u state (B1u-geometry) which is characterized as a quinoid structure. The B1u-geometry further relaxes into the globally stable geometry in S1 (tS1-geometry) which takes a trans-bent form. Around tS1-geometry, DPA moves into the lowest triplet state through intersystem crossing and finally relaxes into the stable geometry in T1 with D2h. The vibrational analyses at the important conformations mentioned above are in good agreement with the experimental findings of time-resolved transient spectroscopy.
Ab initio calculations of geometries and force fields using the 4- 3 1 G basis set were carried out at the RHF and ROHF versions of the SCF level on the ground state S0, radical cation R.+, radical anion R.-, and lowest excited triplet state T1 of diphenylacetylene. It was shown that the molecular geometry approaches a quinoidal structure in the following sequence: S0, R.+, R.-, and T1. Force constants were obtained in terms of local symmetry coordinates and were adjusted with the scale factors transferred from the ones determined in benzene and methylacethylene. Good agreement between observed and calculated normal frequencies was obtained for S0, R.+, and R.- but not for T1. For the T1 state, the scale factors for the C-Ph stretch and phenyl skeletal stretches were found to be not transferable. In addition, off-diagonal force constant matrix elements representing the interactions between these coordinates of the different phenyl groups were overestimated, which may be correlated with the instability of the restricted Hartree-Fock solutions.1
Picosecond time-resolved CARS spectra of diphenylacetylene and its 13C species were reported. CARS bands due to two transient species with different lifetimes were observed. The short-lived species (lifetime < 20 ps) has been identified as the S2 state and the long-lived species (lifetime ≈ 200 ps) as the S1 state. The 2099 cm−1 band of the S2 state has been assigned to the central CC bond stretch while the 1577 cm−1 and 1557 cm−1 bands of the S1 state are assignable to the normal modes which contain contributions of the central CC stretch vibration. The bond order of the central CC part decreases markedly in the S1 state.
Picosecond transient infrared spectra of diphenylacetylene (DPA) were obtained in cyclohexane and acetonitrile solutions for the 1640–940 cm−1 wavenumber region, using a method based on optically heterodyned detection of absorption anisotropy. The observed transient species was assigned to the S1 state of DPA on the basis of its temporal behavior. Comparison with the reported CARS spectra suggests that S1 DPA has a planar (probably trans-bent) structure with a center of symmetry in both solutions.
Molecules in the excited singlet and triplet state and photoproducts occuring after photoisomerization or proton transfer are investigated by time-resolved resonance Raman and resonance CARS spectroscopy with nanosecond time resolution. From the time-resolved spectra information on structures and bond strengths of these short-lived species and on their kinetics are obtained.
Diffuse reflectance UV–vis and Raman spectroscopies show complete sorption of neutral diphenylacetylene (DPA) in the void space of M6.6ZSM-5 zeolites (M = Li+, Na+, K+, Rb+, Cs+) after several months of exposure of solid DPA to empty zeolite at room temperature. After a long organization period, the laser photolysis of DPA occluded in M6.6ZSM-5 generates long-lived DPA+ radical cation as primary phenomenon. Charge recombination occurs mainly through electron transfer and DPA@M6.6ZSM-5−+ electron–hole pair formation. This subsequent electron transfer takes place between the electron deficient radical cation DPA+ and the electron donor oxygen atom of zeolite framework. The multivariate curve resolution analysis of the DRUVv spectra recorded during the reaction sequence including charge separation, electron transfer and charge recombination provide the specific absorption spectra and respective spectral concentrations of all species as function of time. The DRUVv spectrum assigned to the long-lived DPA@M6.6ZSM-5−+ electron–hole pair exhibits broad bands between 450 and 550 nm. The electron–hole pair recombination depends on M+ and appears to be in relation with the electron donor properties of the framework. The charge recombination rate decreases in the order Cs+ > Rb+ ∼ K+ > Na+ > Li+. The electron–hole pair lifetime exceeds several hours at room temperature. The stabilization of DPA+-electron pair and DPA@M6.6ZSM-5−+ electron–hole pair depends on the combined effects of confinement which dramatically reduces the DPA mobility in the zeolite void space and on the intrazeolithe electrostatic field of DPA@MnZSM-5 (M = Li+, Na+, K+, Rb+, Cs+).
