Shift Of Emission Maximum Research Articles

Optical insights of indium-doped β–Ga2O3 nanoparticles and its luminescence mechanism

Undoped and In3+ doped β–Ga2O3 nanoparticles have been synthesized at 900 °C using polyol-mediated technique. The effect of Indium dopant on structural, morphological and photoluminescence properties of β–Ga2O3 nanoparticles were investigated in detail. X-ray diffraction patterns demonstrate the monoclinic crystalline structure and indium doping leads to substantial changes in the lattice parameters of β–Ga2O3 nanoparticles. The scanning electron microscope (SEM) images showed reduction in the particle size on doping as due to grain growth inhibition effect. Observed red shift in emission maxima and is increasing with increased In3+ content. Indeed, the shift changes are due to the interactions between donors and acceptors, which are identified as donor–acceptor pair recombination. To understand the red-shift phenomena, we performed time-resolved and steady-state spectroscopic studies for the doped samples. The red shift in the emission maxima of Indium-doped samples was further confirmed with the band gap measurements using absorption spectroscopy and ab initio calculation results.

Synthesis and Optical Properties of the New Kaede Chromophore Analog

A novel derivative of Kaede protein chromophore was synthesized. The compound showed the shift of absorption and emission maxima to the longwave region in comparison with the classical Kaede chromophore analog due to an increase in the conjugated π-system in the imidazolone fragment.

An ESIPT blocked highly ICT based molecular probe to sense Zn (II) ion through turn on optical response: Experimental and theoretical studies

A simple and low cost optical sensor (L) is synthesized by the condensation reaction and characterized systematically. Among the various tested metal ions, L selectively interacts with Zn2+ ion by inducing a 17-fold high fluorescence intensity with a 60 nm blue shift of emission maxima, changing colorless solution to intense yellow solution in 20 % aqueous acetonitrile. A mechanism for selective turn on optical response of L for Zn2+ was studied using UV–vis absorption and Fluorescence emission and is correlated with theoretical results. We propose that, a dual mechanism (ESIPT/ICT) is responsible for selective sensing of Zn2+ in 20 % aqueous acetonitrile. The Job’s plot, B-H plots and ESI-MS studies confirm the 1:1 stoichiometry between host-guest interaction. A reversible optical probe with nanomolar level detection limit is non-toxic and it could render pH dependent fluorescence measurements in a live physiological environment. The practical application of L for Zn2+ was explored through bio-imaging experiment in HeLa cells.

Cyan emitting Ca3Sc2Si1.5Ge1.5O12:Ce3+ phosphor with 10.4 ns lifetime

Synthesis and photoluminescence properties of Ca3Sc2Si1.5Ge1.5O12:Ce3+ phosphor are described and compared with that of Ca3Sc2Si3O12:Ce3+. Partial replacement of Si by Ge, produces interesting changes in luminescence properties of Ca3Sc2Si3O12:Ce3+. Emission maximum shifts from 510 to 485 nm and that of excitation from 450 to 428 nm. The blue shifts are attributable to the splitting of Ce3+ 5d levels by crystal field. Centroid shift also contributes to these shifts. Cyan emitting phosphor, in combination with other phosphors, can be useful for generating true white spectrum. Moreover, lifetime of Ca3Sc2Si1.5Ge1.5O12:Ce3+ phosphor is very short, 10.4 ns, as compared to 62.7 for Ca3Sc2Si3O12:Ce3+. Short lifetime makes Ca3Sc2Si1.5Ge1.5O12:Ce3+ suitable for applications like scintillator, time of flight camera, etc.

A Fluorescent Kinase Inhibitor that Exhibits Diagnostic Changes in Emission upon Binding

AbstractThe development of a fluorescent LCK inhibitor that exhibits favourable solvatochromic properties upon binding the kinase is described. Fluorescent properties were realised through the inclusion of a prodan‐derived fluorophore into the pharmacophore of an ATP‐competitive kinase inhibitor. Fluorescence titration experiments demonstrate the solvatochromic properties of the inhibitor, in which dramatic increase in emission intensity and hypsochromic shift in emission maxima are clearly observed upon binding LCK. Microscopy experiments in cellular contexts together with flow cytometry show that the fluorescence intensity of the inhibitor correlates with the LCK concentration. Furthermore, multiphoton microscopy experiments demonstrate both the rapid cellular uptake of the inhibitor and that the two‐photon cross section of the inhibitor is amenable for excitation at 700 nm.

