The photophysical studies of a mixture of CdTe quantum dots and negatively charged zinc phthalocyanines

Fluorescence resonance energy transfer (FRET) studies were carried out with quantum dots capped with thioglycolic acid (TGA) and 2-mercaptoethanol (2-ME) and negatively charged phthalocyanines {Zn tetracarboxy (ZnTCPc), Zn octacarboxy (ZnOCPc) and Zn tetrasulfo (ZnTSPc) phthalocyinines} in a 0.1 NaOH:EtOH (50:50) solvent mixture. The best overlap between emission spectra of the donor (QDs) and the absorption spectra of the acceptor (ZnPc derivatives) was observed for TGA capped QDs, very little overlap was obtained for 2-ME QDs. ZnTSPc gave the highest FRET efficiency (0.3), with ZnOCPc and ZnTCPc giving a FRET efficiency of 0.2. The Φ_T values of the MPcs generally decreased in the presence of the QD whereas the triplet lifetimes (τ_T) of the ZnPc derivatives were higher in the presence of QDs.     

Photosensitizing properties of octacarboxy metallophthalocyanines in aqueous medium and their interaction with bovine serum albumin

Photosensitizing properties of aluminium, silicon, zinc and germanium octacarboxy phthalocyanines ((OH)AlOCPc, (OH)₂SiOCPc, ZnOCPc and (OH)₂GeOCPc) were studied in aqueous medium and in the presence of bovine serum albumin (BSA). Triplet quantum yields increased with increasing atomic number of the central metals of the metallophthalocyanine. The efficiency of singlet oxygen generation via energy transfer from the excited triplet state of the octacarboxy metallophthalocyanines (MOCPcs) to ground state oxygen increased markedly in the presence of BSA. The triplet state lifetimes of the MOCPc complexes in the presence of BSA were found to be longer than in the absence of BSA, ranging from 110 to 580 μs. These complexes bind readily to BSA. Stern–Volmer quenching constant K_SV as well as the binding constant k_b values were calculated. The probable mechanism of quenching of BSA fluorescence by the MOCPc complexes is by static quenching.     

Wavelength encoded analytical imaging and fiber optic sensing with pH sensitive CdTe quantum dots

CdTe quantum dots (QDs), capped with mercaptopropionic acid (MPA), were synthesized and the variation of their fluorescence properties (steady state and lifetime) with pH was assessed in solution and when immobilized in a sol-gel host. Three different sizes of CdTe QDs with excited state lifetimes ranging from 42 to 48 ns and with emission maximum at 540 nm (QD₅₄₀), 580 nm (QD₅₈₀) and 625 nm (QD₆₂₅) were selected. The solution pH affects the maximum emission wavelength (shifts to higher wavelengths of 23, 24 and 27 nm for QD₅₄₀, QD₅₈₀ and QD₆₂₅, respectively), the excited state lifetime and the fluorescence intensity in a reversible way. Linearization of the maximum emission wavelength variation with the pH allows the estimation of an apparent ionization constant (pK_a) for each QD: 6.5 ± 0.1 (QD₅₄₀), 6.1 ± 0.5 (QD₅₈₀) and 5.4 ± 0.3 (QD₆₂₅). The variation of the QDs fluorescence properties was further explored using confocal laser scanning microscopy allowing the implementation of a new calibration method for pH imaging in solution. QDs were successfully immobilized on the tip of an optical fiber by dip-coating using sol-gel procedure. The immobilized QDs showed a similar pH behaviour to the one observed in solution and an apparent lifetime of 80, 68 and 99 ns, respectively. The proposed QDs based methodology can be successfully used to monitor pH using wavelength encoded data in imaging and fiber optic sensing applications.     

Synthesis and photophysical properties of lead phthalocyanines

This work reports on the synthesis and photophysical parameters of tetra-and octa-substituted new lead phthalocyanines. The complexes synthesized are: 1,4-(tetraphenoxyphthalocyaninato)lead (7a), 1,4-(tetra-tert-butylphenoxyphthalocyaninato)lead (7b), 2,3-(tetraphenoxyphthalocyaninato)lead (8a), 2,3-(tetra-tert-butylphenoxyphthalocyaninato)lead (8b), 2,3-octaphenoxyphthalocyaninatolead (9a) 2,3-[octakis(4-t-butylphenoxyphthalocyaninato)]lead (9b). Photophysical properties were studied for these complexes in a dimethylsulfoxide, dimethylformamide, toluene, tetrahydrofuran and chloroform. The fluorescence spectra were different from excitation spectra due to demetallation upon excitation. High triplet quantum yields ranging from 0.70 to 0.88 (in DMSO, DMF and toluene) and low triplet lifetimes (20–50 μs in DMSO, and <10 μs in the rest of the solvents) were observed due to the presence of heavy atom.     

