TRIPLET STATE PROPERTIES OF C60PMMA CO-POLYMERS IN ORGANIC SOLUTION AND PMMA FILM

Two star-like C60-polymethylmethacrylate (C60PMMA) copolymers, which are soluble in a wide range of organic solvents, have been synthesized by free-radical polymerization. The polymers can be described by the formula 1%C60PMMA and 10%C60PMMA. They consist of a C60 core with a maximum of 6 polymethylmethacrylate (PMMA) chains. The difference between these derivatives is the weight distribution of C60. Nanosecond pulse radiolysis and laser flash photolysis studies, UV/VIS spectroscopic and fluorescence measurements have been performed to investigate the photophysical properties of 1%C60PMMA and 10%C60PMMA. The absorption spectra of the C60PMMA co-polymers exhibit a band at 210 to 220nm for PMMA and at 330nm for C60 independent of the solvent polarity showing that they have a small dipole moment in the electronic ground state. The triplet-triplet (T-T) absorption spectra of 10%C60PMMA in toluene and chloroform peak at the same wavelength and are broader than those of C60, indicating that they are addition spectra of 10%C60PMMA and neat C60. Physical addition of PMMA increases the solubility of C60 in chloroform, but does not change the T-T absorption spectrum, unless PMMA is chemically bound to C60. Gaussian band analysis of the T-T absorption spectra of 10%C60PMMA results in an additional band for pure 10%C60PMMA at (626.8±15.7)nm in toluene and (652.4±1.9)nm in chloroform. The triplet state lifetime of 10%C60PMMA is smaller than that of C60 at 79μs. The quantum yields of singlet oxygen production (Φ_Δ) decrease with the C60 content in the co-polymer. The values for 1%C60PMMA and 10%C60PMMA in polar chloroform are 4% and 26% respectively. The intersystem crossing from S₁ to T₁ as well as the triplet state lifetime decrease with increasing number and length of PMMA chains connected to C60. 1%C60PMMA also shows no T-T absorption suggesting a relative high photochemical stability for 1%C60PMMA.     

TRIPLET STATE PROPERTIES OF C60PMMA CO-POLYMERS IN ORGANIC SOLUTION AND PMMA FILM

Two star-like C60-polymethylmethacrylate (C60PMMA) copolymers, which are soluble in a wide range of organic solvents, have been synthesized by free-radical polymerization. The polymers can be described by the formula 1%C60PMMA and 10%C60PMMA. They consist of a C60 core with a maximum of 6 polymethylmethacrylate (PMMA) chains. The difference between these derivatives is the weight distribution of C60. Nanosecond pulse radiolysis and laser flash photolysis studies, UV/VIS spectroscopic and fluorescence measurements have been performed to investigate the photophysical properties of 1%C60PMMA and 10%C60PMMA. The absorption spectra of the C60PMMA co-polymers exhibit a band at 210 to 220nm for PMMA and at 330nm for C60 independent of the solvent polarity showing that they have a small dipole moment in the electronic ground state. The triplet-triplet (T-T) absorption spectra of 10%C60PMMA in toluene and chloroform peak at the same wavelength and are broader than those of C60, indicating that they are addition spectra of 10%C60PMMA and neat C60. Physical addition of PMMA increases the solubility of C60 in chloroform, but does not change the T-T absorption spectrum, unless PMMA is chemically bound to C60. Gaussian band analysis of the T-T absorption spectra of 10%C60PMMA results in an additional band for pure 10%C60PMMA at (626.8±15.7)nm in toluene and (652.4±1.9)nm in chloroform. The triplet state lifetime of 10%C60PMMA is smaller than that of C60 at 79μs. The quantum yields of singlet oxygen production (Φ_Δ) decrease with the C60 content in the co-polymer. The values for 1%C60PMMA and 10%C60PMMA in polar chloroform are 4% and 26% respectively. The intersystem crossing from S₁ to T₁ as well as the triplet state lifetime decrease with increasing number and length of PMMA chains connected to C60. 1%C60PMMA also shows no T-T absorption suggesting a relative high photochemical stability for 1%C60PMMA.     

