Experimental and Theoretical Study of the p- and n-Doped States of Alkylsulfanyl Octithiophenes

The charge-transfer and spectral properties of two octithiophenes, namely 4′,4′′′,3′v,3v′-tetra(octylsulfanyl)-2,2′:5′,2′′:5′′,2′′′:5′′′,2′v:5′v,2v:5v,2v′:5v′,2v′′-octithiophene and 4,3′′,4v,4v′′-tetrabromo-4′,4′′′,3′v,3v′-tetra[(R)-2-methylbutylsulfanyl]-2,2′:5′,2′′:5′′,2′′′:5′′′,2′v:5′v,2v:5v,2v′:5v′,2v′′-octithiophene, OT1 and OT2, respectively,are characterized by cyclic voltammetry and spectroelectrochemistry under ultradry conditions. The analysisof the voltammetric results shows the formation of up to the dication for both OT1 and OT2 and up to thetetraanion (OT1) and trianion (OT2) anions. The optical properties of the OT1 (2+, 1+, neutral, 1-, 2-)species were probed by in situ UV-vis-NIR spectroelectrochemistry. The calculated standard potentials atthe B3LYP/cc-pVTZ level of the theory allowed the rationalization of the experimental electrochemical results.The UV-vis-NIR spectra were successfully compared with the theoretical electronic transitions and oscillatorstrength data obtained by time-dependent B3LYP/6-31G* calculations. Theoretical redox potentials and opticaltransitions properties are calculated including “the solvent effect” within the CPCM model. The consistencyobtained between experimental and theoretical results indicates the existence of the hypothesized high-spin/high-charge p- and n-doped electronic states for the OT1 and OT2 octithiophenes here studied.