Photosensible spiropyrans used as thermal sensor

Abstract

Hybrid organic-inorganic materials are constituted by the combination of organic and inorganics compounds with a broad range of application and are an alternative for the production of novel multifunctional materials [1]. These materials may be incorporated into a polymeric matrix, in conjunction with photosensitive or thermochromic molecules. Photochromism or the photochromatic effect is responsible for changing the colour of a material when exposed to a radiation source (UV and IR Spectra). The process is reversible and occurs through the light exposition, heating or chemical oxidation [2]. Raditoiu et al. [3] incorporated thermochromic materials in the silicon aiming at stabilizing the thermal cycle and provide protection against solar rays and/or heating to avoid the photodegradation. Several molecules have photosensitive with thermochromic proprieties, and in this work, Spiropyran molecule (1,3,3-Trimethylindolino-βnaphthopyrylospiran) will be explored (Figure 1) [3]. Spiropyran is a reversible photosensitive molecule which is transformed into a polar hydrophilic isomer, the structure may return to the original form after being heated up and/or exposed to ultraviolet radiation [2,4,5]. Spiropyrans are adapted to two stable modes: (1) open ring state, called MC, and (2) closed ring state, called SP [4]. In this process that corresponds to a photoreversible and thermic process, MC may return to the original closed SP form due to heating and irradiation. During the reversion stage, notable changes in the molecule structure and charge distribution occur [4,5].