Photoconductive molecular glasses consisting of twin molecules

Synthesis and properties of photoconductive low-molar-mass glass-forming compounds consisting of twin molecules in which two bulky groups, i.e. 3-(9-carbazolyl)carbazole, 3-(N-diphenylamino)carbazole, 3-(10-phenothiazinyl)carbazole and 3,6-di(9-carbazolyl)carbazole are linked by flexible aliphatic units are reported. These compounds are found to form stable glasses with glass-transition temperatures in the range of 94–179 °C as characterised by differential scanning calorimetry (DSC). The electron photoemission spectra of the molecular glasses synthesised have been recorded and the ionisation potentials have been established. The lowest value of ionisation potential (5.32 eV) was observed for the molecular glass containing 3-(N-diphenylamino)carbazole moieties. The molecular glass containing 3-(9-carbazolyl)carbazole moieties exhibited ionisation potential of 5.80 eV, which is close to that of the polymer containing electronically isolated carbazole chromophores. Hole drift mobilities of the synthesised materials measured by the time of flight method are in the range of 10−4 to 10−7 cm2 V−1 s−1 at an applied electric field of 3.6×105 V cm−1.