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A static electron-transfer quenching mechanism for iodide photooxidation with visible light is demonstrated. The spectroscopic data suggests that the Ru(II)-iodide adducts arise from interactions between iodide and diimine ligand(s) as well as ion pairing.

The time-resolved fluorescence profiles of the anthracene chromophore after excitation of the naphthalene chromophore at 285 nm have allowed the kinetics of the energy-transfer process to be evaluated. A comparison of the experimentally determined EET rate constant with those modeled via a direct Coulombic (Forster-type) interaction between the two chromophores indicated excellent agreement for both [ZnL(super 3)](super 2+) and [ZnL(super 4)](super 2+).

Capacitance-voltage and admittance spectroscopy is used to investigate the effect of incorporating an InAlAs layer before an InGaAs cap layer on electron emission in self-assembled InAs quantum dots (QDs). This incorporation of a high potential barrier increases the emission time of the electrons thermally activated from the QD ground to the first excited state.

The quantum yield of the singlet and triplet products and the free radicals production are found analytically, assuming that the recombination of the diffusing radicals occurs at contrast. All the yields are related to the singlet and triplet populations of the recombining radical pair, subjected to spin conversion and contact exchange interaction.

TDDFT/B3LYP and RI-CC2 calculations with different basis sets are performed for vertical and adiabatic excitations and emission properties of the lowest singlet states for the neutral, protonated and deprotonated forms of 7-Hydroxy-4-methylcoumarin in the gas phase and in solution. It is found that, depending on the polarity of the medium, the solvent shifts vary, leading to a change in the character of the lowest excitation and fluorescence transition.

The activation energy barrier present for carboxylic acid catalyzed double proton transfer in different states is presented. The results show that the activation energy barrier present for carboxylic acidcatalyzed double proton transfer in the ground state is significantly lower in the first excited state, vanishing in the fourth excited state of the lumichrome-acid hydrogen-bonded complex.

Comprehensive excitation behaviors of 7-N,N-diethylamino-3-hydroxyflavone are investigated. The results show that the relationship of dipole moments, and hence their associated solvent polarization potential, among normal ground state (N), excited state normal (N*) and excited proton-transfer tautomer (T*) is crucial to account for the observed relaxation dynamics.

The method of similarity transformation is used to investigate the identifiability of three kinetic models namely model without added quencher, model with added quencher and the model with added quencher and coupled species-dependent rotational diffusion, described by Brownian reorientation. For these three models, an infinite number of alternative spectroscopic parameters associated with excitation and emission are found.

The two lowest electronically adiabatic potential energy surface of ammonia in the region of the conical interaction and at a sequence of geometries are calculated by employing a multireference (MR) method and a single-reference (SR) method. The MR calculations are based on multiconfiguration quasigenerated perturbation theory and the SR calculations, carried out with the same basis, employ completely renormalized equation-of-motion coupled-cluster method with single and double and a noniterative treatment of triples.

A report is presented on photobleaching mechanism of perylene orange embedded in thin sol-gel films, which are derived from single molecule studies. The study demonstrates that perylene orange is not a very efficient emitter in sol-gel films but that photobleaching can be slow.

The stabilization of cyclic-O(sub 3) with transition metals is studied using density functional theory. It is found that it is possible to use one-photon coherent anti-Stroke Raman Spectroscopy (CARS) scheme to detect the formation of cyclic-O(sub 3) and cyclic-SO(sub 2) because of the vibrational and electronic state spacings.

The dual fluorescence of 4-(dialkylamino) benzonitriles, the photodegradation of 4-(dimethylamino)benzonitrile (DMABN) and 4-(diethylamino)benzonitrile(DEABN) in a polar solvent was discussed. It was concluded that the photoproduct of these aminobenzonitriles was formed by subtraction of a substituent.

The C 1s excitation spectra of propyne, trifluoropropyne, and propargyl alcohol are determined using synchrotron radiation and ion time-of-flight mass spectrometry. This represents a significant improvement in resolution over the previous electron energy loss spectra, revealing structure not previously observed.

