Intramolecular Energy Transfer Process Research Articles

On the dependence of the luminescence intensity of rare-earth compounds with pressure: a theoretical study of Eu(TTF) 32H 2O in polymeric solution and crystalline phases

Theoretical models for ligand–rare-earth-ion energy-transfer processes and numerical solutions of the rate equations are used to analyse the dependence of the 4f–4f emission intensity and the 5 D 0 excited state lifetime with an applied external pressure, in Eu 3+ complexes. Pathways for the intramolecular energy-transfer process between the ligands and the rare-earth ion are proposed. The theoretical results agree well with the experimental data for the Eu(TTF) 32H 2O compound in a polymeric solution and crystalline form.

Photoacoustic spectroscopy study on lanthanide ternary complexes with dibenzoylmethide and phenanthroline

The photoacoustic (PA) spectra of Eu(Dbm) 3·Phen and coprecipitates Eu 0.8Ln 0.2(Dbm) 3·Phen complexes (Ln 3+: Nd 3+, Gd 3+, Tb 3+; Dbm: dibenzoylmethide; Phen: phenanthroline) are reported. The PA intensity in the region of the ligand absorption increases for Eu 0.8Gd 0.2(Dbm) 3·Phen, Eu 0.8Tb 0.2(Dbm) 3·Phen, Eu(Dbm) 3·Phen and Eu 0.8Nd 0.2(Dbm) 3·Phen, respectively. It is indicated that additions of the second lanthanide ions change the relaxation processes of the complexes. The changes of fluorescence spectra turn out to be complementary to the PA spectra. The intramolecular energy transfer and intermolecular energy transfer processes in the coprecipitates are discussed.

Photophysical study of a multi-chromophoric dendrimer by time-resolved fluorescence and femtosecond transient absorption spectroscopy

The photophysical properties of a dendrimer ( 1) bearing eight peryleneimide chromophores on a polyphenylene core were investigated by picosecond fluorescence and femtosecond transient absorption techniques. A peryleneimide attached to a hexaphenylbenzene unit ( 2) served as model compound. Multi-exponential fluorescence and fs-transient absorption decays were observed only for 1, which could therefore be attributed to excimer-like interactions among neighbouring peryleneimides. The comparative time-resolved polarisation results on 1 and 2 indicate the occurrence of different depolarisation processes in the dendrimer assignable to the rotation of the molecule, a fractional motion maybe of a dendrimer branch and to an intramolecular energy transfer process.

Sensitized luminescence of the Eu 3+/La 3+/cinnamic acid mixed complex: comparison to the Eu 3+/Gd 3+/cinnamic acid mixed complex

The photoluminescence properties of europium and lanthanum mixed complexes with cinnamic acid are described. The maximum emission intensity is found to be at about 80% Eu 3+/20% La 3+ content at room temperature. The roles of intramolecular and intermolecular energy transfer processes are discussed. Comparison to photoluminescence properties of Eu 3+/Gd 3+/cinnamic acid mixed complexes is given. A slight photochemical degradation of the samples is found, the degree of which depends on the Eu 3+/La 3+ ratio.

A theoretical approach to intramolecular energy transfer and emission quantum yields in coordination compounds of rare earth ions

A recently developed theoretical approach to the evaluation of ligand–rare earth ion energy transfer rates in coordination compounds is discussed in the context of a scheme for the modeling of highly luminescent rare earth compounds. This scheme is based on the joint application of the theory of 4f–4f transition rates (radiative and nonradiative), the sparkle model to describe the electronic structure of the organic part and coordination geometries of the compounds, and the present theoretical approach to intramolecular energy transfer processes.

Intramolecular energy transfer mechanism between ligands in ternary rare earth complexes with aromatic carboxylic acids and 1,10-phenanthroline

A series of binary and ternary rare earth (Gd, Eu, Tb) complexes with aromatic acids and 1,10-phenanthroline have been synthesized. The lowest triplet state energies of ligands have been obtained by measuring the phosphorescence spectra of binary gadolinium complexes. By comparing the phosphorescence spectra of binary complexes with those of ternary ones, it is found that there exists another intramolecular energy transfer process from the aromatic acids to 1,10-phenanthroline besides the intramolecular energy transfer process between the aromatic acids and the central rare earth ions. The intramolecular energy transfer efficiencies have been calculated by determining phosphorescence lifetimes of binary and ternary gadolinium complexes. The luminescence properties of corresponding europium and terbium complexes are in agreement with the prediction based on energy transfer mechanism.

