Abstract

Abstract Thiophenolate-capped US particles (PhS-capped CdS) of two different particle sizes (∼18 A and ∼30 A) were subjected to nanosecond laser flash photolysis (299 or 355 nm) in acetonitrile in the presence and absence of a hole scavenger. The effects of particle size and of the identities of the capping agent and hole scavenger on the efficiency of the formation and decay of trapped holes at the surface of these particles were studied. The transient absorption of the thiophenyl radical (PhS), produced by hole trapping in the presence of diethyldithiocarbamate (Et 2 NCS 2 − ), differs from that reported for non-capped CdS colloids. The observed transi absorption spectrum shifted to shorter wavelengths with a decrease in particle size. The transient bleaching observed at short wavelengths in the large (∼30 A) PhS-capped CdS particles was not observed in the analogous small (∼18 A) particles. The decay of the transient absorption of the small (∼18 A) PhS-capped CdS particles is faster than that of large (∼30 A) ones. The dominant decay pathway for trapped holes is the reaction of surface-bound PhS- with adsorbed phenolate groups that exists in excess at the surface of the capped particle.

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