Near-Infrared Luminescence in Trinuclear Mixed-Metal Chalcogenolate Complexes of the Types [M$_{2}$Ti(EPh)$_{6}$(PPh$_{3}$)$_{2}$] (M = Cu, Ag; E = S, Se) and [Na(thf)$_{3}$]$_{2}$[Ti(SPh)$_{6}$]

The optical properties of four new trinuclear chalcogenolato bridged metal complexes [Ag$_{2}$Ti(SPh)$_{6}$(PPh$_{3}$)$_{2}$], [Na(thf)$_{3}$]$_{2}$[Ti(SPh)$_{6}$], [Cu$_{2}$Ti(SePh)$_{6}$(PPh$_{3}$)$_{2}$], and [Ag$_{2}$Ti(SePh)$_{6}$(PPh$_{3}$)$_{2}$] have been investigated by absorption and photoluminescence spectroscopy as well as time-dependent density functional theory (TDDFT) calculations and compared to the results published recently for [Cu$_{2}$Ti(SPh)$_{6}$(PPh$_{3}$)$_{2}$]. All of these compounds are distinguished by efficient near-infrared luminescence at ∼880–1200 nm in the solid state at low temperatures, which remains quite intense for the copper–titanium complexes at ambient temperature with PL quantum yields of 9.5 and 4.8% at λPL = 1090 and 1240 nm for [Cu$_{2}$Ti(EPh)$_{6}$(PPh$_{3}$)$_{2}$], E = S, Se, respectively. According to the calculations, a peculiar feature of the lowest-energy electronic transitions in these complexes is their high localization on the metal and chalcogen atoms, with negligible contributions of the “external” ligand groups. Correspondingly, the type of atoms in the M$_{2}$TiE$_{6}$ (M = Cu, Ag, Na) core structure determines optical properties such as the absorption and emission wavelengths and PL lifetime.