title: Exciton-coupled charge-transfer dynamics in a porphyrin J-aggregate/TiO(2) complex.
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.
authors.affiliation: Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
authors.forename: Sandeep
authors.initials: S
authors.lastname: Verma
authors.forename: Amrita
authors.initials: A
authors.lastname: Ghosh
authors.forename: Amitava
authors.initials: A
authors.lastname: Das
authors.forename: Hirendra N
authors.initials: HN
authors.lastname: Ghosh