The photomerization properties of tris(bipyridine)cobalt complexes containing six or three azobenzene moieties are investigated. The photoexcited state of azobenzene moieties in the Co(III) complex are strongly deactivated by electron transfer from the azobenzene moiety to the cobalt center to form an azobenzene radical cation and Co(II) center.

The spectrum and stability of transverse electromagnetic excitations in a dc-biased semiconductor superlattice in microstrip line geometry is analyzed. The low-frequency branch displays a negative refraction region which is associated with the backward wave excitation in a superlattice and it gives the potential possibility of the subwavelength focusing of electromagnetic radiation in terahertz (THz) frequency domain by means of a superlattice flat slab.

The radical cations of trans-stilbene and substituted trans-stilbenes are generated from the resonant two-photon ionization (TPI) in acetonitrile with irradiation of one-laser and with simultaneous irradiation of two-color two-lasers with the pulse width of 5 ns each. The TPI proceeds through two-step two-photon excitation with the S0 -> S1 -> S(sub n) transition.

The absorption and emission spectra of the Pt(II) complexes containing N^C^N-coordinating tridentate ligands, platinum(II) 1,3-di(2-pyridyl)benzene chloride [Pt(dpb)Cl] and platinum(II) 3,5-di(2-pyridyl)toluene chloride [Pt(dpt)Cl], together with their corresponding free ligands, 1,3-di(2-pyridyl)benzene (dpbH) and 3,5-di(2-pyridyl)toluene (dptH) are analyzed. The results proved that the time dependent density functional theory approach is rational for analysis of the excited-state properties of the objective complexes.

The photochemical properties of a series of newly synthesized dendrimers, having a 2-(2'-hydroxyphenyl)-benzoxazole (HBO) core, are studied in benzene. The results of the dendrimer effect on the fluorescence quantum yield of the excited-state intermediate are the evidence of an efficiency increase with relation to the deactivation process of (E)-keto form (super 1)K(sub E) by isomerization to give the ground-state (Z)-keto form (super 1)K(sub z).

The control over the donor strength in a series of trannulenes-based donor-acceptor ensembles is used to alter the deactivation path of the photoexcited-state chromophore and to modulate the rates of intramolecular electron transfer. The investigation shows that the integration of trannulenes, as a versatile electron-acceptor building block, consistently produces charge recombination in the inverted Marcus region.

The ground-state electronic and magnetic properties of one of the possible structures of the trinuclear Cu(super II) site in the native intermediate (NI) of the multicopper oxidases, the mu(sub 3)-ox-bridged structure, are evaluated using the C3-symmetric Cu(sub 3)(super II) complex. The important contribution of the mu(sub 3)-oxo bridge to the ground-to-ground and ground-to-excited-state superexchange pathways that is responsible for the isotropic, antisymmetric and anisotropic exchanges are discussed.

Investigations indicate that dmso isomerization in ruthenium occurs within a strong-field ligand environment. Isomerization in these complexes occurs following format ion of an equilibrated S-bonded excited state.

Hypocrellin A (HA), an efficient phototherapeutic agent, can chelate with lanthanum ion to form a 1:1 complex, which exhibits enhanced (super 1)O2 generation yield, a red-shifted absorption window greatly improved water solubility, a much lengthened triplet excited state lifetime, and an increased affinity to DNA with respect to HA. The effects in turn lead to a more potent photodamage ability on calf thymus DNA for La(super 3+)-HA in both aerobic and anaerobic conditions, indicating the potential application of La(super 3+) HA in the field of photodynamic therapy.

Ultrafast structural dynamics concomitant to excitation energy transfer in DNA is studied using a pair of pyrene-labeled DNA bases. The temporal evolution of the femtosecond pump-probe spectra reveals the existence of two electronic coupling pathways, through-base stack and through-space, which lead to excitation energy transfer and excimer formation, the local structural dynamics and flexibility and flexibility of DNA are characterized on the picosecond and nanosecond time scale.

Forty states of the diatomic iron carbide cation FeC(super +) are studied by multireference methods coupled with relatively large basis sets. The ground state is of (super2)delta symmetry, with the first excited state [a(super 4)sigma(super -)] lying 18 kcal/mol higher.

