Hydrogen bonding,polarity and matrix effects on the spectroscopic and photophysical properties of some N- and 3-substituted derivatives of carbazoles

Fluorescence spectra and photophysical properties of N-cyano and N-carboethoxy carbazole derivatives have been compared to the equivalent 3-substituted compounds in fluid polar and unpolar solutions and in a low temperature rigid matrix at 77 K. The 3-carboethoxy derivatives have been shown to form an excited state complex (exciplex) with ethanol in fluid solutions. On the other hand the photophysical properties of the N-substituted derivatives are much affected by the solvent polarity in fluid solutions in that the radiationless decay rate constants show a marked increase in these media. A tentative explanation has been given in terms of the relative energy gap existing between the ¹L_b and the ¹L_a states of these molecules.     

Aggregation and photophysical properties of phthalocyanines in supramolecular complexes

The concentration dependence of the degree of association of zinc and aluminum phthalocyanines in supramolecular systems is determined. Complexes containing rare photoactive associates with an absorption maximum significantly shifted to longer wavelengths are obtained. The radiative lifetimes, extinction coefficients, and energy of HOMO-LUMO electronic transitions of isolated and associated metal phthalocyanine complexes are determined. It is demonstrated that the existence of the metal phthalocyanine largely in an aggregated state is characteristic of zinc phthalocyanine systems, while aluminum phthalocyanine, having an additional extraligand, chloride ion, is stabilized in the isolated state.     

Synthesis and photophysical properties of a novel soluble polyquinoline

Synthesis, characterization and photophysical properties of the poly{[(2,2′-bis-(4-phenylquinoline)-1,4-phenylene]-alt-phenoxy}_n, a novel quinoline derived copolymer with ether linkages, are described. Polymerization reaction occurred through nucleophilic aromatic substitution between an aromatic halogen and a phenol. Structural characterization was made by FTIR, NMR, DSC, TGA and GPC. Ultraviolet, fluorescence and excitation spectroscopy were used for analysis of photophysical properties. The ether linkages, apart from providing better solubility compared to full conjugated quinoline copolymers, made it possible to access the photophysical properties of the quinoline moiety as a constituent of a polymer backbone, since these linkages are responsible for the confinement of the chromophoric unit. The role played by protonation in photophysical behavior was also considered, since this class of polymers is only soluble in strong acid media. This work comprised the study of the photophysical properties of nitrogen containing polymers with confined conjugation and the role of this element in some interesting properties.     

Quantum-chemical study of the spectral properties of stilbene isomers

Calculations of absorption spectra of cis-and trans-forms of stilbene by the quantum-chemical method of intermediate neglect of differential overlap with spectroscopy parametrization were carried out. The electron structure of a stilbene molecule was studied and energy-level diagrams were drawn and analyzed. Rate constants of different photophysical processes occurring in a stilbene molecule after absorption of a photon were calculated in relation to the molecule conformation. On the basis of the obtained results, possible configurations of photoisomer molecules were considered and the most probable configurations of excited stilbene molecules were determined. It was shown how the change in the configurations of cis-and trans-forms of stilbene affects its spectral properties.     

Study of photophysical properties of capped CdS nanocrystals

Here, we have examined the role of capping agent on the optical properties of CdS nanoparticles by steady-state and time-resolved photoluminescence (PL) spectroscopy. The estimated particles sizes are 3.45, 2.5 and 2.39 nm for uncapped, capped with silica (SiO₂) and thiosalicylic acid (TSA), respectively. The absorption and emission spectra show a clear blue shift to shorter wavelengths in presence of TSA- and SiO₂-capped nanoparticles. It is found that the average decay time 〈τ〉 are 6.24, 4.54 and 2.84 ns for uncapped, capped with SiO₂ and TSA nanoparticles, respectively. Our analysis suggests that the hole or the electron is trapped on thiol molecule of TSA or hydroxyl group of SiO₂, then radiative recombination of the electron and hole is delayed, resulting in strong quenching of PL efficiency.     

Substituent effects on the photophysical properties of amino-aurone-derivatives

ABSTRACT

Aurones are potential candidates to be employed as fluorescent probes or as pharmacophores for biological applications. This work describes a density functional theory (DFT) and time-dependent -DFT study at the PBE0/6-31?+?G(d) level of theory to analyse the structural, electronic and photophysical properties of a series of new proposed 4′-amine-aurone derivatives in its E and Z isomeric conformations. The maximum absorption wavelength of the proposed aurones appears in the range 390???514?nm, while the most allowed emission pathways were computed in the range 493–530?nm. The bathochromic shift of these compounds with respect to the non-substituted aurone is modulated by the acceptor strength of the added 4-substituents, in addition to the ability of the substituents to localise the frontier molecular orbitals over the acceptor benzofuranone moiety without losing the tricyclic planarity, which favours the push–pull nature of these molecules. The influence of the 4-substituent is also evidenced in the Stokes shifts for the whole series; as the electron-withdrawing character of the 4-substituents enhances, higher is the polarisation of the structure resulting in higher Stokes shifts. As a result, -CF₃ and -NO₂ substituents were responsible of larger Stokes shifts, then compounds containing these substituents are proposed as potential fluorescence probes for useful applications in biological systems.     

