Showing papers on "Stokes shift published in 2012"
TL;DR: A red-emitting BODIPY-based fluorescent-resonance-energy-transfer (FRET) molecular probe 1 for selective detection of cysteine and homocysteine was designed and used for in vivo fluorescent imaging of cellular thiols.
Abstract: A red-emitting BODIPY-based fluorescent-resonance-energy-transfer (FRET) molecular probe 1 for selective detection of cysteine and homocysteine was designed. The fluorescence OFF–ON switch is triggered by cleavage of the 2,4-dinitrobenzensulfonyl (DNBS) unit from the fluorophore by thiols. The FRET energy donor (λabs = 498 nm, λem = 511 nm) is a parent BODIPY moiety and the energy acceptor is based on 4-hydroxylstyryl BODIPY moiety (λabs = 568 nm, λem = 586 nm). The unique C–C linker between the energy donor and acceptor was established using a Suzuki cross-coupling reaction. A polyether chain was also introduced into the probe to improve solubility in aqueous solution. While probe 1 itself is non-fluorescent, in the presence of cysteine or homocysteine a red emission at 590 nm is switched on (excitation at 505 nm), producing a pseudo-Stokes shift of up to 77 nm, which is in stark contrast to the small Stokes shift (ca. 10 nm) observed for typical BODIPY dyes. Excitation of the energy donor leads to the red emission from the acceptor of the probe, and demonstrates a high energy transfer efficiency. The probe was used for in vivo fluorescent imaging of cellular thiols. The fluorescence sensing mechanism of the probe and the photophysical properties of the fluorescent intermediates were fully rationalized by DFT calculations. The lack of fluorescence of probe 1 is attributed to the dark excited state S1 (oscillator strength f = 0.0007 for S0 → S1, based on the optimized S1 state geometry), which is due to the electron sink effect of the DNBS moiety. Cleavage of the DNBS moiety from the fluorophore by thiols re-establishes the emissive S1 state of the fluorophore (f = 1.4317 for S0 → S1), thus the red emission can be observed in the presence of thiols (fluorescence is turned on). The FRET effect of the probe was rationalized by DFT calculations which indicated that upon excitation into the S4 excited state (localized on the energy donor unit), the S1 state (localized on the energy acceptor, i.e. styryl-BODIPY) is populated via internal conversion (IC), thus red emission from the styryl-BODIPY energy acceptor is observed (Kasha's rule).
244 citations
TL;DR: DFT calculations propose the large Stokes shifts of BS-SS and BS-DS are due to the remarkable geometry relaxation upon photoexcitation and its substantial effect on the energy levels of molecular orbitals.
Abstract: 2-Thienyl and 2,6-bisthienyl BODIPY derivatives (BS-SS and BS-DS) were prepared that show intense absorption (e = 65000 M–1 cm–1 at 507 nm) and a large Stokes shift (96 nm) vs the small Stokes shift of typical BODIPY (<15 nm). Control compounds with a thienyl unit at the 8-position or phenyl substituents at the 2,6-positions were prepared (BS-1 and 9). BS-1 shows absorption/emission in the blue-shifted range and a small Stokes shift (12 nm). Compound 9 shows absorption in the red-shifted range, but the Stokes shift (<30 nm) is much smaller than that for BS-SS and BS-DS. DFT calculations propose the large Stokes shifts of BS-SS and BS-DS are due to the remarkable geometry relaxation upon photoexcitation and its substantial effect on the energy levels of molecular orbitals. For the dyes with small Stokes shifts, much smaller geometry relaxations were found. The fluorophores were used for fluorescent thiol probes, with 2,4-dinitrobenzenesulfonyl (DNBS) as the fluorescence switch. Both fluorescence OFF–ON and...
243 citations
TL;DR: A white-light-emitting diode (white LED) with good color rendering index is fabricated based on a blue LED combined with high-fluorescence CdS:Cu/ZnS quantum dots (QDs) and YAG:Ce phosphors with low absorption of light of wavelengths longer than 470 nm.
Abstract: A white-light-emitting diode (white LED) with good color rendering index is fabricated based on a blue LED combined with high-fluorescence CdS:Cu/ZnS quantum dots (QDs) and YAG:Ce phosphors. The reabsorption problem is overcome by the excellent optical properties and enlarged Stokes shift of the QDs with low absorption of light of wavelengths longer than 470 nm.
