Oligothiophenes absorption spectra

Although the triplet spectra and the ISC quantum yield of oligothiophenes are well characterized, the location of the lowest triplet state Ti could not be determined in solution and in isolated molecules so far because of a lack of phosphorescence (95PAC9 96JPC18683). Attempts have also been made to detect an So-Ti transition by absorption measurements in highly concentrated solutions, but these attempts were not very successful. The only So-Ti spectrum that has been reported was measured for 3T (90PP(52)655). 

Recently Egelhaaf et al produced oligothiophene radical cations on silica gel by two-photon ionization with laser intensities I > 5x 106 W cm and laser flash energies above 15 mJ [38]. The electron is excited into a continuum state and no anion is formed. The absorption spectra are very similar to those observed for radical cations in solution. The ESR signal exhibits a signal with, g = 2.0028 at room temperature. At T= 77 K an anisotropic ESR spectrum is found. 

Figure 1.6 Absorption (blue line) and emission spectrum (red line) of cyclo(terthienylbutadiene) 4.30. Reproduced from C. Fuhrmann, Synthesis and characterization of oligothiophene-based fully it-conjugated macrocycles, G. Fuhrmann, PhD Thesis, University of Ulm, 2006...

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