Naphthalene-based fluorophores: Synthesis characterization, and photophysical properties

U-type, 1,8-diarylnaphthalenes and 1,8-diarylethynylnaphthalenes were synthesized and their structures were characterized by spectroscopic methods. Emission performance of these compounds with donor and acceptor was largely depended upon the solvent polarity and environmental acidity, which implied that they might be used as solvent polarity sensors or pH sensors as well. Moreover, some 1,8-diarylnaphthalenes exhibited aggregation-induced emission enhancement (AIEE) based on their photophysical investigation and might be used as light emitting materials for optoelectronic applications.     

Quantum-chemical modeling of the structure of strained silicon nanocrystals on a germanium substrate

The results of optimization of the atomic and electronic structure of strained silicon clusters Si₅₁ on a germanium substrate are presented. The interaction of boundary nanocluster atoms with the substrate is studied. The effect of strain and impurities on the distribution of electronic states is analyzed.     

A quantum-chemical study of photophysical properties of complex compounds

For complexes of Re(I), Ru(II), and Os(II) containing some derivatives of 2,2′-bipyridine, the Franck-Condon components of the probabilities of nonradiative transitions involving excited states resulting from metal-to-ligand charge transfer are calculated. Two versions of the theory are used: with account of all the normal accepting modes and in the approximation of a single vibration of an efficient acceptor. Data on vibrational frequencies and changes in the geometrical parameters of the ligands upon excitation are obtained from ab initio quantum-chemical calculations. The calculated and experimentally determined constants of nonradiative transitions were found to correlate well with each other. The proposed procedure allows one to predict the photophysical properties of coordination compounds.     

Quantum-chemical modeling of energy parameters and vibrational spectra of chain and cyclic clusters of monohydric alcohols

The specific peculiarities of alcohols such as heightened viscosity, boiling temperature and surface tension can be explained by the capability of their molecules to form relatively stable associates named clusters due to hydrogen bonding. In present work the stability of different chain-like and cyclic clusters of methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol and 1-hexanol was investigated by means of quantum-chemical simulation and particular by recently developed DFT exchange–correlation functional M06-2X. The relative stability of the cluster structure was evaluated by the total energy per molecule at low temperatures (where all alcohols exist in solid state) and by the changing of the free Gibbs energy upon cluster formation at the room temperature. For the verification of revealed results the conformity of calculated IR spectra of the most stable cluster structures with the experimental IR spectra at different temperatures was analyzed.     

Quantum-chemical modeling of ferroelectric solids with hydrogen-bond networks of different dimensionalities and their deuterated analogs

The application of quantum chemistry methods in the microscopic theory of H/D-bonded ferroelectrics and antiferroelectrics is illustrated using a comparative analysis of low-temperature order-disorder structural phase transitions in zero-dimensional materials of the K₃H(SO₄)₂ family, zero-dimensional crystals of 5-halo derivatives of 9-hydroxyphenalenone (5Hal-9HPO), and three-dimensional crystals of potassium dihydrogen phosphate (KDP) and potassium dideuterium phosphate (DKDP) as examples. In the framework of the Ising model with tunneling, it is demonstrated that (in agreement with experimental data) the transition to the low-temperature ordered phase in zero-dimensional materials is possible only in the case of their deuteration, whereas the quantum paraelectric behavior is characteristic of undeuterated samples. This behavior for KDP crystals is impossible due to the sharp increase in the Ising parameters as compared to zero-dimensional materials. The factors responsible for the increase in these parameters are considered.     

Spectral and transport properties of the PT-symmetric dimer model

We study the scattering properties of the PT-symmetric tight-binding model with balanced gain and loss parameters. Our main interest is to establish the link between the spectral properties of scattering states and transport characteristics for the case of non-equal couplings between gain/loss sites. The analytical approach we have used allows one to reveal a quite unexpected role of this set-up in comparison with that of equal couplings. In particular, we demonstrate that for the exceptional points characterized by equal eigenvalues of the transfer matrix, the transmission coefficient can be different from one in contrast with the model with equal couplings. The analytical results are complemented by the numerical data.     

Laser study of the photophysical properties of UF6

The purpose of this paper is to review the most relevant theoretical and experimental results reported in recent years, on the photophysical properties of the uranium hexafluoride molecule in the gas phase. Details of the structure of the molecular orbitals of UF₆ are discussed with reference to theoretical calculations of the electronic states. Tentative assignments of the electronic transitions in the experimental visible-uv absorption spectrum are also considered. The fluorescence properties of the excited states of UF₆ are critically reviewed. The use of laser beams to excite the fluorescence emission of UF₆ is shown to be a fruitful experimental technique. The measurement of fluorescence parameters (i.e. the emission and excitation spectra, the decay time and quantum yield) is a particularly valuable and sensitive way of studying the dynamics and structure of the excited electronic states. The different mechanisms of fluorescence quenching that have been proposed are also critically reviewed.     

