Showing papers on "Stokes shift published in 2008"
TL;DR: Four new dimeric bis(BF(2))-2,2'-bidipyrrins (bisBODIPYs), and their corresponding BODipY monomers, have been prepared and studied with respect to their structural and photophysical properties, indicating potential uses of these new fluorophoric materials as functional dyes in biomedical and materials applications and also in model compounds for BODIPy aggregates.
Abstract: Four new dimeric bis(BF(2))-2,2'-bidipyrrins (bisBODIPYs), and their corresponding BODIPY monomers, have been prepared and studied with respect to their structural and photophysical properties. The solid-state molecular structure of the dimers and the relative orientation of the subunits have been revealed by an X-ray diffraction study, which showed that the molecules contain two directly linked BODIPY chromophores in a conformationally fixed, almost orthogonal arrangement. Two of the fluorine atoms are in close contact with each other and the (19)F NMR spectra show a characteristic through-space coupling in solution. The new chromophores all exhibit a clear exciton splitting in the absorption spectra with maxima at about 490 and 560 nm, and are highly luminescent with an intense emission band at around 640 nm. The Stokes shift, which is the difference between the maximum of the lowest-energy absorption band and the maximum of the emission band, has a typical value of 5 to 15 nm for simple BODIPYs, whereas this value increases to 80 nm or more for the dimers, along with a slight decrease in fluorescence quantum yields and lifetimes. These properties indicate potential uses of these new fluorophoric materials as functional dyes in biomedical and materials applications and also in model compounds for BODIPY aggregates.
224 citations
TL;DR: Bulky 4-tritylphenylethynyl substituted boradiazaindacene with pure red emission, relatively large Stokes shift, high fluorescence quantum yield, and low self-quenching was efficiently synthesized and qualified as a potential EL dopant.
169 citations
TL;DR: Novel isomeric fluorine-boron complexes with donor-acceptor architecture with significant features, such as strong solid and liquid fluorescence, unusual large Stokes shifts, and lower LUMO levels and higher HOMO levels, are observed in these potential multifunctional molecules.
166 citations
TL;DR: The 3-chloromethylpyridyl bipyridine fac tricarbonyl rhenium cation is a thiol-reactive luminescent agent with a long luminescence lifetime and large Stokes shift that is demonstrated by co-localisation studies to accumulate in mitochondria.
Abstract: The 3-chloromethylpyridyl bipyridine fac tricarbonyl rhenium cation is a thiol-reactive luminescent agent with a long luminescence lifetime and large Stokes shift that is demonstrated by co-localisation studies to accumulate in mitochondria. This represents the first application of a 3MLCT luminescent agent for the specific targeting of a biological entity in imaging.
140 citations
TL;DR: Each of the new fluorophores described is a minimal template structure for evaluation of their basic spectral properties, which may be further functionalized and optimized yielding concomitant improvements in their photophysical properties.
Abstract: A readily accessible new class of near infrared (NIR) molecular probes has been synthesized and evaluated. Specific fluorophores in this unique xanthene based regioisomeric seminaphthofluorone dye series exhibit a combination of desirable characteristics including (i) low molecular weight (339 amu), (ii) aqueous solubility, and (iii) dual excitation and emission from their fluorescent neutral and anionic forms. Importantly, systematic changes in the regiochemistry of benzannulation and the ionizable moieties afford (iv) tunable deep-red to NIR emission from anionic species and (v) enhanced Stokes shifts. Anionic SNAFR-6, exhibiting an unusually large Stokes shift of ≈200 nm (5,014 cm−1) in aqueous buffer, embodies an unprecedented fluorophore that emits NIR fluorescence when excited in the blue/green wavelength region. The successful use of SNAFR-6 in cellular imaging studies demonstrates proof-of-concept that this class of dyes possesses photophysical characteristics that allow their use in practical applications. Notably, each of the new fluorophores described is a minimal template structure for evaluation of their basic spectral properties, which may be further functionalized and optimized yielding concomitant improvements in their photophysical properties.
114 citations
TL;DR: In this article, the behaviors of Y, Tb, and Gd garnet phosphor powders activated by cerium were studied and emission spectra with a continuous yellowish range from green-yellow to yellow-orange were produced by controlling the compositions of the solid solution.