Spectral properties of 1H-pyrazolo[3,4-b]quinoline substituted with N,N-diethylamine moiety

Photophysical properties of 6-N,N-diethyl-3-methyl-1-phenyl-1H-pyrazol[3,4-b]quinoline (DEPQ), a potential material for electroluminescent applications, were investigated. The absorption and fluorescence spectra and fluorescence lifetimes were recorded in a great number of solvents with different polarity. The red shifts in absorption and fluorescence maxima with the solvent's polarity were observed. Different trends in values of quantum yield for non-polar and polar solvents suggest two different deactivation ways of the excited state, depending on solvent polarity. DEPQ in non-polar solvents emits from locally excited states while deactivation DEPQ in polar solvents indicates charge transfer (CT) fluorescence. Several electro-optical parameters were also calculated.     

Laser Photolysis Study on Mechanism and Efficiency of Electron Transfer Between Fullerenes (C60 and C70) and Tetraselenafulvalenes

Efficient electron-transfer reactions from three kind of tetraselenafulvalenes (TSeF's) to photoexcited triplet state of C₆₀ or C₇₀ in polar solvents have been confirmed by transient absorption spectroscopy observing the decay of ³C₆₀*/³C₇₀* and rise of C₆₀^-•/C₇₀^-•. Growth of single crystal seems to be stimulated by laser irradiation of the solution containing C₆₀ and bis(ethylenedithio)tetraselena-fulvalene (BEDT-TSeF), in which C₆₀^-• was effectively formed.     

Ion-induced manipulation of photochemical pathways in crown ether compounds based on fluorinated oligophenylenevinylenes: the border between ultrafast photoswitches and photoproduced nanomaterials

The photochemical and photophysical properties of the crown ethers trans,trans-1,4-bis[2-(3',4'-benzo 15-crown 5)ethenyl]-2,3,5,6-tetrafluorobenzene (1) and trans,trans-1,4-bis[2-(3',4'-benzo 18-crown 6) ethenyl]-2,3,5,6-tetrafluorobenzene (2) were investigated in the absence and presence of groups I and II metal ions. The photophysical methods used include steady state flurescence, uv spectroscopy, and ultrafast transient absorption spectroscopy. Both compounds showed solvatochromic behavior, due to intramolecular charge transfer state formation, and efficient fluorescence in polar solvents. Photophysical behavior was dependent on the metal ion. The addition of metal ions that completely fit into the crown ether cavity resulted in significant blue shifts in the fluorescence emission spectra (chemosensing properties). Partially fitting ions changed the fluorescence spectra slightly. Transient absorption measurements revealed fast and slow decay components with time constants of 10-20 and 500-600 ps for all fitting ions, respectively. The latter is assigned to a trans-cis photoisomerization process, which decreased in efficiency in the presence of partially fitting ions, i.e., increasing ion size. Steady state irradiation showed clear evidence of a change in the absorption spectra. Trans-cis photoisomerization and [2 + 2] photocycloaddition were found to compete with fluorescence. The ions Li+, Na+, and Ca2+, which fit into the cavity, direct the photoisomerization. Larger ions (K+, Rb+, Sr2+ and Ba2+) that partially fit the cavity cause photocycloaddition. Quantum yields of the photoreaction are between 0.1 and 0.3. Analysis of the photo-product obtained for the 1-Sr2+ system revealed a compound with a molecular weight of nanosize dimension, which was equivalent to seven mass units of 1. The higher molecular weight product was formed due to alternately stacked supramolecular assemblies.     

Synthesis, characterization, photophysical properties of a novel organic photoswitchable dyad in its pristine and hybrid nanocomposite forms

In the present paper the method of synthesis and characterization of a novel organic dyad, 3-(1-Methoxy-3,4-dihydro-naphthalyn-2-yl-)-1-p-chlorophenyl propenone, have been reported. In this paper our main thrust is to fabricate new hybrid nanocomposites by combining the organic dyad with different noble metals, semiconductor nanoparticle and noble metal-semiconductor core/shell nanocomposites. In this organic dyad, donor part is 1-Methoxy-3, 4-dihydro-naphthalen-2-carboxaldehyde with the acceptor p-chloroacetophenone. We have carried out steady state and time-resolved spectroscopic measurements on the dyad and its hybrid nanocomposite systems. Some quantum chemical calculations have also been done using Gaussian 03 software to support the experimental findings by theoretical point of view. Both from the theoretical predictions and NMR studies it reveals that in the ground state only extended (E-type or trans-type) conformation of the dyad exists whereas on photoexcitation these elongated conformers are converted into folded forms (Z- or cis-type) of the dyad, showing its photoswitchable character. Time resolved fluorescence spectroscopic (fluorescence lifetime by TCSPC method) measurements demonstrate that in chloroform medium all the organic-inorganic hybrid nanocomposites, studied in the present investigation, possess larger amount of extended conformers relative to folded ones, even in the excited singlet state. This indicates the possibility of slower energy destructive charge recombination rates relative to the rate processes associate with charge-separation within the dyad. It was found that in CHCl3 medium, the computed charge separation rate was found to be approximately 10(8) s(-1) for the dyad alone and other hybrid nanocomposite systems. The rate is found to be faster than the energy wasting charge recombination rate approximately 10(2)-10(1) s(-1), as observed from the transient absorption measurements for the corresponding hybrid systems. It indicates the conformational geometry has a great effect on the charge-separation and recombination rate processes. The suitability for the construction of efficient light energy conversion devices especially with Ag-Dyad nanocomposite of all the systems studied here is hinted from the observed long ion-pair lifetime.     

