摘要:

AbstractIn a mixture of tetraphenylporphyrin (TPP) and fullerene (C60) doped in a PMMA film, fluorescence of TPP is enhanced and de‐enhanced by an electric field in zinc and free‐base compounds, respectively, indicating that the electron transfer from the excited state of TPP to C60is decelerated in zinc compounds and accelerated in free‐base compounds by an electric field. TPP was found to form complex upon mixing with C60which exhibits a broad emission in the wavelength region longer than that of the TPP emission. The complex emission is significantly quenched by an external electric field in both zinc and free base compounds, suggesting that the nonradiative decay of the excited complex is accelerated by an electric field in both

ISSN:0009-4536    

DOI:10.1002/jccs.200600011

出版商:WILEY‐VCH Verlag    

年代:2006

数据来源: WILEY

摘要:

AbstractPhotoinduced electron‐transfer processes between fullerenes (C60) and three triphenylamines (TPA's) including bis(tolylaminophenyl)cyclohexane in the absence and presence of hexylviologen dication (HV2+) and 1‐benzyl‐1,4‐dihydronicotinamide (BNAH) have been studied by the transient absorption method in the visible and near‐IR regions. Electron‐transfer takes place initially from TPA's to the triplet states of fullerenes (3C60*), giving the radical anions of fullerenes (C60−) and the radical cations of TPA's (TPA+). The rate constants and efficiencies of electron transfer are quite high, because of the high electron‐donor abilities of TPA's as their low oxidation potentials indicate. On addition of HV2+to the C60and TPA systems, the electron‐mediating process from C60−to HV2+occurs, yielding the viologen radical cation (HV+). In the further addition of BNAH, which acts as a sacrificial donor, steady‐state concentration of HV+was accumulated during continuous photoirradiation and pers

ISSN:0009-4536    

DOI:10.1002/jccs.200600012

出版商:WILEY‐VCH Verlag    

年代:2006

数据来源: WILEY

摘要:

AbstractThe photophysical properties of [fac‐Ir(ppy)3] have been studied using time‐dependent density functional theory with one‐center spin‐orbit coupling approximation. The phosphorescent state of [fac‐Ir(ppy)3] was characterized by a mixture of 40%3MLCT and 58% intra‐ and inter‐ligand3ππ*with charge distribution being partially localized to a single ligand. Zero‐field splittings and oscillator strengths calculated for the sublevels of the lowest triplet state were in agreement with the observed values. The spin components in the sublevels and the mechanism of phosphorescence were well rationalized using a localized model for a hypothetical M‐LL unit withC2vsymmetry similarly to the cases for [Ru(bpy)3]2+or [Os(bpy)3]2+. Furthermore, it was revealed that the excited states were characterized by both high density‐of‐state (approximately 70 states per eV) and considerable mixing between singlet and triplet states due to str

ISSN:0009-4536    

DOI:10.1002/jccs.200600013

出版商:WILEY‐VCH Verlag    

年代:2006

数据来源: WILEY

摘要:

AbstractTime‐resolved photoelectron imaging (TR‐PEI) allows accurate measurements of photoelectron angular distribution as a function of the pump‐probe time delay, providing a new powerful tool to study photon‐induced d

ISSN:0009-4536    

DOI:10.1002/jccs.200600014

出版商:WILEY‐VCH Verlag    

年代:2006

数据来源: WILEY

摘要:

AbstractTrititanate (H2Ti3O7) nanotubes were prepared by a non‐hydrothermal digestion of TiO(OH)2solution with 5 M NaOH, and their optical properties and exciton dynamics were studied by using steady‐state and time‐resolved photoluminescence (PL) spectroscopy. Based on TEM, AFM and XRD measurements, the tubular structure was identified to be the same as that of trititanate crystalline multi‐walled scroll nanotubes prepared hydrothermally, which has intershell d‐spacing of 0.79 nm with inner diameters of 5 nm and the lengths of several tens of nanometers. The UV‐absorption spectrum of trititanate nanotubes showed weak surface‐state absorption at 425 nm as well as the absorption maximum band around 350 nm with onset energy 3.03 eV corresponding to the indirect band gap energy. The steady‐state PL spectra of the trititanate nanotubes showed a band‐edge emission band around 360 nm as well as a broad surface emission band originating from widely dispersed surface‐state energy levels (2.84, 2.65, 2.41 2.21 2.03 eV), exhibiting higher relative intensity ratio of the band‐edge emission to the surface emission as compared to that of TiO2nanoparticles. These results with PL excitation spectra indicate that the density of the surface states was found to be higher in the nanotubes than in TiO2nanoparticles. The PL decay profiles were measured by using the time correlated single photon counting system (TCSPC) adopting fs‐Ti‐Sappire laser at 350 nm, and they were analyzed to fit a tri‐exponential equation. The decay times depend on monitoring emission wavelength, and at least four different decay time components (˜28 ps, ˜70 ps, ˜700 ps and ˜4 ns) were resolved, implying the existence of charge‐carriers trapping surface states with different energy levels. The two longer decay times are attributed to the deep‐trap surface states of trititanate nanotubes, which are much longer than those of TiO2nanoparticles. These results suggest that the nonradiative route to the surface excitons recombination is more dominant in trititanate nanotubes than in titania nanoparticles because of strong coupling of excitons