215 citations
TL;DR: In this article, a monomeric orange fluorescent protein with a large Stokes shift (LSS), called LSSmOrange (excitation/emission at 437/572 nm), was presented, which fills up an existing spectral gap between green-yellow and red LSSFPs.
Abstract: Multicolor imaging based on genetically-encoded fluorescent proteins (FPs) is a powerful approach to study several dynamic processes in a live cell. We report a monomeric orange FP with a large Stokes shift (LSS), called LSSmOrange (excitation/emission at 437/572 nm), which fills up an existing spectral gap between the green-yellow and red LSSFPs. Brightness of LSSmOrange is 5-fold larger than that of the brightest red LSSFP and similar to the green-yellow LSS-FPs. LSSmOrange allows numerous multicolor applications using a single excitation wavelength that was not possible before. Using LSSmOrange we developed a four-color single-laser fluorescence cross-correlation spectroscopy, solely based on FPs. The quadruple cross-correlation combined with photon counting histogram techniques allowed quantitative single-molecule analysis of the particles labeled with four FPs. LSSmOrange was further applied to simultaneously image two Forster resonance energy transfer pairs, one of which is the commonly used CFP-YFP pair, with a single excitation laser. The combination of LSSmOrange-mKate2 and CFP-YFP biosensors enabled imaging of apoptotic activity and calcium fluctuations in real time. The LSSmOrange mutagenesis, low-temperature and isotope effect studies revealed a proton relay for the excited state proton transfer responsible for the LSS phenotype.
199 citations
TL;DR: In this paper, the photoluminescent (PL) peaks are associated with the C-OH, the aromatic CC and the CO functional groups in the GO sheets, respectively, and three PL emission peaks exhibit a red-shift with an increase in the excitation wavelength.
Abstract: Chemically modified graphene oxide (GO) sheets exhibit three “fingerprinting” photoluminescent (PL) peaks, which originate from the σ* → n, π* → π and π* → n electronic transitions between the antibonding and the bonding molecular orbitals. The three PL peaks are associated with the C–OH, the aromatic CC and the CO functional groups in the GO sheets, respectively. The relative intensities of the three PL peaks are modulated by varying the oxygen-containing functional groups. The three PL emission peaks exhibit a red-shift with an increase in the excitation wavelength. The difference between the emission peak and the excitation wavelength shows a constant Stokes shift of 53.3 nm, 112.1 nm and 217.9 nm for the σ* → n, π* → π and π* → n transitions, respectively.
193 citations
TL;DR: Two energy transfer cassettes that exhibit a large pseudo Stokes' shift due to efficient through-bond energy transfer (up to 99%) have been constructed.
172 citations
TL;DR: In this paper, a red-emissive zwitterionic hemicyanine dye, named TPE-Cy, containing tetraphenylethene (TPE) and N-alkylated indolium is designed and synthesized.
Abstract: In this work, a red-emissive zwitterionic hemicyanine dye, named TPE–Cy, containing tetraphenylethene (TPE) and N-alkylated indolium is designed and synthesized. TPE–Cy inherits the aggregation-induced emission (AIE) feature of TPE and displays a large Stokes shift (>185 nm), overcoming the limitations of the concentration-quenching effect and small Stokes shift (from a few to 20 nm) encountered by conventional cyanine dyes. By taking advantage of the photophysical AIE property and chemical reactivity towards OH−/H+, TPE–Cy is able to sense pH in a broad range (the broadest to date) by showing different emission colors and intensities: strong to moderate red emission at pH 5–7, weak to no emission at pH 7–10, and no emission to strong blue emission at pH 10–14. The acid/base-switched red/blue emission transition is reversible and can be repeated for many cycles. By means of NMR and HRMS analyses, we have drawn a mechanistic picture at molecular level to illustrate how this dye works as a pH-sensitive fluorescent probe.
162 citations
TL;DR: In this paper, Coumarin derivatives containing 8-benzothiazole (C-2 ) and its difluoroboron bound derivative (c-3 ) were prepared.
142 citations
TL;DR: In this paper, the effects of large copper deficiency and surface modification on the photoluminescence of CuInS2 nanocrystals were explored, and the effect of surface modification was attributed to the efficient reduction of nonradiative recombination originated from surface trap states, the activation energy of which was estimated to be 85 meV.