A Fluorescent Kinase Inhibitor that Exhibits Diagnostic Changes in Emission upon Binding.

The development of a fluorescent LCK inhibitor that exhibits favourable solvatochromic properties upon binding the kinase is described. Fluorescent properties were realised through the inclusion of a prodan‐derived fluorophore into the pharmacophore of an ATP‐competitive kinase inhibitor. Fluorescence titration experiments demonstrate the solvatochromic properties of the inhibitor, in which dramatic increase in emission intensity and hypsochromic shift in emission maxima are clearly observed upon binding LCK. Microscopy experiments in cellular contexts together with flow cytometry show that the fluorescence intensity of the inhibitor correlates with the LCK concentration. Furthermore, multiphoton microscopy experiments demonstrate both the rapid cellular uptake of the inhibitor and that the two‐photon cross section of the inhibitor is amenable for excitation at 700 nm.

Molecular recognition of 3 + 1 hybrid human telomeric G-quadruplex DNA d-[AGGG(TTAGGG)3] by anticancer drugs epirubicin and adriamycin leads to thermal stabilization

Recent reports suggest influence of anti-cancer anthracyclines on telomere dysfunction and their possible interaction with G-quadruplex (G4) DNA as an alternate pathway to apoptosis. We have investigated interaction of epirubicin and adriamycin with G4 DNA [d-AGGG(TTAGGG)3] comprising human telomeric DNA sequence by surface plasmon resonance, absorption, fluorescence, circular dichroism and thermal denaturation. Epirubicin and adriamycin bind with affinity, Kb, = 2.5×105 and 5.2×105M−1, respectively in monomeric form leading to decrease in absorbance, fluorescence quenching and ellipticity changes without any significant shift in absorption emission maxima with corresponding induced thermal stabilization by 13.0 and 11.6°C in K+ rich solution. Na+ ions did not induce any thermal stabilization. Molecular docking confirmed external binding at grooves and loops of G4 DNA involving 4OCH3 of ring D, 9COCH2OH of ring A, 4′OH/H and 3′NH3+ of daunosamine sugar. Thermal stabilization induced by specific interactions is likely to hamper telomere association with telomerase enzyme and contribute to drug-induced apoptosis in cancer cell lines besides causing damage to duplex DNA. The findings pave the way for drug designing in view of immense possibilities of altering substituent groups on anthracyclines for enhancement of efficacy, reduced cell toxicity as well as specificity towards G-quadruplex DNA.

Naphthoimidazolium based ratiometric fluorescent probes for F− and CN−, and anion-activated CO2 sensing

The results of the current study show that fluoride and cyanide recognition by two naphthoimidazolium derivatives can be applied to CO2 sensing. Among various anions, only fluoride and cyanide promote changes in absorption and fluorescence wavelegnth maxima of the naphthoimidazolium derivative in CH3CN. The changes are attributed to (C–H)+--anion- ionic hydrogen bonding interactions between the conjugated imidazolium salts and these anions. Especially important is the observations that the fluorescence emission maxima of the naphthoimidazolium derivative at 465 nm undergo hysochromic shifts to 375 nm upon addition of fluoride and cyanide exclusively. The naphthoimidazolium derivatives undergo highly selective changes in their fluoerecence maximum from 465 nm to 375 nm upon addition of CN− even when 2% water is present in the CH3CN solution. Moreover, exposure of the solution of CN− activated naphthoimidazolium derivative to CO2 promotes a red shift of emission maximum back to 465 nm. The results demonstrate that the naphthoimidazolium derivatives can be utilized for anion activated ratiometric sensing of CO2.

