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Conductivity relaxation of neutral poly(3-hexylthiophene) is analyzed based on temperature and frequency dependence of its electric conductivity and electric modulus. The frequency dependence of the electric modulus is well fitted by the nonexponential decay function, exp[−(t/τp)β], with fractional exponent β (0

The conductivity relaxation of poly(3-alkylthiophene)s (P3ATs) is analyzed by use of electric modulus analysis together with non-exponential decay function to investigate intrinsic conduction mechanism of neutral P3ATs. A correlation with the thermal transitions from dynamic mechanical analysis and UV-Vis spectroscopy is attempted. It is found that conductivity relaxation behavior is highly related to the molecular motion. The side chain motion has no significant effect on the charge transport. While in the glass transition and rubbery region, relaxation time distribution becomes broadened with temperature. As the coplanar subchains in the ordered region melt, the conjugation length decreases and its distribution (and therefore relaxation time distribution) becomes narrower. The intrinsic conduction mechanism of neutral P3AT is determined by thermal activated hopping of charge carriers over energy barrier resulting from conformational defects such as soft or localized conformons.

Photoresponsive conductivities of copolymers of 3-hexylthiophene and azobenzene-modified 3-hexylthiophene prepared by chemical oxidation with FeCl3 were measured by placing a thin film (40 μm thick) in between an ITO glass and a disk-like Cu electrode. Upon irradiation of UV-light (γ=365 nm) (100 W Hg-lamp), conductivities of the copolymersincrease by a factor of 0.1 to 1.5 depending on the amount of the azobenzene moiety within 5 min to maxima and, upon turning off the light, return to original levels within the same period of time. Reversibility of the photoresponsive conductivity is excellent. It is found that the increase in conductivity upon irradiation is not due to a variation in interchain distance resulting from trans-cis isomerization in the azobenzene-moiety. This phenomenon can be attributed mainly to a generation of photoexcited hopping sites in the azobenzene moiety.

Poly(3-ether substituted thiophene)s are prepared from chemical oxidation with FeCl3 and have the structures: where (i) X  H; Y  (OC 7 H 15 ) 1 , (O(CH 2 ) 2 OC 4 H 9 ) 2 , (O(CH 2 )O(CH 2 )OCH 3 ) 3 ; (ii) X  CH 3 ; Y  (OC 7 H 15 ) 4 , (O(CH 2 ) 2 OC 4 H 9 ) 5 ; (iii) X  H; Y  (CH 2 OC 6 H 13 ) 6 ; (iv) X  H; Y  ((CH 2 ) 2 OC 5 H 11 ) 7 . The polymers of type (i) are crosslinked; only their oligomers are soluble. The polymer of type (iii) can not be obtained from its monomer by the present chemical method, since its monomer contains an allylic oxygen, which is easy to be attacked. The polymers of type (ii) and (iv) are soluble and have high molecular weight. FeCl3-doped polymer 7 at the doping level 0.04 is soluble and can be cast into flexible free standing film with a conductivity of 10−4S /cm. Those with an oxygen atom in the repeated unit of the side chain (polymers 4 and 7) have lower conjugation length in solution and solid forms in comparison with poly(3-octylthiophene) (P3OT) and have no appreciable thermochromism. The oxidation potential of polymer 7 is 1.0 V/SCE which is comparable with that of P3OT (1.01 V/SCE). Polymer 5, which has two oxygen atoms in the repeated unit, has higher conjugation length (λmax=535 nm) and lower oxidation potential (0.6 V/SCE) compared to P3OT (λmax = 500 nm, 1.01 V/SCE).