Upconversion and reduced 4F(3/2) upper-state lifetime in intensely pumped Nd:YLF

Nonexponential decay of the 4F(3/2) upper laser state in Nd:YLF was observed with time-resolved fluorescence spectroscopy and small-signal gain probes in low-doped (1.16-at. %) samples when intensely pumped to high population inversions. A rapid initial decay is observed after Q-switched laser pumping, followed by a longer nonexponential decay that is clearly identified as a phase of migration-assisted energy-transfer upconversion (ETU) in the hopping regime. During this phase, a rate-equation treatment is valid and the macroscopic ETU coefficient, alpha2 = (0.98 +/- 0.03) x 10(-16) cm3/s, is directly evaluated from the decay kinetics. The ETU and the migration microparameters are also estimated to be C(da)* approximately 200 x 10(-40) cm6/s and C(dd) approximately 1000 x 10(-40) cm6/s, respectively, and are compared with theoretical values found in the literature. On the basis of these values, rate-equation treatments of intensely pumped Nd:YLF are not strictly valid.     

Laser Photolysis Study on Mechanism and Efficiency of Electron Transfer Between Fullerenes (C60 and C70) and Tetraselenafulvalenes

Abstract

Efficient electron-transfer reactions from three kind of tetraselenafulvalenes (TSeF's) to photoexcited triplet state of C₆₀ or C₇₀ in polar solvents have been confirmed by transient absorption spectroscopy observing the decay of ³C₆₀*/³C₇₀* and rise of C₆₀ ^??/C₇₀ ^??. Growth of single crystal seems to be stimulated by laser irradiation of the solution containing C₆₀ and bis(ethylenedithio)tetraselena-fulvalene (BEDT-TSeF), in which C₆₀ ^?? was effectively formed.     

Aggregation of Endometallofullerene Y@C82 in Polar Solvents

Having studied the optical absorption, fluorescence spectra and dynamic light scattering (DLS) of solutions of Y-EMF in polar solvents, we demonstrated for the first time that the endohedral metallofullerenes (EMF) forms nanoparticles, the mean size of which ranges up to 100 nm.     

Photoelectric Properties of Soluble ZnPc-Epoxy Derivative Doped with C60

A kind of soluble phthalocyanine derivative （ZnPc-epoxy derivative） was synthesized, and the influence of C60 on the photoelectric properties of the derivative was studied. The results of ultraviolet-visible （UV-Vis） spectra show that the absorption of the complex is larger than that of the ZnPc-epoxy derivative at B belt. But compared with the derivative, the absorption of the complex decreased at Q belt. The fluorescence spectra show that C60 takes role as annihilation in ZnPc-epoxy derivative. Photo-current tests show that the ZnPc-epoxy derivative-C60 film exhibits increasing photoconductive property.     

Enhanced performance of SubPC/C60 solar cells by annealing and modifying surface morphology

The performance effect of organic solar cells with subphthalocyanine (SubPC)/fullerene (C60) bilayer was investigated with thermal treatment while changing the vacuum deposition rate of SubPC. The thermal annealing at 100 degrees C increases the optical absorption intensity of SubPC film at the spectral range of 550-630 nm. The X-ray diffraction (XRD) patterns indicates that the thermally annealed film formed the much-ordered morphology, as compared to the non-annealed film. Consequently, thermally treated solar cell exhibited almost 10% higher power conversion efficiency (PCE) compared to the non-annealed device. The fill factor (FF) and PCE of the devices were increased as the deposition rate of SubPC was increased up to 5 A/s and then saturated at higher deposition rates (> 5 A/s). The surface roughness of SubPC films, measured with an atomic force microscope, increased from 1.1 to 5 nm as the deposition rate increased from 1 to 7 A/s. These results imply that rough surface increases the interfacial area between SubPC and C60 and thereby improves the separation of photogenerated electron and hole pairs at the SubPC/C60 interface.     

