Longer oligothiophenes

The formation of Langmuir-Blodgett films by mixing 3T or 4T with arachidic acid in the molar ratio 1 2 failed, in contrast to longer oligothiophenes (see next sections) [27]. 

Longer oligothiophenes such as 6T or higher, give spectra which are very similar to (real) polythiophenes, e.g. a band-gap of around 2.2-2.3 eV This can either be due to a short effective conjugation length of polythiophene or due to defect induced gap-states (X-traps, see below) [ 150]. 

Longer oligothiophenes can only be studied in solution when they are alkyl-substituted. Dimethyl-oligothiophenes (DManT) with = 4,6,8,10 were studied by Zotti et at. [205]. For DMa4T they found... 

IPCE value for the P-POT resulted from a low electron transport efficiency of its longer oligothiophene chain. 

Summarizing all the optical spectroscopy on isolated molecules, 6T can well be assumed to be a model compound for longer oligothiophenes and especially for polythiophene from all the experimental data as well as theoretical approaches. The similarity between 6T and polythiophene was not only revealed by the transition energies, but also appeared from many other spectroscopic experiments, e.g. photoinduced absorption (PA) spectra [91], or photoemission spectroscopy on the valence levels [92], and have been discussed elsewhere [29, 30]. 

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