Molecular design of photorefractive polymers

Abstract

This review article describes the current state-of-the-art research on organic photorefractive polymer composites. A historical background on photorefractive materials is first introduced and is followed by a discussion on the opto-physical aspects and the mechanism of photorefractivity. The molecular design of photorefractive polymers and organic compounds is discussed, followed by a discussion on optical applications of the photorefractive polymers. Polymer Journal (2016) 48, 571-588; doi:10.1038/pj.2015.131; published online 27 January 2016 BACKGROUND In this report, the molecular design of organic photorefractive (PR) polymers is reviewed. Organic PR polymers are materials that possess both electro-optical and photoconductive properties. Research on photoconductive polymers, whose pioneering polymer is poly(N-vinyl carbazole) (PVK, PVCz), began in the 1960s. From the 1980s, research on organic nonlinear optical (NLO) materials has been widely conducted in the fields of organic electro-optics and optical nonlinearity. From the 1990s, new technology using organic photorefractivity combined with photoconductive and electro-optical properties was introduced in the field of organic semiconducting materials, 1 and organic light-emitting diodes 2-6 and organic fieldeffect transistors 7 were also debuted in this field. At the same time, the interest of researchers also turned toward the development of organic photovoltaic cells and organic solar cells. [8][9][10][11] The transport of charge carriers through photoconductive manifolds is a common phenomenon found in PR, organic light-emitting diode or organic photovoltaic materials. Thus, the development of materials in each field is expected to merge together to trigger the development of novel materials.The PR effect is a well-known phenomenon that is observed in materials in which refractive index modulation is induced by the space-charge field that results from the redistribution of positive and negative charge carriers separated through photo-excitation. 12 This phenomenon was first reported in inorganic crystals of lithium niobate (LiNbO 3 ) and lithium tantalate (LiTaO 3 ) and was observed through heterogeneous optically induced refractive indices in 1966. 13 Since then, the PR effect has extensively been investigated in many inorganic crystals, and theoretical approaches have been established to explain this phenomenon. 14 In 1991, 1 the first study of PR polymers reported a low diffraction efficiency of 10 −3 to 1% and a small optical gain of 0.33 cm À1 . In 1994, 15 a high diffraction efficiency of 86% (the remaining 14% was attributed to optical losses) and a large optical gain exceeding 200 cm À1 was reported in photoconductive PVK-based PR composites. Over the past two decades, many featured review articles [16][17][18][19][20][21][22][23][24][25][26][27] and book

Phosphine-Catalyzed Vinylation at Low Acetylene Pressure

“…N -Vinyl compounds are important monomers for polymeric materials with exceptional properties. Some of the most versatile examples are poly­( N -vinylpyrrolidone) and other N -vinylpyrrolidone (NVP, 1a ) copolymers, which found extensive use in the pharmaceutical, cosmetic, and food industries. , Other popular examples are the thermoresponsive poly­( N -vinylcaprolactame) from N -vinylcaprolactame ( 1b ), , the photorefractive polyvinylcarbazole from N -vinylcarbazole ( 1c ), and, as a more recent example, N -vinyl-5-methyloxazolidinone ( 1d ) copolymers, which show excellent adhesion qualities on common substrates. − …”

“…Some of the most versatile examples are poly(N-vinylpyrrolidone) and other Nvinylpyrrolidone (NVP, 1a) copolymers, which found extensive use in the pharmaceutical, cosmetic, and food industries. 1,2 Other popular examples are the thermoresponsive poly(N-vinylcaprolactame) from N-vinylcaprolactame (1b), 3,4 the photorefractive polyvinylcarbazole from N-vinylcarbazole (1c), 5 and, as a more recent example, N-vinyl-5-methyloxazolidinone (1d) copolymers, which show excellent adhesion qualities on common substrates. 6−8 The industrial synthesis of N-vinyl compounds is classically achieved as described by Reppe et al with acetylene under high pressure and in the presence of a strong base.…”

Graphitic nanosheets via two-dimensional polymerization enhancing organic all-optically controlled photorefractive performance

“…The PR effect is based on the first-order electro-optic effect, also known as Pockels effect or Kerr effect, which is the nonlinear change in refractive index in the noncentrosymmetric materials induced by the direct current (DC) field [16][17][18][19][20]. The PR processes consist of nonuniform light formation, exciton generation, charge-separated diffusion, built-in electric-field formation, refractive index modulation and optical signal processing.…”

Holography with Photochromic Diarylethenes

“…Other strategies and materials are possible to use to obtain reconfigurable holograms: photorefractive materials and photosensitive liquid crystals are two interesting families. As for photorefractive materials, they show a refractive index modulation as the result of the photoconductive and the Pockels effects [20], which makes them suitable for phase holographic elements [21]. Fast reconfigurable holograms [22,23], 3D holographic displays [24,25], and holographic memories [26] can be obtained thanks to the rapid growth of refractive index modulation, a very peculiar characteristic of such systems.…”