Photofragmentation dynamics of n-dodecanethiol-derivatized silver nanoparticles in cyclohexane

Photochemical reaction of n-dodecanethiol-derivatized silver nanoclusters dispersed in cyclohexane has been studied in the picosecond-second time range and has been found to depend nonlinearly on the irradiance of photolysis light. The static absorption bleach by excitation at 532 and 355 nm increases with the irradiance raised to the powers of 1.9 and 1.4, respectively. Furthermore, transient absorption produced with a high-energy pulse rises further on a time scale of a few nanoseconds, whereas that with low-energy pulse decays. Transient absorption owing to the dielectric change of the immediately surrounding medium arises in 0.5 ns with the conduction of the thermalized photon energy. It decays in 1.4 ns as the heat spreads further. A fraction of excited nanoparticles experience a further absorption increase as hot alkanethiols dissociate for a period determined by the heat dissipation time (3.6 ns). The fraction increases with excitation-pulse energy. Within the recombination time (40 ns) of thiols, some dethiolated particles are also subject to fragmentation. Absorption bleach caused by disintegration recovers partially with a time constant of 0.13 s, as the fragments reassemble.