Study of temperature influence on electron transport in higher plants via delayed luminescence method: experiment, theory

The temperature dependence of steady-state millisecond delayed luminescence (DL) is studied within the temperature range from -23 to 45 degrees C in leaf segments of chinese rose (Hibiscus rosa-sinensis L.) and bean (Ficia faba). To describe the experimental dependence of DL steady-state intensity on temperature theoretically, we suggest the temperature dependences of rate constants in earlier proposed model of photosynthesis. Under these conditions, the temperature dependence of DL steady-state value has the same form as experimental curve.     

DELAYED MICROSECOND LUMINESCENCE OF PHYCOBILISOMES

The time-resolved luminescence spectra (in the microsecond range) of phycobilisomes and biliproteins in buffer and polymer matrix were measured in the temperature range from 8 K. to 293 K. Delayed luminescence located in the same spectral region as prompt fluorescence of investigated samples (DLF) and the long-wavelength delayed emission in the720–760 nm range (DL1) was observed. The temperature and viscosity dependencies of DLF and DL1 luminescences were different, but both do not have uniexponential decays and are not quenched by oxygen. This means that delayed luminescence could be generated without the participation of the triplet states, or the chromophores could be shielded by protein against interaction with oxygen. The linear dependence of delayed luminescence on exciting light intensity shows that delayed luminescence is monophotonically induced. It seems that both DLF and DL1 are related to electron-cation recombination, which yields excited singlet states. The DLF is emitted from the first excited singlet state of biliprotein chromophores and DL1 from the same state of the excimers or from the triplet state of some groups of chromophores. Ionization energy of chromophores can be lowered as a result of their interactions with the environment. Delay of emission is due to the trapping or solvation of electrons. Every type of biliprotein consisting of phycobilisomes possesses its own “trap” and can emit the DL. In the case of native phycobilisomes a competition between the excitation energy trapping and transfer occurs.     

Rapid detection of Aspergillus flavus contamination in peanut with novel delayed luminescence spectra

Employing a luminescence spectrometer the usefulness of light-induced delayed luminescence (DL) for the detection of aflatoxinB1 (AfB1) contamination in whole peanut was studied. Peanut was artificially contaminated with Aspergillus flavus (7.5 x 10(5)conidia/mL) and incubated for 0-72 h. The DL and fluorescence spectra of contaminated peanut were obtained by a luminescence spectrometer. The correlation between the spectra and contamination levels was established. The DL and fluorescence intensity has a negative correlation with the AfB1 concentration. Our results suggested that the DL technique might be useful for the rapid and noninvasive evaluation of AfB1 contamination levels in whole peanut.     

Universal growth of microdomains and gelation transition in agar hydrogels

Investigations were carried out on aqueous sols and gels of agar (extracted from red seaweed Gelidiella acerosa) to explore the growth of microdomains en route to gelation. Isothermal frequency sweep studies on gel samples revealed master plots showing power-law dependence of gel elastic modulus, |G*|, on oscillation frequency, omega as |G*| approximately omegan, independent of temperature, with 0.5Tg). The S(q,t) behavior close to the gel transition point (Tg approximately (38+/-3 degrees C determined from rheology) followed a stretched exponential function: S(t)=A exp(-t/ts)beta. The beta factor increased from 0.25 to 1 as the gel temperature approached 25 degrees C from Tg, and relaxation time, ts, showed a peak at T approximately 30 degrees C. The SLS data (in the sol state) suggested the scaling of scattered intensity, Is(q) approximately epsilon(-gamma) (epsilon=(T/Tg-1), T>Tg) with gamma=0.13+/-0.03, and the presence of two distinct domains characterized by a Guinier regime (low q) and a power-law regime (high q). Close to and above Tg (+2 degrees C), IS(q) scaled with q as Is(q) approximately q(-alpha) with alpha=2.2+/-0.2, which decreased to 1.4+/-1 just below Tg (-2 degrees C), implying a coil-helix transition for 0.2% (w/v) and 0.3% (w/v) samples. For a 0.01% sample, alpha=3.5+/-0.5 which indicated the presence of spherical microgels.     