Effects of temperature on the triplet behavior of the styrylphenanthrene isomers

The properties of the triplet state of five styrylphenanthrene (StPh) trans isomers were studied in 2-methyltetrahydrofuran (MTHF) as a function of temperature. At room temperature the T-T absorption was observed only for 4- and 9-StPh, while under these conditions 1-, 2-, and 3-StPh have too low a quantum yield of triplet formation (Φ_T <0.02); their T-T absorption spectra were obtained at low temperature. Φ_T of 1- and 2-StPh increases more than tenfold on going from 293 to 77 K, and the triplet lifetime (τ_T) increases by four orders of magnitude and approaches values of 5–40 ms at 77 K. The change in τ_T is explained in terms of an equilibrium between trans and perpendicular (perp) conformations of the lowest triplet state in fluid solution and temperature and viscosity effects on the trans → perp rotation. Evidence is presented for the existence of two conformeric trans triplet states of 3-StPh at 77 K. Semi-empirical calculations were performed to obtain the energy of the triplet state, the wavelengths of several T-T absorption maxima (λ_T), and the oscillator strength. The calculated λ_T values coincide with those measured in n-hexane.     

Photoreaction of nitrobenzenes with hydrobromic acid

Nitrobenzene and three of its derivatives (3-CO₂H, 3-OH, and 4-OH) react efficiently when irradiated (λ >340 nm) in concentrated hydrobromic acid typically to give high yields of 2,4,6-tribromoanilines. The quantum yield (Φ = 0.16 for nitrobenzene) is not changed appreciably by the electron withdrawing carboxy substituent, but is lowered by the electron donating hydroxy substituent. The reactivity suggests that electron transfer from bromide ion to the n,π* triplet is the primary process.     

Influence of quantum dot's quantum yield to chemiluminescent resonance energy transfer

The resonance energy transfer between chemiluminescence donor (luminol-H₂O₂ system) and quantum dots (QDs, emission at 593 nm) acceptors (CRET) was investigated. The resonance energy transfer efficiencies were compared while the oil soluble QDs, water soluble QDs (modified with thioglycolate) and QD-HRP conjugates were used as acceptor. The fluorescence of QD can be observed in the three cases, indicating that the CRET occurs while QD acceptor in different status was used. The highest CRET efficiency (10.7%) was obtained in the case of oil soluble QDs, and the lowest CRET efficiency (2.7%) was observed in the QD-HRP conjugates case. This result is coincident with the quantum yields of the acceptors (18.3% and 0.4%). The same result was observed in another similar set of experiment, in which the amphiphilic polymer modified QDs (emission at 675 nm) were used. It suggests that the quantum yield of the QD in different status is the crucial factor to the CRET efficiency. Furthermore, the multiplexed CRET between luminol donor and three different sizes QD acceptors was observed simultaneously. This work will offer useful support for improving the CRET studies based on quantum dots.     

Excited-state absorption of mono-, di- and tri-nuclear cyclometalated platinum 4,6-diphenyl-2,2′-bipyridyl complexes

The ground-state absorption cross-sections (σ_g), triplet excited-state absorption cross-section (σ_T) at 532 nm, singlet excited-state absorption cross-sections (σ_s) at various visible wavelengths, singlet and triplet excited-state lifetimes, and triplet quantum yields of three cyclometalated platinum(II) 4,6-diphenyl-2,2′-bipyridyl complexes, are reported. The presence of metal-metal and π-π interactions in the dinuclear and trinuclear complexes results in a significant increase in their respective σ_g’s in the visible spectral region. As a result, the ratio of σ_s/σ_g and σ_T/σ_g at each wavelength is significantly greater for the mononuclear complex than for the dinuclear and the trinuclear complexes.     

Asymmetric cyano-ethoxycarbonylation of aldehydes catalyzed by self-assembled titanium catalyst

A new self-assembled catalyst based on titanium complex has been developed for the effective enantioselective cyano-ethoxycarbonylation of aldehydes. The self-assembled catalyst was readily prepared from (R)-3,3′-bis((methyl((S)-1-phenylethyl)amino)methyl)-1,1′-binaphthyl-2,2′-diol (1h), N-((1S,2R)-2-hydroxy-1,2-diphenylethyl)acetamide (2b), and tetraisopropyl titanate (Ti(OiPr)₄). A variety of aromatic aldehydes, aliphatic aldehydes, and α,β-unsaturated aldehydes were found to be suitable substrates in the presence of the self-assembled titanium catalyst (5 mol % 1h, 5 mol % 2b, and 5 mol % Ti(OiPr)₄). The desired cyanohydrin ethyl carbonates were afforded with high isolated yields (up to 95%) and moderate to good enantioselectivities (up to 92% ee) under mild conditions (at −15 °C). A possible catalytic cycle based on the experimental observation was proposed.     

