Synthesis, Characterization, and Redox Properties of Electron-Deficient Porphyrins with Dual Applications

To investigate the optoelectronic properties of extensively electron-deficient porphyrins, a series of mixed functionalized porphyrins with adjacent nitro (-NO₂) and cyano (-CN) functional groups at the β-pyrrolic positions were designed and synthesized via nucleophilic substitution reactions. The synthesized porphyrins were characterized by several spectroscopic techniques and confirmed by single-crystal X-ray diffraction analysis. The electron-deficient nature of porphyrins, as highlighted by their redox properties, makes the macrocycle a selective optical sensor for cyanide ions with a limit of detection of nearly 1 ppm. Furthermore, porphyrins were evaluated for their nonlinear optical responses. Femtosecond laser intensity-dependent third-order nonlinear optical studies were performed using a laser with the following specifications: 800 nm, 120 fs, and 84 MHz at an intensity of 3.0 × 10¹³ W/m². Among all analyzed porphyrins, free-base porphyrins exhibited higher nonlinear coefficients compared to metalated porphyrins. Moreover, highly substituted porphyrins showed high nonlinear coefficient values. 3-H₂ shows the highest (∼119 × 10^-11) two-photon absorption coefficient (β) and the highest negative nonlinear refractive index (-28.2 × 10^-17), making it suitable for optical limiting applications.