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New photochromic pigments for interactive papers
Author(s): R. Guglielmetti
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Paper Abstract

2H-1-Benzopyrans (or 2H-Chromenes) are an important family of oxygenated heterocycles particularly attractive because of their photochromic properties. Indeed, 2H-Chromenes undergo a reversible ring opening of the pyran cycle. The Csp3-O-bond is cleaved by UV irradiation leading to opened colored forms (generally called 'photomerocyanines'). The opened isomer reverts to its original form via a thermal pathway. The first described chromenes, 2,2-dimethyl [2H]-chromenes and their benzo annulated derivatives (naphthopyrans) showed photochromic behavior only at low temperatures and, moreover led to undesirable by-products. Interest in research in this field was developed only recently because of the industrial applications of materials undergoing variable optical transmission of light. For this purpose the desirable properties could be summarized as follows: light efficiency for coloring in the near ultra violet region, low quantum yield for bleaching with visible light and fast thermal fading at ambient temperatures. Another important criterium concerns the good resistance to the fatigue under continuous irradiation. These kinds of requirements have led to several structural modifications in the chromene series. Particularly, improvement of photochromic properties ('colorability') was obtained by the annulation of the chromene ring in the 7,8 positions, by appropriate substitution of the naphthopyran cycle replacing the alkyl groups on the Csp3 carbon atom by cyclopropyl groups, spiro adamantyl groups, and overall, by aryl groups. This last kind of substitution is nearly indespensible for showing good photochromic properties. Our interest in benzopyran chemistry has been focused on the design and study of heterocyclo-fused analogues, in order to modify the photochromic parameters. So we have introduced five-ringed and six-ringed heterocyclic systems involving oxygen, sulphur and nitrogen heteroatoms, particularly with an annulation in 5,6 positions. The general methods (A and B) have been used for the synthesis, they are briefly described.

Paper Details

Date Published: 4 August 1997
PDF: 5 pages
Proc. SPIE 3227, Interactive Paper, (4 August 1997); doi: 10.1117/12.280770
Show Author Affiliations
R. Guglielmetti, Lab. de Chimie et Materiaux Orgeniques Modelisation (France)

Published in SPIE Proceedings Vol. 3227:
Interactive Paper
Graham G. Allan; Jean J. Robillard, Editor(s)

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