title: Effect of Molecular Coupling on Ultrafast Electron-Transfer and Charge-Recombination Dynamics in a Wide-Gap ZnS Nanoaggregate Sensitized by Triphenyl Methane Dyes.
abstract: Wide-band-gap ZnS nanocrystals (NCs) were synthesized, and after sensitizing the NCs with series of triphenyl methane (TPM) dyes, ultrafast charge-transfer dynamics was demonstrated. HRTEM images of ZnS NCs show the formation of aggregate crystals with a flower-like structure. Exciton absorption and lumimescence, due to quantum confinement of the ZnS NCs, appear at approximately 310 and 340 nm, respectively. Interestingly, all the TPM dyes (pyrogallol red, bromopyrogallol red, and aurin tricarboxylic acid) form charge-transfer complexes with the ZnS NCs, with the appearance of a red-shifted band. Electron injection from the photoexcited TPM dyes into the conduction band of the ZnS NCs is shown to be a thermodynamically viable process, as confirmed by steady-state and time-resolved emission studies. To unravel charge-transfer (both electron injection and charge recombination) dynamics and the effect of molecular coupling, femtosecond transient absorption studies were carried out in TPM-sensitized ZnS NCs. The electron-injection dynamics is pulse-width-limited in all the ZnS/TPM dye systems, however, the back electron transfer differs, depending on the molecular coupling of the sensitizers (TPM dyes). The detailed mechanisms for the above-mentioned processes are discussed.
authors.affiliation: Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400 085, India.
authors.forename: Tushar
authors.initials: T
authors.lastname: Debnath
authors.affiliation: Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400 085, India.
authors.forename: Partha
authors.initials: P
authors.lastname: Maity
authors.affiliation: Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400 085, India.
authors.forename: Jayanta
authors.initials: J
authors.lastname: Dana
authors.affiliation: Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400 085, India. hnghosh@barc.gov.in.
authors.forename: Hirendra N
authors.initials: HN
authors.lastname: Ghosh
keywords: ZnS; charge transfer; electron injection; nanostructures; triphenyl methane dyes