Neutral and Charged Oligomers

Tkble II. Absorption Maximum (Amax) and Molar Absorption Coefficient (s) for Oligothiophenes 

A substituted dodecamer with 12 thiophene rings (Fig. 6e R = QH13) shows quite different spectral changes upon oxidation. The spectral changes of the dodecamer upon the THI (C104) 

60- and 1.46-eV bands are attributed to the radical cation of the dodecamer, whereas 0.76- and 1.59-eV bands are ascribed to the dication of the dodecamer. Similar spectral changes were reported by van Haare et al. [35] for a dodecamer with different alkyl substituents. They also clarified that the divalent cation is singlet by using ESR spectroscopy. 

Hill et al. [40, 41] and Bauerle et al. [30, 31] reported the singlet TT-dimer formation of the radical cations of oligothiophenes. Upon lowering the temperature of a solution of a radical cation, the LE and HE bands of the radical cation show blue shifts, and an ESR signal that originates from the radical cation disappears. Consequently, the new absorption bands have been ascribed to the singlet rr-dimer of the radical cations. These absorption bands due to the dimer are called Dj and D2 herein. A band that appears in the near-infrared range upon dimer formation is called Dq. The observed positions of the Dq, Dj, and D2 bands are listed in Table III. There exists a monomer-dimer equilibrium, 

Tkble IV. Maximum Wavelength ( p) and Quantum Efficiency ( t p) of Fluorescence at Room Temperature for Oligothiophenes 

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