Freeze drying photochromic filters
US3968051A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 14, 1971 |
| Grant date | Jul 6, 1976 |
| Priority date | — |
| Expiry date | Jul 14, 1991 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY10S522/912
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
A fast-acting photochromic filter--i.e. a filter whose optical density in the visible light range of 4000 to 7500 angstroms is increased when subject to radiation shorter than 6000 angstroms--which is room temperature stable, that is from at least about 20.degree. to 80.degree.C., consists of (1) a solid optically transparent polymeric matrix, (2) essentially free from non-combined or molecular oxygen, and preferably protected from diffusion of atmospheric oxygen, in which is (3) dispersed, in solid solution, at least one light absorbing compound having a polynuclear conjugated condensed aromatic ring structure, whose molecules are capable of assuming a metastable triplet state by a process of intersystem crossing (not necessarily of the moiety which assumes the metastable triplet state) and in the triplet state, because of closer triplet states, has energy absorption bands whicch occur at lower energies (larger wavelengths) than the singlet-singlet absorption for such molecules. A synergic component may also be used as a physically adjacent moiety or molecule in which intersystem crossing occurs more readily than in the light absorbing compound, and which transfers triplet energy …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.