Exploring Unusual Electrochemistry and Nlo Properties of Highly Electron-Deficient β-Functionalized Porphyrins

Abstract

A series of β-tetracyanobutadiene(TCBD) appended porphyrins, M-TCBDP (M = 2H (2), Cu(II) (3), Ni(II) (4), Co(II) (5), Zn(II) (6)) were synthesized and characterized by various spectroscopic and electrochemical techniques. These porphyrins exhibit mutiredox process. Particularly, the unusual reduction potential in the range of -0.06 to -0.10 V is the consequence of TCBD group present at the β-position. The existence of enhanced polarization and intramolecular charge transfer in the absorption spectra are held responsible for nonlinear optical responses exhibited by the M-TCBD series as compared to the precursor (H2-PE2 (1)). Femtosecond Z-Scan experiments were performed to elucidate the third-order nonlinear optical properties and the temporal response of these porphyrin molecules are investigated using pump-probe spectroscopy to study the excited state transient absorption dynamics. Z-scan measurement reveals that Co-TCBD (5) exhibits better nonlinear optical response as compared to free base porphyrins. Two-photon absorption coefficient (β) and the imaginary part of third-order NLO susceptibility (χ(3) ) were procured from open aperture experiment whereas close aperture experiment delivers magnitude and sign of nonlinear optical refractive index (η2) and the real part of χ(3) . The excellent optical limiting threshold of synthesized porphyrins makes them adorable material for laser protection.