Luminescence emission spectra in the temperature range of the structural phase transitions of Na2SO4

The spectral properties of Na2SO4 have been studied by means of infrared stimulated luminescence (IRSL), thermoluminescence (TL) and radioluminescence (RL) in the range of 200-800 nm. The observed changes in the RL emission spectra after an annealing treatment (400 degrees C for 1 h) could be linked to thermal phase transformations and alkali self-diffusion through the lattice of this salt. Despite the complexity of the luminescence spectra structure, five emission bands peaked at 330, 345, 385, 460 and 630 nm could be distinguished. The UV-blue TL emission of this material exhibits a maximum peaked at 230 degrees C which is well correlated with the differential thermal analysis (DTA) and can be associated with the thermal transformation of the orthorhombic sodium sulphate (Na2SO4) V (thenardite) phase into Na2SO4 III, II and I phases. Taking into account the observed changes on the structural phase transition by X-ray diffraction (XRD) from 16 degrees C onwards, this material does not show satisfactory features for radiation dosimetry, but could be employed for temperature calibration of TL readers.     

DELAYED EMISSION OF CHLOROPHYLL a AGGREGATES AND RHODAMINE 6G EMBEDDED IN POLYMER MATRIX*

Delayed luminescence (in the microsecond time range) of the chlorophyll (Chl) a“dry” form as well as hydrated dimers located in a polyvinylalcohol film was measured from room temperature down to 8 K. In the same matrix the delayed luminescence of rhodamine 6G (Rhod) was investigated. The delayed emission both of Chl a and Rhod is probably due to the formation and delayed recombination of a radical pair. It seems that this process occurs without participation of triplet states, as it does not reflect their well-known sensitivity to oxygen. The temperature dependence of the delayed luminescence of vanous Chl forms is different. In the region around 678 nm (dry monomer) delayed luminescence needs a thermal activation energy of about 0.03 eV, whereas at 740 nm (wet aggregates) delayed luminescence intensity increases linearly with decreasing temperature. Its assignment as a-type delayed luminescence from the low-lying triplet state can consistently be excluded from both the weak temperature dependence of the delayed fluorescence and its large intensity as compared to the prompt fluorescence. Delayed luminescence of Rhod is almost independent of temperature between 8 K and 300 K. The dependence of delayed luminescence intensity on exciting light intensity is linear at lower intensities and tends to saturation at higher. Therefore the delayed luminescence is not related to exciton annihilation. Positions and intensities of the Chl delayed luminescence bands show that it is not phosphorescence (β-type delayed luminescence). The aggregation of both Chl and Rhod molecules strongly influences delayed luminescence since it differs in several properties if excited in the monomer or in the aggregate absorption range. Every aggregational form of dye emits its characteristic delayed luminescence band.     

Conformational control of excited-state dynamics in highly distorted Ru(II) polypyridyl complexes

Tris(bipyridyl)ruthenium(II) complexes modified such that one of the bipyridines is appended with a crown ether display luminescence that is responsive to complexation with metal ions. The parent species, Ru(bpy)3(2+), is moderately luminescent, with an emission lifetime of about 1 micros in fluid solution at room temperature. The modified complexes are much less emissive, with lifetimes near 1 ns. Conformational flexibility and distortion in the crown-ether complexes enhance nonradiative decay. Noncovalent binding of metal ions, however, restores luminescence intensity by reducing nonradiative decay and increasing the lifetime 10- to 100-fold. Reported here are the syntheses and steady-state and time-resolved luminescence measurements in addition to other supporting spectroscopic characterization. Seven metals were investigated; significant luminescence enhancements occur in the presence of Mg2+, Ca2+, and Pb2+. Effective concentrations of metal ions range from tens of microM to hundreds of mM. The steady-state enhancements are readily measured, but they are less than would be expected from the lifetime changes, partly because only a portion (not more than 50%) of the fast (1 ns) decay in Ru(bpy)2(bpy-crown) is capable of converting to the conformation possessing the longer lifetime. A photophysical model is proposed to explain these and other observations.     