Synthesis and properties of a new [60] fullerene-donor system containing dicyanovinyl groups

C₆₀ covalently connected with dicyanovinyl functionalized tris[4-(2-thienyl)phenyl]amine [C₆₀-TTPA(DCV)] (compound 1) has been successfully prepared and it was found to exhibit excellent solubility in common organic solvents with a broad visible-light harvest. The theoretical calculation of its molecular geometry and electronic structure indicates that the TTPA(DCV) moiety and C₆₀ part are acting as donor and acceptor respectively; By comparing with the UV-visible absorption spectra of amine 2, the slight red shift of compound 1 could explain the existence of a small portion of charge transport between the two parts; and the fluorescence spectra of compound 1 show that the intramolecular photo-induced electron transfer from the TTPA(DCV) to C₆₀ is the main pathway for the emission quenching.     

Oxidation of Fullerenes by Ozone

Like typical alkenes, fullerenes can be oxidized by ozone. Epoxidation reaction takes place on C₆₀, and C_6oOn (n = 1-5) are formed. Mass spectrometry and chromatography identified the stable existence of two isomers for the dioxides and three for the trioxides in the product mixtures. At lower temperatures, fragmentation occurs and results in the formation of the polar products. C₇₀ and carbon nanotubes also react with ozone but at a much slower rate.     

Synthesis and properties of novel photosensitive poly(arylene ether sulfone) containing chalcone moiety in the main chain

A new series of photosensitive poly(arylene ether sulfone)s containing chalcone moiety in the main chain were synthesized from 4,4′-dihydroxychalcone (4DHC), 4,4′-difluorodiphenylsulfone (DFDPS) and bisphenol A (BPA). This series of polymers were characterized by ¹H NMR, FT-IR, UV spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The polymers were stable up to 400 °C, which indicates that the polymers possess good thermal properties. The polymers were found to be soluble in polar solvents and chlorinated solvents. However, the polymers were insoluble in hydrocarbons and in hydroxyl group-containing solvents. After the irradiation of UV light, the thin polymer film was crosslinked to give an insoluble film in the absence of a photoinitiator or sensitizers. The rate of photocrosslinking was also examined and discussed.     

Ozone reaction with carbon nanostructures. 1: Reaction between solid C60 and C70 fullerenes and ozone

The exposure of powdered crystals of C60 and C70 fullerenes to ozone with an O3/O2 ratio of 9.7% w/w causes their immediate oxidation. The FT-IR spectroscopy shows the formation of CO2 and the accelerated disappearance of ozone. The infrared spectra of crystalline C60 and C70 powders that were exposed to ozone show absorption bands indicating that oxidation was accompanied by formation of alpha,beta-unsaturated carboxylic groups, aldehyde and other ketonic moieties. The spontaneous decay of O3 in the O3/O2 atmosphere monitored by FT-IR spectroscopy was found to follow a pseudofirst order kinetic law with k0 = 6.9 x 10(-5) s(-1). When powdered C60 is present in the system a k(C60)(1) = 2.0 x 10(-4) s(-1); k(C70)(1) = 1.4 x 10(-4) s(-1) for C70. The accelerated disappearance of O3 is due to its adsorption/reaction with the powdered fullerenes. After about approximately 1000 s the reaction enters in a second step wherein the disappearance of O3 slows down significantly due to the lack of further reaction sites on the powdered fullerene surfaces and due to accumulated CO2 in the gas phase which exerts an inhibitory effect in the ozone spontaneous decomposition.     

Electrical conductivity and luminescence of 9-chloro-10,10′-bis-(dichloromethyleno)-(9′H)-10,10′-dihydro-9,9′-bianthryl (CDDB)

The absorption and fluorescenc of 9-chloro-10,10′-bis-(dichloromethyleno)-(9′H)-10,10′-dihydro-9,9′-bianthryl (CDDB) has been studied in polar and nonpolar solvents and also in microcrystal. In polar solvents CDDB emits from two molecular forms, the normal charge transfer form (locally excited, LE form) and the solvent-induced twisted intramolecular charge transfer (TICT) form. Electrically, CDDB possesses semiconducting property with conductivity approximately 10⁻⁹ S cm⁻¹ and this conductivity further increases to 10⁻⁷ S cm⁻¹ on photoexcitation. Intramolecular charge transfer by hopping mechanism is assumed to be the main process for controlling activation energy and electronic conduction.     

