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Twisting inter-ring deviation from planarity in oligo- and polythiophenes

5 Twisting (inter-ring deviation from planarity) in oligo- and polythiophenes [Pg.384]

Elmaci and Yurtsever used DPT to study the relationship between thermochromism and internal rotation in poly thiophenes [59b]. For head-to-tail methyl-substituted thiophenes, rotational potential maps of the dimer and trimer were calculated. Using a time-dependent DFT methodology, the UV-Vis absorption spectra of these oligomers were calculated as functions of the torsional angles. Theoretical temperature-dependent UV-Vis spectra were generated from the distribution of torsional angles. The results show that the internal rotation alone is not sufficient to explain the mechanism of thermochromism. [Pg.385]

It is also found that the thermochromic transition temperature for poly(3-alkylthiophene) thin films decreases as the length of the alkyl side-groups increases [71]. If the main chain is distorted by either twisting or folding, the alkyl chains take mn-trans conformations. This is explained as a transfer of thermal energy from the side-chains, where it is stored, to the polymer skeleton, which then breaks the stiffness of the backbone and decreases the r-conjugation length. [Pg.385]

Di Cdsare et al. studied the lowest energy structures of several bithiophenes substituted with methoxy and methyl groups in various positions using HF/3-21G calculations, and also performed a detailed conformational analysis [74]. The effect of the position of substituents on structural parameters and on torsional potentials was examined. The results of these calculations are in good agreement with available experimental data. [Pg.386]




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And planarity

Deviation from planarity

Oligo

Oligos

Planar rings

Polythiophen

Polythiophene

Polythiophenes

Ring twisting

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