Crystallization-Driven Self-Assembly toward Uniform Nanofibers Containing a Donor–Acceptor Core with Near-Infrared Absorption/Emission, Photodynamic, and Photothermal Activities: A Small Variation on the Structure of Donor–Acceptor Segment Matters

Abstract

Although living crystallization-driven self-assembly (CDSA) has emerged as a facile approach to generate uniform π-conjugated-polymer-based fiber-like micelles, the extension of living CDSA to prepare uniform donor–acceptor (D–A) fiber-like micelles of controlled length with attractive near-infrared (NIR) absorption/emission, photodynamic (PD), and photothermal (PT) properties is virtually unexplored. Herein, three block copolymers composed of the same corona-forming P2VP 44 (P2VP = poly(2-vinylpyridine), the subscript is the degree of polymerization) but different D–A π-conjugated core-forming co-oligomers of OPE 4 -DPP-OPE 4 (OPE 4 = oligo( p -phenylene ethynylene), DPP = diketopyrrolopyrrole) are designed and synthesized to probe the steric and electronic effect of co-oligomers of OPE 4 -DPP-OPE 4 on their CDSA behaviors and photophysical properties. One co-oligomer contains a DPP with two 2-ethylhexyl side chains flanked by two thiophene-OPE 4 segments ( b -T-OPE 4 -DPP-OPE 4 ). The variation of the second one is the replacement of 2-ethylhexyl side chains with linear octyls ( l -T-OPE 4 -DPP-OPE 4 ). The last one is composed of a DPP with two linear octyl side chains flanked by two phenylene-OPE 4 segments ( l -P-OPE 4 -DPP-OPE 4 ). Uniform fiber-like micelles can be generated by a self-seeding approach for b -T-OPE 4 -DPP-OPE 4 - b -P2VP 44 and l -P-OPE 4 -DPP-OPE 4 - b -P2VP 44, whereas polydisperse fiber-like micelles only can be obtained for l -T-OPE 4 -DPP-OPE 4 - b -P2VP 44 likely due to the multiple packing modes of l -T-OPE 4 -DPP-OPE 4 . Intriguingly, the aging of micelles of l -T-OPE 4 -DPP-OPE 4 - b -P2VP 44 can promote the conversion of the packing mode of l -T-OPE 4 -DPP-OPE 4 units to their most thermodynamically stable packing mode, and thus, self-seeding of aged seed micelles of l -T-OPE 4 -DPP-OPE 4 - b -P2VP 44 gave uniform fiber-like micelles of controlled length. More interestingly, micellar solution of b -T-OPE 4 -DPP-OPE 4 - b -P2VP 44 exhibits NIR absorption/emission, PT, and PD activities upon the light irradiation at 660 nm. Although micellar solution of l -T-OPE 4 -DPP-OPE 4 - b -P2VP 44 also shows NIR absorption/emission and PT activity, its PD activity is much lower relative to that of b -T-OPE 4 -DPP a -OPE 4 - b -P2VP 44 . The micellar solution of l -P-OPE 4 -DPP-OPE 4 - b -P2VP 44 exhibits neither NIR absorption/emission nor PT/PD activities upon the light irradiation at 660 nm. All these results showed that a small variation of structure of OPE 4 -DPP-OPE 4 can lead to distinct CDSA behaviors and absorption/emission/PD/PT properties.

Topics & Concepts