Photoluminescence\nSwitching in Quantum Dots Connected\nwith Carboxylic Acid and Thiocarboxylic Acid End-Group Diarylethene\nMolecules

We contrast the switching of photoluminescence (PL) of\nPbS quantum\ndots (QDs) cross-linked with photochromic diarylethene molecules with\ndifferent end groups, 4,4′-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic\nacid] (<b>1C</b>) and 4,4′-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenethiocarboxylic\nacid] (<b>2T</b>). Our results show that the QDs cross-linked\nwith the carboxylic acid end group molecules (<b>1C</b>) exhibit\na greater amount of switching in photoluminescence intensity compared\nto QDs cross-linked with the thiocarboxylic acid end group (<b>2T</b>). We also demonstrate that regardless of the molecule used,\ngreater switching amounts are observed for smaller quantum dots. Varying\nthese parameters allows for the fabrication of photoswitches with\ntunable PL change. We relate these observations to the differences\nin the HOMO energy levels between the QDs and the photochromic molecules.\nOur findings demonstrate how the size of the QDs and the energy levels\nof the linker ligands influences the charge tunneling rate and thus\nthe PL switching performance in tunneling-based photoswitches.