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Exciton‐Coupled Charge‐Transfer Dynamics in a Porphyrin J‐Aggregate/TiO 2 Complex
Author(s) -
Verma Sandeep,
Ghosh Amrita,
Das Amitava,
Ghosh Hirendra N.
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201002537
Subject(s) - j aggregate , exciton , porphyrin , delocalized electron , ultrafast laser spectroscopy , chemical physics , electron transfer , materials science , electron , photochemistry , chemistry , spectroscopy , condensed matter physics , physics , organic chemistry , quantum mechanics
Abstract Exciton‐coupled charge‐transfer (CT) dynamics in TiO 2 nanoparticles (NP) sensitized with porphyrin J‐aggregates has been studied by femtosecond time‐resolved transient absorption spectroscopy. J‐aggregates of 5,10,15‐triphenyl‐20‐(3,4‐dihydroxyphenyl) porphyrin (TPPcat) form CT complexes on TiO 2 NP surfaces. Catechol‐mediated strong CT coupling between J‐aggregate and TiO 2 NP facilitates interfacial exciton dissociation for electron injection into the conduction band of the TiO 2 nanoparticle in pulse width limited time (<80 fs). Here, the electron‐transfer (<80 fs) process dominates over the intrinsic exciton‐relaxation process (J‐aggregates: ca. 200 fs) on account of exciton‐coupled CT interaction. The parent hole on J‐aggregates is delocalized through J‐aggregate excitonic coherence. As a result, holes immobilized on J‐aggregates are spatially less accessible to electrons injected into TiO 2 , and thus the back electron transfer (BET) process is slower than that of the monomer/TiO 2 system. The J‐aggregate/porphyrin system shows exciton spectral and temporal properties for better charge separation in strongly coupled composite systems.