Synthesis of the New Green Fluorescent Protein Chromophore Analogue Starting from a Cinnamic Aldehyde Derivative

A novel derivative of green fluorescent protein chromophore (Z)-5-((E)-3-(4-hydroxyphenyl)allylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one was synthesised. The desired compound was prepared by the synthetic approach based on the use of carboxyimidate. Comparison of optical properties of the obtained compound and of the classical GFP chromophore analogue (Z)-5-(4-hydroxybenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one showed the shift of absorption and emission maxima to the long-wavelength region induced by the increase of the conjugated π-system in the benzylidene fragment.

Phenothiazine derivatives - synthesis, characterization, and theoretical studies with an emphasis on the solvatochromic properties

A series of ethynylated N-octylphenothiazine aldehydes (PTZ1–PTZ4) with terminal substituents of different electronic ability (p-methoxyphenyl, p-fluorophenyl, p-trifluoromethylphenyl and 2,5-bis(trifluoromethyl)phenyl) acting as A/D-π-D-A system were synthesized and fully characterized. The influence of these terminal groups on their photophysical, thermal, and biological properties was thoroughly examined and confronted with theoretical calculations. The novel compounds exhibit high thermal stability up to 238–318 °C. Compounds showed an intramolecular charge transfer (ICT) absorption band at about 399 nm and emission band at 535 nm with quantum yields between 40 and 63% in chloroform solution. All compounds exhibit positive solvatochromism in the full range of solvent polarities from hexane to DMSO, whereas in the methanol solution they demonstrate the hypsochromic shift of emission maximum compared to DMSO with significant fluorescence quenching. PTZ1–PTZ4 compounds possess a significant emission from blue to yellow region 488–542 nm, high quantum yields 24–91%, and lifetimes ranging from 6.03 to 8.56 ns in solvents of different polarity. The marked positive solvatochromism indicates the considerable ICT in PTZ1–PTZ4 compounds. A noticeable increase in dipole moment in the excited state calculated in various solvent causes o significant red shift in the emission spectrum of PTZ1–PTZ4. This work demonstrates the strong variation of photophysical properties with a simple alteration of the chemical structure of the phenothiazine framework by terminal groups. The toxicity of the compounds that were obtained was evaluated on cancer as well as normal fibroblast cell lines. The applicatory potential of those phenothiazines as cellular probes have been also evaluated.

Photochemical synthesis and characterization of multi-component (Gd,Lu)3(Ga,Al)5O12:Ce garnet powders

Photochemical synthesis was used for the formation of solid precursors for multi-component Ce-doped (Gd1-xLux)3(Ga1-yAly)5O12. Elemental composition of the solid precursors was evaluated by X-ray fluorescence spectroscopy and the samples were then heated in air to obtain garnet powders. The calcination temperature was correlated with the composition of the powder. The X-ray diffraction revealed that for high Gd content at lower temperatures, impurities such as Gd3(GaO4)O2 were present along with the garnet phase; increased calcination temperature was required for a pure garnet phase. The highly luminescent powders exhibited typical Ce3+ 5d-4f emission in visible range when excited by X-rays, with shifts in emission maximum caused by the changes in sample composition.

Electronic Communication in Pyrrolo[3,2‐b]pyrroles Possessing Sterically Hindered Aromatic Substituents

An investigation of the multicomponent reaction of aldehydes deriving from polycyclic aromatic hydrocarbons with aromatic amines and butane‐2,3‐dione led to the development of new conditions for the synthesis of tetraaryl‐pyrrolo[3,2‐b]pyrroles. A major improvement lies in the use of toluene as a co‐solvent, enabling both the aldehyde and the initially formed imine to be soluble in the reaction mixture. A variety of aldehydes possessing a naphthalene subunit were transformed into a library of pyrrolopyrroles decorated with large aromatic substituents at the 2 and 5 positions, providing yellow‐orange‐emitting dyes with large fluorescence quantum yields and large Stokes shifts. We show that there is a significant π‐conjugation between the peripheral polycyclic subunits and the electron‐rich core, which translates into pronounced bathochromic shifts in absorption and emission maxima compared to the parent molecule. An analysis of the relationship between the degree of planarization of tetraaryl‐pyrrolopyrroles and their photophysical properties is reported. The computational studies, performed with Time‐Dependent Density Functional Theory (TD‐DFT), have revealed that typically electron‐rich polycyclic arenes became electron‐acceptors when attached to pyrrolo[3,2‐b]pyrrole core. It has also been shown that there is a significant change of geometries of these heterocycles between the ground and the excited states.

