Abstract: The present invention relates to compounds and derived materials based on compositions of matter consisting of appropriately substituted 3H-fluoren-3-ylidenes shown in figure A wherein the large dots (.circle-solid.) represent specific substituents define in the invention. ##STR1## These compounds and derived materials are able to undergo substantial changes in their optical properties in response to environmental changes. Such compounds and materials, for example, undergo substantial changes in their optical emission and absorption as well as refraction in different environments. In addition, by virtue of their ability to undergo permanent changes in refraction on exposure to certain predetermined wavelengths of radiation, the compounds and materials are photoprocessable by conventional techniques for the fabrication of optical devices and circuits, for computer, telecommunications, entertainment, defense, and sensor applications.