Carrier mobility of photochromic diarylethene amorphous films

•Hole mobility of photochromic diarylethene films is studied.•Diarylethenes with hole-transport substitutes show better mobility.•Colored films with a high isomerization ratio have large mobility.•Hole trapping effect reduces mobility for low-isomerization-ratio films.

Photochromic diarylethenes (DAEs) have gained attention as attractive current switching materials by light irradiation in the organic electronics field. We investigated the hole mobility of amorphous films consisting of three types of DAEs using a space-charge-limited current method and a better chemical structure to achieve high mobility. The hole mobility of open-ring (colorless) DAE having benzothiophene rings substituted with triphenylamine (TPA) as an aryl group was 2 × 104 times (2 × 10−6 cm2/V s) larger than that of DAE containing thiophene rings without TPA. When the DAE film was irradiated with ultraviolet (UV) light, the hole mobility decreased temporarily at 4% of closed-ring (colored) isomers and then increased to two-three times of the initial colorless state at 85% of the closed-ring isomers. The temporary decrease in the hole mobility originated in the hole trapping effect of the closed-ring molecules in a matrix consisting of open-ring isomers.

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