Synthesis,\nStructural, Electrochemical, and DFT Studies\nof Highly Substituted Nonplanar Ni(II) Porphyrins and Their Intensity-Dependent\nThird-Order Nonlinear Optical Properties

We designed and successfully synthesized highly substituted\nelectron-deficient\nnonplanar Ni(II) porphyrins and their derivatives (<b>1–7</b>) in moderate to good yields. These derivatives were comprehensively\ncharacterized by various spectroscopic techniques and single-crystal\nX-ray diffraction (SCXRD) analysis. SCXRD analysis confirmed the structures\nof compounds <b>2</b>, <b>4</b>, and <b>7</b>, adopting\nsaddle-shape geometry. These nonplanar porphyrins demonstrated significant\nbathochromic shifts in their absorption spectra compared to parent\nNiTPP, attributed to the influence of bulky <i>β</i>-substituents and/or peripheral fusion. π-Extended porphyrins <b>6</b> and <b>7</b> displayed panchromatic absorption spectra\nextending into the NIR region. Porphyrins <b>6</b> and <b>7</b> demonstrated a profound anodic shift (∼400 mV) in\ntheir first reduction peak potentials compared to precursor NiTPP(NO<sub>2</sub>)Br<sub>6</sub>. The experimental absorption spectral pattern\nmatches the simulated absorption spectra obtained from TD-DFT studies.\nThe femtosecond laser intensity-dependent third-order nonlinear optical\nstudies revealed that NiDFP(VCN)<sub>2</sub>Br<sub>6</sub> (<b>6</b>) and NiDFP(VCN)<sub>2</sub>(PE)<sub>6</sub> (<b>7</b>) displayed giant optical nonlinearities compared to the other porphyrins.\nAmong all, NiDFP(VCN)<sub>2</sub>Br<sub>6</sub> (<b>6</b>) possessed\nthe highest two-photon absorption coefficient (<i>β</i>) and cross-section (σ<sub>TPA</sub>) values in the range of\n22–33 × 10<sup>–10</sup> m/W and 3.77–6.95\n× 10<sup>6</sup> GM, respectively. These findings suggest that\nthe investigated nonplanar π-extended porphyrins are promising\ncandidates for future optoelectronic applications.