Abstract: Effects of large copper deficiency and surface modification on the photoluminescence of CuInS2 nanocrystals were explored. The large copper deficiency improved PL intensity due to the enhanced internal defect-related emission. Surface modification of copper deficient nanocrystals by simply refluxing with zinc acetate and fatty acid resulted in more than 10 times improvement in the photoluminescence intensity and a large blueshift of the photoluminescence spectra. The uniformity in size/shape distribution after surface modification was attributed to the origin of shrinkage in Stokes shift from ∼600 meV to ∼300 meV in Cu0.2InS2/ZnS nanocrystals. Furthermore, the contribution of lattice strain to this large blueshift in emission wavelength in Cu0.2InS2/ZnS nanocrystals was proposed and tested with the CdS shell layers. The electronic process underlying the large enhancement of PL intensity was studied with time-resolved and temperature-dependent photoluminescence. This drastically enhanced photoluminescence after surface modification was attributed to the efficient reduction of non-radiative recombination originated from surface trap states, the activation energy of which was estimated to be 85 meV.
137 citations
TL;DR: Spectral investigations on novel N,O-chelated naphthyridine-BF(2) complexes with push-pull structures reveal that photoinduced intramolecular charge transfer occurs and results in a large Stokes shift, which is further supported by density functional theory based theoretical calculations.
120 citations
TL;DR: It is proposed that Bodipy derivatives containing excited state intramolecular proton transfer (ESIPT) chromophores 7-9 do not undergo ESIPT upon photoexcitation, as well as for applications of these compounds in photovoltaics, photocatalysis and luminescent materials, etc.
Abstract: Bodipy derivatives containing excited state intramolecular proton transfer (ESIPT) chromophores 2-(2-hydroxyphenyl) benzothiazole and benzoxazole (HBT and HBO) subunits were prepared (7–10). The compounds show red-shifted UV–vis absorption (530–580 nm; e up to 50000 M–1 cm–1) and emission compared to both HBT/HBO and Bodipy. The new chromophores show small Stokes shift (45 nm) and high fluorescence quantum yields (ΦF up to 36%), which are in stark contrast to HBT and HBO (Stokes shift up to 180 nm and ΦF as low as 0.6%). On the basis of steady state and time-resolved absorption spectroscopy, as well as DFT/TDDFT calculations, we propose that 7–9 do not undergo ESIPT upon photoexcitation. Interestingly, nanosecond time-resolved transient absorption spectroscopy demonstrated that Bodipy-localized triplet excited states were populated for 7–10 upon photoexcitation; the lifetimes of the triplet excited states (τT) are up to 195 μs. DFT calculations confirm the transient absorptions are due to the triplet stat...
TL;DR: All fluorophore emission maxima, and nearly all absorption maxima were significantly red-shifted when compared to Prodan, and the cyclopentane portion of the fluorophores structure provides an attachment point for biomolecules that will minimize disruptions of the photophysical properties.
Abstract: The synthesis and photophysical properties of a series of naphthalene-containing solvatochromic fluorophores are described within. These novel fluorophores are prepared using a microwave-assisted dehydrogenative Diels–Alder reaction of styrene, followed by a palladium-catalyzed cross coupling reaction to install an electron donating amine group. The new fluorophores are structurally related to Prodan. Photophysical properties of the new fluorophores were studied and intriguing solvatochromic behavior was observed. For most of these fluorophores, high quantum yields (60–99%) were observed in methylene chloride in addition to large Stokes shifts (95–226 nm) in this same solvent. As the solvent polarity increased, so did the observed Stokes shift with one derivative displaying a Stokes shift of ∼300 nm in ethanol. All fluorophore emission maxima, and nearly all absorption maxima were significantly red-shifted when compared to Prodan. Shifting the absorption and emission maxima of a fluorophore into the visib...
TL;DR: The rational design of FRET-based polymeric nanoparticles for NIR and FRET imaging, which resulted in a large Stokes shift of the emission maxima, and the transfer efficiency could be fine-tuned by further adjusting the doping ratio of the donor and acceptor fluorophores.
TL;DR: Ca5Mg4(VO4)6 could be suggested to be a potential yellow-emitting phosphor for the application on near-UV excited white LEDs and deference was discussed on the base of the relationship between the micro-structure and the charge transfer transitions in [VO4]3- groups in the lattices.