The visualization and thickness evaluation for the insulator patterns through the photoluminescence (PL) measurement of CdSe/ZnS nanocrystals (NCs) placed on the patterns is demonstrated. The effective excitation intensity for CdSe/ZnS nanocrytsals (NCs) depends on the insulator thickness and excitation wavelength through the multireflection/interference of the excitation light.

Different types of antenna are used for helicon excitation but none of them generate a radio-frequency field that matches the helicon wave field determined by the dispersion equation. This match can be obtained to a very good approximation by using a birdcage type antenna.

A theoretical characterization of the potential energy surfaces of the singlet benzene excimer states derived from the B(sub 2u) monomer excited state is performed using time-dependent density functional theory. The calculated values are found to be in semiquantitative agreement when compared to experimentally determined values for the benzene excimer energetics.

A total of eight isotopically variant reactions OH/OD+CH4/CD4/CHD3 are investigated under crossed-beam conditions. The resulted water products are highly vibrational-excited, with the newly formed bond containing typically 50-60% of total available energy.

Excited-state proton transfer (ESPT) of 2-(2'-pyridyl)benzimidazole (2PBI) in reverse micelles is studied by steady-state and time-resolved fluorescence spectroscopy. The requirement of ESPT to occur in microheterogenous media is that the medium should be a ternary system comprised of water and a hydrophobic phase separated by a negatively charged interface.

Excitation functions from quasiclassical trajectory calculations on the H+H2O->OH+H2, H+HF->F+H2, and H+H'F->H'+HF reactions indicate a different behavior at low and high vibrational excitation of the breaking bond. Results indicate that the excitation functions for the reaction of an atom with a vibrational excited reactant undergoes a qualitative change as the vibrational excitation increases, independently whether the reaction is exothermic or endothermic.

Sequential hydration energies of SO4(H2O)(sub n)(super 2-) are obtained from determinations of the equilibrium constants of reactions like SO4(H2O)(sub n)(super 2-)=SO4(h2O)(sub n-1)(super 2-) + H2O ions are produced by electrospray. The dissociation SO4(H2O)12(super 2-) = SO4(H2O)11(super 2-) + H2O occurs at a very much lower effective excitations energy in the BIRD experiments.

Spectroscopic properties for a series of 2,5-diarylidencyclopentanones in weak and strong acid environments are reported. Results reveal that 2,5-bis(3-pehnylallylidene)cyclopentanone and 2,5-bis(5-phenylpenta-2,4-dienylidene)cyclopentanone undergo S1 excited-state proton transfer in glacial acetic acid and diluted sulfuric acid solutions at room temperature.

An investigation of the excited-state dynamics of SO2(H2O)(sub n) clusters following excitation by ultrafast laser pulses to 4.7 eV and 9.3 eV is presented. A lack of cluster size dependence in the measured time constants indicates surface solvation of SO2 rather than a cluster structure with the SO2 molecule fully encompassed by water molecules.

Closed loop automated pulse shaping experiments are conducted to investigate population transfer in solutions of the laser dye LD750 in acetonitrile and ethanol. It is concluded from the weak solvent dependence that rapid spectral evolution in emission of LD750 is not strongly altered by the shift between these solvents.

A study of the excited-state dynamics of (SO2)(sub m) clusters following excitation by ultrafast laser pulses in the range of 4.5 eV (coupled (super 1)A2, (super 1)B1 states) and 9 eV (F band) is presented. Results for the coupled (super 1)A2 and (super 1)B1 states are in good agreement with published computational work on the properties of these coupled states.

The kinetic energy release distributions (KERDs) for the fluorine atom loss from the 1,1-difluoroethene cation is recorded with two spectrometers in two different energy ranges. In both energy domains, KERDs are found to be bimodal.

