Sergio Dellonte

Spectroscopic and photophysical properties of the Europium (III) Cryptate [Eu3+ ⊂ 2.2.1]

Abstract The spectroscope and photophysical properties of [Eu 3+ ⊂ 2.2.1] have been investigated. High-resolution emission spectra in aqueous solution are compatible with the presence of only one Eu-containing species with C 2v symmetry. The emission quantum yields indicate that the conversion of the charge-transfer levels to the 5 D 0 emitting state is relatively inefficient. Luminescence decay measurements show that encapsulation of Eu 3+ in the cryptand cage does not completely shield the metal ion from interaction with the solvent, since three water molecules are still coordinated to Eu 3+ through the cryptand holes.

Absorption and emission properties of a europium(II) cryptate in aqueous solution

Abstract The absorption spectrum of the complex between Eu 2+ and the [2.2.2] cryptand shows narrow, weak transitions within 4f 7 superimposed on broad, strong transitions from 4f 7 to 4f 6 5d. Emission from 4f 6 5d to 4f 7 can be observed at 77 K λ max = 420 nm, τ = 0.55 μs) and at 293 K (λ max = 460 nm, τ = 3 ns) in aqueous solution.

On the energy-transfer rate parameters of liquid alkanes

Abstract The quenching of emission intensity and emission lifetime of cyclohexane and decalin as a function of benzene concentration has been studied. The energy-transfer rate parameters obtained have been found to agree with those derived by the Stokes-Einstein relation.

Two-photon excitation of saturated hydrocarbons

Abstract Two-photon excitation of some alkanes by a pulsed nitrogen laser is reported on the basis of the observed emission spectra, decay times and the quadratic dependence of emission intensity on the laser beam intensity.

Temperature dependence of fluorescence lifetime of cyclic alkanes: mechanism of S1 deactivation

Abstract Non-radiative decay originating from S 1 has been investigated by measuring the emission lifetime as a function of temperature for some alkanes. For most of them the decay rate is composed of an activated Arrhenius-type and a temperature-independent process which are attributed to internal conversion and intersystem crossing respectively.

Effect of temperature on the photophysical properties of styrylpyridines

The effect of temperature on the photophysical parameters (fluorescence quantum yield and lifetime) of the three isomeric trans-styrylpyridines has been studied in 3-methylpentane and a mixture of ethyl ether, isopentane and ethanol in the proportions 5 : 5 : 2 (v/v). The Arrhenius parameters (A= 1012–1013 S–1, ΔE= 1–3 kcal mol–1) indicate that the activated twisting around the double bond, which is dominant at room temperature, takes place in the singlet manifold, as in stilbene. At low temperature (below 100–150 K, depending on nitrogen position) the S1 [graphic omitted] T1 process becomes important and, because of differences in the relative weight of intersystem crossing, different photophysical behaviour is exhibited by the three isomers. The observed dependence of the lifetimes on the excitation wavelength gives hints about the presence of conformational isomers.

Temperature effects on the photophysical behaviour of phenol and anisole in various solvents

Abstract A photophysical study of phenol and anisole in polar and non-polar solvents performed at various temperatures is presented. The main mechanisms responsible for the deactivation of S 1 are identified and are discussed in the light of radiationless transition theory. The results indicate that the lowest singlet of these molecules deactivates via a triplet manifold. The type of final state reached, i.e. associative or dissociative, depends on the relative position of the energy surfaces and on the influence of the solvent on the molecular states.

Photophysical properties of liquid alkanes studied by N2 laser two-photon excitation

Abstract Upon excitation of neat liquid alkanes by the focussed nitrogen laser pulse, a very short lived emission in the region 210–260 nm is observed. This emission is assigned to the fluorescence of the alkane excited by two-photon absorption, since its intenstity is proportional to the square of the exciting light intensity and its lifetime, τ, calculated by deconvolution, is in good agreement with the lifetime of alkane fluorescence reported in the literature. The nature of the non radiative decays orginating from S1 has been investigated by measuring τ as a function of temperature. The decay rate is composed of two terms; k = 1 τ =k 0 + Aexp (-E/RT) with A ⋍ 10 12 s -1 , E ⋍ 4kcal/mole and ⋍108s-1. From the size of A and k0, it is concluded that the decay of S1 takes place mainly via i.c. The rate of energy transfer from cyclohexane, perdeuterated cyclohexane and decalin to benzene as solute has been studied by lifetime and intensity measurements as a function of benzene concentration. The results of lifetime experiments follow the linear Stern-Volmer equation and the rate parameter has the size of diffusional processes with an interaction radius ⋍ 10 A. The results of intensity measurements indicate a larger quenching rate parameter. The discrepancy with respect to the lifetime results may be accounted for the transient dynamic effect, at least for decalin.

Aryloxy-substituted cyclophosphazenes: a new class or intramolecular excimers

Abstract Hexa-aryloxy-substituted cyclophosphazenes show eximer emission due to intramolecular interaction. Values of the excimer stabilization energy and activation energy of exeimer formation have been obtained. The effect of steric hindrance on excimer formation has been examined for p -alkyl-substituted hexa-phenoxy-cyclophosphazenes.

The lowest triplet state of substituted azobenzenes: An energy transfer investigation☆

Abstract The energy transfer process from aromatic hydrocarbons to some para-substituted azobenzenes was studied by flash kinetic spectrophotometry. The energies of the lowest triplet states of the azo derivatives investigated do not depend very much on the substituent and are in the range 30 – 35 kcal mol−1 (125 – 145 kJ mol−1). Neither the donor nor the acceptor substituents produce inversion in the 3(π,π*)—3(n,π*) state order, so that the lowest triplet state has n,π* character and appears to be distorted as in azobenzene. Inversion can be postulated for double substitution with strongly conjugated groups, i.e. in 4-N(C2H5)2-4′-NO2-azobenzene.