The photorefractive effect was first observed in 1960s in inorganic crystals.A. Ashkin et al., Appl. Phys. Lett. 9, 72 (1966) The effect was called optical damage, since for the purpose of light frequency-doubling (which was the primary application of these crystals), it was adverse. Later, it was realized that the damage reproduced the original intensity variation in the form of varying dielectric constant and therefore, it was suitable for holographic recording and other applications. The first photorefractive organic materials, an organic crystalK. Sutter and P. Gunter, J. Opt. Soc. Am. B 7, 2274 (1990) and a polymer composite,S. Ducharme et al., Phys. Rev. Lett. 66, 1846 (1991) were reported in 1990 and 1991, respectively. Since then, dramatic improvement in the PR (photorefractive) performance of organics has been achieved owing to significant advances in synthesis, numerous physical studies that identified key mechanisms and parameters, and research of structure–property relationships.