Synthesis, Photophysical, and Electrochemical Properties of β-Substituted Imidazole-Appended Metalloporphyrins and their NLO Application

Abstract

A new series of asymmetric β-substituted porphyrins, 2-(1H-imidazo[4,5-f][1,10] phenanthroline-2-yl)-5,10,15,20-tetraphenylporphyrin (MTPP(Phen)), where M = 2H, Co(II), Ni(II), Cu(II), or Zn(II) has been synthesised in good yields and thoroughly characterized using several spectroscopic methods, and MALDI mass spectrometry. The imidazole substitution on the porphyrin framework offers novel opportunities to explore their electronic and chemical characteristics, particularly redox and NLO activities. The redox behaviour of these complexes is notably affected by the central metal ion. All porphyrin complexes exhibited two reversible one-electron oxidations, except for CoTPP(Phen), which demonstrated three oxidation peaks, with the first occurring at 0.75 V, corresponding to the oxidation of Co(II) to Co(III). Femtosecond laser intensity-dependent third-order nonlinear optical studies revealed that CoTPP(Phen) exhibited the strongest optical nonlinearities compared to the other porphyrins under study. Among the series, CoTPP(Phen) showed the highest two-photon absorption coefficient (β) and cross-section (σ2PA) values, ranging from 14.53 to 70.08 × 10^−12 m/W and 0.299 to 1.55 × 10^5 GM, respectively.