The discrimination between triplet state and radical cation in the pulse radiolysis of bithiophene in CCl4

Complete text of publication follows. In a previous investigation on oligothiophenes we described the spectrum of bithiophene radical cation, 2T+, produced by pulse radiolysis in CH2Cl2. In that spectrum we noticed that a second peak appeared besides the typical absorption due to the known bithiophene radical cation. The same feature pertians to the CCl4 environment, the only difference being that the relative intensities of the two peaks are reverted. While the radical cation peaks at 420 nm, the second maximum is exhibited at 360 nm and is twice as intense as the former. The lifetime of the two peaks is different, the 360 peak living longer. Adding tetrachloroethylene as a scavenger, the almost entire suppression of the 360 nm peak is verified, while the 420 peak is only partially reduced. The two absorption bands at 360 and 420 nm are respectively attributed to 32T and to 2T+·. The triplet, first induced in an excited state through a Foerster mechanism, probably undertakes a conformational rearrangement (K360-build-up = 6.8 x 106 s-1). The radical cation is produced via two processes, the first being a resonance charge transfer, the second a diffusional process; the two oxidizing species are respectively CCl4+· and [CCl3+//Cl-]solv through the mediation of 12T