Rotational isomerism involving acetylene carbons has been studied by experimental and theoretical methods conventionally used for conformational analysis. The rotational barriers and populations of alkyne conformers are influenced by various factors, such as steric and electronic effects, as discussed in general kinetic and thermodynamic studies. Other intermolecular and intramolecular interactions, such as hydrogen bond, solvation, electronic states, state of sample, and external stimulus, are possible factors affecting the rotational isomerism. The presence of one electronegative or one electropositive substituent at the propargylic position results in small effects on the energy profile. The observed and calculated data suggested that the barrier heights were influenced by electronic effects, steric effects, weak interactions, and other factors, some of which were only recently revealed by modern techniques.
The vibrational spectrum of a high-temperature (330 C) polymerization reaction was successfully monitored in real time with the use of a modulated fiber-optic Fourier transform (FT)-Raman spectrometer. A phenylethynyl-terminated monomer was cured, and spectral evidence for two different reaction products was acquired. The products are a conjugated polyene chain and a cyclized trimer. This is the first report describing the use of FT-Raman spectroscopy to monitor a high temperature (greater than 250 C) reaction in real time.
By using MO calculations based on DFT, absorption, and fluorescence spectroscopy, we have comprehensively studied the low-lying excited singlet states of alpha,omega-diphenylpolyynes (DPY) having 1-6 triple bonds. The a(g) vibrational modes of the C(triple bond)C stretching and of the phenyl ring motion were observed in the fluorescence spectra of diphenylacetylene and 1,4-diphenylbutadiyne. On the other hand, in the fluorescence spectra of the long DPY with the triple-bond number (N) more than two, the phenyl ring motion with a(g) symmetry disappeared and the b(1g) modes of the phenyl ring twisting (approximately 400 cm(-1)) and of the C-H bending (approximately 900 cm(-1)) were detected. The observed fluorescent states of DPY with N < or = 2 and N > or = 3 are assigned to the 1(1)B(1u) (pi(x)pi(x*)) and 1(1)A(u) (pi(x)pi(y*) and/or pi(y)pi(x*)) states, respectively, based on the vibronic structures, the relatively short lifetimes, and the solvatochromic shifts of the fluorescence spectra. Not only the allowed transition of 1(1)B(1u) <-- S(0) but also the forbidden transition of 1(1)A(u) <-- S(0) was detected in the fluorescence excitation spectra of the long DPY with N > or = 3. The low-lying excited state with A(u) symmetry is characteristic in polyyne, which does not exist in polyene. The oscillator strength (f) of the first absorption band in DPY decreases with an increase in N, which is the opposite behavior of the all-trans-alpha,omega-diphenylpolyenes. The N-dependence of the f value is understood by the configuration interaction between the 1(1)B(1u) and 2(1)B(1u) (pi(y)pi(y*)) states, which is consistent with the reduction of the nonlinear optical response of polyyne.
The reaction dynamics and coherent nuclear motions in the photodissociation of diphenylcyclopropenone (DPCP) were studied in solution using time-resolved absorption spectroscopy. Subpicosecond transient absorption spectra were measured in the visible region with excitation at the second absorption band of DPCP. The photodissociation takes place from the precursor excited state with the time constant of 0.2 ps. The results show that the diphenylacetylene (DPA) generated by photodissociation possess a cis-bent skeletal structure, which is different from the linear structure of DPA generated by direct photoexcitation.