Characterization of buffalo native pregnancy-associated glycoprotein: mass spectrometry-based glycan composition analysis, sugar-binding characteristics and proteolytic activity assay

Pregnancy-associated glycoproteins constitute a large family of extensively glycosylated secretory proteins which are specifically expressed in outer epithelial cell layer (chorion/trophectoderm) of placenta. The present study reports purification and characterization of buffalo pregnancy-associated glycoprotein (BuPAG) from foetal cotyledons during early pregnancy (< 3 months). Native BuPAG was purified by anion-exchange and Vicia villosa affinity chromatography. Three distinct bands were observed in SDS-PAGE and Western blot with higher molecular weight range of ~ 55–70 kDa in comparison to the calculated one (~ 40 kDa) which may be attributed to the presence of glycosylation in BuPAG. Glycan analysis of purified BuPAG by high-resolution mass spectrometry (ESI-qTof) revealed the presence of nine N-glycan structures and three O-glycan structures. Interaction analysis of various sugars with purified BuPAG using fluorescence quenching assay showed decrease in fluorescence intensity without any shift in emission maxima. BuPAG exhibited proteolytic activity within pH range of 2.0–5.5 with highest activity at pH 3.0. In the presence of inhibitor pepstatin A, proteolytic activity reduced by 84%. The glycan structures and sugar-binding characteristics of BuPAG are identified for the first time in this study. The activity of BuPAGs as active peptidases indicates their possible role in various molecular pathways required for sustenance of pregnancy.

Photophysical Studies of Acridinedione Dyes With Amino Acids in Water

Abstract Photophysical studies of resorcinol based acridinedione (ADDR) dyes with a simple amino acid like glycine were carried out in water. Addition of glycine to photoinduced electron transfer (PET) based dye resulted in a fluorescence enhancement. Interestingly, addition of glycine to PET dye not only results in a fluorescence enhancement but a significant shift in the emission maximum towards the red region was observed. The fluorescence enhancement is attributed to the suppression of the PET process through space between the donor and the acceptor moiety of acridinedione dye ring structure. Both hydrogen-bonding along with hydrophobic interactions influences the excited state properties of ADDR dyes in the presence of glycine are elucidated by fluorescence spectral techniques. The existence of dye in two different environments is established from Time resolved fluorescence lifetime studies. The addition of glycine to non-PET dye does not influence the excited state properties clearly reveals that the PET process is influenced by the presence of glycine in water.

Effect of donor substituents on thermally activated delayed fluorescence of diphenylsulfone derivatives

Diphenylsulfones substituted by acridan, carbazole, phenothiazine and phenoxazine moieties were synthesized and characterized by thermal analysis, UV-, steady-state and time-resolved luminescent spectrometries, cyclic voltametry. Quantum chemical calculations on the molecular level were performed to interpret photophysical properties of the derivatives. Structural parameters, electronic properties, HOMO-LUMO gaps, molecular orbital densities, ionization potentials, reorganization energies were determined. The lowest excitation energies and the wavelengths of absorption maxima were also estimated using the time-dependent density functional theory. All the compounds were found to be capabale to form glasses with glass transition temperatures ranging from 82° to 91°C. They exhibited high thermal stabilities, with 5% weight loss temperatures exceeding 385 °C. Strong solvatochromism arising from the intramolecular charge transfer in the excited state was evidenced by bathochromic shifts of emission maxima with increasing solvent polarity. The compounds containing acridan and phenoxazine moieties showed relatively high photoluminescence quantum yield (up to 35%) in the non-doped solid state, long delayed fluorescence lifetime (in µs range) and small singlet-triplet energy splitting (ΔEST) that is attributed to thermally activated delayed fluorescence. These compounds were tested as emissive species for the fabrication of OLEDs. The sky-blue and green devices showed maximum brightness of 3200 and 12300 cd/m2 and maximum external quantum efficiency of 6.3% and 6.9%, respectively.

