Synthesis and Characterisation of Photo-Cross-Linkable Liquid Crystalline Poly(n-[n′-flurobenzoylstyryloxy]alkylmethacrylate)s and Their Fluorescence Lifetime Properties
This paper reports a study on photo-cross-linkable polymer containing pendant chalcone moiety exhibiting liquid crystalline as well as fluorescence lifetime properties in detail. The photoresponsive polymers were prepared, and their structure has been characterized by 1H-NMR, 13C-NMR, and UV-Visible spectroscopy. The photo-cross-linking behavior of polymers has been studied by UV-Visible and fluorescence spectroscopy. UV spectral studies revealed that the polymers follow cyclo addition reactions when they undergo photo-cross-linking under the influence of UV-light. Number and weight average molecular weight of the polymers were determined by Gel Permeation Chromatography (GPC) and polydispersity index value near to 1.5. The thermal and thermooxidative stability of the polymers were determined by Thermogravimetric Analysis (TGA). Thermal transitions were studied by DSC, and presence of mesophases was identified at 147 and by hot stage polarized light optical microscopy (HPOM). Fluorescence lifetime measurements using the time-correlated single photon counting (TCSPC) method reveal that the average lifetime values decrease from 5.94？ns to 5.32？ns on UV-irradiation were discussed in detail. 1. Introduction Liquid crystalline polymers have generated considerable interest in recent years, and the photo-cross-linkable LCPs have driven special attention if they contain both mesogen and photoactive groups in their structure [1–5]. The former incorporates LC properties to the polymer, and the later facilitates cross-linking of the chain under the influence of UV radiation. These classes of polymers are very useful in fabricating anisotropic networks, information storage devices [6, 7] and nonlinear optical devices [8]. Many research articles reported photochemical and liquid crystalline behaviours of these polymers using UV-Visible spectral studies and polarised optical microscopic characterisations. In addition to these studies, fluorescence lifetime measurement has been used as a new instrumental technique to support photoreactive behaviour of photo-cross-linkable liquid crystalline polymers. Fluorescence lifetime measurements encompass tremendously large fields of science. Since the mid-19th century, nearly every great breakthrough in chemistry and physics has aided the development of fluorescence lifetime techniques, and a growing number of discoveries in biology and medicine owe their existence to fluorescence lifetime. A variety of fluorescence detection methods are available for lifetime measurements but the advent of time-correlated single photon
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