Intermolecular Interactions in Conjugated Oligothiophenes. 3. Optical and Photophysical Properties of Quaterthiophene and Substituted Quaterthiophenes in Various Environments

Abstract

A detailed analysis of the optical and photophysical properties of 2,2‘:5‘:2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (QT), 3,3‘ ‘‘-dimethoxy-2,2‘:5‘:2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (DMOQT), 3,3‘ ‘‘-dimethyl-2,2‘:5‘:2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (DMQT) and 3‘,4‘ ‘-didecyl-2,2‘:5‘:2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (DDQT) in various environments is reported. In solution at room temperature, the optical properties of the free molecules are obtained and discussed in terms of the effect of the substitution on the conformation adopted by each derivative in the electronic ground and first excited states. In a tetradecane matrix at 77 K, the optical properties are obtained for the isolated molecules in this rigid medium where the oligothiophenes adopt conformations similar to those found in the solid state. The optical properties of the quaterthiophene derivatives in their aggregated forms and in the solid state are also reported and discussed in terms of the substitutional effect on the intermolecular interactions, which affect the spectral and photophysical properties of the isolated molecules. For the first time, a β,β‘-disubstituted oligothiophene (DMQT) showing an excitonic splitting similar to that obtained for QT is reported. All other substituted oligothiophenes presented show a conformational change, following the aggregation process. This difference is explained by more disordered crystalline forms for DMOQT and DDQT. Theoretical calculations using the ZINDO/S semiempirical method are also performed on the crystalline structure of each derivative in an attempt to correlate the optical properties of these molecules in their aggregated forms and in the solid state with the molecular arrangement found in the crystal.

Optical and Electrochemical Transducers Based on Functionalized Conjugated Polymers

“…On the other hand, as observed with poly(3,3'-dialkyl-2,2'-bithiophene)s ( possible by the adequate steric hindrance created by the methyl group at the 4-position, which forces the formation of a nonplanar conformation when highly conjugated (coplanar) polythiophene assemblies are disrupted [66][67][68]. Recent calculations and experimental studies on oligomeric model compounds are in agreement with this model and have also indicated that the chromic effects in neutral substituted polythiophenes could be mainly due to conformational changes instead of excitonic effects [69][70][71]. However, important excitonic effects may take place in polydiacetylenes and unsubstituted oligothiophenes [69][70][71][72][73].…”

Oxidative Bond Formation in Dithienyl Polyphenylenes: Optical and Electrochemical Consequences

“…This concentration dependence is thought to be due to excited-state molecules aggregating more readily than those in the ground state, giving rise to excimeric species. [25,27,28] The emission spectra of the dimers (at low concentration, Figure 6; Supporting Information, Table S3) show a highenergy band at similar energy to the emission (Supporting Information, Table S2) attributed to the thienyl rings of the starting materials. This implies that there is no increase in the delocalization of electronic density upon dimerization, and it is consistent with a twisted conformation in dilute solutions (Scheme 3A).…”

Thermochromism in Oligothiophenes: The Role of the Internal Rotation

“…The thermochromism of terthiophenes and quaterthiophenes has been reported by Cesare et al in a series of papers. [16][17][18] The thermochromism in substituted terthiophenes is coupled with the conformational changes in contrast to the unsubstituted terthiophene which shows an important excitonic effect.…”