Synthesis of Photochromic Dyes Based on Annulated Coumarin Systems

Abstract

Novel 2H-chromenes derived from hydroxycoumarins were synthesized, and their photochromic behaviour was studied under flash-photolysis conditions, showing a wide absorption range in the visible region. All the compounds exhibit low fluorescence, which apparently has no negative effect on their photochromic properties.1. Introduction. ± Photochromic systems have the ability to undergo a reversible transformation between two states giving rise to different absorption spectra, induced, at least in one direction, by electromagnetic radiation [1]. If one of the states absorbs in the visible region under appropriate conditions, a noticeable, reversible change of color occurs as a consequence of the transformation. Such phototransformations open a wide field of potential applications based upon the reversible color change or upon reversible changes in physical or chemical properties as a consequence of the structural modification accompanying such transformations [2].In the last two decades, the commercial success of plastic ophthalmic lenses that darken in sunlight, increased the interest in the search for new matrix-compatible organic molecules that allow the development of photochromic systems with enhanced properties. In the field of these variable-transmission optical materials, the main characteristics strived for, are i) the ability to be activated by sunlight (heliochromism) and bleached through a thermal process, ii) extended absorption in the visible region to provide a neutral colour upon irradiation, iii) a suitable fading rate (which is related to the stability of the coloured state), iv) high efficiency of coloration upon irradiation (−colorability×), and v) a high resistance to photodegradation (−fatigue resistance×) [3].Together with spiro-pyrans and spiro-oxazines, the 2H-chromenes (2H-[1]benzopyrans) have been extensively studied. These colorless molecules undergo, upon near-UV irradiation, a photo-induced reversible cleavage of the C(2)ÀO bond, followed by isomerization, leading to a (quasi-planar) colored open form that returns to the starting material by heating or by irradiation with visible light (Scheme 1).In the activated state, these molecules display a yellow-orange color (400 ± 500 nm) making them very attractive to be incorporated into lenses together with spirooxazines. The latter are excellent photochromic compounds, but they exhibit relatively narrow absorption bands, usually in the 560 ± 630 nm range, making it difficult to obtain

4-Phenoxybutoxy-substituted heterocycles – A structure–activity relationship study of blockers of the lymphocyte potassium channel Kv1.3

“…In a second step 40 (4.8 g, 21.6 mmol) was demethylated with boron tribromide (4.18 mL, 43.4 mmol) according to procedure C. The crude compound was purified by MPLC (cyclohexane/ethyl acetate (80:20)) to give 5-hydroxy-2 H -[1]benzopyran-2-one ( 41 , yield: 65%). 1 H NMR data were in accordance to literature [34]. In a final step 41 (520 mg, 3.2 mmol), CsF-celite (2.97 g, 14 mmol) and 4-PBB (1.47 g, 6.4 mmol), dissolved in 5 mL of dried acetonitrile, were reacted according to general procedure A.…”

Simple Coumarins and Analogues in Medicinal Chemistry: Occurrence, Synthesis and Biological Activity

“…This type of olefination of ortho-hydroxycarbonyl aromatic compounds, followed by further lactonisation, is a well-known method for the preparation of coumarin derivatives [9,108,122,[144][145][146][147][148][149] other type of coumarin derivatives (Scheme 8) [96,[158][159][160]. These coumarins are suitable starting materials for obtaining another type of compounds such as styril and acetyl derivatives, hydrazones, etc.…”

Xenobiotic Reductase A in the Degradation of Quinoline by Pseudomonas putida 86: Physiological Function, Structure and Mechanism of 8-Hydroxycoumarin Reduction

“…Coumarin and 2-cyclohexenone were obtained from Fluka. 8-Hydroxycoumarin was prepared essentially as described by Cerqueira et al 33 All chromatography materials were from Amersham Biosciences.…”