Photo-switchable iron-terpyridine complexes functionalized with styrylbenzene unit

Abstract

The manuscript deals with synthesis, characterization, photophysics, and reversible trans-cis photoisomerization behaviours of three homoleptic Fe(II)-terpyridine complexes, ([Fe(tpy-pvp-X)2]2+ where XH, Me, and NO2) covalently coupled with photo-active styrylbeneze moiety. The complexes underwent trans-trans to cis-cis isomerization upon the action of both visible and UV light with remarkable change in their absorption and emission spectral profiles. The isomerization studies were performed in four different solvents, viz. DCM, MeCN, MeOH and DMSO with both UV and visible light sources. The reversal from cis-cis to trans-trans isomerization also proceeds, albeit very slowly, on keeping and can be accelerated upon heating. The rate, rate constant and quantum yield of photoisomerization were determined in all the solvents. The rate and quantum yield of isomerization found to be much higher in presence of visible light source in all solvents than that of UV light. To better understand the electronic structures and correctly assign the experimental optical spectral bands, DFT and TD-DFT computational studied were also carried out in their trans-trans, trans-cis and cis-cis forms. Reasonably good correlation between the experimental and calculated bands could lead us to assign the main absorption spectral bands of the compounds.