Abstract: The behaviors of Y, Tb, and Gd garnet phosphor powders activated by cerium were studied. Emission spectra with a continuous yellowish range from green-yellow to yellow-orange were produced by controlling the compositions of the solid solution. By increasing the substitution concentration of large cations in the garnet phosphor, the emission intensity tended to decrease and the temperature sensitivity of phosphors tended to increase. The redshift of the emission wavelength depended on the radius size of the substituted cation at the dodecahedral site of the garnet structure. Using a quantum mechanically based configurational coordinate diagram, the thermal quenching behavior, emission spectra, Stokes shift, nonradiative transitions in different host environments, and activator concentrations are discussed.
113 citations
TL;DR: In this paper, the effect of temperature on the optical properties of CdS QDs embedded in silica matrix was assessed before and after exposure of the samples to sunlight for up to 4 weeks.
106 citations
TL;DR: The design and synthesis of novel water-soluble far-red emitting phenol-based fluorophores derived from 7-hydroxycoumarin are described and their utility was illustrated by the preparation of an original fluorogenic probe of penicillin G acylase whose fluorescence is unveiled through an enzyme-initiated domino reaction.
104 citations
TL;DR: In this article, a tetraphenylimidazole-based excited-state intramolecular proton transfer (ESIPT) molecules with covalently linked charge-transporting functional groups was designed and synthesized for highly efficient blue electroluminescence.
Abstract: Aiming for highly efficient blue electroluminescence, we have designed and synthesized a novel class of tetraphenylimidazole-based excited-state intramolecular proton-transfer (ESIPT) molecules with covalently linked charge-transporting functional groups (carbazole- and oxadiazole-functionalized hydroxyl-substituted tetraphenylimidazole (HPI), i.e., HPI-Cbz and HPI-Oxd, respectively). High Tg (ca. 130 °C) amorphous films of HPI-Cbz and HPI-Oxd showed intense and ideal blue-light emission (λ max = 462 and 468 nm, Φ PL = 0.44 and 0.38) with a large Stokes shift of over 160 nm and a narrow full width at half-maximum of less than 65 nm. Organic light-emitting devices using HPI-Cbz and HPI-Oxd as the emitting layer generated an efficient blue electroluminescence (EL) emission peaking at around 460 nm with excellent CIE coordinates of (x, y)=(0.15,0.11). A maximum external quantum efficiency of 2.94%, and a maximum brightness of 1 229 cd m -2 at 100 mA cm -2 , as well as a low turn-on voltage of 4.8 V were achieved in this work.
98 citations
TL;DR: In this article, the 4 f − 5 d absorption and emission spectra of YAG (Y 3 Al 5 O 12 ) were simulated with a quantum chemical ab initio embedded cluster approach applied to Ce 3 + substitutional defects of D 2 local symmetry.
97 citations
TL;DR: The bathchromic shift observed in absorption and fluorescence spectra of C307 and C522B with increasing solvent polarity indicates that transition involved are pi-->pi* and excited state dipole moments are greater than their ground state counterparts in all the solvents studied.
TL;DR: The synthesis of a novel conjugate between a near-infrared indocyanine dye and an organic polyamine polymer (polyethylenimine, PEI) with high chemical stability and good optical properties is reported, making IR820-PEI one of the most effective and versatile indochenine dye polymeric-conjugate reported so far.
TL;DR: In this paper, a detailed study of photoluminescence excitation spectra in a wide range of excitation photon energies (270-420nm) reveals specific behavior of the Stokes shift of the fast ultraviolet-blue photoluminance (PL) band that agrees well with theoretical calculation of optical transitions in small silicon nanocrystals.
Abstract: Colloidal suspensions of small silicon nanoparticles (diameter around 2nm) with fast and efficient ultraviolet-blue photoluminescence (PL) band are fabricated by enhanced electrochemical etching of Si wafers. The detailed study of photoluminescence excitation spectra in a wide range of excitation photon energies (270-420nm) reveals specific behavior of the Stokes shift of the fast PL band that agrees well with theoretical calculation of optical transitions in small silicon nanocrystals and is distinct from emission of silicon dioxide defects.
TL;DR: In this article, a broad photoluminescence band with a large Stokes shift is observed, and its decay time depends strongly on the emission energies, attributed to radiative recombination of photo-excited carriers after multiple-step hopping among deep trapping sites on nanoparticle surfaces.
TL;DR: In this article, a series of (Ca1−x−ySrx)Si2O2N2:yEu2+ (x=0.0-0.97, y= 0.03) phosphors were synthesized by high-temperature solid-state reaction.