Photoacoustic spectra of complexes of tryptophan with Sm(III), Tb(III) and Dy(III)

Crystals of the complexes of Tryptophan with Sm(III), Tb(III) and Dy(III) were synthesized and the photoacoustic (PA) spectra in the UV–vis region were recorded. The PA intensities of the central lanthanide ions are interpreted in terms of the probability of nonradiative transitions. It is found that the PA intensity of the ligand bears a relation to the intramolecular energy transfer process. For the title complexes, the different PA intensities of the ligand, tryptophan, are interpreted by comparison with the fluorescence spectra. The relaxation process models are also studied based on the PA and fluorescence spectra.

Synthesis, Luminescence and Intramolecular Energy Transfer of Binary and Ternary Rare Earth Complexes with Aromatic Carboxylic Acids and 1, 10‐Phenanthroline

AbstractA series of binary and ternary rare earth complexes with para‐substitued benzoic acids and 1,10‐phenanthroline were synthesized. The phosphorescence spectra were measured and the lowest triplet state energies of ligands were determined, the phosphorescence lifetimes were obtained and intramolecular energy transfer mechanism between ligands was studied. The luminescence properties were also measured and were in agreement with the prediction. The energy match and intramolecular energy transfer process in these binary and ternary complexes were discussed in detail.

Kinetic determination of bromadiolone based on lanthanide-sensitized luminescence

A very fast, selective kinetic method for the determination of bromadiolone is proposed. The analytical parameter used is the initial rate of the luminescence reaction between bromadiolone and terbium(III) in the presence of Triton X-100. The luminescence signal arises from an intramolecular energy transfer process between excited bromadiolone and terbium(III), which is followed by the lanthanide emission. The use of stopped-flow mixing technique allows to obtain kinetic data within only 0.2 s and automatize the method. The calibration graph is linear over the range 1.5–18 μg ml −1 bromadiolone and the detection limit is 0.3 μg ml −1. The mid-range relative standard deviation is close to 2%. The recoveries obtained by applying the method directly to the analysis of irrigation water samples ranged from 86.7 to 100.0%.

Properties of molecular switch triad compounds for photoinduced intramolecular energy transfer

This paper reports the synthesis and transient absorption decay kinetics of several triad compounds, in which a sulfur aryl section is used as the spacer for intramolecular energy transfer (IET). After flash photolysis the producing sulfur radicals will provide an ‘energy trap’ to stop the IET process, after stopping flash photolysis the sulfur radicals reversibly recombine and the IET process recovers, and then a rapid photoinduced IET switchable function is realized.

Spectroscopic properties of a new light-converting device Eu(thenoyltrifluoroacetonate) 3 2(dibenzyl sulfoxide). A theoretical analysis based on structural data obtained from a sparkle model

We report the synthesis, characterization and spectroscopic properties of the compound Eu(thenoyltrifluoroacetonate), 2(dibenzyl sulfoxide) which is highly luminescent under UV excitation. Experimental and theoretical results on ligand field parameters, 4f-4f intensities and intramolecular energy transfer processes are described. The characteristic emission spectrum of the Eu 3+ ion shows a very high intensity for the hypersensitive 5D 0 → 7F 2 transition, pointing to a highly polarizable chemical environment around the Eu 3+ ion. No emission at low temperature from the organic part of the compound is observed, in contrast to the case of the analog compound with Gd 3+, indicating that energy transfer from the ligands to the Eu 3+ ion is quite efficient. Lifetime measurements confirm that the Eu 3+ luminescence has a higher efficiency than in the case of the hydrated compound (two water molecules in the place of the dibenzyl sulphoxides). The theoretical calculations are based on an optimized coordination geometry and electronic structure obtained from the SMLC/AM1 (Sparkle Model for the calculation of lanthanide complexes within the Austin Model 1), recently introduced in the literature, and ligand field and 4f-4f intensity models previously developed. A comparison with experiment is made. Considerably high values of intramolecular energy transfer rates are predicted.