Chemically bonded metallic (Eu, Tb, Zn) hybrid materials through sulfide linkage: Molecular construction, physical characterization and photophysical properties

In this paper, a kind of aromatic carboxylic acid of sulfhydryl group (2-mercaptonicotinic acid) is modified with four silane crosslinking reagents (3-methacryloyloxypropyltrimethoxysilane (S₁), 3-glycidoxypropyltrimethoxysilane (S₂), 3-aminopropyltrimethoxysilane (S₃), and 3-(triethoxysilyl)propylisocyanate (S₄)) to achieve four new kinds of functionalized molecular bridge (P_i (i = 1-4)). Subsequently, four molecular bridges and lanthanides (europium and terbium) or zinc ions have been assembled via chemical bonds through a sol-gel (cohydrolysis and copolycondensation) process with inorganic precursor (tetraethoxysilane, TEOS), resulting in four novel series of chemically bonded hybrid materials which named as Ln (Zn)-M_i (i = 1-4). The coordinated bonding makes metal ions evenly dispersed in a stable hybrid system. The intramolecular energy transfer process between lanthanide ions and the molecular bridges take place within these molecular-based hybrids and especially the luminescent quantum efficiency of them are determined, suggesting that the hybrid material systems derived from different molecular bridges present different luminescence efficiencies.     

Preparation of strongly fluorescent silica nanoparticles of polyelectrolyte-protected cadmium telluride quantum dots and their application to cell toxicity and imaging

Based on the polyelectrolyte-protected CdTe quantum dots (QDs), which were prepared by self-assembling of QDs and poly-diallyldimethylammonium chloride (PDADMAC) in the help of electrostatic attraction, the strong fluorescence silica nanoparticles (QDs-PDADMAC@SiO₂) have been prepared via a water-in-oil reverse microemulsion method. Transmission electron microscopy and Zeta potential analysis were used to characterize the as-prepared nanoparticles. All of the particles were almost spherical and there is a uniform distribution of the particle size with the average diameter about 25 nm. There is a large Zeta potential of −35.07 mV which is necessary for good monodispersity of nanoparticles solution. As compared with the QDs coated by SiO₂ (QDs@SiO₂), the QDs-PDADMAC@SiO₂ nanoparticles have much stronger fluorescence, and their fluorescence stability could be obviously improved. Moreover, QDs-PDADMAC@SiO₂ exhibits good biological compatibility which promotes their application in cellular imaging.     

Synthesis,photophysical and nonlinear optical properties of microwave synthesized 4-tetra and octa-substituted lead phthalocyanines

This work presents the photophysical and nonlinear optical behaviour of newly synthesized complexes: 2,(3)-tetrakis(4-benzyloxyphenoxyphthalocyaninato) lead (5a) and 2,3-octakis(4-benzyloxyphenoxyphthalocyaninato) lead (6a). The nonlinear optical behaviour of complexes 5a and 6a are compared with those of 2,(3)-tetraphenoxyphthalocyaninato lead (5b), 2,(3)-tetrakis(4-t-butylphenoxyphthalocyaninato) lead (5c), 2,3-octaphenoxyphthalocyaninato lead (6b) and 2,3-octakis(4-t-butylphenoxyphthalocyaninato) lead (6c). The synthesis of 5a and 6a was performed using microwave irradiation. Photophysical properties were studied for these complexes in dimethylsulfoxide, dimethylformamide, toluene, tetrahydrofuran and chloroform. The fluorescence spectra were different from excitation spectra due to demetallation upon excitation. High triplet quantum yields ranging from 0.80 to 0.86 (in DMSO, DMF and toluene) and low triplet lifetimes (20–50 μs in DMSO, and <10 μs in the rest of the solvents) were observed due to the presence of heavy atom. Nonlinear optical properties were studied in dimethylsulfoxide. The optical limiting threshold intensity (I_lim) for the PbPc derivatives were calculated and ranged from 2.1 to 6.6 W/cm².     

