Vibronic coupling density analysis for α-oligothiophene cations: A new insight for polaronic defects

Graphical abstract: Electron-density difference is distributed mainly in the central four thiophene rings, suggesting that the polaronic defect occurs in the four rings. - Abstract: Vibronic coupling density (VCD) analyses for α,α'-oligothiophenes (denoted α-nT, where n stands for the number of thiophene rings) cations are presented. VCD analysis can reveal the origin of vibronic couplings based on the electronic and vibrational structures. We can gain a new insight for the reason why a polaronic defect of α-oligothiophenes occurs mainly in four thiophene rings for even n and at most five thiophene rings for odd n. A role of electron-density difference in the formation of polaronic defects is discussed.