Improved thermal stability in photochromism-based optically controllable organic thin film transistor Yasushi Ishiguro a,b , Michel Frigoli c,⇑ , Ryoma Hayakawa b , Toyohiro Chikyow b , Yutaka Wakayama a,b,⇑ a Department of Chemistry and Biochemistry, Faculty of Engineering, Kyushu University, 1-1 Namiki, Tsukuba 305-0044, Japan b International Center for Materials Nanoarchitechtonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan c Institut Lavoisier Versailles, UMR CNRS 8180, Université de Versailles St-Quentin-en-Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles, France article info Article history: Received 8 April 2014 Received in revised form 23 May 2014 Accepted 27 May 2014 Available online 7 June 2014 Keywords: Photochromism Optical switching Organic thin film transistor abstract Thermally induced structural change in photoisomerization molecules is a serious obstacle to the development of optically controllable organic field-effect transistors (OFETs). This is because the thermal relaxation of molecular structures degrades photo-induced change in drain current and removes the memory function. To deal with this issue, a naphthopyran (NP) derivative, namely 3,13-dihydro-3-(4-triphenylaminyl)-3,13-diphenylbenzo- pyrano[5,6-a]carbazole (NP-TPAC) was tested that displays pseudo p-type photochromism at room temperature. The NP-TPAC-doped poly(triarylamine) (PTAA) film exhibited a reversible change in transistor properties; the drain current was reduced by ultraviolet (UV) and returned to its original value by visible (VIS) light irradiation. Importantly, no change in the drain current was observed at room temperature for more than 30 h under dark conditions. This was because the open-ring trans–trans (TT) isomer of NP-TPAC is thermally stable owing to the CH-p interaction and the steric force exerted by the phenyl ring of the carbazole unit onto the double bond responsible for the thermal back reaction. In other words, the thermal stability of photochromism-based optical devices can be greatly improved by adopting an appropriate molecular design. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Recently, organic field-effect transistors (OFETs) inte- grated with specific functionalities, e.g., light-emitting OFETs [1,2], pressure sensors [3,4], and gas sensors [5] have attracted considerable attention. A typical example of a functional OFET is an optically controllable OFET, which makes it possible to develop new optical devices such as photo-controlled memory devices and optical sen- sors. For these purposes, photoisomerization molecules have been employed, in which the transistor properties were optically modulated in association with the photoiso- merization [6–13]. Orgiu et al. have developed an optical switching transistor by doping photochromic diarylethene (DAE) molecules into poly(3-hexylthiophene), where the DAE molecules worked as hole trap sites [6]. The open- closed ring isomerization of DAE molecules involved a var- iation in the highest occupied molecular orbital (HOMO) level, which triggered the optical switching of the drain currents. Samorì et al. have developed an optical switching transistor by using a self-assembled monolayer of photo- chromic azobenzene molecules, where the carrier injection barriers were tuned by varying the energy levels, which http://dx.doi.org/10.1016/j.orgel.2014.05.030 1566-1199/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding authors. Address: International Center for Materials Nanoarchitechtonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan. Tel.: +81 298604403 (Y. Wakayama). E-mail addresses: michel.frigoli@uvsq.fr (M. Frigoli), WAKAYAMA. Yutaka@nims.go.jp (Y. Wakayama). Organic Electronics 15 (2014) 1891–1895 Contents lists available at ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel