We report on an organic field effect transistor (OFET) with a photochromic dielectric layer, operating as an opto-electrical switch device. The structure contained a photochromic material dissolved in the polymer dielectric layer. The photochromic material was spiropyran exhibiting a large difference of the dipole moments of the stable and metastable forms; poly(methyl methacrylate) was a polymeric insulator; and an n-type perylene derivative was used as the organic semiconductor. Illumination of the structure with UV light resulted in a reversible increase of the source-drain current, accompanied by a reversible decrease of the threshold voltage. The initial parameters were restored by a thermal relaxation in the dark or by illumination with visible light. The photoswitching ratio was found to be dependent on the gate voltage ranging between ca. 2 just above the threshold voltage and ca. 1.3 at the highest voltage employed (90 V). The switching has been attributed to reversible changes of dielectric properties of OFET's insulator (dielectric layer) due to a reversible light-triggered reaction of polar photochromic species, dissolved in the bulk of the dielectric layer. The contribution of dipoles aggregated on the semiconductordielectric interface was estimated to be negligible at gate voltages exceeding ca. 10 V.

The multifunctional properties of carbon nanotubes (CNTs) make them a powerful platform for unprecedented innovations in a variety of practical applications. As a result of the surging growth of nanotechnology, nanotubes present a potential problem as an environmental pollutant, and as such, an efficient method for their rapid detection must be established. Here, we propose a novel type of ionic sensor complex for detecting CNTs – an organic dye that responds sensitively and selectively to CNTs with a photoluminescent signal. The complexes are formed through Coulomb attractions between dye molecules with uncompensated charges and CNTs covered with an ionic surfactant in water. We demonstrate that the photoluminescent excitation of the dye can be transferred to the nanotubes, resulting in selective and strong amplification (up to a factor of 6) of the light emission from the excitonic levels of CNTs in the near-infrared spectral range, as experimentally observed via excitation-emission photoluminescence (PL) mapping. The chirality of the nanotubes and the type of ionic surfactant used to disperse the nanotubes both strongly affect the amplification; thus, the complexation provides sensing selectivity towards specific CNTs. Additionally, neither similar uncharged dyes nor CNTs covered with neutral surfactant form such complexes. As model organic molecules, we use a family of polymethine dyes with an easily tailorable molecular structure and, consequently, tunable absorbance and PL characteristics. This provides us with a versatile tool for the controllable photonic and electronic engineering of an efficient probe for CNT detection.

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