Optical spectra obtained from amorphous films of rubrene: Evidence for predominance of twisted isomer

TL;DR

This study investigates the optical properties of rubrene, revealing that the twisted isomer predominantly influences the optical spectra in thin films through combined experimental and theoretical analysis.

Contribution

It provides a detailed vibronic analysis of rubrene's optical spectra and demonstrates the dominance of the twisted isomer in thin film spectra using both experimental data and DFT calculations.

Findings

The vibronic progression of rubrene's absorption band was characterized.

Density functional calculations matched experimental spectra well.

The twisted isomer dominates the optical spectra in thin films.

Abstract

In order to investigate the optical properties of rubrene we study the vibronic progression of the first absorption band (lowest \pi -> \pi^* transition). We analyze the dielectric function of rubrene in solution and thin films using the displaced harmonic oscillator model and derive all relevant parameters of the vibronic progression. The findings are supplemented by density functional calculations using B3LYP hybrid functionals. Our theoretical results for the molecule in two different conformations, i.e. with a twisted or planar tetracene backbone, are in very good agreement with the experimental data obtained for rubrene in solution and thin films. Moreover, a simulation based on the monomer spectrum and the calculated transition energies of the two conformations indicates that the thin film spectrum of rubrene is dominated by the twisted isomer.