Intermolecular and intramolecular energy and electron transfer reactions between porphyrin and fluorescein

A porphyrin (TTP)-fluorescein (FL) heterodimer covalently linked with a flexible polyatomic chain has been synthesized and characterized. The rate constants and the efficiencies of the inter- and intramolecular energy and electron transfer processes were determined. Their UV-Vis absorption, steady-state and time-resolved fluorescence spectra were investigated. The UV-Vis absorption and 1H NMR spectroscopy suggest that there is some exciton coupling between the two chromophores in this system, whilst fluorescence spectroscopy shows that the FL unit transfers singlet-state excitation energy to the TTP. From time-resolved fluorescence studies, it is concluded that the heterodimer exists in solution in different, nonequili-brating, conformations. The effects of the solvent polarity on the intramolecular energy and electron transfer efficiencies are discussed. The results showed that on selective excitation of the FL chromophore, only a very efficient singlet state energy transfer process from FL to TTP was observed in different solvents, but on selective excitation of the TTP chromophore, only in a polar solvent (DMF) could the intramolecular electron transfer reaction occur. The difference of intramolecular interaction in solvents of various polarity may be explained in terms of conformational change due to the nature of solvent interaction.

Isolation of the Stereoisomers of [{Ru(bpy)2}2{Os(bpy)2}(μ-HAT)]6+ (HAT = 1,4,5,8,9,12-Hexaazatriphenylene; bpy = 2,2‘-Bipyridine)

[Extract] The synthesis and physical properties of polymetallic ligandbridged molecular assemblies have been topics of intense interest, motivated by their possible application to photochemical molecular devices. An aspect receiving limited (but increasing) attention is the existence of stereoisomerism within such assemblies and its influence on intramolecular energy and electron transfer processes. The stereoisomers of the trinuclear Ru2Os species [{Ru(bpy)₂}₂{Os(bpy)₂}(μ-HAT)]⁶⁺ (HAT = 1,4,5,8,9,12-hexaazatriphenylene; bpy =2,2'-bipyridine) have been isolated using a combination of stereoselective syntheses and chromatographic procedures and characterized by NMR and CD spectroscopy.

ChemInform Abstract: Synthesis of a Variety of Bichromophoric “Ball‐and‐Chain” Systems Based on Buckminsterfullerene (C60) for the Study of Intramolecular Electron and Energy Transfer Processes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Anomalous asymmetry splittings in a molecule with internal rotation in the presence of classical chaos.

Rotation-torsion energy levels of acetaldehyde calculated from a spectroscopic Hamiltonian obtained from the fit of high-resolution microwave and far-infrared spectra, exhibit anomalously large splittings for some asymmetry doublets. It is shown that these anomalies are caused by chaos-enhanced quantum dynamical tunneling between classically disconnected regions of the phase space. A major consequence of this phenomenon is the magnification of intramolecular energy-transfer processes. {copyright} {ital 1996 The American Physical Society.}

Synthesis of a Variety of Bichromophoric “Ball-and-Chain” Systems Based on Buckminsterfullerene (C60) for the Study of Intramolecular Electron and Energy Transfer Processes

Diels−Alder reaction of C60 with the 1,3-dienes 7e−h, 8a, 8b, and 8d−h affords the “ball-and-chain” systems 2e−h, 3a, 3b, and 3d−h bearing two chromophores linked via a rigid, hybrid saturated polynorbornane−bicyclo[2.2.0]hexane (“norbornylogous”) hydrocarbon bridge. Analogous reaction with the bis(diene) 9 affords the soluble dumbbell system 4 bearing two C60 chromophores. The norbornylogous bridge is a strong mediator of electron and energy transfer via a through-bond coupling mechanism. The norbornylogous donor−bridge−diene units 7d−h, 8a, 8b, and 8d−h were prepared in a straightforward manner from bicyclo[2.2.2]octane precursors by extending the bridges with linearly fused norbornane−bicyclo[2.2.0]hexane moieties through execution of the tandem Mitsudo−Smith series of reactions. The X-ray structure of the dimethoxybenzene−bridge−C60 system 3a reveals favorable self-complementarity manifested by the unusual packing structure of 3a in the crystal. Molecular mechanics, semiempirical, and ab initio conformational analyses of compounds 2e, 3a, 3b, 3e, 3f, 3h, 68, and 70 (MM2, Sybyl, CVFF, AM1, HF/3-21G) were performed to quantify their ability to adopt two nondegenerate boat conformations, i.e., extended and folded conformers, as well as their kinetic barrier of interconversion. A similar treatment of the C60−bridge−C60 system 4 revealed unusual preference for the folded−folded conformer (18.9 kcal/mol at CVFF level), which was not reproduced by the AM1 method (0.11 kcal/mol). The reduction potentials of the systems 2e, 3a, and 3e were about 0.1−0.5 V more negative than C60, and the third reduction potential (E3) of the 6-bond system 2e was 0.14 V more negative than the corresponding wave for the 10-bond system 3e. This shift was attributed to the closer proximity of the dimethylaniline donor group to the C60 surface for 2e vs 3e.

