We have been studying conjugated polymers, in particular, poly(alkyl thiophene-3-carboxylates) (1  ) and poly(dialkyl 2,2'-bithiophene-4,4'-dicarboxylates), and examining regiorandom and regioregular backbones looking for intramolecular interactions. Based on spectroscopic data and ab-initio quantum mechanical calculations on bithiophene model compounds it was concluded that there are attractive interactions between the carbonyl oxygen in one ring and the sulfur atom in the adjacent thiophene ring (2  ). X-ray crystal structures of these model bithiophenes showed conclusively that this was indeed the case. In simple head-to-head methyl esters there was too much steric interaction and so the bithiophene was severely twisted. However, with the carbonyl groups in 5-membered rings, even the head-to-head systems (3  ) were planar as shown by quantum mechanical calculations and X-ray structure determination. In these systems, when the carbonyl was replaced with a CH2 group (4 ?) the bithiophenes were calculated to be twisted. Work on additional systems 5  and 6  , including syntheses and X-ray structure determination, will be presented. We have looked for a similar electrostatic attraction between the sulfur atom of one thiophene and an electronegative fluorine atom in the benzylic position of the adjacent thiophene. Compounds 7  and 8  were synthesized and studied. Compound 7  was a liquid so 8  was prepared. X-ray structure determination showed that any intramolecular S�F interactions in 8  are very weak at best, however there are significant intermolecular S�F interactions which affect the crystal structure.

Studies of bi- and terthiophenes as models for some conjugated polymers: Intra- and intermolecular interactions and their structural implications

247th National Meeting (2014)

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