Crystallization-Driven Self-Assembly of Oligo(p-phenylenevinylene) Derivatives toward π-Conjugated Nanostructures:...

Crystallization-driven self-assembly (CDSA) of π-conjugated homopolymers/oligomers has emerged as a versatile strategy to generate various nanostructures without an extra polymer corona layer. However, this field remains in its infancy, with rare reports concerning this topic. To get an in-depth understanding of how the structure of π-conjugated homopolymers/oligomers affects CDSA behavior, in this contribution, a series of oligo(p-phenylenevinylene) derivatives (OPV_n, where the subscript represents the number of repeat units) with different chain lengths (n = 3, 4, or 5) and chain end groups of aldehyde (CHO) and cyano/carboxyl (CN/COOH) were synthesized. The influence of the chain length and structure of the chain end groups of OPV on CDSA behavior was examined in detail. It was found that the increase in the chain length of OPV would increase the stacking strength of OPV units for both CHO- and CN/COOH-terminated OPV. In addition, the introduction of more electron-deficient CN/COOH units would lead to a more pronounced electron pull-push effect, which not only resulted in the red shift of the UV/vis absorbance and fluorescence bands of OPV but also increased the stacking strength of OPV units as a consequence of the enhancement of charge transfer interactions. CHO-terminated OPV₃-CHO and OPV₄-CHO and CN/COOH-terminated OPV₃-COOH remained in unimolecularly dissolved states in n-butanol at 25 °C. On the contrary, OPV₅-CHO formed ribbon-like micelles with widths in the range from ∼20 to ∼150 nm and lengths up to several micrometers, and OPV₄-COOH formed ribbon-like micelles with a width of ∼20 nm under the same conditions. Interestingly, tube-like micelles with a length of tens of micrometers could be formed for OPV₅-COOH. By virtue of acid-base interactions, amino-based porphyrins can be immobilized onto the surface of the micelles of OPV₅-COOH. This work demonstrates a vital role of the chemical structure of π-conjugated oligomers/polymers in determining CDSA behavior, which will be beneficial to extending CDSA toward the creation of various functional π-conjugated nanostructures.