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We report on the fabrication of organic phototransistors based on the spiro-conjugated molecule 2,7-bis-(N,N′-diphenylamino)-2′,7′-bis(biphenyl-4-yl)-9,9′-spirobifluorene. Intramolecular charge transfer leads to an increase in charge carrier density, providing the amplification effect. The sensitivity is better than 1 A/W for ultraviolet light at 370 nm, making the device interesting for sensor applications.

The charge‐transport properties of the spiro‐linked compounds 2,2′,7,7′‐tetrakis(diphenylamino)‐9,9′‐spirobifluorene, 2,2′,7,7′‐tetrakis(N,N′‐di‐p‐methylphenylamino)‐9,9′‐spirobifluorene, 2,2′,7,7′‐tetra(m‐tolyl‐phenylamino)‐9,9′‐spirobifluorene, and 2,2′,7,7′‐tetra(N‐phenyl‐1‐naphthylamine)‐9,9′‐spirobifluorene, and their corresponding parent compounds, N,N,N′,N′‐tetraphenylbenzidine, N,N,N′,N′‐tetrakis(4‐methylphenyl)benzidine, and N,N′‐bis(3‐methylphenyl)‐(1,1′‐biphenyl)‐4,4′‐diamine, N,N′‐diphenyl‐N,N′‐bis(1‐naphthyl)‐1,1′‐biphenyl‐4,4′‐diamine, are investigated. The field‐effect mobilities of charge carriers in thin films of the parent compounds are slightly higher than those of the spiro‐linked compounds. However, the transistor action of the parent‐compound thin films vanishes because the films crystallize after being stored in ambient atmosphere for a few days. In contrast, the hole mobilities in thin films of the spiro‐linked compounds do not change significantly after the samples are stored in ambient atmosphere for up to nine months. Also discussed is the temperature dependency of the mobilities of charge carriers, which is presented using two models, namely the Arrhenius and the Gaussian disorder models.

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