The Low‐Lying Excited States of 2,2′‐Bithiophene: A Theoretical Analysis

Abstract

The low-energy region of the singlet-->singlet, singlet-->triplet, and triplet-->triplet electronic spectra of 2,2'-bithiophene are studied using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbitals (ANO) basis sets. The computed vertical, adiabatic, and emission transition energies are in agreement with the available experimental data. The two lowest singlet excited states, 1(1)Bu and 2(1)Bu, are computed to be degenerate, a novel feature of the system to be borne in mind during the rationalization of its photophysics. As regards the observed high triplet quantum yield of the molecule, it is concluded that the triplet states 2(3)Ag and 2(3)Bu, separated about 0.4 eV from the two lowest singlet excited states, can be populated by intersystem crossing from nonplanar singlet states.

Absorption and fluorescence properties of oligothiophene biomarkers from long-range-corrected time-dependent density functional theory

“…Throughout this work we use the CC2 energies as reference values for assessing the quality of the various TDDFT methods. We have previously found that the CC2 method correctly reproduces CASPT2 emission energies for unsubstituted bithiophene 61 and terthiophene 62 within 0.1 eV and 0.2 eV, respectively. 63 For absorption energies, a complete CASPT2 study of these systems is not available since small changes in the ground-state torsional angles can yield large variations (0.2 -0.3 eV 61,62 ) in the excitation energies.…”

The Versatile Thiophene: An Overview of Recent Research on Thiophene‐Based Materials

“…M. Rubio et al carried out a study on the low-lying excited states of 2,2¢-bithiophene using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbitals (ANO) basis sets. [105] Vertical excitation and emission energies as well as adiabatic transition energies were computed and related to experimental data. According to the authors, a noteworthy result of their study was the degeneracy found for the 1 Fig.…”

The elusive excited states of bithiophene: a CASPT2 detective story

“…It is perhaps the reason that there have been only few theoretical studies dealing with the excited states of bithiophene. Rubio et al [25,26] applied the CASSCF/CASPT2 methodology to study the lowest p-p* excitations of 2T. They reported a pair of B u states of similar energies (3.88 and 4.15 eV) and a third state of considerably higher energy (5.53 eV).…”