Abstract: The self-activated yellow-emitting phosphors of vanadates Ca5M4(VO4)6 (M = Mg, Zn) were synthesized via the solid-state reaction route. The formation of single phase compound with garnet structure was verified through X-ray diffraction (XRD) studies. The excitation and emission spectra and the thermal quenching of luminescence intensities were measured. The different luminescence properties of Ca5Mg4(VO4)6 and Ca5Zn4(VO4)6 phosphors were presented, e.g., the spectra shift, the luminescence lifetimes, the absolute quantum efficiency, the color coordinates and the Stokes shift. This deference was discussed on the base of the relationship between the micro-structure and the charge transfer transitions in [VO4]3- groups in the lattices. Ca5Mg4(VO4)6 could be suggested to be a potential yellow-emitting phosphor for the application on near-UV excited white LEDs.
TL;DR: High resolution spectra of singly doped LuAG (with Ce(3+) or Tb(3+)) are reported and insight into the energy level structure of the two ions in LuAG is provided, and Luminescence decay measurements confirm efficient energy transfer from Tb (3+) to Ce( 3+) and provide a qualitative understanding of the energy transfer process.
Abstract: Lu3Al5O12 (LuAG) doped with Ce3+ is a promising scintillator material with a high density and a fast response time. The light output under x-ray or y-ray excitation is however well below the theoretical limit. In this paper the influence of co-doping with Tb3+ is investigated with the aim to increase the light output. For singly doped LuAG (with Ce3+ or Tb3+) high resolution spectra are reported giving insight in the energy level structure of the two ions in LuAG. For Ce3+ zero-phonon lines and vibronic structure is observed for thetwo lowest energy d-bands and the Stokes shift (2350 cm-1) and Huang-Rhys coupling parameter (S = 9) have been determined. For Tb3+ transition to the high spin (HS) and low spin (LS) states are observed (including a zero-phonon line and vibrational structure for the highspin state). The HS-LS splitting is 5400 cm-1 which is smaller thanusually observed and is explained by a reduction of the d-f exchangecoupling parameter J by covalency. Upon replacing the smaller Lu3+ion with the larger Tb3+ ion, the crystal field splitting for the lowest d-states increases and the Ce3+ emission shows a redshift, causing the lowest d-state to shift below the 5D4 state of Tb3+ and allowing for efficient energy transfer from Tb3+ to Ce3+ down to the lowest temperatures. Luminescence decay measurements confirm efficientenergy transfer from Tb3+ to Ce3+ and provide a qualitative understanding of the energy transfer process. Co-doping with Tb3+ does not result in the desired increase in light output and an explanation based on electron trapping in defects is discussed.
TL;DR: It is demonstrated that g-NQDs afford significantly enhanced operational stability compared to their conventional NQD counterparts and minimal self-reabsorption losses and the facile fabrication of white-light devices with correlated color temperature tuned from ∼3200 to 5800 K is demonstrated.
Abstract: A new class of nanocrystal quantum dot (NQD), the "giant" NQD (g-NQD), was investigated for its potential to address outstanding issues associated with the use of NQDs as down-conversion phosphors in light-emitting devices, namely, insufficient chemical/photostability and extensive self-reabsorption when packed in high densities or in thick films. Here, we demonstrate that g-NQDs afford significantly enhanced operational stability compared to their conventional NQD counterparts and minimal self-reabsorption losses. The latter results from a characteristic large Stokes shift (>100 nm; >0.39 eV), which itself is a manifestation of the internal structure of these uniquely thick-shelled NQDs. In carefully prepared g-NQDs, light absorption occurs predominantly in the shell but emission occurs exclusively from the core. We directly compare for the first time the processes of shell→core energy relaxation and core→core energy transfer by evaluating CdS→CdSe down-conversion of blue→red light in g-NQDs and in a comparable mixed-NQD (CdSe and CdS) thin film, revealing that the internal energy relaxation process affords a more efficient and color-pure conversion of blue to red light compared to energy transfer. Lastly, we demonstrate the facile fabrication of white-light devices with correlated color temperature tuned from ∼3200 to 5800 K.
TL;DR: In this article, a set of imidazole derivatives displaying excited state intramolecular proton transfer (ESIPT) was designed and synthesized, and the effect of structural variation on photophysical properties was studied in detail for nine dyes.
