Jonathan Matichak's research while affiliated with University of Oxford and other places

We report the synthesis of LH2-like supramolecular double- and triple-strand complexes based upon porphyrin nanorings. Energy transfer from the antenna dimers to the π-conjugated nanoring occurs on a sub-picosecond timescale, rivaling transfer rates in natural light harvesting systems. The presence of a second nanoring acceptor doubles the transfer rate, providing strong evidence for multi-directional energy funneling. The behavior of these systems is particularly intriguing because the local nature of the interaction may allow energy transfer into states that are, for cyclic nanorings, symmetry forbidden in the far-field. These complexes are versatile synthetic models for natural light harvesting systems.

The vacuum thermal evaporation of poly(3-hexylthiophene) (P3HT) and poly(thiophene) (PTh) conductive polymers with and without side groups is reported. The role of side groups in relation to structural and electronic properties is examined. FT-IR and GPC analysis is used to study the effect deposition has on conjugation of the polymer. Topography and grain structure of the polymer films are studied using MicroXAM, AFM and TEM. XRD and TEM data reveal enhanced molecular packing and crystallinity of PTh. This results in significantly improved charge transport properties with relatively high hole mobilities (10−4 cm2/Vs). Evaluation of PTh and P3HT electronic properties is performed on simple geometry planar C60 heterojunction solar cells. PTh/C60 devices exhibit almost a 70% increase in efficiency as compared to P3HT/C60 devices, demonstrating enhanced charge collection in PTh films through improved molecular order. ► Vacuum evaporation of polymers with (P3HT) and without side groups (PTh) is reported. ► Polymer side groups influence structural and electronic properties of the films. ► Molecular order and charge transport in PTh are significantly better than in P3HT. ► High PTh hole mobilities (10−4 cm2/Vs) and PTh/C60 device efficiencies are achieved. ► Vacuum thermal evaporation is suitable for the deposition of low solubility polymers.

[2]Rotaxanes consisting of butadiyne-linked porphyrin dimers threaded through a phenanthroline-containing macrocycle, can be synthesised by an active-metal template directed copper-mediated Glaser coupling, in yields of up to 61%, without requiring a large excess of the macrocycle. The crystal structure of one of these rotaxanes confirms that the macrocycle is clasped around the centre of the porphyrin dimer. A radial hexa-pyridyl template was used to convert the alkyne-terminated [2]rotaxane into a [4]catenane cyclic porphyrin hexamer in 62% yield, via palladium-catalysed Glaser coupling. The related [7]catenane porphyrin dodecamer complex was also isolated as a by-product of this cyclisation, in 6% yield. These results illustrate the scope of template-directed synthesis for creating complex interlocked structures directly from simple starting materials.

Dying by Design To make optical-switching applications a reality, losses from scattering and other absorption processes have to be minimized. Hales et al. (p. 1485 , published online 18 February; see the Perspective by Haque and Nelson ) present a strategy to explore the refraction and absorption properties of a group of cyanine dyes for designing materials that have properties corresponding to technologically interesting telecommunications windows. The optical properties of the cyanine molecule was controlled by adding heavy chalcogen atoms (selenium) into the end groups of the molecular structure. While producing a series of molecules meeting criteria for feasible application, the work also demonstrates a route to improve the performance of nonlinear optical materials.

The linear and nonlinear absorption properties of a squaraine-bridged porphyrin dimer (POR-SQU-POR) are investigated using femto-, pico-, and nanosecond pulses to understand intramolecular processes, obtain molecular optical parameters, and perform modeling of the excited-state dynamics. The optical behavior of POR-SQU-POR is compared with its separate porphyrin and squaraine constituent moieties. Linear spectroscopic studies include absorption, fluorescence, excitation and emission anisotropy, and quantum yield measurements. Nonlinear spectroscopic studies are performed across a wide range (approximately 150 fs, approximately 25 ps, and approximately 5 ns) of pulsewidths and include two-photon absorption (2PA), single and double pump-probe, and Z-scan measurements with detailed analysis of excited-state absorption induced by both one- and two-photon absorption processes. The 2PA from the constituent moieties shows relatively small 2PA cross sections; below 10 GM (1 GM = 1 x 10(-50) cm4 s/photon) for the porphyrin constituent and below 100 GM for the squaraine constituent except near their one-photon resonances. In stark contrast, the composite POR-SQU-POR molecule shows 2PA cross sections greater than 10(3) GM over most of the spectral range from 850 to 1600 nm (the minimum value being 780 GM at 1600 nm). The maximum value is approximately 11,000 GM near the Nd:YAG laser wavelength of 1064 nm. This broad spectral range of large 2PA cross sections is unprecedented in any other molecular system and can be explained by intramolecular charge transfer. A theoretical quantum-chemical analysis in combination with different experimental techniques allows insight into the energy-level structure and origin of the nonlinear absorption behavior of POR-SQU-POR.

The nonlinear absorption mechanisms of a bis(porphyrin)-substituted squaraine have been studied with femtosecond, picosecond, and nanosecond pulsewidths. The two-photon absorption is ~10× larger than those of the constituents and is explained by intra-molecular charge transfer.