Suppression of Photoexcited Small Polarons-Mediated Energy Transfer to Boost Photoluminescence of Lanthanide-Titanium Nanoclusters.

Lanthanide (Ln)-titanium-based molecular nanoclusters (NCs) have attracted much attention due to their atomically precise total structure and promising optical behavior, while there is still minimal cognition of structure-dictated electron relaxation dynamics in such an NCs regime with unsatisfied photoluminescence quantum yield (PLQY, in general below 20%). Herein, the photoexcited small polarons (i.e., local electron-phonon coupling) are identified and emphasized in modulating the emission of Ln NCs. Taking 4--butylbenzoate coordinated EuTi NCs as a model, the excited electron is capable of being captured by the Ti to form the Ti-dominated small polarons, which allows influencing the ligands-sensitive antenna effect for Eu emission. Most importantly, by chelating the EuTi NCs with EuTi units bilaterally, the evolved EuTi NCs perform suppressed lattice vibration and therefore eliminate the photoexcited small polaron-mediated energy transfer, giving a remarkable enhancement in PLQY, from 17.6% to 73.1%.