Transient absorption studies of the photochromic behavior of 3H-naphtho[2,1-b]pyrans linked to thiophene oligomers via an acetylenic junction.

The photophysical and photochemical properties of four 3,3-diphenyl-3H-naphtho[2,1- b]pyrans substituted, via an acetylenic junction, to (thiophene) n oligomers (n = 0-3 units) were investigated by transient absorption in the femtosecond to microsecond time domain and by stationary absorption and fluorescence. The decay of the initially produced excited S1(pi pi*) state is found to occur via three competing processes: fluorescence, intersystem crossing, and a ring-opening reaction leading to a colored merocyanine product, with relative yields varying drastically with n. Whereas ultrafast (sub-picosecond) reaction dynamics and high product quantum yield are observed for n = 0 and 1, the reaction is considerably slowed down on going to the n = 2 (105 ps) compound and does not occur for n = 3.

Photochromism of photoenolizable ketones in quinoline and 1,8-naphthyridine series studied by time-resolved absorption spectroscopy.

For the two photochromic molecules, 3-benzoyl-2-benzyl-1-methyl-1H-quinolin-4-one (QC1) and 3-benzoyl-1,2-dibenzyl-1H-1,8-naphthyridin-4-one (QC18a) as well as the nonphotochromic 3-benzoyl-1-benzyl-2-methyl-1H-1,8-naphthyridin-4-one (QC18b), the full photochemical mechanism, which is based on the photoenolization process, has been elucidated using stationary and time-resolved spectroscopy techniques. After photoexcitation, the S1(n,pi*)-T1(n,pi*) ISC process involving the exocyclic carbonyl chromophore is demonstrated to occur. Subsequently, gamma-hydrogen transfer proceeds very rapidly to give rise to the triplet photoenol with a probable 1,4-biradical structure.

The structure of pyrazoles in the solid state: a combined CPMAS, NMR, and crystallographic study.

The structures of six N-unsubstituted pyrazoles, three already known and three newly synthesized, have been studied by a combination of X-ray crystallography, multinuclear NMR (solution and solid state), and density functional theory (DFT) calculations. In those cases where crystal structure and CPMAS NMR were available, the agreement was almost perfect, allowing a prediction of the tautomer (with certitude) and the tetrameric structure (with high probability) in the case of 5-isopropyl-3-phenyl-1H-pyrazole without knowing the X-ray structure. In the case of the 5-(2-benzylphenyl)-3-trifluoromethyl-1H-pyrazole above represented, the DFT calculations at the B3LYP/6-31G level justify the great stability of this tautomer by the presence of an intramolecular N-H.

Photoinduced processes in dipyrrolyl-perfluoro-cyclopentenes.

The photobehavior of five photochromic dipyrrolyl-perfluoro-cyclopentenes was studied by steady state and time-resolved absorption spectroscopy. The quantum yields of the UV-photoinduced ring-closing reaction (coloration) and the visible-stimulated cycloreversion reaction (bleaching) were measured. Kinetic and thermodynamic parameters of thermal bleaching were also determined.

A thieno-2H-chromene alpha-amino acid derivative: synthesis and photochromic properties.

[structure: see text] A new photochromic thieno-2H-chromene alpha-amino acid derivative was prepared by C-N palladium-catalyzed cross-coupling of a bromothieno-2H-chromene with the aminated aromatic side chain of the methyl ester of a N,N-diprotected amino acid. Its good photochromic properties demonstrated by flash photolysis and continuous irradiation indicate a possible application in ophthalmic lenses. It may also be inserted into peptides to give photoinduced reversible structural changes.

Effect of oligothiophene substituents on the photophysical and photochromic properties of a naphthopyran.

A spectrokinetic study of the photophysical and photochemical properties of a series of photochromes bearing thienyl (T(1)), dithienyl (T(2)) and terthienyl (T(3)) groups linked to a naphthopyran in position 3 (sp(3) carbon) or 8 (naphtho moiety) has been carried out. The effect of the number and position of the thienyl groups on the excited state properties of the six compounds in the singlet and triplet manifold has been investigated by stationary and pulsed fluorimetric techniques, laser flash photolysis and kinetic analysis of the colouration/decolouration processes upon continuous irradiation. On increasing the length of the oligothiophene moiety, the contribution of fluorescence to the deactivation processes becomes detectable, while the photocolouration yield decreases.

Comprehensive photokinetic and NMR study of a biphotochromic supermolecule involving two naphthopyrans linked to a central thiophene unit through acetylenic bonds.

