A Versatile Strategy toward Donor–Acceptor Nanofibers with Tunable Length/Composition and Enhanced Photocatalytic Activity

Abstract

Living crystallization-driven self-assembly (CDSA) has emerged as an efficient strategy to generate nanofibers of π-conjugated polymers (CPNFs) in a controlled fashion. However, reports of donor–acceptor (D–A) heterojunction CPNFs are extremely rare. The preparation of these materials remains a challenge due to the lack of rational design guidelines for the D–A π-conjugated units. Herein, we report a versatile CDSA strategy based upon carefully designed D–A-co-oligomers in which electron-deficient benzothiadiazole (BT) or dibenzo[b,d]thiophene 5,5-dioxide (FSO) units are attached to the two ends of an oligo(p-phenylene ethynylene) heptamer [BT-OPE₇-BT, FSO-OPE₇-FSO]. This arrangement with the electron-deficient groups at the two ends of the oligomer enhances the stacking interaction of the A–D–A π-conjugated structure. In contrast, D–A–D structures with a single BT in the middle of a string of OPE units disrupt the packing. We employed oligomers with a terminal alkyne to synthesize diblock copolymers BT-OPE₇-BT-b-P2VP and BT-OPE₇-BT-b-PNIPAM (P2VP = poly(2-vinylpyridine), PNIPAM = poly(N-isopropylacrylamide)) and FSO-OPE₇-FSO-b-P2VP and FSO-OPE₇-FSO-b-PNIPAM. CDSA experiments with these copolymers in ethanol were able to generate CPNFs of controlled length by both self-seeding and seeded growth as well as block comicelles with precisely tunable length and composition. Furthermore, the D–A CPNFs with a BT-OPE₇-BT-based core demonstrate photocatalytic activity for the photooxidation of sulfide to sulfoxide and benzylamine to N-benzylidenebenzylamine. Given the scope of the oligomer compositions examined and the range of structures formed, we believe that the living CDSA strategy with D–A-based co-oligomers opens future opportunities for the creation of D–A CPNFs with programmable architectures as well as diverse functionalities and applications.