Relating Chromophoric and Structural Disorder in Conjugated Polymers

TL;DR

This study explores how conformational and chromophoric disorder in conjugated polymers like P3HT influence their optical properties, revealing that side-chain torsional disorder affects spectral signatures and excited state behavior.

Contribution

It provides a detailed quantum-classical simulation analysis linking structural disorder to optical spectral features in conjugated polymers, highlighting the role of side chains.

Findings

Chromophoric disorder results from excited state delocalization and electron-hole polarization.

Torsional disorder from side chains controls chromophoric disorder.

Increasing temperature causes a red-shift in absorption despite shorter chromophores.

Abstract

The optoelectronic properties of amorphous conjugated polymers are sensitive to conformational disorder and spectroscopy provides the means for structural characterization of the fragments of the chain which interact with light - "chromophores". A faithful interpretation of spectroscopic conformational signatures, however, presents a key challenge. We investigate the relationship between the ground state optical gaps, the properties of the excited states, and the structural features of chromophores of a single molecule poly(3-hexyl)-thiophene (P3HT), using quantum-classical atomistic simulations. Our results demonstrate that chromophoric disorder reflects an interplay between excited state de-localization and electron-hole polarization, and is controlled by torsional disorder that is specifically associated with the presence of side chains. Within this conceptual framework, we predict and explain a counter-intuitive spectral signature of P3HT: a red-shifted absorption, despite shortening of chromophores, with increasing temperature.