Excited-State Structure Modifications Due to Molecular Substituents and Exciton Scattering in Conjugated Molecules

TL;DR

This paper uses tight-binding models to analyze how chemical substituents affect exciton scattering and excited-state structures in conjugated polymers, providing a theoretical framework for understanding property modifications.

Contribution

It introduces an analytical approach using exciton scattering matrices to describe the impact of molecular substitutions on excited states in conjugated polymers.

Findings

Scattering matrices effectively describe substituent effects on excitonic states.

Resonant and bound excitations are linked to zeros and poles of scattering amplitudes.

Application to phenylacetylenes with perylene substitution illustrates the model's utility.

Abstract

Attachment of chemical substituents (such as polar moieties) constitutes an efficient and convenient way to modify physical and chemical properties of conjugated polymers and oligomers. Associated modifications in the molecular electronic states can be comprehensively described by examining scattering of excitons in the polymer's backbone at the scattering center representing the chemical substituent. Here, we implement effective tight-binding models as a tool to examine the analytical properties of the exciton scattering matrices in semi-infinite polymer chains with substitutions. We demonstrate that chemical interactions between the substitution and attached polymer are adequately described by the analytical properties of the scattering matrices. In particular, resonant and bound electronic excitations are expressed via the positions of zeros and poles of the scattering amplitude, analytically continued to complex values of exciton quasi-momenta. We exemplify the formulated concepts by analyzing excited states in conjugated phenylacetylenes substituted by perylene.