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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.

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The kinetics of the thermal cis-trans isomerization was determined in a series of crown ethers containing the azobenzene moiety incorporated into the crowns of various sizes (10- to 19-membered crowns), dissolved in liquid isooctane and in polymer matrixes (PMMA and polystyrene). The kinetic parameters (activation energies and pre-exponential factors) were determined from temporal evolution of the absorbance measured at one of the maxima due to the pi-pi* transition of the trans forms of the molecules, using both isothermal and nonisothermal procedures. Molecular structures and electronic spectra of both trans and cis forms were calculated employing an ab initio method with 3-21G* basis set and semiempirical ZINDO-S, respectively. A comparison of the quantum-chemical calculations with the experimental results shows that one may exclude the splitting of the UV absorption bands of the trans forms of the molecules under study that resulted from a coexistence of several conformations of these molecules. A linear relationship was found between the activation energy and logarithm of the pre-exponential factor of the thermally driven cis-trans isomerization: all molecules follow a common dependence, except for the smallest (10-membered) crown ether.

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