Evidence for quantum interference in collision-induced intramolecular energy transfer within CO singlet–triplet mixed states

The quantum interference effect associated with one type of radiationless transition, the collisional energy transfer between singlet–triplet mixed molecular states, is studied. The experiments are conducted on CO(A 1Π,e 3Σ−)–He(Ar) via the ultrasensitive optical–optical double resonance multiphoton ionization (OODR-MPI) technique which measures state-to-state cross sections to an accuracy of ±10%, irrespective of the lifetime of the excited state. Distinct evidence of a quantum interference effect on the transfer rate has been obtained for mixed state CO intramolecular energy transfer processes. A simple, explicit expression for the cross section for mixed state energy transfer, based on the first order Born approximation of time dependent perturbation theory, is derived. The use of a transition phase angle θST is incorporated in the expression to describe the phase angle difference between singlet and triplet channels. This greatly refines the existing theory of quantum interference for collisional processes in that it successfully calculates the energy transfer cross sections and interprets the observed quantum interference effect under various quantum transitions. Experimental values of θST obtained for the CO–He system are 66° for J=9 and 73° for J=13. These results indicate that the infinite-order-sudden approximation which calls for θST=0 cannot satisfactorily account for the quantum interference effect. In addition, measured θST values for CO–Ar system are consistent with our theoretical expectations.

Photosensitization of wide bandgap semiconductors with antenna molecules

Polynuclear metal complexes, supporting efficient intramolecular energy transfer processes, can be used to increase the light harvesting efficiency of sensitized wide bandgap semiconductors. Experimental studies are discussed to emphasize: (i) how structural changes at the molecular level may affect the performances of photoelectrochemical cells based on antenna-sensitizer molecular assemblies, (ii) the availability of fast time-resolved resonance Raman and infrared spectroscopies for monitoring intercomponent energy transfer processes, and (iii) the possibility to design extended antenna units acting as molecular conduits for long-range energy transfer.

Luminescence and intramolecular energy-transfer processes in isomeric cyano-bridged rhenium(I)-rhenium(I) and rhenium(I)-ruthenium(II)-rhenium(I) polypyridyl complexes

Reference LPI-ARTICLE-1992-015doi:10.1021/ic00051a016View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

Dynamical inhomogeneous broadening and lattice-assisted intramolecular energy transfer in the fundamental A1 vibrations of liquid chloroform Cl-35

This report gives extensive isotropic Raman spectral data and their numerical Fourier transformation into the time domain (∼0–20 ps) for the three A1 vibrational fundamentals of Cl-35 isotopically pure chloroform. It was found that the vibrational amplitude correlation decay of the ν1 mode (C–H stretch) at 300 K follows a rapid vibrational dephasing process (inhomogeneous broadening with motional narrowing) that is 1.7 times faster than the concomitant intramolecular energy transfer to the overtone of the C–H bending mode. From the temperature dependence (213 K, 300 K) of the amplitude correlation decay of the ν3 mode (C–Cl deformation) we deduce that it relaxes essentially only by vibrational dephasing and in such a fast modulation regime that the ν3 oscillator is effectively decoupled from the local lattice anisotropies. From the temperature dependence of the amplitude correlation decay of the ν2 mode (C–Cl stretch) we infer a simultaneous vibrational dephasing and lattice-assisted intramolecular energy transfer process, the latter possibly to the overtone of ν3. This paper concludes with some general remarks on the predictability of relative contributions of various types of vibrational relaxation processes to vibrational amplitude correlation decay in molecular liquids and, in an Appendix, gives estimates on the rates of excess phonon depopulation into the lattice as governed by a permanent dipole–transition dipole coupling process for modes ν6, ν3, ν2, and ν5 of liquid chloroform.