RESEARCH NOTE: TRIPLET RADICAL ION PAIR STATE OF THE Zn-PORPHYRIN-VIOLOGEN DYAD AS A MAGNETIC FIELD SENSITIVE PROBE OF PHASE TRANSITIONS IN SMALL UNILAMELLAR VESICLES

The magnetic field effect on the recombination kinetics of the triplet radical ion pair state (RIPS) of the Zn-porphyrin-viologen dyad (P-Ph-Vi2+) in the small unilamellar vesicles (SUV) of D,L-dipalmitoyl-alpha-phosphatidylcholine has been studied by the nanosecond laser flash photolysis technique at 5-60 degrees C. The increase in temperature from 25 to 40 degrees C enhances the rate constant (kr) of the RIPS recombination in zero magnetic field from 0.9 x 10(6) to 1.6 x 10(6) s-1, while kr is temperature insensitive at 5-25 and 40-60 degrees C. The typical break in the kr temperature dependence is observed in the temperature range of the phase transition of the SUV bilayers from the solid to the fluid state. The kr value in a strong magnetic field (B = 0.24 T) is equal to 2.7 x 10(5) s-1 and it is independent of temperature at 5-60 degrees C. The shape of the magnetic field dependence of kr is unaffected by the phase transition of the SUV bilayers and is characterized by the existence of an initial plateau of kr at B = 0 to 0.5 mT.     

Phase behaviour of the discotic mesogen 5,10,15,20-tetrakis (4-n-dodecylphenyl)porphyrin under pressure

The phase behaviour of the discotic mesogen 5,10,15,20-tetrakis(4-n -dodecylphenyl)porphyrin (C12TPP) was investigated under hydrostatic pressures up to 300MPa by high pressure DTA and wide angle X-ray diffraction methods. The typical enantiotropic phase transitions of C12TPP, low- to high-temperature crystal (Cr2-Cr1), Cr1-discotic lamellar phase (DL), and DL-isotropic liquid (I) are observed at pressures up to 10MPa. Application of hydrostatic pressure to the sample generates a pressure-induced crystal polymorph (Cr3) between the Cr2 and Cr1 phases, and the phase transitions Cr2-Cr3-Cr1-DL-I occur reversibly in the pressure region between 10 and 180MPa. On heating at higher pressures above 180MPa, the fourth crystal polymorph (Cr4) is formed between the Cr2 and Cr3 phases at lower temperatures, and at the same time the fifth crystal polymorph (Cr5) appears abruptly between the Cr1 and DL phases at high temperatures. The Cr2-Cr4-Cr3-C1-(Cr5)-DL-I transition processes were observed at 180 200MPa. Further increasing the pressure above 270MPa induces entirely different thermal behaviour: only two peaks for the pressure-induced transition between the sixth and fifth polymorphs (Cr6-Cr5) and the Cr5-I transitions are detected at low and high temperatures on heating, while both the DTA and WAXD experiments on cooling show the formation of the DL phase as a monotropic phase between the I and Cr5 phases, indicating the I DL Cr5 Cr6 process. The thermal behaviour was ambiguous and complex in the pressure region between 200 and 260MPa because the peaks for the intermediate crystal transitions were too small to detect with confidence. The two different sequences of the Cr2-Cr4-Cr3-Cr1-DL-I and Cr6-Cr5-(DL)-I processes seems to occur competitively. The T vs. P phase diagram of a sample cooled at 300MPa was studied to determine the triple point of the DL phase and to investigate the phase stability of the pressure-induced crystal polymorphs. The Cr6-Cr5-I transition process was observed on heating at 200 and 300MPa, while the Cr6-Cr5-DL-I process was detected at lower pressures below 100MPa. Since the Cr5-DL transition temperature changes linearly with a slope dT/dP 40 degrees C/100 MPa, while the DL-I transition temperature changes slightly (dT/dP 5.5 degrees C/100MPa), the DL phase forms a triangle in the T vs. P diagram. The triple point of the DL phase was found to be 240.8MPa and 168.8 C. The Cr6 polymorph reorganized to the stable Cr2 form under atmospheric pressure on annealing at room temperature overnight.     

