Fluorescence photoisomerization

Also, using dyes as laser media or passive mode-locked compounds requires numerous special parameters, the most important of which ate the band position and bandwidth of absorption and fluorescence, the luminiscence quantum efficiency, the Stokes shift, the possibiHty of photoisomerization, chemical stabiHty, and photostabiHty. AppHcations of PMDs in other technical or scientific areas have additional special requirements. 

Brejc, K., et al. (1997). Structural basis for dual excitation and photoisomerization of the Aequorea victoria green fluorescent protein. Proc. Natl. Acad. Sci. USA 94 2306-2311. 

The validity of the above conclusions rests on the reliability of theoretical predictions on excited state barriers as low as 1-2 kcal mol . Of course, this required as accurate an experimental check as possible with reference to both the solvent viscosity effects, completely disregarded by theory, and the dielectric solvent effects. As for the photoisomerization dynamics, the needed information was derived from measurements of fluorescence lifetimes (x) and quantum yields (dielectric constant, where extensive formation of ion pairs may occur [60], the observed photophysical properties are confidently referable to the unperturbed BMPC cation. Figure 6 shows the temperature dependence of the... 

The iodine-catalyzed photoisomerization of all-trans- a- and (3-carotenes in hexane solutions produced by illumination with 20 W fluorescence light (2000 lux) and monitored by HPLC with diode-array detection yielded a different isomer distribution (Chen et al. 1994). Four cis isomers of [3-carotene (9-cis, 13-cis, 15-cis, and 13,15-cli-r/.v) and three cis isomers of a-carotene (9-cis, 13-cis, and 15-ri.v) were separated and detected. The kinetic data fit into a reversible first-order model. The major isomers formed during the photosensitized reaction of each carotenoid were 13,15-di-d.v- 3-carotene and 13-ds-a-carotene (Chen et al. 1994). 

Ephardt H, Fromherz P (1989) Fluorescence and photoisomerization of an amphiphilic aminostilbazolium dye as controlled by the sensitivity of radiationless deactivation to polarity and viscosity. J Phys Chem 93(22) 7717-7725... 

Voliani V, Bizzarri R, Nifosi R, Abbruzzetti S, Grandi E, Viappiani C, Beltram F (2008) Cis-trans photoisomerization of fluorescent-protein chromophores. J Phys Chem B 112 10714-10722... 

Yang JS, Huang GJ, Liu YH, Peng SM (2008) Photoisomerization of the green fluorescence protein chromophore and the meta- and para-amino analogues. Chem Commun 1344-1346... 

Nifosi R, Tozzini V (2006) Cis-trans photoisomerization of the chromophore in the green fluorescent protein variant E(2)GFP a molecular dynamics study. Chem Phys 323 358-368... 

Figure 8.11. Diffuse reflectance absorption spectra of a strongly fluorescent sample (1,6-diphenylhexatriene adsorbed on porous alumina) (a) conventional measurement w ith monochromatic irradiation and detection via an integrating sphere (b) measurement in a fluorimeter with two monochromators. Reaction spectra during Irons - cis photoisomerization are also given (adapted from Ref. 26).

Cyclophanes are naturally suited for MMPI (15b) calculations. The results ofsuch calculations regarding the structures and electronic spectra of the [m] paracyclophanes (n = 5-10) agreed well with the experimental data (169). Attempted X-ray analyses of [2.4]- and [2.5](9,10)-anthracenophanes (46) encountered serious disorder in the ahphatic bridges. MMPI calculations of all possible conformers of these molecules revealed four and six energy minima for 46a and 46b, respectively. Comparison of the calculated C10 C10 distances and bridge conformations with X-ray information unambiguously identified two conformations each for 46a and 46b as the final solutions. These and the calculated structures of photoisomer 47 were highly useful in the interpretation of fluorescence spectra and photoisomerization processes of 46 (170). 

Diphenyl-1,3-butadiene. The excited-state behavior of this diene differs significantly from stilbene and is the subject of a review. Unlike tS in which the lowest vertical excited singlet state is the 1 B state and S2 is the 2 Ag state in solution, these two excited states lie very close to each other in all-trans-1,4-diphenyl-1,3-butadiene (DPB). The additional carbon-carbon double bond introduces a new conformational equilibrium involving the s-trans and s-cis rota-mers. Most spectroscopic studies in solution have concluded that the l B state is S. The DPB compound has a low quantum yield for photoisomerization, so the use of DPB in time-resolved spectroscopic studies on photoisomerization, especially those that monitor only fluorescence decay, needs to be considered cautiously and critically. 

The excited-state behavior of 1,1,2,2-tetraphenylethene (TPE) has been studied by means of picosecond fluorescence, absorption, and Raman spectroscopies and picosecond optical calorimetry. It has been shown that, like stilbene, TPE derivatives substituted with minimally perturbing stereochemical labels such as methyl groups undergo efficient photoisomerization. However, unlike stilbene, strong spectroscopic evidence exists for the direct detection of the twisted excited singlet state, 5ip herein but traditionally designated as of TPE. 

The time-resolved spectroscopy is a sensitive tool to study the solute-solvent interactions. The technique has been used to characterize the solvating environment in the solvent. By measuring the time-dependent changes of the fluorescence signals in solvents, the solvation, rotation, photoisomerization, or excimer formation processes of a probe molecule can be examined. In conventional molecular solutions, many solute-solvent complexes. 

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