A fluorescent probe for hydrazine based on a newly developed 1-indanone-fused coumarin scaffold

A 7-diethylaminocoumarin and 1-indanone-fused fluorescent dye (CI) was developed. CI was superior to traditional coumarins in terms of bathochromic shift in absorption and emission maxima (λabs/λem = 518/598 nm in ethanol). To illustrate its value, we rational designed a new hydrazine-selective fluorescent probe by the judicious anchoring of CI to malononitrile to form CI-DCV. Upon mixing with hydrazine, the dicyanovinyl group of CI-DCV was converted to the corresponding hydrazone, which inhibited the intramolecular charge transfer within the probe, thereby affording remarkable blue shifts in the absorption and fluorescence spectra. The proposed probe shows high selectivity toward hydrazine over other structural analogs and reductive species and can be applied in hydrazine detection in a variety of samples.

Supramolecular-Assisted RNA-Templated Fluorescing Colloidal CdSe QDs Organized in Porous Morphology in the Presence of 1,3-Diaminopropane: Study of Their Multifunctional Behavior

The synthesis of colloidal CdSe nanostructures mediated by ribonucleic acid (RNA) in the presence of 1,3-diaminopropane (DAP) and excess Cd2+ produces CdSe QDs (average diameter, 4.5 nm) forming a chainlike morphology (SP1-DAP) with fairly high fluorescence efficiency and average lifetime (⟨τ⟩): 36% and 121 ns (λflu,sh = 650 nm), respectively. The addition of DAP induces its transformation to porous morphology in the process of self-assembly (SP1A-DAP), as evidenced by atomic force microscopy and transmission electron microscopy, and increase in rotational time constant from 14.7 to 31.5 ns. These changes are associated with a blue shift in emission maxima from 545 to 530 nm and an increase in ⟨τ⟩ from 102 to 111 ns (λmax,flu = 545 nm). For SP1A-DAP, the development of distinct bands (cm–1) in IR analysis (1240 (s) and 1183 (sh)), blue shift in positive peak at 271.1 nm in circular dichroism spectra, and changes in 1H and 31P NMR spectra indicating RNA configuration change from C2′-endo to C3′-endo, clear...

Synthesis and Properties of a Decacyclene Monoimide and a Naphthalimide Derivative as Three-Dimensional Acceptor-Donor-Acceptor Systems.

A method involving the Diels-Alder (DA) cycloaddition of diacenaphtheno[1,2-b;1',2'-d]thiophenes (DATs) with N-alkylacenaphthylene-5,6-dicarboximides (AIs) was developed to synthesize decacyclene monoimides (DCMIs). The reactions generate the corresponding 1:2 adducts (BAIAs) as major products together with 1:1 adducts (the DCMIs). The molecular structure of BAIAb (N-octyl derivative) was unambiguously assigned as the bis-adduct having an endo,endo spatial disposition of the two acenaphthylene-5,6-dicarboximide moieties by using X-ray crystallographic analysis. Relative to the absorption spectrum of decacyclene triimide (DCTIa, N-2-ethylhexyl derivative), that of the analogous N-2-ethylhexyl-substituted monoadduct, DCMIa, is bathochromically shifted despite the fact that it possesses a less delocalized π-electron system. DCMIa does not fluoresce in various organic solvents, whereas DCTIa emits yellow fluorescence in CH2 Cl2 with a low quantum yield (ΦSN ). Moreover, DCMIa in CDCl3 displays concentration-dependent 1 H NMR spectroscopy behavior, which suggests that it self-aggregates with an association constant (Ka ) of (193±50) m-1 at 20 °C. Despite the presence of four bulky tert-butyl groups in DCMIa, its Ka value for aggregate formation is comparable to that of DCTIa [(495±42) m-1 ], which does not contain tert-butyl substituents. Spectroscopic studies with the bis-adduct BAIAa (N-2-ethylhexyl derivative) show that it displays remarkable solvatofluorochromism corresponding to an emission maximum shift (ΔλEM ) of 100 nm. The results of density functional theory calculations on BAIAc (N-methyl derivative) demonstrate that a considerable spatial separation exists between the HOMO and LUMO coefficient distributions, which indicates that the ground-to-excited state transition of the novel three-dimensional acceptor-donor-acceptor BAIAa system should have intramolecular charge-transfer character.