A photophysical and photochemical study of a biphotochromic compound where two naphthopyran units are linked by an acetylene-thiophene-acetylene bridge has been carried out in toluene. Both fluorescence and intersystem crossing to the triplet manifold were found to compete with the photocoloration process. Two photoproducts (transoid-trans and transoid-cis stereoisomers), absorbing at approximately 480 nm and corresponding to the opening of a single photochromic unit, were detected by spectrophotometric analysis after short irradiation time in diluted solution and identified by 1H-nuclear magnetic resonance (NMR) spectroscopy.

NMR characterisation of photo-electrocyclised structures of a spirooxazine derivative.

Three electrocyclised structures (C-DPh, TTC-DPh and CTC-DPh), produced after UV irradiation of a spirooxazine linked by a (Z)-ethenic bridge to a 2-methoxynaphthalene nucleus, have been identified by NMR spectroscopy.

Continuous irradiation and flash-photolysis studies of new[3H]naphtho[2,1-b]pyrans linked by covalent bonds to oligothiophene units. Effect of thiophene substituents on the photochromism.

The influence of oligothiophene substituents on five new [3H]naphtho[2,1-b]pyrans has been investigated using flash photolysis and continuous irradiation techniques. Photochromic properties strongly depend on the number and position of the thienyl units. Thienyl substitution increases the UV/visible absorbance of the lower energy transition of both the naphthopyran and merocyanine isomers.

A novel photoreversible photochromic system involving a hydrogen transfer/cyclization sequence.

A novel photoreversible photochromic system, 3-(2-benzylbenzoyl)-1,2-R,R(1)-4(1H)-quinolinones/12-hydroxy-5-R-5a-R(1)-6-phenyl-5a,6-dihydrobenzo[b]acridin-11(5H)-ones, is described.

Studies of polyphotochromic behaviour of supermolecules by NMR spectroscopy. Part 2. A bis-[3H]naphthopyran with a (Z)-ethenic bridge between each moiety.

The behaviour of a new biphotochromic molecule (CC-Z), formed by two naphthopyran moieties linked through a (Z)-ethenic double bond, has been studied by 1H and 19F NMR spectroscopy. To facilitate the investigations, a naphthopyran (CHR) and a model constituted by a naphthopyran entity linked through a double bond spacer to a methoxynaphthalene nucleus (C-Z) were also studied. At first, the studies were performed at low temperature (228 K) to extract the 1H and 19F NMR chemical shifts characterising photomerocyanines.

Studies of polyphotochromic behaviour of supermolecules by NMR spectroscopy. Part 1. A bis-spirooxazine with a (Z)-ethenic bridge between each moiety.

The photoproducts resulting from the irradiation of a closed colourless biphotochromic molecule formed by two spironaphthoxazine entities linked through an ethenic bridge and its model compound, a singular spironaphthoxazine joined by a double bond to a 2-methoxynaphthalene nucleus in the Z configuration have been studied by high resolution 1H NMR spectroscopy. At low temperature, a clean conversion between closed and open structures has been observed with the demonstration of mono and bi opening of the biphotochromic molecule. In contrast, studies at ambient temperature have implied an irreversible loss of the photochromic properties, with the formation of diastereoisomers, resulting from the cyclisation-oxidation reaction of the systems.

A Proton-Ionizable Ester Crown of 3,5-Disubstituted 1H-Pyrazole Able To Form Stable Dinuclear Complexes with Lipophilic Phenethylamines.

A convenient synthesis of the proton-ionizable crown 3 is reported that uses dibutyltin oxide. In acetonitrile, the reaction of 3 (LH(2)) with phenethylamine and homoveratrylamine (molar ratio 1:2) affords solid dinuclear complexes [LH(2)]2RNH(2) (4a,b), which spectroscopic (FAB-MS, IR, (1)H and (13)C NMR) data point toward a strong participation of the pyrazole nitrogens in the amine complexation. In DMSO-d(6) solution, a (13)C NMR study demonstrates the formation in situ of analogous neutral 4a-d[LH(2)]2RNH(2) or charged 5a-d[L(2)(-)]2RNH(3)(+) dinuclear complexes by reaction of 3 [LH(2)] or 3'[L(2)(-)]2Na(+) with RNH(2) (phenethylamine, homoveratrylamine, dopamine, and norepinephrine) or their RNH(3)(+)Cl(-) salts, respectively.