Synthesis and comparative studies of photophysical and electrochemical properties of three different types of new heteroleptic 5-arylazo-8-hydroxyquinoline complexes of rhodium including trans → cis isomerism studies

Refluxing [Rh(2-phpy)₂(Cl)]₂ separately with the equivalent amount of 5-phenylazo-8-hydroxyquinoline (Hq¹), 5-(4-fluorophenylazo)-8-hydroxyquinoline (Hq²) and 5-(4-nitrophenylazo)-8-hydroxyquinoline (Hq³) in toluene in aerobic condition afforded mononuclear orange coloured compounds having general formula [Rh(2-phpy)₂(q)] in excellent yields. The complexes were substantiated by IR, ¹H NMR, ESI-mass, EPR, UV–Vis and emission spectra, cyclic voltammetry, single-crystal X-ray structure determinations and density functional theory (DFT) calculations. Synthesis and comparison of their photophysical and electrochemical properties of a new branch of rhodium(III) complexes of 8-hydroxyarylazo analogues are presented which are never studied before. The ground and excited-state geometries, absorption, and emission properties of the complexes were examined by DFT and TDDFT methods. The excitations and emissions are investigated by the natural transition orbital (NTO) analysis. The emission occurred via ³MLCT or ³ILCT transition by theoretical analysis of triplet state DFT calculations. The cis-trans isomerism studies for the azo complexes have been done by experimental as well as theoretical analysis.