Near-IR Electrochromic Dihydroindolo(2,3a)carbazole-Based Macrocycles and Their [b]-Annulated BODIPY Complexes

A new class of redox-active dihydroindolo(2,3a)carbazole(InC)-based porphyrin-like macrocycles (thiophene embedded: InCT and p-phenylene embedded: InCB) and the corresponding [b]-annulated BODIPY complexes (InCTBF2 and InCBBF2) are reported. A facile synthetic methodology is adopted to accomplish the new expanded-porphyrin-like macrocyclic systems using the key precursor 11 based on 11,12-dihydroindolo(2,3a)carbazole building block 4. In these macrocyclic systems, the subunit 4 is deemed to be a donor and an azafulvene-extended with & pi;-conjugated fragment (thiophene or p-phenylene) acts as an acceptor. Single crystal X-ray structures are obtained for both InCT and InCB. Spectroelectrochemical studies on these macrocycles and their BF2 complexes display intriguing near-IR electrochromic properties with reversible multi-color switching upon cathodic scans at room temperature. InCTBF2 shows high stability with a radical comproportionation constant (K-c) of 1.22 x 10(6). Thiophene and p-phenylene subunits in InCT and InCB exhibit ring rotation at room temperature as evident from NMR studies. Such ring rotation is restricted upon BF2 complexation, and they show unusual stability in acidic conditions.