| 摘要 |
1,210,219. Photochromic materials. HAWKER SIDDELEY DYNAMICS Ltd. 30 Jan., 1968 [10 Feb., 1967], No. 6627/67. Heading C4S. A filter comprises a photo-chromic compound in a solvent, absorption being due only to changes in the triplet state population of the compound. Aromatic compounds comprising two or more condensed or conjugated rings e.g. dibenzanthracene, benzoperylene, chrysene, benzochrysene, naphtho chrysene, coronene, pyrene and picene are dissolved in hexane, ethanol, benzene paraffin or glycerol. Several compounds may be dissolved to vary the absorption band. To increase the triplet population the compound may contain N, S and O atoms, also compounds which transfer energy to the p.c. compound may be dissolved e.g. an aromatic compound as above benzamide or biacetyl. The triplet lifetime which can be from microseconds to 1 second can be increased by replacing hydrogen in the compound with deuterium or tritium and excluding oxygen and reactive impurities from the solvent. The solution is in a cell connected to a reservoir and may be preceded by filters absorbing wavelengths longer and shorter than those activating the p.c. compound. To reduce convection and diffusion which degrade the filter, fine particles having a refractive index close to that of the liquid may be added. |