Abstract: A diverse set of imidazole- and π-expanded imidazole derivatives displaying excited state intramolecular proton transfer (ESIPT) was designed and synthesized. The effect of structural variation on photophysical properties was studied in detail for nine dyes. The relationship between the structure and photophysical properties was thoroughly elucidated also by comparing with analogues with blocked ESIPT functionality. All but one of the obtained compounds exhibit ESIPT, as demonstrated by large Stokes shifts (6500–15 600 cm−1). The type of π-expansion strongly influences the overall optical phenomena: while typical π-expansion preserves ESIPT activity, the direct fusion of imidazole with a naphthalene unit at positions 4 and 5 results in dyes which do not exhibit ESIPT. The compound possessing an acidic NH group as part of an intramolecular hydrogen bond system has a much higher fluorescence quantum yield and Stokes shift than its analogue bearing an OH group. The occurrence of ESIPT for tosylamide analogues is less affected by the hydrogen-bonding ability of the solvents compared to the unprotected amines. Two-photon absorption cross-sections of the selected derivatives are in the range of 5–100 GM.
TL;DR: From the experimental data and MO calculations, the π-electron-donating strength of the 1,3-diethyl-1,3,2-benzodiazaborolyl group was found to lie between that of methoxy and dimethylamino groups, and B3LYP predicts that both the absorption and emission processes have strong charge-transfer character.
Abstract: Four linear π-conjugated systems with 1,3-diethyl-1,3,2-benzodiazaborolyl [C(6)H(4)(NEt)(2)B] as a π-donor at one end and dimesitylboryl (BMes(2)) as a π-acceptor at the other end were synthesized. These unusual push-pull systems contain phenylene (-1,4-C(6)H(4)-; 1), biphenylene (-4,4'-(1,1'-C(6)H(4))(2)-; 2), thiophene (-2,5-C(4)H(2)S-; 3), and dithiophene (-5,5'-(2,2'-C(4)H(2)S)(2)-; 4) as π-conjugated bridges and different types of three-coordinate boron moieties serving as both π-donor and π-acceptor. Molecular structures of 2, 3, and 4 were determined by single-crystal X-ray diffraction. Photophysical studies on these systems reveal blue-green fluorescence in all compounds. The Stokes shifts for 1, 2, and 3 are notably large at 7820-9760 cm(-1) in THF and 5430-6210 cm(-1) in cyclohexane, whereas the Stokes shift for 4 is significantly smaller at 5510 cm(-1) in THF and 2450 cm(-1) in cyclohexane. Calculations on model systems 1'-4' show the HOMO to be mainly diazaborolyl in character and the LUMO to be dominated by the empty p orbital at the boron atom of the BMes(2) group. However, there are considerable dithiophene bridge contributions to both orbitals in 4'. From the experimental data and MO calculations, the π-electron-donating strength of the 1,3-diethyl-1,3,2-benzodiazaborolyl group was found to lie between that of methoxy and dimethylamino groups. TD-DFT calculations on 1'-4', using B3LYP and CAM-B3LYP functionals, provide insight into the absorption and emission processes. B3LYP predicts that both the absorption and emission processes have strong charge-transfer character. CAM-B3LYP which, unlike B3LYP, contains the physics necessary to describe charge-transfer excitations, predicts only a limited amount of charge transfer upon absorption, but somewhat more upon emission. The excited-state (S(1)) geometries show the borolyl group to be significantly altered compared to the ground-state (S(0)) geometries. This borolyl group reorganization in the excited state is believed to be responsible for the large Stokes shifts in organic systems containing benzodiazaborolyl groups in these and related compounds.
TL;DR: Two novel vis-NIR pH probes based on styrylcyanine with acidic pH response are easily synthesized, which display large Stokes shift and high sensitivity.
TL;DR: In this paper, the structure of CdSe nanocrystals was investigated by X-ray diffraction, transmission electron microscopy (TEM) and high-resolution transmission electron microscope (HRTEM).
TL;DR: Estimated experimental dynamic Stokes shift for coumarin 153 in these mixtures lies in the range, 1000 < Δν(t)/cm(-1) < 1700, and is in semi-quantitative agreement with predictions from the authors' semi-molecular theory.
