Precision Preparation of π-Conjugated-Polymer-Based Nanofibers with Shell Tailorability by Combining Living Crystallization-Driven Self-Assembly with Nitrile <i>N</i>-Oxide-Based Cycloaddition

Living crystallization-driven self-assembly (CDSA) has been regarded as a powerful strategy to generate π-conjugated-polymer-based nanofibers (CPNFs). However, the limited morphological stability and surface tailorability of the resulting CPNFs hinder board applications. Development of highly efficient and facile strategies endowing CPNFs with morphological stability and surface tailorability is, thus, highly desirable. Herein, we report a versatile and facile platform to create uniform CPNFs with controlled length/composition, excellent stability, and surface tailorability by combining living CDSA with the nitrile N-oxide (NNO)-based “click” reaction. We prepare uniform CPNFs of controlled length/composition containing a PNAAM (poly(N-allyl acrylamide)) corona and an OPV5- (OPV = oligo(p-phenylenevinylene)) or OPE4-DPP-OPE4-based (OPE = oligo(p-phenylene ethynylene), DPP = diketopyrrolopyrrole) core by living CDSA. It is found that NNO units selectively react with alkenes (vinyls) of the PNAAM segment, leaving the chemical structure of the alkene- and alkyne-containing OPV5- and OPE4-DPP-OPE4 intact. 1,3-Dipolar cycloaddition of nitrile N-oxide (NNO) with alkenes of PNAAM segments is then employed to make the shell of the CPNFs cross-link at ambient temperature without the usage of any catalyst and production of any byproduct; the resulting CPNFs exhibit excellent morphological stability in organic solvents and at elevated temperature. By the cycloadditions, additional fluorescent dyes also are introduced into the corona-forming PNAAM segment, which allows the preparation of uniform continuous and segmented CPNFs with high fluorescence by the living CDSA. Additionally, the resulting CPNFs show limited cytotoxicity against both H1299 and HepG2 cell lines, even if the micelles can be uptaken by H1299 cells. This works not only broadens the application scope of NNO-based click ligation but also provides a versatile platform to create CPNFs of varying functionalities and high stability by combining living CDSA and NNO-based click reaction.