Reversible mechanofluorochromism of aniline-terminated phenylene ethynylenes.

Seven three-ring phenylene-ethynylene (PE) structural analogs, differing only in the lengths of alkyl chains on terminal aniline substituents, show 50-62 nm bathochromic shifts in emission maxima in response to mechanical force (mechanofluorochromism, MC). These shifts are fully reversible with heat or solvent fuming. Shearing of these solids yields a transition from green-emitting crystalline phases to orange-emitting amorphous phases as established by differential scanning calorimetry and X-ray diffraction. Molecules with shorter alkyl chain lengths required higher temperatures to recover the hypsochromically shifted crystalline phases after grinding, while the recovery with chain lengths longer than butyl occurred at room temperature. In addition to this structure-dependent thermochromism, these compounds retain their MC properties in polymer hosts to various extents. The crystalline phases of these materials have PE chromophores that are twisted due to non-covalent perfluoroarene-arene (ArF-ArH) interactions involving perfluorophenyl pendants and the terminal rings of the PE chromophore, resulting in interrupted conjugation and an absence of chromophore aggregation. The MC behavior of an analog without the perfluoroarene rings is severely attenuated. This work demonstrates the general utility of twisted PEs as stimuli-responsive moieties and reveals clear structure-property relationships regarding the effects of alkyl chain length on these materials.

Probing the temperature-dependent changes of the interfacial hydration and viscosity of Tween20 : cholesterol (1 : 1) niosome membrane using fisetin as a fluorescent molecular probe.

A detailed photophysical study of fisetin in a Tween20 : cholesterol (1 : 1) niosome membrane has been carried out. Fisetin is found to partition well into the Tween20 : cholesterol (1 : 1) niosome membrane at low temperature (Kp = 2.7 × 104 M-1 at 10 °C). Cetylpyridinium chloride quenching study confirms the location of fisetin molecules in the interfacial domain of Tween20 : cholesterol (1 : 1) niosome membrane. The emission from the prototropic forms of fisetin (neutral form, excited state anion, ground state anion and phototautomer form) is found to sensitively reflect the local heterogeneities in Tween20 : cholesterol (1 : 1) niosome membrane. The shift in anionic emission maximum with variation in temperature shows the sensitivity of fisetin towards water accessibility at the interfacial domain of Tween20 : cholesterol (1 : 1) niosome membrane. Zeta potential value confirms that there is no role of surface charge in the multiple prototropism of fisetin in Tween20 : cholesterol (1 : 1) niosome membrane. The microviscosity changes with temperature, as reflected in fluorescence anisotropy values of fisetin phototautomeric species FT*, give information about the temperature-induced changes in the motional resistance offered by the interfacial domain of the niosomal membrane to small molecules. A temperature-dependent fluorescence lifetime study confirms the distribution of FT* in the two different sites of niosomal interfacial domain, i.e. water-deficient inner site and water-accessible outer site. This heterogeneity in distribution of FT* is further confirmed through time-resolved fluorescence anisotropy decay resulting in two different rotational time constants (faster component of ∼1.04 ns originates from water-accessible outer site and slower component of ∼16.50 ns originates from water-deficient inner site). The interfacial location of fisetin in Tween20 : cholesterol (1 : 1) niosome membrane has an important implication with regards to antioxidant activity as confirmed from a DPPH radical scavenging study.