Spectroscopy Analysis of the Ring Opening Reaction in Functionalized Spiropyran Films
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Spectroscopy Analysis of the Ring Opening Reaction in Functionalized Spiropyran Films Raúl J. Delgado-Macuil1, Marlon Rojas-López1, Valentín L. Gayou1, Abdu Orduña-Díaz1, Joel Díaz-Reyes1 and Virginia Camacho-Pernas2. 1
Centro de Investigación en Biotecnología Aplicada del IPN. Tepetitla, Tlaxcala. 90700. México. Universidad Politécnica de Puebla, Carrera de Electrónica y Telecomunicaciones. Puebla, Pue. México. Author contact: [email protected]
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ABSTRACT In this work we used the Fourier Transform Infrared spectroscopy and UV/Vis spectroscopy to analyze the behaviour of self-ensemble films of spiropyran when the films were irradiated by UV. In UV/Vis spectroscopy is possible observe the generation of the absorption peak, at 575 nm, associated to the merocyanine state when the ring-opening process is induced by UV light. In ATR the kinetics of the ring-opening was determinate too; following the spectra changes in real time. INTRODUCTION Actually, the design and generation of organic materials in compact and order arrays, is one of the goals of many researchers groups [1]. The most important of this, it is the development of surfaces generation protocol, which increases their value with all applications that can be conceived. The main applications can be: superficial organic reactions [2-3], studies of electronic transfers’ process [4-5], electrochemical or optical sensors for molecular recognition [6-8], nanometric design of electronic devices [9-10], etc. By the other hand, the increase and demand of information induces to the electronics and information industries to require materials with high optical properties. Since the discovery of the spiropyrans photochromic reactions in 1952 by Fisher and Hirshberg [11], the interest in the use of spiropyran dyes, for photoelectric and photoelectrochemical devices, has been increasing. The spiropyrans have been the most extensively photochromic material studied over the past decades.
Figure 1. Schematic molecular structure of the sample before the UV illumination and after the isomerization. The process is reversible under visible illumination.
In general, spiropyran (SP) absorbs in the ultraviolet (UV) region and not in the visible region. Upon UV illumination, the SP colourless isomer undergoes heterolytic cleavage of the NO bond to form the coloured isomer (merocyanine). The coloration change (colourless to blue) in the sample is the physical observation of the molecular transformation. This process can be reversed by visible illumination, see figure 1. No matter the applications where the spiropyrans have been found, it is necessary a detailed understanding of the transitions kinetics between the spiropyran (SP) to merocyanine (MC) forms. For this, it is necessary to analyze the molecular behaviour of these kinds of structures. In this context, vibrational spectroscopies would seem to be appropriated to study them, since they provide subtle details about molecular structure in liquids, gas or solid state. For example, Infrared [12-15, 8] and Raman [8,15] spectrosc
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