WAVELENGTH-DEPENDENT QUANTUM YIELD FOR Z →E ISOMERIZATION OF BILIRUBIN COMPLEXED WITH HUMAN SERUM ALBUMIN

The quantum yield, phi ZE, for configurational photoisomerization (4Z,15Z----4Z,15E) of bilirubin bound non-covalently to human serum albumin was determined (at 23 +/- 2 degrees C) by laser excitation and chromatographic analysis of products. Values obtained for photoexcitation at 465 nm were about one-half those previously reported. The quantum yield was dependent on excitation wavelength, decreasing from a value of 0.109 +/- 0.010 for excitation at 457.9 nm to a value of 0.054 +/- 0.005 for excitation at 514.5 nm. The wavelength dependence is consistent with rapid transfer of excitation energy between the two non-identical pyrromethenone chromophores of bilirubin in the singlet excited state. Since the quantum yields for photoisomerization and luminescence of bilirubin bound to serum albumin at room temperature are both low, internal conversion processes, rather than Z----E configurational isomerizations, are probably the major pathways for deactivation of photo-excited bilirubin.     

Phase behaviour of the discotic mesogen 5,10,15,20-tetrakis (4-n-dodecylphenyl)porphyrin under pressure

The phase behaviour of the discotic mesogen 5,10,15,20-tetrakis(4-n -dodecylphenyl)porphyrin (C12TPP) was investigated under hydrostatic pressures up to 300MPa by high pressure DTA and wide angle X-ray diffraction methods. The typical enantiotropic phase transitions of C12TPP, low- to high-temperature crystal (Cr2-Cr1), Cr1-discotic lamellar phase (DL), and DL-isotropic liquid (I) are observed at pressures up to 10MPa. Application of hydrostatic pressure to the sample generates a pressure-induced crystal polymorph (Cr3) between the Cr2 and Cr1 phases, and the phase transitions Cr2-Cr3-Cr1-DL-I occur reversibly in the pressure region between 10 and 180MPa. On heating at higher pressures above 180MPa, the fourth crystal polymorph (Cr4) is formed between the Cr2 and Cr3 phases at lower temperatures, and at the same time the fifth crystal polymorph (Cr5) appears abruptly between the Cr1 and DL phases at high temperatures. The Cr2-Cr4-Cr3-C1-(Cr5)-DL-I transition processes were observed at 180 200MPa. Further increasing the pressure above 270MPa induces entirely different thermal behaviour: only two peaks for the pressure-induced transition between the sixth and fifth polymorphs (Cr6-Cr5) and the Cr5-I transitions are detected at low and high temperatures on heating, while both the DTA and WAXD experiments on cooling show the formation of the DL phase as a monotropic phase between the I and Cr5 phases, indicating the I DL Cr5 Cr6 process. The thermal behaviour was ambiguous and complex in the pressure region between 200 and 260MPa because the peaks for the intermediate crystal transitions were too small to detect with confidence. The two different sequences of the Cr2-Cr4-Cr3-Cr1-DL-I and Cr6-Cr5-(DL)-I processes seems to occur competitively. The T vs. P phase diagram of a sample cooled at 300MPa was studied to determine the triple point of the DL phase and to investigate the phase stability of the pressure-induced crystal polymorphs. The Cr6-Cr5-I transition process was observed on heating at 200 and 300MPa, while the Cr6-Cr5-DL-I process was detected at lower pressures below 100MPa. Since the Cr5-DL transition temperature changes linearly with a slope dT/dP 40 degrees C/100 MPa, while the DL-I transition temperature changes slightly (dT/dP 5.5 degrees C/100MPa), the DL phase forms a triangle in the T vs. P diagram. The triple point of the DL phase was found to be 240.8MPa and 168.8 C. The Cr6 polymorph reorganized to the stable Cr2 form under atmospheric pressure on annealing at room temperature overnight.     

