Radical Ions from 3,3′′′,3′′′″‐Tris(butylsulfanyl)‐2,2′:5′,2″:5″,2′′′,5′′′,2′′′′:5′′′′,2′′′″‐sexithiophene: An Experimental and Theoretical Study of the p‐ and n‐Doped Oligomer

Abstract

The 3,3''',3'''''-tris(butylsulfanyl)- 2,2':5',2'':5'',2''',5''',2'''':5'''',2'''''-sexithiophene 1 was investigated through spectroscopic (NMR, EPR, UV/Vis-NIR), electrochemical, spectroelectrochemical and theoretical (DFT) studies. The charged species obtained upon its oxidation and reduction were characterised, showing that 1 can exist in at least five different oxidation states, that is, a neutral species, a radical cation, a dication, a radical anion, and a dianion. The long term stability of the radical cation 1+. was evidenced by the 1H NMR study in the presence of small quantities of trifluoroacetic acid (TFA). This approach allowed a comparison of the relative broadening of proton signals of 1, induced by the electron exchange process with traces of radical cation 1+., and the hfc (hyperfine coupling) constants obtained from the EPR study and DFT calculations. In the radical cation, all of the heterocyclic sulphur atoms are not significantly involved in the delocalisation of the unpaired electron, whereas the opposite holds for the radical anion. Time-dependent DFT calculations reproduced well the wavelengths of the optical transitions observed in the spectroelectrochemical experiments for all the five oxidation states and support the formation of the dianion 1(2-).

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

“…[103] A theoretical DFT study on the radical cations and anions of a sexithiophene bearing four beta alkylsulfanyl groups was reported by A. Alberti et al, and the results compared experimental electrochemical, electron paramagnetic resonance, and NMR data. [104] A few theoretical investigations into the excited states of thiophene oligomers have been reported, aimed at gleaning information on the nature of the states involved in the lightemission process and on the influence of interchain interactions on light-emission properties in the solid state. 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.…”

Photoswitchable Sexithiophene-Based Molecular Wires

“…3 In this regard, oligothiophenes offer considerable advantages over polythiophenes due to the precisely defined structures that can be prepared and probed electrochemically and spectroscopically. 4 R,R′,R′′-Sexithiophene and its derivatives 5 attracted widespread interest in recent years not only as models for polythiophenes but also in their own right as versatile active components in electronic devices such as electrochromic materials, 6 field-effect transistors, 7 OLEDs, 8 molecular wires, 9 and photovoltaic cells. 10 Control over their electronic properties can be achieved through synthetic modification 11 or postsynthetically through processing.…”

In Situ Spectroelectrochemical Studies on Ladder‐Type Oligomers in Solution and the Solid State

“…For anions the transition at higher wavelengths can be assigned to excitation of the unpaired electron from SOMO to LUMO, as was observed in oligomeric extended p systems. [14] The smaller energy difference between HOMO and SOMO in cations compared with that between SOMO and LUMO in anions indicates different charge distributions in positively and negatively charged structures A and B, as was already indicated by cyclovoltammetric and ESR experiments. Furthermore, a characteristic red shift was observed for both anions and cations, which increases with increasing chain length ( Table 2).…”