Abstract: A series of (Ca1−x−ySrx)Si2O2N2:yEu2+ (x=0.0–0.97, y=0.03) phosphors were synthesized by high-temperature solid-state reaction. The XRD patterns confirm the formation of a solid solution of (Ca1−x−ySrx)Si2O2N2:yEu2+. An intense tunable green light is observed with the increasing ratio of Sr/Ca. With an increase in x, the excitation and emission spectra show a redshift and blueshift, respectively, due to large centroid shift and small Stokes shift. The temperature dependent luminescence is also investigated in the temperature range of 77–450 K. The Huang–Rhys factor and the thermal-quenching temperature are determined. Intense green LEDs were successfully fabricated based on the (Ca1−x−ySrx)Si2O2N2:yEu2+ phosphor and near-ultraviolet (∼395 nm) GaN/blue (460 nm) InGaN chips. All the results indicate that the solid solution (Ca1−x−ySrx)Si2O2N2:yEu2+ is a promising phosphor applicable to near-UV and blue LEDs for solid-state lighting.
TL;DR: It is firmly established that protein flexibility is required to observe slow Stokes shift dynamics in this case and examines the underlying dynamics of protein side groups, backbone, and water dynamics to obtain a full picture of the relaxation process.
Abstract: Molecular dynamics simulations are used to calculate the time-dependent Stokes shift following photoexcitation of Trp-7 (W7) in myoglobin. In agreement with experiment, a long time (∼60 ps) component is observed. Since the long time Stokes shift component is absent when we repeat the calculation with protein frozen at the instant of photoexcitation, we firmly establish that protein flexibility is required to observe slow Stokes shift dynamics in this case. A transition between sub-states near the middle of a 30 ns ground-state trajectory gave us an opportunity to compare solvation dynamics in two different environments. While some of the superficial features are different, we find that the underlying dynamics are shared by the two isomers. It is necessary to look beyond a decomposition of the Stokes shift into protein and water contributions and probe the underlying dynamics of protein side groups, backbone, and water dynamics to obtain a full picture of the relaxation process. We analyze water residence ...
TL;DR: X-ray analysis of the silylene-bridged silafluorene revealed that the molecular framework was perfectly planar and four Si-C(methyl) sigma bonds were completely orthogonal to the plane and both the silicon atoms and the benzene rings were significantly deformed from the normal tetrahedral and hexagon shapes.
Abstract: The preparation of 4,5-dimethylsilylene- or 4,5-tetramethyldisilylene-bridged 9-silafluorenes was achieved by lithiation of 2,2',6,6'-tetrabromobiphenyls followed by silylation with dichlorodimethylsilane or 1,2-dichloro-1,1,2,2-tetramethyldisilane, respectively. X-ray analysis of the silylene-bridged silafluorene revealed that the molecular framework was perfectly planar and four Si-C(methyl) sigma bonds were completely orthogonal to the plane. Both the silicon atoms and the benzene rings were significantly deformed from the normal tetrahedral and hexagon shapes, respectively. The silicon bridge at the 4,5-positions was found to induce a red shift of the absorption and fluorescence spectra measured in cyclohexane, compared with 9-silafluorenes. It is remarkable that the disilylene-bridged silafluorene emitted blue light (lambda(em)=450 nm) with a large Stokes shift. The emission maxima of the silicon-bridged silafluorenes in thin films were similar to those measured in cyclohexane solution. DFT calculations suggested that introduction of the silicon bridge led to increases in both the HOMO and LUMO levels compared with 9-silafluorene.
TL;DR: Examples are described, which show the usefulness of Keima for dual-color fluorescence imaging technologies, such as fluorescence cross-correlation spectroscopy (FCCS) and two-photon laser scanning microscopy (TPLSM).
TL;DR: In this article, a series of highly π-conjugated hockey stick-shaped non-symmetrical 1,2,4-oxadiazoles, with liquid crystalline properties, have been studied.
Abstract: Thermal and optical behaviours of a series of highly π‐conjugated hockey stick‐shaped non‐symmetrical 1,2,4‐oxadiazoles, with liquid crystalline properties, have been studied. All of them presented liquid crystalline phases, in particular smectic and nematic phases typical of calamitic compounds. Although these substances are thermally less stable than their 1,3,4‐oxadiazole isomers, they showed better liquid crystalline behaviour with lower melting points. UV–visible spectra of compounds 1a–1f in solution displayed similar absorption patterns with maxima around 320 and 350 nm (e ∼ 2.0–6.0×104 L mol−1 cm−1). All compounds exhibited strong blue fluorescence ( = 405–468 nm) with large Stokes shift (79–117 nm). The quantum yields (ΦF) are 42–65%, except for compounds 1c and 1f where the yields are 2 and 14%, respectively. These compounds also exhibited blue emission in the solid phase ( = 408–492 nm).
