The electrodeless flash-photolysis time-resolved microwave conductivity technique (FP-TRMC) has been used to study the photogeneration of charge carriers in spin-coated films of regioregular poly(3-hexylthiophene) ͑P3HT͒, over the photon energy range from 1.9 to 5.2 eV for incident light intensities from 10 13 to 10 16 photons/ cm 2 per ͑3 ns͒ pulse. The initial, single-photon quantum yield of photoionization, , has been estimated from the low-intensity limit to the photoconductivity based on a charge carrier mobility of 0.014 cm 2 /Vs (determined in separate pulse-radiolysis TRMC experiments on bulk P3HT). The value of is constant at ͑1.7± 0.4͒% within the range 1.9-3.0 eV, which encompasses the first electronic absorption band of P3HT. Above 3.0 eV, increases, up to a value of ͑7±2͒% at 5.2 eV. The activation energy of the photoconductivity was found to be approximately 50 meV at all photon energies. The high-intensity, sublinear dependence of the photoconductivity can be described by the occurrence of either exciton-exciton annihilation or diffusional charge recombination with rate coefficients of 2.3ϫ 10 −8 cm 3 / s and 1.1ϫ 10 −8 cm 3 /s.

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A review is given of the one-dimensional, intrachain and intracolumnar, charge mobilities, Σµ 1D , determined for π-bond-conjugated polymeric and for π-π-stacked columnar discotic materials using the pulse-radiolysis time-resolved microwave conductivity technique. The largest values, on the order of 10 cm 2 /(V s), are found for single-crystal polydiacetylenes polymerized either thermally or with low doses of radiation. Much lower values of Σµ 1D , covering the range from 0.009 to 0.125 cm 2 /(V s), are found for solution-synthesized conjugated polymers for which six different backbone structures have been investigated. This is attributed mainly to their complex morphology and the resulting static disorder in the backbone structure. The highest mobilities for this class of material, ca. 0.1 cm 2 /(V s), are found for liquid crystalline derivatives of polyfluorene and poly(phenylenevinylene). Larger mobilities are found for discotic materials, with maximum values close to 1 cm 2 /(V s) in both the crystalline solid and liquid crystalline phases. This is attributed to their self-organizing nature and hence higher degree of structural order, which compensates for the weaker electronic coupling between monomeric units in the discotics compared with the covalently bonded conjugated polymers.

Peripherally alkyl‐substituted aromatic molecules are of interest because they are predicted to promote the rapid vectorial conduction of electronic charge. It is shown—using the example of HHTT, see Figure—that the results obtained by flash‐photolysis time‐of‐flight conductivity and pulse‐radiolysis time‐resolved microwave conductivity measurements are complementary, allowing the charge‐carrier mobility to be determined in all four phases of HHTT. magnified image

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