Synthesis, structural elucidation, electrochemical and UV/Visible absorption studies of pyridyl-carotenoid ligands to rhenium (I) and platinum (II)

Abstract

Condensation of all-trans-retinal and β-apo-8’-carotenal with 4-pyridyl acetonitrile monohydrochloride were performed. UV-Visible absorption data in acetonitrile of the condensed ligands show a bathochromic shift in its π→π* transition observed at λmax = 446 and 502 nm from 380 and 458 nm respectively. X-ray data for the pyridyl-retinal ligand showed space group symmetry of P21/n. Metal complexes of these ligands were further synthesized. Mass spectrometric analysis for the rhenium (I) complexes showed molecular ion peaks at m/z (ESI) = 811 for the retinal while the carotenal is observed at m/z (FAB) = 943. UV-Visible absorption data of the rhenium (I) complex showed solvatochromic behavior. The λmax of the shortchain was red shifted to 464 nm in acetonitrile and 511 nm in methylene chloride. The λmax of the long-chain was observed at 522 nm in acetonitrile and 612 nm in methylene chloride. UV-Visible absorption data of the platinum (II) complex of the short-chain also showed solvatochromism. It was observed at 458 nm in acetonitrile and 481 nm in dichloromethane. The λmax of the longchain was observed only at 542 nm in dichloromethane. Cyclic voltammetry showed irreversible oxidation peaks for all ligands and metal complexes.