Leicestershire, U K LEZZ 3TU Central Laser Facility, Rutherford Appleton Laboratory, Didcot, Oxfordshire, U K O X 1 2 OQX The photochemical formation of the open merocyanine forms of several naphthoxazine-spiro-indolines in different solvents have been studied using both picosecond transient absorption (PTA) and picosecond time-resolved resonance Raman (PTR3) methods.The PTA studies have established the presence of several metastable species in the photochemical formation of the coloured merocyanine form of these photochromic compounds. The primary photochemical step occurs on the sub-ps timescale and is followed by the formation of a cisoid intermediate over the next 6-30 ps. This cisoid species then isomerises to the equilibrated distribution of transoid isomers of the merocyanine form with a lifetime that is dependent upon both solvent viscosity and polarity as well as the nature of the substituents on the naphthalene part of the molecule. However, the rate of this cis --+ trans isomerisation is unaffected on changing the N-alkyl group on the indoline part of the molecule from a methyl to an isobutyl group. The PTR3 studies have demonstrated that, in butan-1-01, there are at least three different transient species with characteristic vibrational spectra which evolve with different lifetimes to give the final isomeric distribution over the first few ns of the reaction. In cyclohexane it is likely that the formation of a single species is being probed, which is fully developed after the first 200 ps of the reaction. This single species has a spectrum which is the same as the equilibrated steady-state resonance Raman merocyanine spectrum. It is likely that the evolution in the PTR3 spectra obtained here, in butan-1-01, results from an equilibration of initially formed transoid merocyanine isomers to give a more stable distribution in this polar hydrogen-bonded solvent.Such an equilibration appears to be unnecessary in a non-polar solvent such as cyclohexane and it is suggested that this is because the transoid isomer, initially formed, is already in its most stable form.Naphthoxazine-spiro-indoline (NOSI) compounds that comprise two heterocyclic moieties connected by a tetrahedral spiro linkage represent an important class of photochromic compounds which have greatly improved resistance to prolonged UV irradiation compared with, for example, the structurally related spiro-pyrans. 'L' Both classes of compounds undergo a photoisomerisation reaction following irradiation in the UV region of the spectrum, which causes a breaking of the carbon-oxygen bond at the spiro linkage. Subsequent rotation about the carbon-carbon and carbon-nitrogen bonds, which remain joining together the two parts of the molecule, forms a transoid, more planar-type, structure which has a structure resembling that of a merocyanine dye, and absorbs in the visible region of the spectrum.2 Quinoid, zwitterion and even biradical structures have been proposed for the open merocyanine forms. There are several near-planar isomers arising from rotatio...

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Diffuse reflectance laser flash photolysis was successfully employed to study the triplet states of dyes adsorbed on or chemically attached to cotton. This technique, together with the detection of singlet oxygen from dyes on cotton, made it possible to investigate the diffusion of oxygen in cotton fibres and the mobility of dyes adsorbed onto cotton. Absorption by the triplet states of aluminium phthalocyanine chloride and eosin and the phosphorescence of singlet oxygen produced by sensitisation with rose bengal was used to monitor oxygen diffusion and dye mobility by measuring differences in triplet lifetimes, singlet oxygen lifetimes and in signal intensities. It was found that swollen cotton allows diffusion of oxygen in the fibres. However, a noticeable effect on the triplet state of adsorbed aluminium phthalocyanine chloride is only observed if oxygen is removed or added by thorough evacuation or oxygenation of the samples over several days. Singlet oxygen was quenched dynamically by adsorbed dyes, which were found to be immobilised on the fibres, demonstrating that oxygen is mobile within the fibres at the molecular level.

Luminescence and energy transfer properties of the system Gdl_,Tb,OCl(O < z 2 1) are reported, with special stress on those of TbOCI. Concentration quenching occurs above z = 0.15 at 300 K.Transfer from intrinsic Tb3+ ions to extrinsic Tb3+ ions and t o rare earth ion impurities are observed. The emission spectra of TbOCl are dominated by trap emission, which makes a quantitative analysis of the intrinsic Tb3+ luminescence properties in TbOCl cumbersome.Es wird uber die Lumineszenz und dieEnergieiibertragungseigenschaften des Systems Gdl -,Tb,OCl (0 < z 5 1) berichtet. Konzentrationstilgung erfolgt fur z > 0,15 bei 300 K. Energieubertragung von Tb3+ intrinsic-Ionen auf fehlgeordnete Tb3+-Ionen und auf Seltenerdfremdionen wird beobachtet. Die Emissionsspektren des TbOCl werden von Haftstellenemission bestimmt, was eine quantitative Analyse der Lumineszenzeigenschaften der Tb3+ -1onen auf Eigenstellen in TbOCl schwer macht.