Cyclometalated iridium(iii) complexes of (aryl)ethenyl functionalized 2,2′-bipyridine: synthesis, photophysical properties and trans–cis isomerization behavior

Abstract

The syntheses, photophysical studies and photoinduced behavior of 4,4′-(aryl)ethenyl functionalized 2,2′-bipyridyls (L1, L2) and cyclometalated heteroleptic iridium(III) complexes (1, 2) with L1–L2 as ancillary ligands have been investigated in detail. The explicit characterization by time dependent ¹H and 2D NMR, and time dependent electronic spectra supports an expected isomerization of L1 and L2 from trans–trans configuration to trans–cis and cis–cis configurations on exposure to 366 nm UV-vis light. Interestingly, the isomerization is restricted to only trans–cis configuration from the existing trans–trans form in the ligated L1 and L2 of complexes 1 and 2. The X-ray structure elucidation shows that the spatial arrangements of the (aryl)ethenyl moiety of L2 in complex 2, change with light exposure. The quantum chemical calculations by combined DFT-TDDFT give insight into the observed photophysical data. Furthermore, the rotational barriers of the isomerization of L1 and L2 were studied with variable temperature dependent ¹H NMR.