Exciton Energy and Charge Transfer in Porphyrin Aggregate/Semiconductor (TiO₂) Composites

Abstract

A porphyrin aggregate is reported that exhibits novel exciton state properties for light-harvesting applications. This porphyrin aggregate enables control of energy dissipation of coherent excited states by changing the self-assembly pattern. New exciton spectral features create a new route of energy transfer in this porphyrin aggregate. The kinetic model of exciton state decay is addressed in this Perspective by reporting steady-state and transient emission and absorption studies of porphyrin J- and H-aggregates. The porphyrin J-aggregate emerges with better spectral coverage and exciton dynamics, which are suitable for light-harvesting antenna functions. This motif is explored in a photosensitization study of TiO2 semiconductor materials. The transient absorption studies show that the J-aggregate improves the photoinduced charge separation at the porphyrin/TiO2 interface. The higher charge separation is attributed to exciton-coupled charge-transfer processes in porphyrin J-aggregate/TiO2 hybrid materials. It represents the potential of porphyrin aggregates in biomimetic artificial antenna activity.

WITHDRAWN: Hydrogen-bonding versus π–π stacking in the design of organic semiconductors: From dyes to oligomers

“…The molecules in J-aggregates are retained in the direction parallel to their molecular planes (nematic director of liquid crystal), whereas the direction of Haggregation is perpendicular to molecular planes, i.e., corresponding to "face-to-face" orientation (π-π stacking) of aromatic or hetero-rings. Some cyanines [34] and porphyrines [56] exhibit both J-and H-band on aggregation as it is shown in Figure 13.…”

“…In contrast to J-aggregates manifesting strong long-wavelength absorption and resonant light emission missing in the molecularly-dispersed or solid-state dyes, the hypsochromic shift in absorption spectra and the absence of the photoluminescence are characteristic for so-called H-aggregation [53][54][55][56]. The molecules in J-aggregates are retained in the direction parallel to their molecular planes (nematic director of liquid crystal), whereas the direction of Haggregation is perpendicular to molecular planes, i.e., corresponding to "face-to-face" orientation (π-π stacking) of aromatic or hetero-rings.…”

“…Restriction of the long-range energy transfer in H-aggregate makes J-aggregates more useful in domains requiring absorption and transfer of light energy [56].…”

The impact of trans/cis photoisomerization on photoinduced electron transport between 4,4′-stilbenedicarboxylic acid and columnar perylenediimide aggregates in water

“…Many organic compounds with covalently linked donor and acceptor moiety have been designed and synthesized for the purpose of revealing the origin of PET process [7][8][9]. At the same time, mimicking the natural PET with non-covalently systems based on varies of supramolecular interactions has also gained much attention in the past several decades [10,11]. In these supramolecular systems, electron donors and acceptors selfassemble into complexes, which offer the place for the PET process.…”

Optical properties of porphyrin: graphene oxide composites

“…A range of porphyrins have been found to form nanorod like structures for example Reddy et al [27] demonstrated that H 2 TPP in acidic environments forms well defined nanorods assigned to occur due to J-aggregation. In porphyrins the formation of J aggregates are reported to result in a red-shift in absorption bands [30][31][32].…”