Synthesis and photophysical studies of back-to-back dinuclear platinum terpyridine complexes with different substituents on the bridging ligand

Four back-to-back dinuclear platinum terpyridine complexes with different substituents on the bridging ligand (1a-1d) were synthesized and characterized. Their electronic absorption, photoluminescence and triplet transient difference absorption were systematically investigated. All complexes exhibit strong ¹MLCT/ ¹ILCT absorption bands in the visible region, which significantly red-shifts when electron-donating substituents are introduced on the conjugated bridge and blue-shifts when electron-withdrawing substituents are present. Excitation of 1a and 1d in solution at their respective low-energy absorption band at room temperature results in an orange and red luminescence, respectively, which can be tentatively attributed to the ¹MLCT/ ¹ILCT excited state. These complexes exhibit intense broad triplet transient difference absorption in the visible to the near-IR region, which likely arises from the ligand-localized states ( ³π,π* or ³ILCT). Electron-donating substituent causes a pronounced red-shift, while electron-withdrawing substituents induce a blue-shift of the triplet transient absorption bands.