A relaxation function encompassing the stretched exponential and the compressed hyperbola

A simple relaxation function I(t/tauzero; alpha, beta) unifying the stretched exponential with the compressed hyperbola is obtained, and its properties studied. The scaling parameter tauzero has dimensions of time, whereas the shape-determining parameters alpha and beta are dimensionless, both taking values between 0 and 1. For short times, the relaxation function is always exponential, with time constant tauzero. For small values of alpha, the function is close to exponential for all times, irrespective of beta. The function is also close to an exponential when beta is near unity, irrespective of alpha. For large values of alpha and long times, the function is close to a stretched exponential, provided that beta>0. The compressed hyperbola is recovered for beta=0.Comment: 17 pages, 4 figure

Synthesis, photophysical and electrochemical properties of perylene dyes

ABSTRACT: Perylene dyes comprising: (i) 4-alkoxyphenylamino moiety in the 9-position as a strong donating group, (ii) cyanoacrylic acid as electron acceptor and anchoring group and (iii) a triple bond as short and rigid linker between perylene core and the acceptor group have been successfully synthesized. Their photophysical (i.e. absorption and emission spectra, molar extinction coefficients, fluorescence quantum yields and lifetime measurements) and electrochemical properties were investigated. The dyes display intense absorption in the visible exhibit high molar absorption coefficients making them good light harvesting materials for ss-DSCs.info:eu-repo/semantics/publishedVersio

New coumarin-[60] fullerene dyads connected by an alkynyl linkage: Synthesis and fluorescence studies. Evidence for efficient singlet-singlet energy transfer

Two new coumarin-[60] fullerene dyads, in which an alkyne group covalently links C60 to coumarin, are synthesized via 1,3-dipolar cycloaddition and spectroscopically characterized. Their photophysical properties in apolar (toluene) and polar (THF and benzonitrile) solvents are studied at room temperature, revealing the nature and polarity dependence of the excited-state interactions between the coumarin and C60 moieties. In both dyads and in all solvents, a strong quenching of the coumarin emission by C60 was observed. It mainly results from a fast and efficient singletesinglet resonance energy transfer from the coumarin moiety to the C60 moiety, but an electron transfer contribution, enhanced in polar solvents, also exists. In toluene, the fluorescence emission of the fullerene moiety is increased by the nonradiative energy transfer process, which occurs mainly by a dipoleedipole (FRET) mechanism. In polar solvents (THF and benzonitrile), fast electron transfer from ground-state coumarin to excited fullerene is significant, leading to a partial or complete quenching of the fullerene emission, depending on the dyad

Photonic superdiffusive motion in resonance radiation trapping

In this work we consider the relation between the jump length probability density function and the line shape function in resonance radiation trapping in atomic vapors. The two-sided jump length probability density function suitable for a unidimensional formulation of radiative transfer is also derived. As a side result, a procedure to obtain the Maxwell distribution of velocities from the Maxwell-Boltzmann distribution of speeds was obtained. General relations that give the asymptotic jump length behavior and the Lévy flight parameter niu for any line shape are obtained. The results are applied to generalized Doppler, generalized Lorentz, and Voigt line shape functions. It is concluded that the lighter the tail of the line shape function, the less heavy the tail of the jump length probability density function, although this tail is always heavy, with niu <= 1

Fluorescent homooxacalixarenes: recent applications in supramolecular systems

This review covers recent advances (from 2006 to date) in supramolecular systems based on fluorescent homooxacalixarenes, namely hexahomotrioxacalix[3]arenes, dihomooxacalix[4]arenes and tetrahomodioxacalix[4]arenes, focusing on fluorescence sensing using their intrinsic fluorescence (built-in mesitol-like groups) or the extrinsic fluorescence of organic fluorophores, either covalently linked to the calixarenes or forming supramolecular complexes with them. Sensing applications of ions, ion pairs and neutral molecules are discussed, as well as the potential measurement of temperature based on thermally activated delayed fluorescence

Novel phenoxazine-benzonitrile and phenothiazine-benzonitrile donor-acceptor molecules with thermally activated delayed fluorescence (TADF)

ABSTRACT: Four novel TADF emitters, containing phenothiazine and phenoxazine as electron-donors and benzonitrile derivatives as electron-acceptors were synthesized and fully characterized. Their photophysical (absorption and emission spectra, molar extinction coefficients, fluorescence quantum yields and lifetimes) and electrochemical properties (HOMO and LUMO energy levels) were measured, and drop-cast solid films of the four compounds were obtained to perform TADF studies. The obtained values for Delta E-ST indicate that these compounds are candidates for OLED applications.info:eu-repo/semantics/publishedVersio

Synthesis, optical and electrochemical properties of perylenes dyes for solar cells applications

Perylene monoimides or monoanhydrides are being intensively investigated as sensitizers in DSSCs. Keeping only one acceptor group, i.e. imide or anhydride, and introducing a donor group in the 9-position (such as diarylamine) proved to be important in order to obtain a favorable orbital partitioning strength and dipole moment of perylene compounds for DSSCs [1]. One way to control optical and electrochemical properties of perylenes dyes is achieved by functionalizing periand bay positions of perylene core with different substituents. In a simplified view, the peri groups coarsely tune the spectroscopic and electrochemical properties whereas the bay functional groups provide an additional fine tuning [2,3]. Here we report the design and synthesis of new perylene dyes (Figure 1) comprising: (1) a 4-alkoxyphenylamino moiety in the 9-position as a strong donating group, (2) a cyanoacrylic acid as electron acceptor and anchoring group and (3) a triple bond as short and rigid linker between perylene core and the acceptor group [4]. The photophysical properties (i.e. absorption and emission spectra, absorption extinction coefficients, fluorescence quantum yields and lifetime measurements) and electrochemical properties of the new perylene dyes were investigated and all results will be presented and discussed

Photon trajectories in incoherent atomic radiation trapping as Levy flights

Photon trajectories in incoherent radiation trapping for Doppler, Lorentz, and Voigt line shapes under complete frequency redistribution are shown to be Levy flights. The jump length (r) distributions display characteristic long tails. For the Lorentz line shape, the asymptotic form is a strict power law r ^ (-3/2), while for Doppler the asymptotic is r ^ -2 (ln r)^ (-1/2). For the Voigt profile, the asymptotic form always has a Lorentz character, but the trajectory is a self-affine fractal with two characteristic Hausdorff scaling exponents