Synthesis, characterization and third order nonlinear optical properties of trans-A2B-type cobalt corroles

Abstract

A series of trans-A₂B cobalt corroles, represented as [Cor(p-RPh)₂(p-NO₂Ph)]Co(PPh₃) (1–5), where Cor is trianion of the corrole, R is a CN, F, CH₃, C(CH₃)₃ or PhCH₂O at the para-position of the 5- and 15-meso-phenyl rings of the macrocycle, and NO₂ is at the para-position of the 10-meso-phenyl rings of the macrocycle, were designed and synthesized. Structural elucidation of the investigated cobalt corroles was carried out using common spectroscopic methods such as ¹H-NMR, FT-IR, and UV-vis spectroscopy and MALDI-TOF-MS. Each cobalt corrole undergoes two reversible one-electron oxidations and three reductions with E_1/2 values being linearly related to the sum of the Hammett substituent constants (∑σ). The third-order nonlinear optical (NLO) properties of these corroles were evaluated in DMF using the Z-scan technique characterized as showing a nonlinear reverse saturation absorption and self-defocusing behavior. The values of large nonlinear refractive index (n₂) and the two-photon absorption (β) coefficients were in the range of (−) 1.25–1.50 × 10⁻¹³ cm² W⁻¹ and (1.05–1.45) × 10⁻⁹ cm W⁻¹, respectively, making the current cobalt corroles a promising possibility for device realization.