Oligothiophenes oligomers

Gas phase deposition can be employed for most oligothiophene oligomers up to octithiophene (aST) and also for polythiophene with a polymerization degree of 20-25 monomeric units. An exception are molecules with thermally unstable substituents. 

Only the nitro-substituted oligothiophenes display large bathochromic shifts, large Stokes shifts, high fluorescent quantum yields, and long lifetimes for excited states. As for the other substituents, the trend is mostly noticeable for the short oligomers like terthiophenes and seems to disappear for sexithiophenes. As can be inferred from their solvatochromic effect, an intramolecular charge transfer takes place in the excited states of these molecules. 

Quinodimethane derivatives of terthiophene and other oligomers showed an absorption maximum at 583-688 nm (02JOC6015 03OL1535). Bis(dicyanoethylene) oligothiophene derivatives have been characterized and the compound with four thienyl rings showed an absorption band at 790 nm (02JA12380). This type of compounds was used in thin film transistors (see below) (02JA4184). 

The oligothiophenes 27 bear phenyl groups in the 3 -position of the thiophene cores that are para-substituted with electronically diverse functional groups (R = CF3, H, CH3, OCH3). Here, the phenyl spacers enhance the solubility of the oligomers and warrant the electronic communication between the elements of diver-... 

The second-order hyperpolarizabilities in oligothiophenes measured by THG showed an exponent a=2.8 [78]. DFWM and EFISH data revealed an exponent a= 4.05 [79] and a=4.6 [80],respectively, for these oligomers. These larger exponents, however, can be explained by a two-photon resonance enhancement in the DFWM and EFISH experiments. 

Much effort has been devoted to studies of thiophene oligomers and polymers, in particular in connection with development of new organic materials for electronic applications. Many of the synthetic approaches towards oligothiophenes rely on well-established methodology, such as metalations, halogen-metal exchange reactions, and transition metal catalyzed couplings. 

In addition to work on polymers, there have been several recent results on soluble oligomer semiconductors. In particular, there has been work on various oligothiophene and acene derivatives. The main potential advantage of oligomers is that they tend to form... 

Toward an understanding of the conduction properties of polythiophenes (26) and polypyrroles (25) a large number of soluble oligomers has been prepared. Oligothiophenes, indeed, represent the most common model compounds for electrically conducting polymers [149]. Thereby, lower oligomers... 

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