Coherent dynamics of mixed Frenkel and Charge Transfer Excitons in Dinaphtho[2,3-b:2'3'-f]thieno[3,2-b]-thiophene Thin Films: The Importance of Hole Delocalization

TL;DR

This study combines ab initio calculations and quantum dynamics simulations to explore the coherent mixing and dynamics of Frenkel and charge transfer excitons in DNTT thin films, highlighting the importance of hole delocalization.

Contribution

It introduces a theoretical approach to analyze the optical properties and exciton dynamics in DNTT, revealing the extent of charge transfer character and coherent behavior.

Findings

Frenkel excitons in DNTT have 8-47% charge transfer character.

Coherent exciton dynamics occur within 50 fs after excitation.

Charge delocalization influences exciton mixing and decoherence.

Abstract

Charge transfer states in organic semiconductors play crucial roles in processes such as singlet fission and exciton dissociation at donor/acceptor interfaces. Recently, a time-resolved spectroscopy study of dinaphtho[2,3-b:2'3'-f]thieno[3,2-b]-thiophene (DNTT) thin films provided evidence for the formation of mixed Frenkel and charge-transfer excitons after the photoexcitation. Here we investigate optical properties and excitation dynamics of the DNTT thin films by combining ab initio calculations and a stochastic Schrodinger equation. Our theory predicts that the low-energy Frenkel exciton band consists of 8 to 47% CT character. The quantum dynamics simulations show coherent dynamics of Frenkel and CT states in 50 fs after the optical excitation. We demonstrate the role of charge delocalization and localization in the mixing of CT states with Frenkel excitons as well as the role of their decoherence.