TL;DR: Four different derivatives of diphenyl-diketo-pyrrolopyrrole with alkyl side groups were synthesized to increase their solubility and revealed that the substitution influenced molecular geometry and subsequently modified absorption and photoluminescence spectra.
Abstract: Four different derivatives of diphenyl-diketo-pyrrolopyrrole (DPP) with alkyl side groups were synthesized to increase their solubility Quantum chemical calculations revealed that the substitution influenced molecular geometry and subsequently modified absorption and photoluminescence spectra The theoretical results were confirmed by experimental characterization With increasing phenyl torsion the vibrational structure was less pronounced and larger Stokes shift was observed Simultaneously, the molar absorption coefficient decreased as the deformation increased On the other hand, the measured fluorescence quantum yields were modified only slightly This indicates the possibility to prepare soluble derivatives without loss of quantum yields and to use these materials for construction of efficient and stable electroluminescent devices Furthermore, the electroluminescence of the thin layer devices based on the soluble low molecular DPPs were characterized and discussed
TL;DR: A large Stokes shift dye, composed of water-solubility and near-infrared feature, was developed for multichannel imaging applications.
TL;DR: The present study provides a physical background for the multiparametric sensing of lipid bilayers using ESIPT based probes.
Abstract: The photophysics of a ratiometric fluorescent probe, N-[[4′-N,N-diethylamino-3-hydroxy-6-flavonyl]methyl]-N-methyl-N-(3-sulfopropyl)-1-dodecanaminium, inner salt (F2N12S), incorporated into phospholipid unilamellar vesicles is presented. The reconstructed time-resolved emission spectra (TRES) unravels a unique feature in the photophysics of this probe. TRES exhibit signatures of both an excited-state intramolecular proton transfer (ESIPT) and a dynamic Stokes shift associated with solvent relaxation in the lipid bilayer. The ESIPT is fast, being characterized by a risetime of ∼30−40 ps that provides an equilibrium to be established between the excited normal (N*) and the ESIPT tautomer (T*) on a time scale of 100 ps. On the other hand, the solvent relaxation displays a bimodal decay kinetics with an average relaxation time of ∼1 ns. The observed slow solvent relaxation dynamics likely embodies a response of nonspecific dipolar solvation coupled with formation of probe−water H-bonds as well as the relocati...
TL;DR: In this article, the ground and excited state dipole moments of three laser dyes namely 2, 5-diphenyl-1, 3, 4- oxadiazole (PPD), 2, 2″-dimethyl-p-terphenyl (DMT) and 1, 3-diphhenyl benzene (MT) were determined experimentally by Guggenheim method.
TL;DR: Four kinds of 3,5-dialkylpyrazolate(R2pz)-bridged dinuclear platinum(II) complexes were theoretically investigated by the DFT(B3PW91) method and the Stokes shift of their phosphorescence spectra was discussed on the basis of the potential energy curve (PEC) of the lowest energy triplet excited state (T1).
