Metal-Free Tetraphenylethylene and Dibenzo[g,p]chrysene with Thiazolo[5,4- <i>d</i> ] Thiazole-Based Donor–Acceptor Conjugated Microporous Polymers for the Efficient Photocatalytic Synthesis of 2-Substituted Benzimidazole

Abstract

The synthesis of benzimidazole is important because its derivatives are widely used in pharmaceuticals and functional materials due to their strong biological activity and ability to interact with biological targets. Herein, two photoactive conjugated microporous polymers (CMPs), TPE-TzTz and TBN-TzTz, featuring donor–acceptor (D–A) architectures, were successfully synthesized via a Schiff-base condensation reaction between dithiooxamide (DITH) and electron-rich aromatic donors─1,1,2,2-tetrakis[4-formyl-(1,1́-biphenyl)]ethane (TPE-4Ph-4CHO) and 2,7,10,15-tetra(4-formylphenyl) dibenzo[g,p]chrysene (TBN-4Ph-4CHO)─integrated with a thiazolo[5,4-d]thiazole (TzTz) acceptor unit. Brunauer–Emmett–Teller (BET) and thermogravimetric analysis (TGA) revealed that TPE-TzTz and TBN-TzTz CMP possess high specific surface areas of 484 and 419 m2 g–1, with total pore volumes of 1.2 and 0.2 cm3 g–1, respectively. These two CMPs also exhibited excellent thermal stability with 10% weight-loss temperatures (Td10) of 508 °C for TPE-TzTz CMP and 487 °C for TBN-TzTz CMP. Both TzTz CMPs display extended π-conjugation and efficient charge-carrier separation. Under visible-light irradiation, TPE-TzTz and TBN-TzTz CMPs showed outstanding photocatalytic activity in the oxidative cyclization of o-phenylenediamine with different derivatives of benzaldehyde to form benzimidazole derivatives. Notably, the TBN-TzTz CMP exhibited superior photocatalytic performance, which can be attributed to its more planar and rigid donor backbone, leading to enhanced π–π stacking and improved charge-carrier mobility. Furthermore, a plausible photocatalytic reaction mechanism was proposed based on experimental catalytic results and the calculated energy band structures of the CMPs. This study presents an effective strategy for designing D–A conjugated microporous polymers with high photocatalytic activity and expands the application of TzTz-based CMPs in photocatalytic organic transformations.