Abstract
We report here the synthesis and structural characterization of a new class of homoleptic terpyridine complexes of Ru(II) containing styrylbenzene moieties to improve room-temperature luminescence properties. Solid-state structure determination of 2 was done through single-crystal X-ray diffraction. Tuning of photophysical properties was done by incorporating both electron-donating and electron-withdrawing substituents in the ligand. The complexes exhibit strong emission having lifetimes in the range of 10.0-158.5 ns, dependent on the substituent and the solvent. Good correlations were also observed between Hammett σ(p) parameters with the lifetimes of the complexes. Styrylbenzene moieties in the complexes induce trans-trans to trans-cis isomerization accompanied by huge alteration of their spectral profiles upon treating with UV light. Reversal of trans-cis to trans-trans forms was also achieved on interacting with visible light. Change from trans-trans to the corresponding trans-cis form leads to emission quenching, whereas trans-cis to the corresponding trans-trans form leads to restoration of emission. In essence, "on-off" and "off-on" photoswitching of luminescence was observed. Calculations involving density functional theory (DFT) and time-dependent-DFT methods were performed to understand the electronic structures as well as for appropriate assignment of the absorption and emission bands.