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Publications (12)
Structural order and intermolecular interactions strongly determine the interfacial energy landscape in organic photovoltaics. The finding that the ionization energy and the energy of charge-transfer states can vary by approximately 0.5 eV depending on material order and composition may explain how excitons are able to separate efficiently in organ...
The energy landscape in organic semiconducting materials greatly influences charge and exciton behavior, which are both critical to the operation of organic electronic devices. These energy landscapes can change dramatically depending on the phases of material present, including pure phases of one molecule or polymer and mixed phases exhibiting dif...
A critically important question that must be answered to understand how organic solar cells operate and should be improved is how the orientation of the donor and acceptor molecules at the interface influences exciton diffusion, exciton dissociation by electron transfer, and recombination. It is exceedingly difficult to probe the orientation in bul...
A covalently linked multichromophoric array (BDP-Por) was used as the donor layer in planar heterojunction organic photovoltaic (OPV) cells with the structure ITO/BDP-Por/C60/BCP/Al (BCP = bathocuproine). BDP-Por is a platinum tetrabenzoporphyrin (PtTPBP) core bonded through the phenyl groups to the meso position of four 4,4-difluoro-3,5-dimethyl-4...
A benzannulated BODIPY (bDIP) molecule exhibiting strong absorption at 640 nm was synthesized. The organic dye was used in an organic solar cell as the electron donor with C60 as the acceptor. The BODIPY dye demonstrated the best performance in lamellar architecture (ITO/bDIP/C60/bathocuproine/Al), giving power conversion efficiency up to 4.5 % wit...
Molecular orientation plays a significant role in determining the performance of small molecule solar cells. Key photovoltaic processes in these cells are strongly dependent on how the molecules are oriented in the active layer. We isolate contributions arising from the bulk molecular orientations vs. those from interfacial orientations in ZnPc/C60...
A series of donor-chromophore-acceptor-stable radical (D-C-A-R•) molecules having well-defined molecular structures were synthesized to study the factors affecting electron spin polarization transfer from the photogenerated D+•-C-A-• spin-correlated radical pair (RP) to the stable radical R•. Theory suggests that the magnitude of this transfer depe...
Two X-shaped, cruciform electron Donor2-Acceptor-Acceptor'2 (D2-A-A'2) molecules, 1 and 2, in which D = zinc 5-phenyl-10,15,20-tripentylporphyrin (ZnTPnP) or zinc 5,10,15,20-tetraphenylporphyrin (ZnTPP), respectively, A = pyromellitimide (PI), and A' = perylene-3,4:9,10-bis(dicarboximide) (PDI), were prepared to study self-assembly motifs that prom...
A series of DNA hairpins (AqGn) possessing a tethered anthraquinone (Aq) end-capping group were synthesized in which the distance between the Aq and a guanine-cytosine (G-C) base pair was systematically varied by changing the number (n - 1) of adenine-thymine (A-T) base pairs between them. The photophysics and photochemistry of these hairpins were...
tert-Butylphenylnitroxide (BPNO(•)) and α,γ-bisdiphenylene-β-phenylallyl (BDPA(•)) stable radicals are each attached to zinc meso-tetraphenylporphyrin (ZnTPP) at a fixed distance using one of the ZnTPP phenyl groups. BPNO(•) and BDPA(•) are oriented para (1 and 3, respectively) or meta (2 and 4, respectively) relative to the porphyrin macrocycle. F...
We report the measurement of distance- and temperature-dependent rate constants for charge separation in capped hairpins in which a stilbene hole acceptor and hole donor are separated by A(3)G(n) diblock polypurine sequences consisting of 3 adenines and 1-19 guanines. The longer diblock systems obey the simplest model for an unbiased random walk, p...
Small- and wide-angle X-ray scattering in solution reveals that chlorophyll (Chl) trefoils self-assemble in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) to yield supramolecular cyclic trimers. Two Chls of each trefoil coordinate to DABCO to form the vertices of the hexagonal structure, while the remaining Chl acts like a substituent on the...
