Abstract: Polydiphenylacetylenes (PDPAs) modified with D-/L-phenylglycine side chains have been prepared by post-polymerization modification strategy and their structures were well characterized using multiple spectroscopic technologies. Taking the advantage of the activated ester strategy, the species and content of the D-/L-phenylglycines in the polymers can be well-controlled. The chirality of these phenylglycine-modified PDPAs exhibits unique composition and solvent-dependent behaviors. No circular dichroism (CD) signals have been recorded for the homo-polymers P-L and P-D (with complete substitution by L- and D-phenylglycine) in different solvents. While some of the partially phenylglycine-substituted PDPAs exhibit induced CD signals, P-L (1:19) in tetrahydrofuran (THF) and dichloromethane (DCM) solutions, P-D (1:19) and P-D (1:39) in the mixtures of THF and dimethyl sulfone (DMSO) (the digitals in the brackets stand for the ratio between the L- or D-phenylglycine and activated ester groups). In addition to their chiral characteristics, these PDPAs show typical aggregation-enhanced emission (AEE) behavior. Over 220% enhancement in fluorescence intensity has been recorded for P-L (1:19) in THF/DMSO mixture solvent. Both of the substitution-/solvent-dependent chirality transmission and AEE behaviors can be associated with the strong interactions between the phenylglycine side chains, which are non-facile to the conformational change of the polydiphenylacetylene backbone and hinder the chirality transmission from side to main chains. Meanwhile, the strong interactions reduce the dissipation of the excited state energy by intramolecular motions and induce the fluorescence enhancement. These observations not only are experimentally consistent, but also theoretically compliant with the results of density function theory (DFT) and molecular dynamics (MD) simulations.

Key words: Polydiphenylacetylenes; post-polymerization modification, circular dichroism, aggregation-enhanced emission, hydrogen bond