Tunable red-green upconversion luminescence in novel transparent glass ceramics containing Er: NaYF4 nanocrystals

To develop NaYF(4) as bulk luminescence material, transparent glass ceramics containing Er(3+): NaYF(4) nanocrystals were fabricated for the first time, and the influences of heat-treatment temperature and Er(3+) doping level on their upconversion luminescence were investigated. With increasing heating temperature, the upconversion intensity enhanced accordingly, attributing to the incorporation of more Er(3+) into the grown NaYF(4). Notably, when the heating temperature reached 650 degrees C, the upconversion intensity augmented drastically due to the occurrence of phase transition from the cubic NaYF(4) to the hexagonal one. Interestingly, for the samples heat-treated at 620 degrees C, when the Er(3+) doping level was increased from 0.05 to 2.0 mol %, the upconversion emission was whole-range tunable from monochromatic green to approximately monochromatic red, which could be mainly attributed to the cross-relaxation between Er(3+) ions. The excellent optical properties and its convenient, low-cost synthesis of the present glass ceramic imply that it is an excellent substitution material for the unobtainable bulk NaYF(4) crystal, potentially applicable in many fields.     

Principal component analysis calibration method for dual-luminophore oxygen and temperature sensor films: application to luminescence imaging

Oxygen sensor films are frequently used to image air-pressure distributions on surfaces in aerodynamic wind tunnels. In this application, the sensor film is referred to as a pressure-sensitive paint (PSP). A Stern-Volmer calibration is used to relate the emission intensity ratio of a long-lifetime luminescent dye (the pressure-sensitive luminophore, PSL) to surface air pressure. A major problem in PSP measurements arises because the Stern-Volmer calibration of the PSL's emission varies with temperature. To correct for the temperature dependence, a second luminescent dye that has an emission that varies with temperature (the temperature-sensitive luminophore, TSL) is incorporated into the sensor film. With such a dual-luminophore PSP (DL-PSP), it is possible to measure the surface-temperature distribution with the TSL emission, and this information is then used to correct the temperature dependence of the PSL's pressure response. In the present article, we report the application of a DL-PSP to obtain high-resolution air-pressure distributions on a surface that is subjected to a 20 degrees C temperature gradient. Two different calibration methods are used to generate surface-temperature and air-pressure distributions from the luminescence imaging data, and a quantitative comparison of the results obtained from the two methods is provided. The first method is based on an intensity-ratio calibration that uses luminescence images collected at two wavelengths, one corresponding to the TSL emission and the second corresponding to the PSL emission. The second method is based on principal component analysis (PCA) of luminescence images obtained at four wavelengths throughout the spectral region of the TSL and PSL emission (hyperspectral imaging, 550-750 nm). The results demonstrate that the PCA method allows the measurement of surface air pressure with higher accuracy and precision compared to those of the intensity-ratio method. The improvement is especially significant at pressures near 1 atm, where the temperature interference is most pronounced. Surface-pressure distributions are measured with comparable accuracy and precision with the two methods.     

Heat evolution of micelle formation, dependence of enthalpy, and heat capacity on the surfactant chain length and head group

Micelle formation by many surfactants is endothermic at low temperatures but exothermic at high temperatures. In this respect, dissociation of micelles (demicellization) is similar to dissolving hydrocarbons in water. However, a remarkable difference between the two processes is that dissolving hydrocarbons is isocaloric at about 25 degrees C, almost independently of the hydrocarbon chain length, whereas the temperature (T*) at which demicellization of different surfactants is athermal varies over a relatively large range. We have investigated the temperature dependence of the heat of demicellization of three alkylglucosides with hydrocarbon chains of 7, 8, and 9 carbon atoms. At about 25 degrees C, the heat of demicellization of the three studied alkylglucosides varied within a relatively small range (DeltaH=-7.8+/-0.4 kJ/mol). The temperature dependence of DeltaH(demic) indicates that within the studied temperature range the heat capacity of demicellization (DeltaC(P,demic)) is about constant. The value of DeltaC(P,demic) exhibited an apparently linear dependence on the surfactant's chain length (DeltaC(P,demic)/n(CH(2))=47+/-7 kJ/mol K). Our interpretation of these results is that (i) the transfer of the head groups from micelles to water is exothermic and (ii) the temperature dependence of the heat associated with water-hydrocarbon interactions is only slightly affected by the head group. This implies that the deviation of the value of T* from 25 degrees C results from the contribution of the polar head to the overall heat of demicellization. Calorimetric studies of other series of amphiphiles will have to be conducted to test whether the latter conclusion is general.     