Abstract: Time-resolved fluorescence Stokes shift and anisotropy measurements using a solvation probe in [0.78CH(3)CONH(2) + 0.22{f LiBr + (1-f) LiNO(3)}] melts reveal a strong decoupling of medium dynamics from viscosity. Interestingly, this decoupling has been found to occur at temperatures ∼50-100 K above the glass transition temperatures of the above melt at various anion concentrations (f(LiBr)). The decoupling is reflected via the following fractional viscosity dependence (η) of the measured average solvation and rotation times ( and , respectively): ∝ (η∕T)(p) (x being solvation or rotation), with p covering the range, 0.20 than for , indicating a sort of translation-rotation decoupling. Multiple probes have been used in steady state fluorescence measurements to explore the extent of static heterogeneity. Estimated experimental dynamic Stokes shift for coumarin 153 in these mixtures lies in the range, 1000 < Δν(t)/cm(-1) < 1700, and is in semi-quantitative agreement with predictions from our semi-molecular theory. The participation of the fluctuating density modes at various length-scales to the observed solvation times has also been investigated.
TL;DR: In this article, the diffuse reflection spectra, photoluminescence spectra and chromaticity of ytterbium in CaAlSiN3 at room temperature were reported.
Abstract: This paper reports on the diffuse reflection spectra, photoluminescence spectra and chromaticity of ytterbium in CaAlSiN3 at room temperature. It can be excited efficiently over a broad spectral range between 280 and 580 nm and exhibits a single intense red emission at 629 nm with a full width at half maximum of 75 nm due to the electronic transitions from the excited state of 4f135d to the ground state 4f14 of Yb2+. The low energy of Yb2+ emission in CaAlSiN3 can be attributed to the large nephelauxetic effect and crystal field splitting due to the coordination of Yb2+ by nitrogen. This novel developed CaAlSiN3:Yb2+, which is the first Yb2+-activated nitride red-emitting phosphor, has potential applications in spectral conversion materials for warm-white LEDs. The width of the emission band, Stokes shift and thermal quenching mechanism of Yb2+ in CaAlSiN3 and (oxy)nitride-based phosphors are discussed and compared with those of Eu2+.
TL;DR: A novel Near Infra-Red emitting BODIPY derivative is presented which exhibits the largest Stokes shift thus far reported for a BODipY compound.
TL;DR: With a combination of excellent stability, large Stokes shift, and near-infrared spectral properties, this novel LSS-NFSiNPs provides real-time, deep-tissue fluorescent imaging of live animals and can also be gradually cleared from the body through the urinary clearance system.
Abstract: Fluorescent dye-doped silica nanoparticles are increasingly used for in vivo imaging due to their unique biocompatibility and easy surface modification. However, the utility of existing fluorescent dye-doped silica nanoparticles for in vivo imaging is still limited because most studies are focused on doping single near-infrared (NIR) dyes in the silica matrix, which would cause background and crosstalk between the excitation light and the emitting signals due to the small Stokes shift of the traditional NIR dyes. To address this issue, we present a novel large Stokes shifting NIR fluorescent silica nanoparticles (LSS-NFSiNPs) based on the principle of fluorescence resonance energy transfer. Two highly water-soluble dyes, tris(2,2-bipyridyl)dichlororuthenium(II) hexahydrate (RuBpy) and methylene blue (MB), were chose as the model donor–acceptor pair. The LSS-NFSiNPs were prepared by synchronously doping RuBpy and MB in the silica nanoparticles. By optimizing the molar ratio of RuBpy and MB for doping in th...
TL;DR: In this paper, the effect of dye concentration on the efficiency of a luminescent concentrator based on a perylene diimide (PDI) derivative incorporated in poly(methyl methacrylate) films cast on glass substrates is described.
TL;DR: To this knowledge, this is the first time to explicitly disclose how and why S3 is superior in comparison with other conventional spectroscopic techniques.
Abstract: The Stokes shift spectroscopy (S3) offers a simpler and better way to recognize spectral fingerprints of fluorophores in complex mixtures. The efficiency of S3 for cancer detection in human tissue was investigated systematically. The alterations of Stokes shift spectra (S3) between cancerous and normal tissues are due to the changes of key fluorophores, e.g., tryptophan and collagen, and can be highlighted using optimized wavelength shift interval. To our knowledge, this is the first time to explicitly disclose how and why S3 is superior in comparison with other conventional spectroscopic techniques.
TL;DR: New polycatenar liquid crystals containing two 1,3,4-oxadiazole rings interconnected by a bent 1, 3-substituted benzene ring as the central linking unit and three alkoxy chains at each terminal have been synthesized and investigated by polarizing microscopy, DSC, XRD scattering, UV-vis spectroscopy and photoluminescence measurements.