Penning ionization of phenylacetylene and diphenylacetylene upon collision with metastable He*(2(3)S) atoms was studied by collision-energy-/electron-energy-resolved two-dimensional Penning ionization electron spectroscopy (2D-PIES). On the basis of the collision energy dependence of partial ionization cross-sections (CEDPICS) obtained from 2D-PIES as well as ab initio molecular orbital calculations for the approach of a metastable atom to the target molecule, anisotropy of interaction between the target molecule and He*(2(3)S) was investigated. For the calculations of interaction potential, a Li(2(2)S) atom was used in place of He*(2(3)S) metastable atom because of its well-known interaction behavior with various targets. The results indicate that attractive potentials localize in the pi regions of the phenyl groups as well as in the pi-conjugated regions of the acetylene group. Although similar attractive interactions were also found by the observation of CEDPICS for ionization of all pi MOs localized at the C[triple bond]C bond, the in-plane regions have repulsive potentials. Rotation of the phenyl groups about the C[triple bond]C bond can be observed for diphenylacetylene because of a low torsion barrier. So the examination of measured PIES was performed taking into consideration the change of ionization energies for conjugated molecular orbitals.
A series of low-coordinate, paramagnetic iron complexes in a tris(thioether) ligand environment have been prepared. Reduction of ferrous {[PhTt(tBu)]FeCl}2 [1; PhTt(tBu) = phenyltris((tert-butylthio)methyl)borate] with KC8 in the presence of PR3(R = Me or Et) yields the high-spin, monovalent iron phosphine complexes [PhTt(tBu)]Fe(PR3) (2). These complexes provide entry into other low-valent derivatives via ligand substitution. Carbonylation led to smooth formation of the low-spin dicarbonyl [PhTt(tBu)]Fe(CO)2 (3). Alternatively, replacement of PR 3 with diphenylacetylene produced the high-spin alkyne complex [PhTt(tBu)]Fe(PhCCPh) (4). Lastly, 2 equiv of adamantyl azide undergoes a 3 + 2 cycloaddition at 2, yielding high-spin dialkyltetraazadiene complex 5.
Die Belichtung von Diphenylacetylen (I) in einer Cyclohexan-Matrix bei -10°C ergibt das Phenylbenzocyclobutadien (II), das thermisch über die Zwischenstufen (III) und (IV) zu dem Triphenylnaphthalin (V) und dem Triphenylazulen (VI) dimerisiert.
The electronic absorption spectra of radical ions produced by γ-ray irradiation of (E)-stilbene and related compounds in frozen matrices were measured. On illumination and on controlled warming, the spectra of the radical ions of sterically uncrowded stilbenes and diphenylacetylene remained almost unchanged, while those of the radical ions of sterically crowded stilbenes changed noticeably. Examination of the spectra and of their changes led to the following conclusions: (a) The relaxed geometry of the radical ions of sterically uncrowded stilbenes is planar or nearly planar; (b) in the unrelaxed geometries of the radical ions of (E)-α,β-dialkylstilbenes the torsion angles of the Ph–C bonds are nearly as large as in the parent molecules, and on relaxation these angles become smaller and the torsion angle of the central ethylenic bond deviates from 0° to a considerable extent; (c) for the radical ions of ortho-substituted (E)-stilbenes the geometrical change on relaxation is comparatively small.
The most probable configuration of triphenylethylene as well as that of tetraphenylethylene has been inferred to be the one in which all of the phenyl groups are rotated out of the plane of the ethyl-enic bond, on the basis of the analysis of the ultraviolet absorption spectra by application of the method based on the simple LCAO molecular orbital method described in the preceding part of this series. Some physical and chemical properties of these compounds have been discussed with reference to the spatial configurations.
The method has been applied also to tolan (diphenylacetylene), and it has been shown that the calculated wavelengths of the bands agree fairly well with the observed ones.
In addition, it has been shown that the spectrum of tolan in the crystalline state measured by the pressed KCl-disk technique resembles the spectrum of the solution in n-heptane on the whole, and that the red-shift of each band associated with the change of the state from the n-heptane solution to the crystalline state increases with almost complete regularity with the wavelength of the band from about 1.3 mμ at 217.2 mμ to about 4.4 mμ at 297.2 mμ, the shifts observed here being appreciably smaller than the analogous shifts observed by Dale in the spectra of naphthalene and anthracene.
Diarylacetylenes are prepared conveniently in good yields by treating aryl iodides with cuprous acetylides in refluxing pyridine under a nitrogen atmosphere. Under these conditions, aryl iodides bearing an ortho nucleophilic substituent are converted exclusively to the corresponding heterocycle in high yields.