The first observation of the effect of dendritic structure to produce the triplet excited state of the core stilbene by dendron excitation

We report that both singlet and triplet energy transfers in stilbene-cored benzophenone dendrimers (trans-BPST) took place quite efficiently. On excitation (290 nm) of stilbene group, the intramolecular singlet energy transfer from the excited core stilbene to the benzophenone part (99.7%) was confirmed by quenching of the fluorescence from the core stilbene. The benzophenone in the excited singlet state is known to undergo intersystem crossing to give its excited triplet state quantitatively. However, the very weak phosphorescence from benzophenone part in trans-BPST was observed even at 77 K. The phosphorescence intensity of trans-BPST is only 1% of that of model compound (4-methylbenzophenone) at 77 K. During the irradiation, the absorption spectra also changed due to the trans-cis isomerization. This is probably due to the ultrafast triplet energy transfer from the benzophenone to produce the triplet state stilbene.     

A novel enzyme-mimic nanosensor based on quantum dot-Au nanoparticle@silica mesoporous microsphere for the detection of glucose

QD-Au NP@silica mesoporous microspheres have been fabricated as a novel enzyme-mimic nanosensor. CdTe quantum dots (QDs) were loaded into the core, and Au nanoparticles (NPs) were encapsulated in the outer mesoporous shell. QDs and Au NPs were separated in the different space of the nanosensor, which prevent the potential energy or electron transfer process between QDs and Au NPs. As biomimetic catalyst, Au NPs in the mesoporous silica shell can catalytically oxidize glucose as glucose oxidase (GOx)-mimicking. The resultant hydrogen peroxide can quench the photoluminescence (PL) signal of QDs in the microsphere core. Therefore the nanosensor based on the decrease of the PL intensity of QDs was established for the glucose detection. The linear range for glucose was in the range of 5–200 μM with a detection limit (3σ) of 1.32 μM.     

Thermodynamic studies on SrFe12O19(s), SrFe2O4(s), Sr2Fe2O5(s) and Sr3Fe2O6(s)

The citrate-nitrate gel combustion route was used to prepare SrFe₂O₄(s), Sr₂Fe₂O₅(s) and Sr₃Fe₂O₆(s) powders and the compounds were characterized by X-ray diffraction analysis. Different solid-state electrochemical cells were used for the measurement of emf as a function of temperature from 970 to 1151 K. The standard molar Gibbs energies of formation of these ternary oxides were calculated as a function of temperature from the emf data and are represented as (SrFe₂O₄, s, T)/kJ mol⁻¹ (±1.7)=−1494.8+0.3754 (T/K) (970?T/K?1151). (Sr₂Fe₂O₅, s, T)/kJ mol⁻¹ (±3.0)=−2119.3+0.4461 (T/K) (970?T/K?1149). (Sr₃Fe₂O₆, s, T)/kJ mol⁻¹ (±7.3)=−2719.8+0.4974 (T/K) (969?T/K?1150).Standard molar heat capacities of these ternary oxides were determined from 310 to 820 K using a heat flux type differential scanning calorimeter (DSC). Based on second law analysis and using the thermodynamic database FactSage software, thermodynamic functions such as Δ_fH°(298.15 K), S°(298.15 K) S°(T), C_p°(T), H°(T), {H°(T)-H°(298.15 K)}, G°(T), free energy function (fef), Δ_fH°(T) and Δ_fG°(T) for these ternary oxides were also calculated from 298 to 1000 K.     

Miscibility and dynamics of the poly(vinylimidazole-co-methyl methacrylate)-silica hybrids studied by solid-state NMR

Poly(vinylimidazole-co-methyl methacrylate)-silica hybrids, bonded through hydrogen bond (PVM-SiO₂) or chemical bond (PVM(5)-SiO₂) between organic and inorganic units, were prepared and characterized. The characterization of PVM-SiO₂ and PVM(5)-SiO₂ hybrids were confirmed by IR, ¹³C and ²⁹Si NMR spectra. The intermolecular interaction between copolymer chains was studied by the spin-lattice relaxation time in the rotating frame (T^H_1ρ), and that between copolymer and silica was evaluated by the time constant for energy change between ¹H and ²⁹Si spin system (T_SiH). T^H_1ρ and T_SiH values in PVM-SiO₂ hybrids were consistent with those in PVM(5)-SiO₂ hybrids, and those were independent of the silica content. Moreover, the T^H_1ρ values are in order of poly(methyl methacrylate)-silica hybrids (PMMA-SiO₂) ≧ PVM-SiO₂ ≒ PVM(5)-SiO₂ > polyvinylimidazole-silica hybrids (PVI-SiO₂), while those of T_SiH are in reverse order PMMA-SiO₂ ≦ PVM(5)-SiO₂ < PVI-SiO₂.     

