Low-Energy Electronic Excitations of N-Substituted Heteroacene Molecules: Matrix Isolation Spectroscopy in Concert with Quantum-Chemical Calculations.

Jean Thusek,Olena Tverskoy,Olaf Hübner,Hans‐Jörg Himmel,Uwe H F Bunz,Marvin Hoffmann,Andreas Dreuw

doi:10.1002/chem.201903371

Abstract

N‐Heteropolycycles are attractive as materials in organic electronic devices. However, a detailed understanding of the low‐energy electronic excitation characteristics of these species is still lacking. In this work, the matrix isolation technique is applied to obtain high‐resolution absorbance spectra for a series of tetracene and core‐substituted N‐analogues. The experimental electronic excitation spectra obtained for matrix‐isolated molecules are then analysed with the help of quantum‐chemical calculations. Additional lower energy excitation bands in the spectrum of the core‐substituted N‐derivatives of tetracene could be explained in terms of intensity borrowing from dipole‐forbidden transitions due to Herzberg–Teller vibronic coupling. In the case of tetracene, evidence for the additional formation of London dimers (J aggregates) is found at higher tetracene concentrations in the matrix.

Highlights

Acenes are linear polyaromatic hydrocarbons formally composed of annulated benzene rings.[1]
A comparative spectroscopic characterisation of a series of unsubstituted and core N-substituted members of the tetracene family was carried out by using classical solution and solid-state electronic absorbance spectroscopy, as well as measurements on samples of the species trapped in matrices of solid neon at 4 K
Compound 1 shows a clear splitting in the matrix electronic absorbance spectrum that is assigned to the formation of dimeric species (J aggregates) upon deposition

Summary

Introduction

Acenes are linear polyaromatic hydrocarbons formally composed of annulated benzene rings.[1] They have been attracting interest from both theoretical and experimental chemists for nearly a century.[2,3,4,5] In recent decades, polycyclic aromatic hydrocarbons, in general,[5,6,7] and acenes, in particular,[8,9,10,11] have gained attention as potential materials in organic electronic devices due to their low and tuneable optical and electronic properties.

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