Order–disorder transitions of π-conjugated polymers in condensed phases. I. General theory

Abstract

A novel statistical mechanical theory for the order–disorder transformations of conjugated polymers in dilute solution and neat amorphous films is proposed. Single chain configurational statistics and the conformation-dependent polymer–solvent interactions are included in the basic formulation. Abrupt transition phenomena arise from the energetic stabilization of the rod-like conformation via the interaction of the delocalized electrons of the polymer backbone with the surrounding polarizable solvent. The theory is developed in detail for π-conjugated polymers (polyenes and polydiacetylenes) in dilute solution and makes a significant number of qualitative and quantitative predictions. Available experimental data are consistent with the theoretical picture and a variety of additional experiments are suggested to critically test the proposed ideas. The statistical mechanical formalism is generalized to allow for intramolecular hydrogen bonding, polydispersity, solvent mixtures, defect correlations, and substituent disorder. These effects have quantitative consequences but do not change the qualitative physics of the proposed three-dimensional solvation mechanism for the coupled electronic-conformational transitions. Preliminary application of the theory to amorphous films is briefly considered.