Experiments showinga rapid and reversible change ofcolor s eem likemagic and are always fascinating. The process involved, photochromism, has a few real and many potential applications. Photochromic glasses thatdarken int he s unlight (protecting eyes from excessive light intensity) and bleach ind im lighta re today a part ofe v eryday life. Organic photochromic compounds in plastic ophthalmic lenses, more comfortable to wear, are now competing with silversalts in glasses, despite the longer lifetime oft he inorganic system. This successful commercial application has given a new impetus to research in the general field of photo chromism, which had its most recent revival in the early eighties. The storyo forganic photochromism with its ups anddowns, from the breakthroughs oft he pioneering periodi n the fifties, through the hardtimes dueto the drawbacks of photodegradation, tot he recent successes is in many ways a saga. The upsurges in this domain were marked by an increasing flow of articles in scientific journals andt he publication of several books (in 1971, 1990, and 1992) that have collectedt he important accumulatedknowledge. Over this period, a considerable number ofpatents have been issued. International meetings have accompanied this activity, the most recent being held in 1993 (ISOP 93 atLes Embiez Island, France) and in 1996 (ISOP 96 inClearwater, Florida). Remark ably, these meetings had good representation from both academia and industry. The next ISOP is planned for 1999 in Fukuoka, Japan.

Zusammenfassung
A treatise on photochromism involving organic molecules and derived systems. It focuses on the physico-chemical properties and photochromic behavior of the best-known systems, which have led to new developments in the known photochromic series or the discovery of new families.

Inhalt
Photochromic Polymers.- Photodegradation of Organic Photochromes.- Photokinetics under Continuous Irradiation.- EPR and Radical Processes.- Molecular Modeling Calculations.- The Enantiomers of 2-Donor-Substituted Benzopyrans and Benzo-1,4-oxazines and Their Thermal Racemization.- Structural Studies by X-Ray Diffraction.- New Trends in Raman Studies of Organic Photochromes.- Biological Applications Supramolecular Chemistry.- Thermochromism of Organic Compounds.