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

Abstract

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 π‐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 (Kc) of 1.22 × 106. 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.

Heterocycle‐ and Amine‐Free Electrochromic and Electrofluorochromic Molecules for Energy‐Saving See‐Through Smart Windows and Displays

“…[74] To visualize the molecular orbitals of the TBF based systems, we used time-dependent density functional theory (TD-DFT) calculations, using a B3LYP exchange-correlation functional [75][76][77] with the Grimme's-D3 empirical dispersion correction [78] /6-31G** basis set. [79] In Figures 6a and b, the HOMOs were more delocalized over the TBF core unit due to their high electron donating nature and the LUMOs were found on the electron accepting units (cyano, fluoro and aldehyde units). The calculated HOMO-LUMO gap shows that TBFFA reduces by 0.1 eV compared to that of TBFCN.…”

Photophysical and redox properties of new donor–acceptor–donor (DAD) compounds containing benzothiadiazole (A) and dimethyldihydroacridine (D) units: a combined experimental and theoretical study

“…10–16 Moreover, these films frequently show interesting electrochemical activity over a wide potential range since both D and A segments are often characterized by several reversible redox couples. 17 Thus, electrochemically prepared films are perspective electrochromic materials providing electrochromism not only in the visible range of the spectrum but also in near infrared, 10,18–21 which is of great technological interest. 22…”