Abstract: Four kinds of 3,5-dialkylpyrazolate(R2pz)-bridged dinuclear platinum(II) complexes [Pt2(mu-R2pz)2(dfppy)2] (dfppy=2-(2,4-difluorophenyl)pyridine; R2pz=pyrazolate in 1, 3,5-dimethylpyrazolate in 2, 3-methyl-5- tert-butylpyrazolate in 3, and 3,5-bis(tert-butyl)pyrazolate in 4) were theoretically investigated by the DFT(B3PW91) method The Stokes shift of their phosphorescence spectra was discussed on the basis of the potential energy curve (PEC) of the lowest energy triplet excited state (T1) This PEC significantly depends on the bulkiness of substituents on pz In 1 and 2, bearing small substituents on pz, one local minimum is present in the T1 state besides a global minimum The local minimum geometry is similar to the S0-equilibrium one The T1 state at this local minimum is characterized as the pi-pi* excited state in dfppy, where the dpi orbital of Pt participates in this excited state through an antibonding interaction with the pi orbital of dfppy; in other words, this triplet excited state is assigned as the mixture of the ligand-centered pi-pi* excited and metal-to-ligand charge transfer excited state ((3)LC/MLCT) The geometry of the T1-global minimum is considerably different from the S0-equilibrium one The T1 state at the global minimum is characterized as the triplet metal-metal-to-ligand charge transfer ((3)MMLCT) excited state, which is formed by the one-electron excitation from the dsigma-dsigma antibonding orbital to the pi* orbital of dfppy Because of the presence of the local minimum, the geometry change in the T1 state is suppressed in polystyrene at room temperature (RT) and frozen 2-methyltetrahydrofuran (2-MeTHF) at 77 K As a result, the energy of phosphorescence is almost the same in these solvents In fluid 2-MeTHF at RT, on the other hand, the geometry of the T1 state easily reaches the T1-global minimum Because the T1-global minimum geometry is considerably different from the S0-equilibrium one, the phosphorescence occurs at considerably low energy These are the reasons why the Stokes shift is very large in fluid 2-MeTHF but small in polystyrene and frozen 2-MeTHF In 3 and 4, bearing bulky tert-butyl substituents on pz, only the T1-global minimum is present but the local minimum is not The electronic structure of this T1-global minimum is assigned as the (3)MMLCT excited state like 1 and 2 Though frozen 2-MeTHF suppresses the geometry change of 3 and 4 in the T1 state, their geometries moderately change in polystyrene because of the absence of the T1-local minimum As a result, the energy of phosphorescence is moderately lower in polystyrene than in frozen 2-MeTHF The T1-global minimum geometry is much different from the S0-equilibrium one in 3 but moderately different in 4, which is interpreted in terms of the symmetries of these complexes and the steric repulsion between the tert-butyl group on pz and dfppy Thus, the energy of phosphorescence of 3 is much lower in fluid 2-MeTHF than in frozen 2-MeTHF like 1 and 2 but that of 4 is moderately lower; in other words, the Stokes shift in fluid 2-MeTHF is small only in 4
TL;DR: In this article, the shape function of the broad vibronic bands arising from the 4f-5d optical transitions in Ba, Ca, and Sr thiogallates doped with Eu 2+ ions was analyzed.
TL;DR: The non-ergodic character of large-amplitude protein/water mobility breaks the strong link between the Stokes shift and the reorganization energy characteristic of equilibrium (ergodic) theories of electron transfer, which might be responsible for fast electronic transitions in natural electron-transfer proteins characterized by low reaction free energy.
Abstract: We report the results of molecular dynamics simulations of electron-transfer activation parameters of plastocyanin metalloprotein involved as an electron carrier in natural photosynthesis. We have discovered that slow, non-ergodic conformational fluctuations of the protein, coupled to hydrating water, result in a very broad distribution of donor-acceptor energy gaps far exceeding those observed for commonly studied inorganic and organic donor-acceptor complexes. The Stokes shift is not affected by these fluctuations and can be calculated from solvation models in terms of the linear response of the solvent dipolar polarization. The non-ergodic character of large-amplitude protein/water mobility breaks the strong link between the Stokes shift and the reorganization energy characteristic of equilibrium (ergodic) theories of electron transfer. This mechanism might be responsible for fast electronic transitions in natural electron-transfer proteins characterized by low reaction free energy.
TL;DR: Preferential solvation of a solvatochromic probe has been studied in binary mixtures comprising of a non-protic and a protic solvent to deduce experimentally the dipole moment ratio of the probe molecule for the excited state to the ground state.
TL;DR: In this paper, the problem of the electron-vibrational interaction in 4f-5d optical transitions and the calculation of the Stokes shift in thiogallate materials is addressed.
TL;DR: In this article, the exciton-exciton interaction energy of tellurium doped CdSe colloidal quantum dots is experimentally investigated, and it is shown that the biexciton blue shift increases linearly with the Stokes shift.
Abstract: The exciton-exciton interaction energy of tellurium doped CdSe colloidal quantum dots is experimentally investigated. The dots exhibit a strong Coulomb repulsion between the two excitons, which results in a huge measured biexciton blue shift of up to 300 meV. Such a strong Coulomb repulsion implies a very narrow hole wave function localized around the defect, which is manifested by a large Stokes shift. Moreover, we show that the biexciton blue shift increases linearly with the Stokes shift. This result is highly relevant for the use of colloidal QDs as optical gain media, where a large biexciton blue shift is required to obtain gain in the single exciton regime.
TL;DR: It was observed that dipole moments of excited state were higher than those of the ground state for all the dyes, and the effects of the solvents upon the spectral properties are discussed.