Delayed fluorescence S2 → S0 of azulene in isopentane,due to hetero-triplet—triplet annihilation of 3azulene* and 3fluoranthene*

The lowest triplet state of azulene, T₁(Az), can be populated efficiently by triplet energy transfer from the lowest triplet state of fluoranthene, T₁(F1). In isopentane at temperatures 120 K ? T ? 193 K a delayed fluorescence S₂(Az) → S₀(Az) is found, caused by hetero-triplet—triplet annihilation T₁(Az) + T₁(Fl) → S₂(Az) + S₀(F1).     

Thermodynamic and conformational investigation of the influence of CdTe QDs size on the toxic interaction with BSA

Water-soluble fluorescent colloidal quantum dots (QDs) have been widely used in some biological and biomedical fields, so the interaction of QDs with biomolecules recently attracts increasing attention. In this study, the fluorescence (FL) quenching method, circular dichroism (CD) technique, attenuated total reflection-Fourier transform infrared (ATR-FTIR) and UV-vis absorption spectra were used to investigate systematically the influence of CdTe QDs size on the toxic interaction with bovine serum albumin (BSA). Three size CdTe QDs with maximum emission of 543 nm (green-emitting QDs, GQDs), 579 nm (yellow-emitting QDs, YQDs) and 647 nm (red-emitting QDs, RQDs) were tested. The Stern-Volmer quenching constant (K_sv) at different temperatures, corresponding thermodynamic parameters (ΔH, ΔG and ΔS), and information of the structural features of BSA were gained. The FL results indicated that QDs can effectively quench the FL of BSA in a size-dependent manner, electrostatic interactions play a major role in the binding reaction, and the nature of quenching is static, resulting in forming QDs-BSA complexes. The CD and ATR-FTIR spectra showed that the secondary structure of BSA was changed by QDs, indicating the toxic on protein.     

Ab initio quantum chemical studies on the reactions of CF3O2 with OH

The potential energy surface for the CF₃O₂ + OH reaction has been theoretically investigated using the DFT (B3LYP/6-311G(d,p)) level of theory. Both singlet and triplet potential energy surfaces are investigated. The reaction mechanism on the triplet surface is simple. However, the reaction mechanism on the singlet surface is more complicated. It is revealed that the formation of CF₃O + HO₂ is the dominant channel on the triplet surface. The potential energy surface (PES) for this reaction has been given according to the relative energies calculated at the DFT/B3LYP/6-311G(d,p) level. Because this reaction involves both triplet and singlet states, triplet–singlet intersystem crossing (ISC) crossing also have been investigated in this paper.     

A novel series of iridium complexes with alkenylquinoline ligands: Theoretical study on electronic structure and spectroscopic property

The ground and the lowest-lying triplet excited state geometries, electronic structures, and spectroscopic properties of a novel series of neutral iridium(III) complexes with cyclometalated alkenylquinoline ligands [(C^N)₂Ir(acac)] (acac = acetoylacetonate; C^N = 2-[(E)-2-phenyl-1-ethenyl]pyridine (pep) 1; 2-[(E)-2-phenyl-1-ethenyl]quinoline (peq) 2; 1-[(E)-2-phenyl-1-ethenyl]isoquinoline (peiq) 3; 2-[(E)-1-propenyl]pyridine (pp) 4; 2-[(E)-1-fluoro-1-ethenyl]pyridine (fpp) 5) were investigated by DFT and CIS methods. The highest occupied molecular orbital is composed of d(Ir) and π(C^N) orbital, while the lowest unoccupied molecular orbital is dominantly localized on C^N ligand. Under the TD-DFT with PCM model level, the absorption and phosphorescence in CH₂Cl₂ media were calculated based on the optimized ground and triplet excited state geometries, respectively. The calculated lowest-lying absorptions at 437 nm (1), 481 nm (2), 487 nm (3), 422 nm (4), and 389 nm (5) are attributed to a {[d_x²-y²(Ir) + d_xz(Ir) + π(C^N)] → [π∗(C^N)]} transition with metal-to-ligand/intra-ligand charge transfer (MLCT/ILCT) characters, and the calculated phosphorescence at 582 nm (1), 607 nm (2), 634 nm (3), 515 nm (4), and 491 nm (5) can be described as originating from the ³{[d_x²-y²(Ir) + d_xz(Ir) + π (C^N)] [π∗(C^N)]} excited state with the ³MLCT/³ILCT characters. The calculated results revealed that the phosphorescent color of these new Ir(III) complexes can be tuned by changing the π-conjugation effect strength of the C^N ligand.