Stepwise Surface Ligand Engineering on Gold Nanoclusters: Controlled Photochemistry, Solvation Dynamics and Photosensitization

The effect of stepwise surface modification of 6-azo-thiothyamine (ATT) protected AuNCs (ATT-AuNCs), initially with l-Arginine (Arg@ATT-AuNCs) and further with cationic surfactants, such as CTAB (CTAB-Arg@ATT-AuNCs) and DTAB (DTAB-Arg@ATT-AuNCs), has been reported here. Stepwise surface ligand engineering (SSLE) significantly slows down the nonradiative transition rate in the following order: ATT-AuNCs < Arg@ATT-AuNCs < DTAB-Arg@ATT-AuNCs < CTAB-Arg@ATT-AuNCs, which increases the average radiative lifetime in the same order. This process also increases the photoluminescence quantum yield (PLQY) of the AuNCs following the same trend (2% < 41% < 58% < 72%). There is a simultaneous effect on the solvation dynamics of the respective AuNCs where the solvation time increases in the order ATT-AuNCs < Arg@ATT-AuNCs < DTAB-Arg@ATT-AuNCs < CTAB-Arg@ATT-AuNCs. Methyl viologen-derived photosensitization of the AuNCs and the subsequent effect on photoinduced electron transfer (PET) efficiency is tested. These AuNCs are singlet oxygen generators which modulate exactly in the same order to that of the solvation time and the PLQY. This, to our knowledge, is the first comprehensive report on the effect of SSLE on AuNCs to control photochemistry, solvation dynamics and photosensitization with singlet oxygen generating propensity.