Abstract: New polycatenar liquid crystals containing two 1,3,4-oxadiazole rings interconnected by a bent 1,3-substituted benzene ring as the central linking unit and three alkoxy chains at each terminal have been synthesized and investigated by polarizing microscopy, DSC, XRD scattering, UV-vis spectroscopy and photoluminescence measurements All compounds form enantiotropic hexagonal columnar phases and have broader mesophase ranges than the corresponding para substituted analogues and show strong blue fluorescence emission with a large Stokes shift in solution
TL;DR: In this article, the spectroscopic properties of Ca3Y2Si3O12 powders activated with Eu (0.1-25%) were investigated in VUV-UV-vis region.
Abstract: Ca3Y2Si3O12 powders activated with Eu (0.1–25%) were prepared by means of ceramic method. Their spectroscopic properties in VUV-UV–vis region were investigated. Luminescence measurements indicated that Ca3Y2Si3O12 prepared in a strongly reducing atmosphere of 20%N2–80%H2 mixture contained both Eu2+ and Eu3+ ions, and both were able to generate their characteristic emissions. A superposition of the broad band luminescence of Eu2+ and narrower 4f → 4f luminescent features of Eu3+ upon excitation with 395 nm light-emitting diode covered almost the whole visible part of spectrum. The ratio between Eu2+ and Eu3+ emissions was reproducible, and, with increasing content of Eu, the relative intensity of the red component from Eu3+ became systematically stronger. The Eu2+ luminescence in Ca3Y2Si3O12 was characterized by an extraordinary large Stokes shift of ∼8960 cm–1 and most probably had an anomalous character with a defect, presumably O-vacancy located in the vicinity of Eu2+, being involved in the emission ge...
TL;DR: The results show that the pronounced geometric distortion due to the rotation of unlocked phenyl groups and intramolecular charge transfer are responsible for the large Stokes shift of 1 and 2, while 3 shows a relatively blue-shifted emission wavelength due to its mild geometric distortion upon photoemission, although it has a comparable energy gap to 1.
Abstract: The geometric and electronic structures and photophysical properties of anilido-pyridine boron difluoride dyes 1-4, a series of scarce 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives with large Stokes shift, are investigated by employing density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to shed light on the origin of their large Stokes shifts. To this end, a suitable functional is first determined based on functional tests and a recently proposed index-the charge-transfer distance. It is found that PBE0 provides satisfactory overall results. An in-depth insight into Huang-Rhys (HR) factors, Wiberg bond indices, and transition density matrices is provided to scrutinize the geometric distortions and the character of excited states pertaining to absorption and emission. The results show that the pronounced geometric distortion due to the rotation of unlocked phenyl groups and intramolecular charge transfer are responsible for the large Stokes shift of 1 and 2, while 3 shows a relatively blue-shifted emission wavelength due to its mild geometric distortion upon photoemission, although it has a comparable energy gap to 1. Finally, compound 4, which is designed to realize the rare red emission in BODIPY derivatives, shows desirable and expected properties, such as high Stokes shift (4847 cm(-1)), red emission at 660 nm, and reasonable fluorescence efficiency. These properties give it great potential as an ideal emitter in organic light-emitting diodes. The theoretical results could complement and assist in the development of BODIPY-based dyes with both large Stokes shift and high quantum efficiency.
TL;DR: The new probe, Zinhbo‐5, has been constructed by using bis(benzoxazole) ligand with 2, 2'‐dipicolylamine (DPA) as metal ion receptor and is demonstrated to be useful for in vivo imaging of the intracellular Zn2+ ion.
Abstract: In order to facilitate the in vivo study of zinc-related biology, it is essential to develop a zinc-selective sensor that exhibits both near-infrared (NIR) emission and larger Stokes shift. A fluorescent sensor, Zinhbo-5, has been constructed by using bis(benzoxazole) ligand with 2, 2'-dipicolylamine (DPA) as metal ion receptor. In aqueous solution, Zinhbo-5 exhibits high sensitivity (K(d) = 2.58 nM(2) ) and selectivity for Zn(2+) cation, revealing about 14-fold fluorescence enhancement upon zinc binding to give green emission. Remarkably, Zn(2+) binding to Zinhbo-5 switches on the excited state intramolecular proton transfer (ESIPT), producing the desirable near-infrared region (over 710 nm) with large Stokes shift (ca. 240 nm). The new probe is demonstrated to be useful for in vivo imaging of the intracellular Zn(2+) ion. The Zinhbo-5 is also useful for detecting zinc ion distribution during the development of living zebrafish embryos.