Study of photophysical properties AlBaq5

Pure and Ba²⁺ doped Alq₃ complexes were synthesized by simple precipitation method at room temperature, maintaining stoichiometric ratio. These complexes were characterized by XRD, UV–vis and FT-IR and photoluminescence (PL) spectra. XRD analysis reveals the polycrystalline nature of the synthesized complexes, while UV and FTIR confirm the molecular structure and the completion of quinoline ring formation and presence of quinoline structure in the metal complex. PL spectra of Alq₃ compared with barium doped complexes exhibit highest intensity in comparison to Alq₃ phosphor, which proves that barium enhances PL emission intensity of Alq₃ phosphor. The excitation spectra of the synthesized complexes are in the range of 300–480 nm with a broad peak in the range of 429–440 nm and shoulder at 380 nm, but with varying intensity. The emission wavelength lies in the range of 501–506 nm. Among all the synthesized complexes, AlBa₂q₅ exhibits maximum emission intensity. These remarkable properties of AlBaq₅ could be considered as promising materials as optoelectronic materials as well as green light emissive materials for OLEDs, PLLCD and solid state lighting applications.     

Syntheses, structures and photophysical properties of heteronuclear Zn-Ln coordination complexes

Four heteronuclear Zn-Ln coordination complexes, [Nd₂Zn₂(p-toluylate)₁₀(phen)₂] (1), [Ln₂Zn₂(p-toluylate)₁₀(phen)₂]·2(HAc)_1/2 (Ln=Tb 2, Ho 3) and [PrZn₂(p-toluylate)₅(Ac)₂(phen)₂] (4) (phen=1, 10-phenanthroline), are synthesized by the hydrothermal method and their structures are measured by single-crystal X-ray diffraction. The IR and UV-vis-NIR absorption spectra and the emission spectra in the visible and near-infrared (NIR) regions of the four complexes are determined at room temperature. In the NIR region (or in the visible region), the complexes show the characteristic emission bands of Ln³⁺ ions, which may be attributed to sensitization from the ligands (the ligand directly-coordinated to Ln³⁺ ions and d-block) to Ln³⁺ ions after forming the Zn-Ln complexes. It is reported for the first time in this paper that the Zn-Pr complex 4 can exhibit the broad emission band in the NIR region. In addition, the shift, split or broadness of the ff emission bands in the NIR region of complexes 1, 3 and 4 are discussed.     

Electronic states and spectroscopic properties of GeSi

Electronic structure and spectroscopy of the GeSi molecule have been investigated by performing ab initio based multireference configuration interaction calculations. Potential energy curves of 29 Λ-S states of singlet, triplet, and quintet spin multiplicities have been constructed. Spectroscopic constants of 24 bound states within 36 000 cm⁻¹ are reported and compared with the available data. The calculated dissociation energy of GeSi in the ground state is 2.80 eV. Effects of the spin-orbit coupling on the spectroscopic properties of the molecule have been found to be small. However, the computed zero-field-splitting of the ground state compares well with the earlier prediction. Transitions such as 2³Σ⁻-X³Σ⁻, 3³Σ⁻-X³Σ⁻, 4³Π-A³Π, 5³Π-A³Π etc. are relatively strong. Radiative lifetimes for several dipole allowed and spin-forbidden transitions are calculated. The estimated lifetimes of the 2³Σ⁻, 3³Σ⁻, and 5³Π states are about 109, 33, and 62 ns, respectively. Dipole moments of most of the low-lying states of GeSi are also reported.     

Heavy-water-based solutions of rhodamine dyes: photophysical properties and laser operation

Photophysical properties of heavy-water-based rhodamine dye solutions have been investigated, with a view to assess the suitability of heavy water as a solvent for high-power, high-repetition-rate dye lasers and amplifiers. We have measured the quantum yield of fluorescence of the commonly used dyes rhodamine-6G, rhodamine-B and kiton-red, dissolved in heavy water, ethanol and normal water. The performance of a heavy-water-based pulsed rhodamine-6G dye laser has been investigated in broadband, as well as in narrowband wavelength-tunable resonator configurations, yielding laser efficiencies comparable to those achieved with ethanolic solutions of the same dye. We have also studied the thermo-optic properties of normal and heavy water, using the Z-scan technique. Finally, photodegradation rates for laser dyes have been compared in heavy water, normal water and ethanol. Our results establish heavy water as a solvent superior to both ethanol and normal water, on account of the lower thermo-optic effects and the higher photostability of rhodamine dyes when dissolved in heavy water. Received: 8 February 2002 / Published online: 8 August 2002