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

Abstract

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.

Tuning the Organelle-Specific Imaging and Photodynamic Therapeutic Efficacy of Theranostic Mono- and Trinuclear Organometallic Iridium(III) Complexes

“…The spectral features are presented in Figure . The usual electronic transition for cyclometalated iridium­(III) complexes with N∩N-type ancillary ligands involves metal-to-ligand charge transfer, where an electron is promoted from a metal d orbital to a vacant π* orbital of the ancillary ligand and ligand-centered (LC) transitions in which an electron is promoted from the π-orbital to one of the coordinated ligands . These assignments fit well with the mononuclear complexes IrA1, IrA2, IrB1, and IrB2, and we observe the lowest energy MLCT absorption maxima around 450–470 nm for IrA1, 2 and IrB1 and around 538 nm for IrB2.…”

Fluorescent metal nanoclusters: prospects for photoinduced electron transfer and energy harvesting

“…Cyclometalated trinuclear iridium (Ir) and rhenium (Re) complexes were also employed to show a photoinduced intramolecular electron transfer (PIIET)-driven excited state intersystem charge transfer (ESICT) to AuNCs. 60 This composite has not been utilized for widespread applications. PET with AuNCs is important in biological systems to target specific enzymes and proteins.…”

“…53,54 In this context, we have significantly contributed towards understanding the photophysical properties of MNCs and ways to manipulate them in various microenvironments. [55][56][57][58][59][60] Harvesting energy and studying photogenerated electron-hole recombination processes are some of the hottest topics of current research. [61][62][63][64] These are the backbones of alternative energy resources and are important for biological events.…”