Synthesis, characterization and emission switching behaviors of styrylphenyl-conjugated Ru(II)-terpyridine complexes via aggregation and trans–cis photoisomerization

[Display omitted] •Experimental and theoretical study on photoisomerization and aggregation behavior of Ru(II)-terpyridine complexes.•Polyaromatic and heteroaromatic moieties increase the emission characteristics via aggregation.•On-off and off-on emission switching is viable upon shining alternatively with visible and UV light.•Decrease in rate constant and quantum yield of photoisomerization with an increase in extent of aggregation.•DFT and TDDFT calculations are performed to interpret experimental spectral bands. An array of styrylphenyl-conjugated Ru(II)-terpyridine complexes have been designed and detailed investigation of their photophysical and electrochemical characteristics have been carried off. The compounds by virtue of the presence of polyaromatic units exhibit both aggregation-induced emission quenching and enhancement. Styrylphenyl units allow the trans–trans to trans–cis photoisomerization in the free- as well as aggregated form of the complexes upon irradiation with visible light which can be reverted back by shining with UV light. Hence, “on–off” and “off–on” switching of emission occurs upon consecutive treatment of complexes with different light sources. The rate constant and quantum yield of photoisomerization in both free and aggregated forms have been calculated and is found to decrease upon increase in extent of aggregation. Theoretical analysis through density functional theory (DFT) and time-dependent DFT methods was also carried out for appropriate band assignment and to have some insight for the occurrence of photoisomerization process.