1. Ch. Bosshard, J. Hulliger, M. Florsheimer, P. Günter, in: Organic Nonlinear Optical Materials, Advances in Nonlinear Optics 1, Gordon and Breach, Basel, Switzerland, 2001.
2. Nonlinear Optical Properties of Organic Molecules and Crystals, vol. 1;Chemla,1987
3. Nonlinear Optics of Organic Molecules and Polymers;Nalwa,1997
4. Optical Properties of Photonic Crystals;Sakada,2005
5. Proton-Transfer-Dependent Reversible Phase Changes in the 4,4′-Bipyridinium Salt of Squaric Acid