Upon photoirradiation, photochromic compounds reversibly change not only the absorption spectra but also other physicochemical properties, such as refractive index, electrical moment dielectric constants, chelate formation, ion dissociation, oxidation/reduction potentials, and phase transitions during the photochromic reaction
a) The photochromic reaction is temperature dependent, with the lens going darker in cold temperatures
b) The photochromic reaction may be enhanced by an MAR coating on the lens
Writing is easily accomplished by exposing a photochromic material to focused spots of light appropriate to induce the photochromic reaction
that changes the colour of the compounds at the storage site.
The principle behind the photochromic reaction
is a switching activity at the molecular level where the molecular structure changes photochemically and the reaction is reversible.
Thus the observed photochromic reaction
mechanism in the present MPDMAPP doped PVA leads to the changes of chemical bond or the motion of molecular segments within the polymer matrix.