Theoretical study on porphyrin arch-tapes of carbonyl-inserted seven-membered rings with high nonlinear optical properties

Porphyrin tapes have attracted extensive attention because their fully conjugated pi-networks act as nonlinear optical (NLO) materials. A family of Ni(ii) and Zn(ii) porphyrin arch-tapes that are connected by varying bridge (B) ligands (meso-meso beta-beta doubly linked dimer 1, meso-meso beta-beta beta-beta triply linked dimer 3, methylene-inserted dimer 2 and trimer 5, carbonyl-inserted dimer 4, trimer 6, and Zn(ii) trimer 7) have been synthesized by a density functional theory (DFT) method. The results show that carbonyl-inserted arch-tapes significantly enhance second hyperpolarizability (gamma), indicating that the remarkably contorted structure incorporated seven-membered ring(s) directly affect their NLO properties of our focus. Moreover, the electronic absorption spectra calculated for all studied complexes with time-dependent DFT theory (TDDFT) predict that carbonyl-inserted complex 4 contributes to a red-shift of the Q-band (160 nm) for the meso-meso beta-beta doubly linked complex 1. The third-order NLO responses and the electron transition properties strongly depend on the nature of the bridge (B) ligand, which means that an active involvement of the carbonyl group presents an advantage for its application in NLO materials. Carbonyl-inserted arch-tapes displayed distinctly nonlinear optical properties owing to an active involvement of the carbonyl group(s) in electronic conjugation.

Automated summary

Porphyrin tapes with varying bridge ligands were synthesized and their nonlinear optical properties and electron conjugation were studied. The carbonyl-inserted arch-tapes showed enhanced nonlinear optical responses and the structure contortion directly affected their optical properties.