The thirty modes of vibration of the regular plane hexagon model for the benzene molecule, including both the hydrogen and carbon atoms, are derived by the group theory method described by Wigner. From these the twenty frequencies of vibration are calculated in terms of a simple potential function involving six force constants. Selection rules for the Raman and infrared spectra are listed. Seven fundamentals are permitted in the Raman spectrum and four fundamentals in the infrared. Both analytical and graphical descriptions of the modes of vibration are given. These depend largely on the symmetry of the molecule and are only in part influenced by the choice of potential function adopted.
The thermodynamic criterion of reversible electron phototransfer correlates with CIDNP effects in sensitized trans-cis photoisomerization of fumaronitrile in acetonitrile. It follows from CIDNP analysis that the free radical anion of fumaronitrile does not undergo geometrical isomerization.
Electron spin resonance (ESR) spectra of the lowest triplet state of diphenylacetlylene diluted and oriented in benzophenone single crystals are analyzed. The fine structure parameters obtained are D/hc = ±0.1426 cm−1 and E/hc = ±0.0306 cm−1. The electronic structure and the fine structure tensor in the triplet state are discussed in relation with the result of a theoretical calculation.
Measurements of a polarized triplet–triplet absorption spectrum using stretched polymer films have been attempted at liquid nitrogen temperature. The polarizations of the triplet–triplet transitions of diphenylacetylene were determined, and the molecular structure in the excited triplet state was discussed.
Resonance Raman spectra of the transient species of 2,2′-spirobi[2H-1-benzopyran] in various solvents reveal that at least two isomers exist in solution, the relative abundance of which depends on the polarity and hydrogen-bond donor ability of the solvent. Vibrational assignment of the transient species based on 13C substitutions shows that the Raman bands mainly attributable to the vibrations of the open benzopyran part are enhanced by the Raman excitation wavelengths longer than 460 nm, whereas those assignable to the vibrations of the closed benzopyran part are observed only by the Raman excitation wavelengths shorter than 460 nm. Semi-empirical molecular orbital calculations show that the contribution of the ortho-quinoidal form to the resonance hybrid structure of the transient species is much larger than that of the zwitterionic form. Also, it is shown that the trans-trans-trans (TTT) configuration about the three CC partial double bonds of the transient species is most stable.
Faraday Soc. 1963,36, 62, 3170. 214. (36) This parameter is equivalent to the a parameter us? in ref 7. The (37) The same numbering is used as in ref 7. value of kNIO is 9.1 X lo9 M-l s-I 8912
- R H Schuler
- P P J Infelta
- Phys
- Chem
- F S Dainton
- A R Gibbs
- D Smithies
- G Scholes
- M Simic
- J J Weiss
- Discuss
Schuler, R. H.; Infelta, P. P. J. Phys. Chem. 1972, 76, 3812. (34) Dainton, F. S.; Gibbs, A. R.; Smithies, D. Trans. Faraday Soc. 1966, (35) Scholes, G.; Simic, M.; Weiss, J. J. Discuss. Faraday Soc. 1963,36, 62, 3170. 214. (36) This parameter is equivalent to the a parameter us? in ref 7. The (37) The same numbering is used as in ref 7. value of kNIO is 9.1 X lo9 M-l s-I 8912 The Journal of Physical Chemistry, Vol. 96, No. 22, 1992 Hiura and Takahashi Figure 5. Comparison of the resonance Raman spectra of the p+ of DPA and its isotopically substituted analogues in acetonitrile: (a) DPA-LI0, (b) DPA-"C, (c) DPA-d,, (d) DPA-d,,. Probe wavelength, 420 nm. Solvent bands were subtracted.
G values, are quoted in the units of molecules
- F S Dainton
- S Logan
All radiation chemical yields, G values, are quoted in the units of molecules/100 eV. (31) Dainton, F. S.; Logan, S. R. Trans. Faraday Soc. 1965. 61. 715. (32) Draganic, Z. D.; Draganic, I. G. J. Phys. Chem. 1973, 77, 765.