ISSN:0009-4536    

DOI:10.1002/jccs.200600015

出版商:WILEY‐VCH Verlag    

年代:2006

数据来源: WILEY

摘要:

AbstractIn this review, we present a microscopic theory for describing photo‐induced radiationless transitions. For this purpose, we state that introducing the density matrix method can not only treat the dynamics due to the radiationless transitions but also deal with the population and coherence dynamics. We briefly review several rate constants of the radiationless transitions and the analytic estimation methods of those rate constants. Finally, we present the applications of the theoretical treatment to the rapid electron transfer and energy transfer taking place in the photosynthetic reaction center

ISSN:0009-4536    

DOI:10.1002/jccs.200600016

出版商:WILEY‐VCH Verlag    

年代:2006

数据来源: WILEY

摘要:

AbstractFluorescence resonance energy transfer (FRET) is routinely used to study equilibrium and dynamical properties of polymers and biopolymers in the condensed phases. It is now being widely used in conjunction with single molecule spectroscopy where one usually employs the Förster expression which predicts (1/R6) distance dependence of the energy transfer rate. However, critical analysis shows that this expression can be of rather limited validity in many cases. We demonstrate this by explicitly considering a donor‐acceptor system, polyfluorene (PF6)‐tetraphenylporphyrin (TPP), where their sizes are comparable to the distance separating them. In such cases, one may expect much weaker distance (as 1/R2or even weaker) dependence. We also discuss recent application of FRET to study biopolymer conformational dynamics. We show that the well‐known Wilemski‐Fixman theory needs to be generalized to treat FRET at short separations. The utility of FRET in studying protein folding is also d

ISSN:0009-4536    

DOI:10.1002/jccs.200600017

出版商:WILEY‐VCH Verlag    

年代:2006

数据来源: WILEY

摘要:

AbstractTheab initio/Rice‐Ramsperger‐Kassel‐Marcus (RRKM) approach in conjunction withab initiocalculations of potential energy surfaces has been applied to investigate the photodissociation mechanism of azulene and its cation at 6.4 eV (wavelength 193 nm) upon absorption of one UV photon followed by internal conversion into the ground electronic state. Reaction pathways leading to several dissociation products have been mapped out at the Gaussian‐3 level and then the RRKM and microcanonical variational transition state theories have been applied to compute rate constants for individual reaction steps. Relative product yields (branching ratios) for dissociation products have been calculated to solve the system of master equations. It is established that the major dissociation channel of neutral azulene is H atom elimination. Pentalene and phenylacetylene as heavy fragments of acetylene elimination reaction could be observed with low yields. Azulene cation dissociates preferably through the pentalene channel. C10H7+, phenylacetylene, and benzocyclobutadiene cations can also be produced with comparable concentrations. Different kinetics of the acetylene elimination reaction have been revealed in the cases of neutral and charged

ISSN:0009-4536    

DOI:10.1002/jccs.200600018

出版商:WILEY‐VCH Verlag    

年代:2006

数据来源: WILEY

摘要:

AbstractSolvation dynamics of a polar probe in many biological systems and organized assemblies displays a surprising ultraslow component. The origin of this anomalous ultraslow component is investigated using experiments, theory and computer simulations. We first summarize some recent experimental results on solvation dynamics, e.g., temperature dependence, site dependence at active site of an enzyme and red edge excitation shift (REES). Then we propose two new theoretical models to explain the ultraslow component. The first one involves the motion of the ‘buried water’ molecules (both translation and rotation) accompanied by cooperative relaxation (‘local melting’) of several surfactant chains. An estimate of the time is obtained by using an effective Rouse chain model of chain dynamics, coupled with a mean first passage time calculation. The second explanation invokes self‐diffusion of the (di)polar probe (created by optical excitation)itselffrom a less polar to a more polar region. This may also involve cooperative motion of the surfactant chains in the hydrophobic core, if the probe has a sizeable distribution inside the core prior to excitation. It may also involve escape of the probe to the bulk from the surface of the self‐assembly. The second mechanism should result in thenarrowing of the full width of the emission spectrum with time, which has indeed been observed in recent experiments. It is argued that both the two mechanisms may give rise to an ultraslow time constant and may be applicable to different experimental situations. The effectiveness of solvation as a dynamical probe in such complex systems has been discussed. Finally, we give a brief overview of recent results on computer simulations on dynamics of water molecules around a protein an

ISSN:0009-4536    

DOI:10.1002/jccs.200600019

出版商:WILEY‐VCH Verlag    

年代:2006

数据来源: WILEY

摘要:

AbstractThree fundamental ultrafast photochemical reactions in solution, i.e., photoisomerization ofcis‐stilbene, photodissociation of diphenylcyclopropenone and excited‐state intramolecular proton transfer of 10‐hydroxybenzoquinoline, were studied by two color pump‐probe spectroscopy with time‐resolution as high as 30 −; 70 fs. The coherent nuclear wavepacket motions of the excited‐states that undergo ultrafast reactions were observed, and their relevance to the reaction was discussed. It was concluded that these reactions are classified to three different types for the relation between the initial nuclear wavepacket motion and the reacti

ISSN:0009-4536    

DOI:10.1002/jccs.200600020

出版商:WILEY‐VCH Verlag    

年代:2006

数据来源: WILEY