Self-diffusion of supercritical water in extremely low-density region

The self-diffusion coefficient D for super- and subcritical water is determined by using the proton pulsed-field-gradient spin echo method at high temperatures and low densities. The density of water is ranged in the steamlike region from 0.0041 to 0.0564 g [corrected] cm(-3) at a supercritical temperature of 400 degrees C, also at 0.0041-0.0079 and 0.0041-0.0462 g [corrected] cm(-3) (the steam-branch densities on the coexistence curve and lower) at 200 and 300 degrees C, respectively. The density is precisely determined on the basis of the PVT dependence of the proton chemical shift. The density-diffusivity products in the zero-density limit divided by the square root of the temperature, (rho D)0/square root of T, are 0.94, 1.17, and 1.35 mg m(-1) s(-1) K(-1/2) (mg=10(-3)g) [corrected] at 200, 300, and 400 degrees C, respectively. The (rhoD)0/square root of T obtained decreases with decreasing temperature and is significantly smaller than the temperature-independent value from the hard sphere model, 1.95 mg [corrected] m(-1) s(-1) K(-1/2). The marked temperature dependence reflects the presence of the strong attractive interaction between a pair of water molecules. The magnitude of the experimental D values and the temperature dependence are well reproduced by the molecular dynamics simulation using TIP4P-FQ model. The initial slope of the product rhoD/square root of T against rho is slightly negative at 300 and 400 [corrected] degrees C.     

Luminescence lifetime-based sensor for cyanide and related anions

A new Ru(II) complex is described which serves as a luminescence lifetime-based sensor for fluoride and cyanide anions (KF = 640 000 mol-1, KCN = 430 000 mol-1). This chromophore displays observable changes in its UV-vis and steady-state luminescence spectra upon cyanide binding. Prior to cyanide addition, this complex exhibits a single-exponential lifetime (tau = 377 +/- 20 ns). With increasing cyanide concentrations, the intensity decays are composed of two exponentials: long tau (320-370 ns) and short tau (13-17 ns). The average lifetimes shorten as a function of cyanide concentration since the fractional intensity shifts from an initial dominant long lifetime component to the short lifetime component. This work represents the first example of a direct method for the luminescence lifetime-based sensing of anions.     

特殊的GdVO_4∶Eu~(3 )发光的温度特性

ＧｄＶＯ4 作为良好的激光基质被广泛研究 ,Ｇｄ ＶＯ4 掺Ｐｒ3 ,Ｎｄ3 ,Ｈｏ3 ,Ｅｒ3 ,Ｔｍ3 ,Ｙｂ3 的激光材料已有报道[1～ 4 ] 。虽然ＧｄＶＯ4 ∶Ｅｕ3 不是激光材料 ,但它是良好的红光材料 ,主峰发射位于 619ｎｍ。ＧｄＶＯ4 ∶Ｅｕ3 的发光强度高 ,与Ｙ2 Ｏ2 Ｓ∶Ｅｕ和ＹＶＯ4 ∶Ｅｕ的发光为同一量级[5] 。Ｇｄ3 Ｅｕ3 是研究能量传递的极好体系。通常发光体的发射强度是随着温度的升高而降低的 ,最近的实验表明ＧｄＶＯ4 ∶Ｅｕ3 的发光强度随着温度的升高不但不降低反而不断增强 ,且温度高达 60 0Ｋ都尚未见饱和。1　 实　验实…     

