Systematic Conversion of Photoinduced Intramolecular Electron Transfer in Trinuclear M‑Ir‑M (M = Re, Ir) Complexes to Intersystem Charge Transfer by Coupling to Gold Nanoclusters

Two trinuclear cyclometalated iridium­(III)-based complexes of M-Ir-M (M = Re, Ir) type were strategically designed with characteristically different electron distributions based on the electronegativities of Re and Ir. Photoinduced intramolecular electron transfer (PIIET) is readily observed in these complexes with different lifetimes of the radicals. The free amine ends of these symmetric complexes act as the electron donor for PIIET. These ends, on the other hand, can also act as centers for reducing gold (Au) salt (HAuCl4·3H2O) to generate Au atomistic nanoclusters (AuNCs) protected and templated by the trinuclear complexes. Formation of the AuNCs completely stops the PIIET and induces excited state intersystem charge transfer (ESICT) from the surrounding complexes to the AuNC core on exciting the system with radiation of the same wavelength. The trinuclear cyclometalated complexes were synthesized by chelation of the transition metal units, such as Re­(CO)3Cl and Ir­(ppy)2, to thiosemicarbazone (TSC) appended with cyclometalated ligands of the precursor Ir­(III) complex. Such a phenomenon of conversion of PIIET in a trinuclear cyclometalated coordination complex completely to ESICT on coupling to a noble metal nanocluster is unique and promising for applications in energy devices.