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A device has been set up to determine quantitatively the weak fluorescence intensities of pigment molecules. It consists of a laser spectrofluorimeter. The excitation beam can be produced with either a He/Cd laser (441.6 nm) or a He/Ne laser (632.8 nm). This system allows us to detect the fluorescence of dilute chlorophyll aor bsolutions of the order of 10−12 mol/l. This sensitivity also permits the study of the emission spectra from chlorophyll in monomolecular or solid states, and since a polarization rotator has been incorporated into our apparatus, one may presume some possible orientation of the molecules.

Surface pressure, surface potential, and ellipsometric–area isotherms have been measured to investigate the properties of chlorophyll a– digalactosyldiacylglycerol monolayers at the nitrogen – water interface. The surface pressure – area isotherms of the mixed film show a pronounced negative deviation with respect to ideality, whereas the surface potential isotherms follow the additivity law for mixed films. As the mole fraction of Chl aincreases from 0.1 to 0.5, each of the corresponding ellipsometric isotherm is shifted towards more negative values in the liquid expanded region. As the mole fraction is increased above 0.5, the ellipsometric δΔ values become more positive, with this trend continuing throughout the 0.5 to 0.9 mole fraction range. The combined effects of anisotropy in both the refractive indices and the absorption coefficient can explain the turnover observed in the ellipsometric δΔ isotherms as the mole fraction of Chl abecomes larger than 0.5.Hydrophilic interactions have been ruled out on the basis of the agreement with the additivity law, which is observed for surface potentials of the mixed monolayers. The observed deviation exhibited in the π–Aisotherms is interpreted in terms of the intermolecular cavity effect. Keywords: chlorophyll a, digalactosyldiacylglycerol, mixed monolayer, ellipsometry.

Some long-chain spiropyranindolines have been studied at the air–water and the air–solid interfaces. We have measured the surface pressure–area isotherms of these compounds and two of them are characterized by a solid film. We have also investigated the spectroscopic properties (uv–visible) of these spiropyranindolines in monolayer and in solution. The deposition of monolayers on quartz slides allowed the study of the photochromic properties of these compounds at the air–solid interface. The 3′,3′-dimethyl-1′-hexadecyl-6-nitrospiro(2H-1-benzopyran-2,2′-indoline), irradiated at 253.7 nm, showed the appearance of a new absorption band at 570 nm which varied in intensity when the number of monolayers and the time of irradiation were changed.

Nine new spiropyranindolines containing an n-hexadecyl substituent at the 1′ or 3′ position have been synthesized. Their spectral properties (nmr, uv, visible) are described.The equilibrium constant between the colored and colorless species of some of the compounds have been measured. The results show that the presence of a long aliphatic chain promotes the colored form.

The aim of this paper is to examine the direct effect of polluting gases on chlorophyll a(chl a) multilayer arrays. The pollutants studied are CO, CO2, SO2, H2S, NO, and NO2. Electronic and infrared spectroscopies were used to monitor the time effect of the polluting gases on chl amolecules. TLC, atomic absorption, and electronic spectroscopies were used to characterise the reaction products. The results show that neither CO nor CO2affect the chl amolecules in the multilayer arrays. Upon exposure to SO2, we notice many modifications on the electronic and ir spectra. All the evidence confirms that one of the reaction products is pheophytin a. A mechanism is presented to explain the reaction of SO2with chl a. The effect of H2S on chl ais less pronounced than that of SO2, but the end products are the same. NO and NO2have exactly the same effect on the chl amultilayer. The reaction is much more drastic than the reaction of chl awith either SO2or H2S. There is opening of the cycle and nitration of the chl amolecule.

Triton X-100 purified rhodopsin has been incorporated into lipid bilayer membranes prepared by the combined lifting-and-touching method. The illumination of the membranes with white light and monochromatic light of λ = 498 nm resulted in a high selective increase of Ca2+diffusion through the lipid bilayers compared to Na+and K+. The stoichiometric ratios of photoinduced ion diffusion were found to be more than 888 Ca2+Rh*−1s−1and 166 Na+Rh*−1s−1at 290 K using the white light, and 1 277 Ca2+Rh*−1s−1, 96 K+Rh*−1s−1, and 50 Na+Rh*−1s−1at 276 K using the monochromatic light. It was inferred that Ca2+is an excellent candidate as internal transmitter in the visual photo-transduction.

The solid films of all-trans, 9-cis, and 13-cisretinals have been found to be fluorescent at room temperature. Their polarization study with the aim of understanding the nature of their fluorescent state has also been carried out at room temperature. The high positive polarization of fluorescence with respect to the excitation carried out in the main 1Bu ← 1Agabsorption transition of retinals suggests that their fluorescent state possesses a large amount of 1Bucharacter. A vibronic coupling mechanism that suggests the 1Ag−(a weakly allowed π,π*) state or 1n,π* state being the lowest singlet state in retinals has also been considered.

The kinetics of the Z–Eisomerization of a series of 3′-nonsymmetrically substituted spiroindolinopyrans bas been studied by nmr in different solvents.The rate-determining step in nonpolar solvents was found to be the cleavage of the C—O bond whereas in polar solvents it was the C(2)—C(3) bond rotation.A strong steric hindrance of substituents at carbon 3 was observed. It was found that the rate of the isomerization is more sensitive to the bulkiness of the substituent at C(3′) than at the N(1′). Protic solvents enhance the reaction more than nonprotic polar solvents.