The effect of decreasing temperature up to chilling values on the in vivo F685/F735 chlorophyll fluorescence ratio in Phaseolus vulgaris and Pisum sativum: the role of the photosystem I contribution to the 735 nm fluorescence band

The effect of leaf temperature (T), between 23 and 4 degrees C, on the chlorophyll (Chl) fluorescence spectral shape was investigated under moderate (200 microE m-2 s-1) and low (30-35 microE m-2 s-1) light intensities in Phaseolus vulgaris and Pisum sativum. With decreasing temperature, an increase in the fluorescence yield at both 685 and 735 nm was observed. A marked change occurred at the longer emission band resulting in a decrease in the Chl fluorescence ratio, F685/F735, with reducing T. Our fluorescence analysis suggests that this effect is due to a temperature-induced state 1-state 2 transition that decreases and increases photosystem II (PSII) and photosystem I (PSI) fluorescence, respectively. Time-resolved fluorescence life-time measurements support this interpretation. At a critical temperature (about 6 degrees C) and low light intensity a sudden decrease in fluorescence intensity was observed, with a larger effect at 685 than at 735 nm. This is probably linked to a modification of the thylakoid membranes, induced by chilling temperatures, which can alter the spill-over from PSII to PSI. The contribution of photosystem I to the long-wavelength Chl fluorescence band (735 nm) at room temperature was estimated by both time-resolved fluorescence lifetime and fluorescence yield measurements at 685 and 735 nm. We found that PSI contributes to the 735 nm fluorescence for about 40, 10 and 35% at the minimal (F0), maximal (Fm) and steady-state (Fs) levels, respectively. Therefore, PSI must be taken into account in the analysis of Chl fluorescence parameters that include the 735 nm band and to interpret the changes in the Chl fluorescence ratio that can be induced by different agents.     

A hemicyanine-conjugated copolymer as a highly sensitive fluorescent thermometer

A simple-structured copolymer, poly(NIPAM-co-HC), consisting of N-isopropylacrylamide (NIPAM) and 4-(4-dimethylaminostyryl)pyridine (hemicyanine, HC) units as thermoresponsive and fluorescent signaling parts, respectively, has been synthesized. This copolymer dissolved in water shows very weak fluorescence at <25 degrees C, while showing fluorescence enhancement at >25 degrees C. The fluorescence intensity increases with a rise in temperature and saturates at >40 degrees C, enabling temperature detection at 25-40 degrees C. The fluorescence enhancement is driven by a heat-induced phase transition of the polymer from coil to globule state. The HC units within the coil state polymer exist as the nonfluorescent benzenoid form; however, the less polar domain formed inside the globule state polymer leads to transformation of the HC unit to the fluorescent quinoid form, resulting in heat-induced fluorescence enhancement. The fluorescence intensity measured at 40 degrees C is >20-fold higher than the intensity at <25 degrees C, which is the highest enhancement value among the fluorescent thermometers proposed so far. The polymer shows reversible fluorescence enhancement/quenching, regardless of the heating/cooling process. In addition, the polymer shows high reusability with a simple recovery process.     

Time-resolved photoluminescence characteristics of subnanometer ZnO clusters confined in the micropores of zeolites

Subnanometric ZnO clusters confined in different micropore zeolites are studied by steady-state and nanosecond time-resolved photoluminescence (PL) spectroscopy. The microsecond-scale lifetime is observed at room temperature for ZnO clusters confined in zeolites, which is significantly different from that of macrocrystalline ZnO on the external surface of zeolites. The dependence of luminescence lifetime on the amount of ZnO in zeolites indicates that the electron-phonon interactions between the ZnO clusters and the zeolite host significantly affect the dynamic relaxation process of ZnO clusters. The long lifetime luminescence of ZnO clusters can be achieved by weakening the coupling of electronic transition to zeolites host phonons. The similar long-lived luminescence is obtained when dispersing ZnO clusters into the porous SiO2. It is suggested that encapsulating the semiconductor cluster in the porous support is a possible way to inhibit or to retard the electron-hole recombination.