Surface Plasmon Enhanced Photocurrent Generation in Tetrapyrrolic Macrocycle Capped Gold Nanoparticles

Understanding the mechanism and charge transport functionality of semiconducting photoresponsive materials will allow the designing of smart photoresponsive devices, such as optical memory devices, photodetectors, and NIR imaging sensors. A novel semiconducting photoresponsive material consisting of a gold-nanocluster functionalized with a tetrapyrrolic macrocycle (rhodin G7) has been developed using the Turkevich method, such that the transfer of the singlet state excitation energy of a macrocycle to the Au nanocluster is feasible. Polydentate chromophoric ligands bearing carboxylic acid functional groups to stabilize gold nanoparticles are rare. Chromophore functionalized gold nanoparticles are generally prepared by a ligand replacement strategy or through the two-phase synthesis protocols (Brust's method). We propose a simple one-phase method, and the possible advantage of this synthesis is that one can get rid of surface contaminants from the costabilizer. Detailed structural, morphological, and spectroscopic characterizations were performed to understand the efficacy of this synthesis process. Transport measurements indicated a clean p-type transport wherein the hole mobility of the pristine molecule increases by at least 2 orders of magnitude upon the incorporation of Au nanoparticles. Consequently, the photoresponsivity increases from 1 to 576 mA/W in the best single-component broadband photodetectors, which overtakes commercial Si photodetectors, indicating the efficacy of the molecular design for smart optical devices.