Synthesis and Solvatochromic Properties of Donor-Acceptor-Substituted Oligothiophenes

Article abstract of DOI:10.1021/jo00112a032

The Pd-catalyzed cross coupling reaction of electron donor-substituted thiophenes 1 with electron acceptor-substituted halothiophenes 2, 10 via organozinc intermediates or organotin compounds 5 to give bi-, ter-, and quaterthiophenes 3, 4, 6, 8, 12, 13, and 14 is desribed. (Dimethylamino)-bithiophenes 8 with acceptor groups of varying reactivity were prepared via 5d in 60-80percent yield, whereas bithiophenes 6d,e were obtained as a mixture with phenylthiophenes 7d,e.Symmetrical substituted byproducts 11 were formed in the conversion of 1b with bromothiophenes 10 via organozinc compounds yielding oligothiophenes 6b and 12.The ter- and quaterthiophenes 13 and 14 were isolated in about 50-70percent yield.The electronic interactions between donor and acceptor end groups in the conjugated bithiophenes 3, 4, and 8 are expressed in the intensive and markedly solvatochromic CT transitions.The solvatochromic behavior of 3, 4 and 8 was determined by linear regression analyses of absorption maxima in 11 solvents, whereby bithiophene 3d was found to be a very appropriate indicator dye whose absorption wavenumbers <*>_max(3d) in aliphatic and dipolar aprotic and - on consideration of the polarizability correction term dδ - in aromatic and chlorinated solvents excellently correlate with the ?^* values defined by Kamlet and Taft.