PHOTOCHROMIC ORGANIC FIELD-EFFECT TRANSISTORS: MOLECULES, DEVICE PERFORMANCE AND LASER PATTERNING

摘要

We developed an optically controllable organic field transistor (OFET) by employing photochromic diarylethene (DAE) molecules as a transistor channel layer. DAE molecules undergo typical photochromic reaction, i.e. reversible conformational change between closed- and open-ring isomers by alternating ultraviolet (UV) and visible (VIS) light irradiation. We found that the drain current in the DAE-based OFET also showed a reversible change accompanied by this conformational change. The closed-ring isomer exhibited a transistor operation under appropriate gate and drain bias voltages, meanwhile the open-ring isomer showed no drain current. As a result, a remarkably high on/off ratio of 1,000 was achieved. The drain current modulation can be attributed to the drastic transformation in the π-conjugation system in association with the photoisomerization. These results present two important messages. The first one is that this compound can be regarded as a new material, which has dual properties: organic semiconductor and photochromism. The second is that a phase transition between semiconductor and insulator can be induced by light irradiation. Based on these achievements, we demonstrate laser drawing of one-dimensional (1D) channels on an OFET with a photochromic DAE layer. The main findings are: (i) a number of 1D channels can be written and erased repeatedly in the DAE layer by scanning UV and VIS focused laser spots alternately between the source and drain electrodes, (ii) the conductivity of the 1D channel can be controlled by the illumination condition such as the laser power density and the scan speed, and (iii) it is possible to draw an analogue adder circuit by optically written 1D channels so as to overlap a portion of the channels and perform optical summing operations by local laser illumination of the respective channels. These findings open new possibilities for realization of various optically reconfigurable low-dimensional organic transistor circuits, whic