André Samat

Synthesis and unexpected photochemical behaviour of biphotochromic systems involving spirooxazines and naphthopyrans linked by an ethylenic bridge

Abstract Using the Wittig reaction, six new biphotochromic compounds have been prepared by the coupling of conveniently functionalised spiro[indoline–naphthoxazines] and naphthopyrans. Compared to molecules taken individually, unusual photochromic behaviour has been detected with compounds for which a double bond of Z -configuration links both entities by the 5 or 5′ positions of the naphthalenic parts. Indeed, in this case the thermally stable uncoloured and coloured forms (bistable system) can be photochemically converted acting as photochemical switches.

Photomodulable Materials. Synthesis and Properties of Photochromic 3H-Naphtho[2,1-b]pyrans Linked to Thiophene Units via an Acetylenic Junction

The synthesis of 3H-naphtho[2,1-b]pyrans linked to mono-, di-, or terthiophene via an acetylenic junction is described (Schemes 2 and 3). The synthetic approaches involve successive Sonogashira coupling reactions. The photochromic properties in solution of these novel materials were investigated under continuous irradiation.

Synthesis and spectrokinetic studies of spiro[thioxanthene-naphthopyrans]

Abstract Several new spiro[thioxanthene-naphthopyrans] were prepared from substituted naphthols using a one step reaction. The photochromic properties of the new compounds were studied under flash photolysis and continuous irradiation. Compared to reference compounds general significant bathochromic shifts in the absorption spectra of the open forms, faster thermal bleaching kinetics and interesting fatigue resistances were observed.

Synthesis and reactivity of formyl-substituted photochromic 3,3-diphenyl-[3H]-naphtho[2,1-b]pyrans

Synthetic accesses to formylated photochromic 3,3-diphenyl-[3H]-naphthopyrans (or 2H-benzochromenes) are developed through classical cyclization between appropriate hydroxynaphthaldehydes and 1,1-diphenylpropyne-1-ol and also via substituent transformations on the naphthopyran skeleton including bromine/lithium exchange and the oxidation of an hydroxymethyl group. Examples of formyl group reactivity (Wittig and Knoevenagel reactions, imine formation) from these compounds are given, showing their interest in the subsequent preparation of supramolecular systems involving a photoreactive entity.

Femto/Picosecond Transient Absorption Spectroscopy of Photochromic 3,3-Diphenylnaphtho[2,1-b]pyran

Abstract Transient absorption spectroscopy with femtosecond time resolution was used to probe the photochemical ring opening process of 3,3-diphenylnaphtho[2,1-b] pyran in solution. Analysis of the temporal evolution of the spectra from 0.4 ps to 100 ps has allowed us to detect and identify some of the intermediates involved in the photochemical formation of colored photomerocyanine isomers. From these data and those of recent ab initio and semi-empirical calculations on related photochromic systems, a simple mechanistic model was proposed for the ring opening/closing reaction in room temperature solution.

Effect of heteroaromatic annulation with five-membered rings on the photochromism of 2H- [1] -benzopyrans

Abstract Photochromic properties (colorability, UV-VIS spectra of photo-merocyanines, rate constant of thermal bleaching) of chromenes annulated with different five-membered azaheterocycles or with furan cycles were investigated under flash photolysis. All the compounds, i.e., the 7H-pyrano[2,3-g]benzazoles 4–6, the 7H-pyrano[3,2-e]benzazoles 7–10, the 7H-pyrano[3,2-e]indoles 11–12, the 3H-pyrano[3,2-a]carbazole 13, the 8H-pyrano [2,3-e] indole 14 and the 3H-furano [ 3,2-f]chromenes 15–18 undergo reversible photochromic reaction at room temperature. They are compared with naphthopyranic parents 1–3. Whatever the structure of the heteroaromatic moiety, the annulation of the benzopyrans leads to the splitting into two bands of the electronic absorption spectra of the photoinduced forms with a significant bathochromic shift, a feature of interest for variable optical absorption systems. Unfortunately, diaryl-substituted azolo-fused chromenes exhibit decreased colorabilities. Furofused benzopyrans are particularly interesting with respect to naphthopyran parents owing to the bathochromically shifted and broadened absorption spectra of photoinduced forms and slightly enhanced colorabilities.

Synthesis and photochromic behaviour of novel 2H-chromenes derived from fluorenone

Abstract The synthesis of 2 H -chromenes based on a fluorenone nucleus is described. Whereas 2,2-diphenyl-2 H -pyranofluorenones 4 – 7 and dicyanomethylidene-2 H -pyranofluorenes 8 – 10 do not exhibit photochromism, 2,2-diphenyl-2 H -pyranofluorenols exhibit photochromic behaviour. The spectrokinetic properties of these compounds in solution are reported.

Formation of mono- and di- nuclear complexes of Zn2+ from a 26 membered tetraester crown of 3,5-disubstituted pyrazole able to act as neutral and dianionic ligand

Abstract A selective synthesis of bis(3,5-diketo-1H-pyrazole)-[26]crown- 12 ( 1 , L 1 ) has been performed. Its deprotonation pK a values, and those of the acyclic analogues ( 3 – 5 ) have been measured. The disodium dipyrazolate salt of 1 ( 2 , [L 2 ] 2- 2Na + ) has been isolated, and mono- and di- nuclear complexes of Zn 2+ obtained from 1 ([L 1 Zn] 2+ ) and 2 ([L 2 Zn 2 ] 2+ ) have been studied by 13 C NMR spectroscopy in DMSO-d 6 solution.

Solvatochromic and photochromic characteristics of new 1,3-dihydrospiro[2H-indole-2,2′-[2H]-bipyrido[3,2-f][2,3-h][1,4]benzoxazines]

The mono-oxime of 1,10-phenanthroline-5,6-quinone reacts with 1,3,3-trimethyl-2-methyleneindoline, derivatives to give the corresponding spirooxazines, i.e. 1,3-dihydrospiro[2H-indole-2,2′-[2H]-bipyrido[3,2-f][2,3-h][1,4]benzoxazines]. These compounds exhibit particular solvatochromic behaviour, strongly dependent on the substitution pattern. At room temperature and without any light excitation, an equilibrium is established between closed and opened forms. The photochromic characteristics have been determined using flash photolysis coupled to a fast scanning spectrometer allowing the determination of rate constants for thermal bleaching, visible absorption and photocoloration. The coloured opened forms, either photoinduced or arising from the solvation effect, appear to be spectroscopically identical. Structural parameters of the short-lived photomerocyanines have also been obtained.

Synthesis of photochromic dyes based on annulated coumarin systems

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.