Fast Visualized Conformational Transition of Polyphenylacetylenes with Stepwise Tunable Circularly Polarized Luminescence.

Abstract

Two novel poly(3,5-diamide substituted phenylacetylene)s bearing L- or D-alanine residues with a long alkyl chain were synthesized. In low polar or apolar solvents, the polymers adopted contracted cis-cisoid helix showing strong yellow fluorescence, which was transferred to stretched cis-transoid helix by adding polar solvents or decreasing temperature, accompanied with the disappearance of fluorescence. The critical conformational transition temperature could be readily tuned in a wide range by altering the content of polar solvent, and the conformational variation at molecular level could be directly read out via the change in fluorescent property. The synergistical participation of amide and ester groups in the formation of intramolecular hydrogen bonds accelerated the conformational transition rate, resulting in remarkable reduction of hysteresis. Moreover, the polymers displayed switchable CPL performance and the luminescent dissymmetry factor could be stepwise amplified by forming chiral aggregates or liquid crystalline structure. This study may open a new avenue for the development of controllable helical structure-based smart CPL materials.