Fluorescence quenching by trapped charge carriers in N,N-dimethylaminobenzylidene 1,3-indandione films

Effects caused by the applied voltage on the steady state and time-resolved fluorescence of vacuum evaporated N,N-dimethylaminobenzylidene 1,3-indandione films sandwiched between gold and aluminium electrodes were investigated and discussed. Fluorescence enhancement and quenching as well as the fluorescence band narrowing depending on the applied voltage have been observed. Fluorescence decay and recovery take place on a time scale of tens of seconds after voltage is switched on and off. Similar fluorescence decay also takes place after switching on the excitation light. These fluorescence changes are attributed to the exciton quenching by trapped charge carriers.     

Fluorescence lifetimes and correlated photon statistics from single CdSe/oligo(phenylene vinylene) composite nanostructures

We present measurements of fluorescence intensity trajectories and associated excited-state decay times from individual CdSe/oligo(phenylene vinylene) (CdSe-OPV) quantum dot nanostructures using time-tagged, time-resolved (TTTR) photon counting techniques. We find that fluorescence decay times for the quantum dot emitter in these composite systems are at least an order of magnitude shorter than ZnS-capped CdSe quantum dot systems. We show that both the blinking suppression and associated lifetime/count rate behavior can be described by a modified version of the diffusive reaction coordinate model which couples slow fluctuations in quantum dot electron (1Se, 1Pe) energies to Auger-assisted hole trapping processes, hence modifying both blinking statistics and excited-state decay rates.     

Direct observation of molecular recognition mediated by triple hydrogen bonds at a water/oil interface: time-resolved total internal reflection fluorometry study

Molecular recognition mediated by hydrogen-bonding interactions at a water/CCl(4) interface was investigated directly by means of time-resolved total internal reflection (TIR) fluorescence spectroscopy. The TIR fluorescence decay profile of riboflavin (RF) in the absence of a guest in the CCl(4) phase was fitted satisfactorily by a single-exponential function. In the presence of N,N-dioctadecyl-[1,3,5]triazine-2,4,6-triamine (DTT) as a guest in the CCl(4) phase, on the other hand, the fluorescence decay profiles were best fitted by double-exponential functions with the relevant amplitude (A(i)) being varied with the concentration of DTT. Furthermore, the rotational reorientation time of RF at the interface determined by fluorescence dynamic anisotropy was 210 ps in the absence of DTT, while fast (160-220 ps) and slow (670-750 ps) rotational reorientation times were observed in the presence of DTT. This slow rotational reorientation time was shown to ascribe to that of the RF-DDT complex formed at the water/CCl(4) interface. These results indicate that molecular recognition mediated by complementary hydrogen bonding takes place effectively at the water/CCl(4) interface, which was observed directly by both fluorescence dynamics and fluorescence dynamic anisotropy measurements under the TIR conditions.     

On the behavior of indole-containing species sequestered within reverse micelles at sub-zero temperatures

We report on the effects of temperature (+30 to -100 degrees C) on the fluorescence from N-acetyl tryptophanamide (NATA) and human serum albumin (HSA) sequestered within Aerosol-OT (AOT) reversed micelles. NATA reports simultaneously from the polar and non-polar side of the reverse micelle interface. As the sample temperature decreases, the relative fraction of NATA molecules associated with the polar side increases. This redistribution process is characterized by DeltaH = -14.8 +/- 0.6 kJ/mol and DeltaS = -54 +/- 2 J/(K mol). The activation energy for thermal quenching (E(a,TQ)) associated with the polar side NATA molecules is 6.7 kJ/mol before the micelles have shed water and 1.0 kJ/mol after water shedding (below approximately -20 degrees C). The time-resolved fluorescence intensity decay for tryptophan-214 in HSA is triple exponential. We suggest that these lifetimes arise from three indole residue conformations in equilibrium. Cooling the sample causes a freezing-in of the least quenched conformer; the other conformers are frozen out. The E(a,TQ) value for the shortest lifetime component is 6 kJ/mol. The E(a,TQ) for the long and intermediate lifetime components are equivalent (approximately 1.5 kJ/mol).