Bis-Fischer Indole[3,2-b]carbazole Modification of [10]Cycloparaphenylenes: Tuning Optical Properties Through Rigid Substitution

Abstract

The rigid bis-Fischer indolo[3,2-b]carbazole and [n]cycloparaphenylenes ([n]CPP) have garnered interest due to their unique electronic behavior and optoelectronic properties. We have combined 2,8-di-tert-butyl-5,11-dihydroindolo [3,2-b]carbazole (BH-ICZ) with [10]CPP to form BH-ICZ[10]CPP, where the introduced BH-ICZ fragment reduces the symmetry of the original [10]CPP parent structure, and amplifies the previously weak absorption band at 450 nm. Compared with unmodified [10]CPP, the fluorescence wavelength shows a significant redshift, and the solvatochromic effect becomes more pronounced with increasing solvent polarity, reaching 553 nm in dimethyl sulfoxide. Its photoluminescence quantum yield (PLQY) initially increases and then decreases, peaking at 0.92 in dichloromethane, which is significantly higher than that of both [10]CPP and BH-ICZ. Calculations highlight the origin of intramolecular charge transfer within BH-ICZ[10]CPP and the elimination of Laporte-forbidden transitions. The interaction between the BH-ICZ fragment and the solvent enhances the solvatochromic effect, underscoring the critical role of the introduced fragment in tuning fluorescence behavior. This research makes it a promising and worthwhile area for exploration.