INTRAMOLECULAR INTERACTIONS BETWEEN THYMINE AND PSORALEN INDUCED BY A POLYOXYETHYLENE CHAIN

Abstract— The electronic absorption, fluorescence emission and photoreaction quantum yields for thymine-psoralen (1), psoralen-psoralen (2) and thymine-thymine (3) linked by triethyleneoxide chains are determined in ethanol and in water. Compounds (1), (2) and (3) are able to complex Li⁺ cations, new and striking effects of which have been revealed in their fluorescence properties and photoreactivities. An important hypochromism effect is observed in the UV spectrum of compound (1) in contrast to compounds (2) and (3).     

Kinetic study of photophysical and photochemical processes in α,ω-(bis-9-anthryl)-n-alkanes (ethane to decane) at room temperature

Fluorescence and photocyclomerization quantum-yield measurements and a transient kinetic analysis were performed for a series of α,ω-(bis-9-anthryl)-n-alkanes (A-C₂-A to A-C₁₀-A and A-mXy-A) in methylcyclohexane and ethanol. Of note is an irregular periodicity of intramolecular excimer fluorescence yields and the rate parameters for excimer collapse to photocyclomer.     

Two connected inverse spectral transforms

We establish a transformation which connects the potentials of the one-dimensional Dirac and Klein-Gordon operators. This transformation links the solutions of the nonlinear evolution equations solvable by means of the two inverse spectral transforms which use the Dirac and Klein-Gordon direct and inverse spectral problems.     

PHOTOSTATIONARY FLUORESCENCE EMISSION AND TIME RESOLVED SPECTROSCOPY OF SYMMETRICALLY DISUBSTITUTED ANTHRACENES ON THE meso AND SIDE RINGS: THE UNUSUAL BEHAVIOR OF THE 1,4 DERIVATIVE*

Abstract— Steady state and time resolved fluorescence emission properties of symmetrical dialkoxy-anthracenes (especially substituted on the side rings) 1-X, Y were studied in methylcylohexane. At room temperature, the fluorescence spectra of 1-X, Y show bands in the region of 380–550 nm and quantum yields (φ_F) in the range of 0.2–1. The fluorescence emission decays were found to be single exponential. The determination of the intersystem crossing quantum yields (φ_isc) for the weakly fluorescent compounds (1–1,5, 1–1,8 and 1–2,3) demonstrates that internal conversion is negligible compared with fluorescence emission and intersystem crossing, as previously observed for other anthracene derivatives. The fluorescence emission efficiency of compounds 1-X,Y is controlled by the relative mutual positions of the second triplet T₂ (whose energy varies significantly with substitution) and the first excited singlet S₁ states, respectively. An unusual solvatochromism was found for compound 1–1,4 which has a very weak permanent dipole moment in the ground state. This behavior was assigned to strong changes in the electronic densities between the excited singlet state and the ground state.