Ultrafast Dynamics and Strong Two-Photon Absorption Properties of Nonplanar β-Functionalized Push-Pull Copper Corroles with a Mixed Substituent Pattern

A new series of nonplanar and unsymmetrically beta-functionalized push-pull copper corroles, CuTPC(CHO)R-7 [R = H, Br, Ph, Me, or 2-thienyl (Th)], were synthesized and characterized to elucidate the effect of beta-functionalization and nonplanarity on the photophysical, redox, and nonlinear optical (NLO) properties on the corrole ring. The synthetic route to unsymmetrically beta-octasubstituted copper corroles includes bromination of CuTPC(CHO) to get CuTPC(CHO)Br-7 in 80% yield, which was further subjected to the Pd-catalyzed Suzuki reaction. CuTPC(CHO)Br-7 exhibited a large red shift in the Soret band (Delta lambda(max) = 35-40 nm) and both the Q bands (Delta lambda(max) = 10-50 nm), as compared to CuTPC and CuTPC(CHO). CuTPC(CHO)Br-7 was 510 and 290 mV anodically shifted in the first oxidation and the first reduction compared to CuTPC owing to the strong -I effect of CHO and Br groups. Density functional theory studies revealed that all the beta-octasubstituted copper corroles exhibited highly nonplanar saddle-shape conformation of the corrole ring. Very high torsional saddling was observed for CuTPC(CHO)Th-7 (79-83 degrees) than that for CuTPC (49-53 degrees), even larger than that for CuTPCBr8 (67-70 degrees). Femtosecond laser-induced third-order NLO studies from these copper corroles showed strong two-photon absorption cross-sections (0.48-6.98 x 10(4) GM) and self-focusing-type positive nonlinear refraction behavior. The observed structure-dependent two-photon absorption coefficients (beta) are in the range of similar to 2.7-20.9 x 10(-12) m/W, and the n(2) values are in the range of similar to 0.64-6.45 x 10(-18) m(2)/W. The present results may facilitate a new window for these copper corroles in nonlinear optical devices, femtosecond optical limiters, and many other ultrafast photonic applications.

Automated summary

This article investigates the photophysical, redox, and nonlinear optical properties of nonplanar and unsymmetrically beta-functionalized copper corroles. The results show the significant impact of beta-functionalization and nonplanarity on the corrole ring. These findings may open up new possibilities for nonlinear optical devices, femtosecond optical limiters, and other ultrafast photonic applications.