<i>Meso</i>‐<i>β</i> Monofused Porphyrins: Synthesis, Structural, Spectral, Electrochemical and DFT Studies and Their Efficient Third‐Order Nonlinear Optical Properties

Abstract Three new series of β ‐to‐ ortho ‐phenyl monofused porphyrins, denoted as MMFP(MN)X 2 (where MFP=monofused porphyrin, MN=malononitrile and X=H or Br) and MMFP(MN)MB (where MB=mono benzo, M=2H, Co(II), Cu(II) and Zn(II)) were designed and successfully synthesized with good yields. These compounds were thoroughly characterized using various spectroscopic techniques and single crystal X‐ray diffraction (SCXRD) analysis. Notably, three of the monofused porphyrins; CoMFP(MN)Br 2 , CuMFP(MN)Br 2 and ZnMFP(MN)MB crystallized unambiguously in a triclinic crystal system with a space group. The twist angle values for these structures ranged from 14.03° to 21.35°. The meso ‐ β peripheral fusion and substituents led to tunable electronic spectral features across the synthesized porphyrins. The first reduction and oxidation potentials of all the investigated monofused porphyrins exhibited significant anodically shift as compared to their parent tetraphenylporphyrins (TPPs), attributed to peripheral fusion and electron‐withdrawing substituents, which collectively led to a reduced HOMO–LUMO gap. Ultrafast third‐order nonlinear optical (NLO) studies revealed that these monofused porphyrins showed a strong two‐photon absorption coefficient ( β =0.18–39.06×10 −11 m/W) and effective cross‐section ( =0.03–8.05×10 5 GM) values along with self‐defocusing negative nonlinear refraction behaviour ( n 2 =(−)0.5–5.28×10 −16 m 2 /W). These findings open new avenues for the application of meso ‐ β fused porphyrins in optical limiters, optical devices and other optoelectronic applications.