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.