A report on an experimental investigation of the effect of excitation wavelength on the ultrafast charge recombination (CR) dynamics of various donor-acceptor complexes (DACs) in several polar solvents characterized by different dynamic properties is presented. It is observed that a weak but distinct excitation wavelength effect requires very specific conditions related not only to the chemical system but also to the experimental parameters.d

The studies of thermochemistry of pyran-2-thione (PT), a sulfur derivative of alpha-pyrone (AP) are reported. Moderate heating of PT results in scrambling of sulfur and oxygen atoms in the molecule and formation of isomeric thiapyran-2-one.

The pi-pi* and n-pi* valence excited states of dibenzo-p-dioxin (DD) were studied through the complete active space SCF and multiconfigurational second-order perturbation theory employing the cc-pVDZ basis set and full pi-electron active space of 16 electrons in 14 active orbitals. Studies into dependence of the oscillator strengths on the extent of the butterfly-like folding showed that the electronic spectrum is more consistent with a folded equilibrium geometry assumed by DD in solution.

A study examining the singlet and triplet excited electronic states of several bromine compounds, using time dependent density functional theory, to access their photostability under stratospheric condition is conducted. The results show that several pentacoordinated bromine/oxygen compounds that could be photostable in the lower stratosphere, but it also shows that monovalent bromine compounds where the bromine atom is bounded to an atom with no lone-pair p-electrons is far and away the most photostable.

Theoretical investigations are performed to study the phenomena of ground and electronic excited state proton transfer in the isolated and monohydrated forms of guanine. The singlet electronic excitation of guanine may not facilitate the excited state proton transfer corresponding to the tautomerization of the keto and enol form.

Classical trajectory calculations are performed to simulate state-resolved energy transfer experiments of highly vibrationally excited pyrazine and CO2, which are conducted using a high-resolution transient infrared absorption spectrometer. The goal is to use classical trajectories to simulate the supercollision energy transfer pathway wherein large amounts of energy are transferred in single collisions in order to compare with experimental results.

A new technique employed to study the photophysical properties of the zinc(II) tetraphenylporphine cation radical is reported. It employs a combination of controlled potential coulometry and femtosecond absorption spectrometry.

The synthesis of a series of poly(p-phenylene ethynylene)s (PPEs) with high ionization potentials and associated high excited-state electron affinities is reported. The excited-state charge-transfer complexes (exciplexes) of the PPEs with analytes were observed thus providing promising opportunities for the formation of sensitive and selective chemical sensors.

The dynamics of H-bond interactions in poly(vinyl alcohol) (PVA) are studied by steady-state and time-resolved fluorescence emission of 4-aminophthalimide (4-AP) and Prodan. These two-probes of similar excited-state sensitivity are used to probe the dynamics of the relaxation process in the nanosecond time window.

A new type of photocatalytic reaction that splits water into H2 and O2 is designed using a two-step photoexcitation system composed of an iodate/iodide [IO3(super -)/I(super -)] shuttle redox mediator and two different photocatalysts, one for H2 evolution and the other for O2 evolution. Photocatalytic oxidation of water to O2 and reduction of IO3(super -) to I(super -) selectively proceeded with good efficiencies over TiO2-rutile and Pt-WO3 photocatalysts under UV and visible light irradiations.

The relative stability and the mechanisms of degradation of four polysilanes, which are reported as active materials in light emitting diodes are investigated theoretically. The correlation of the calculated results with experimental observations suggests that one of the causes of degradation in polysilanes can be the scission of Si-Si bonds in the excited state and that some stabilization is possible when a stable excited state exists.

Doppler-free two-photon excitation (DFTPE) spectra and the Zeeman effects of the 1(super 1)(sub 0)14(super 1) (sub 0) band of the S1 (super 1)B(sub 2u)

The structure, optical and photophysical properties of four 2,7-carbazolenevinylene-based conjugated derivatives namely PCP, PCP-CN, TCT and TCT-CN are discussed. All four compounds became more planar in their S1 relaxed excited state while PCP and TCT were found to be nearly planar in their ground electronic states (S0).

The excitation wavelength dependence of the relaxation dynamics in the carotenoid zeaxanthin was examined for understanding the complexity of excited-state processes in cartenoids. The population of zeaxanthin S* state was found to rise after 400 and 266 nm excitation.