Phosphorescence Behavior Research Articles

Fluorescence and phosphorescence behavior of TPD doped and TPD neat films

Photoluminescence spectra of N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)-benzidine (TPD) are studied in a temperature range from 10 K to room temperature using a neat TPD film, and 5 wt.% TPD doped films with polystyrene (PS), 4,4′-N,N′-dicarbazole-biphenyl (CBP), and polycarbonate (PC) as hosts. The photo-excitation occurred in the singlet absorption region of TPD. The blue fluorescence and green phosphorescence quantum yields, ϕ F and ϕ P, of TPD are determined from their quantum distributions, E F( λ) and E P( λ). The yields are found to be ϕ F = 0.39 and ϕ P = 0.012 for neat films at room temperature, while ϕ F = 0.78 and ϕ P = 0.026 are measured for a TPD doped PS film. The lower luminescence quantum yield in the neat film is caused by self-quenching.

Long lasting phosphorescence behavior of Pr 3+-doped CaTiO 3-based oxides

Ceramic samples with nominal compositions of (Ca 1− x Sr x ) 0.9Pr 0.001Zn 0.099TiO 3 ( x = 0, 0.05, 0.10, 0.15, 0.20) were prepared by a mixed oxide method. When examined by the X-ray diffraction (XRD) analysis, the samples revealed a main CaTiO 3 phase with small amounts of a second Zn 2TiO 4 phase. All of the ceramic samples emitted red phosphorescent light at about 613 nm when excited by light of a wide wavelength range (200 nm to about 500 nm). The partial substitution of Sr for Ca, up to approximately 10 at%, significantly enhanced the phosphorescence intensity and lifetime. The long lasting phosphorescence could be observed with naked eyes in dark room for more than 10 min in both air and water at room temperature.

Synthesis, Crystal Structures, and Photophysical Properties of Lanthanide Complexes Containing Pyrrole‐Derivatized Carboxylate Ligands

AbstractTwo pyrrole‐deriviatized carboxylic acids [L1 = 1‐methylpyrrole‐2‐carboxylate] and [L2 = N‐methyl‐3‐indoleglyoxylate] were used as ligands to prepare six lanthanide coordination compounds [(L1)3Ln]n (Ln = Eu, 1; Gd, 2; Tb, 3) and [(L2)nLn(NO3)(MeOH)2]n (Ln = Eu, 4; Gd, 5; Tb, 6). These complexes have been synthesized and structurally characterized by single‐crystal X‐ray diffraction. The phosphorescence behavior of the ligands in the Gd3+ complexes show that modification of the ligands can tune the triplet energy levels of the ligands so that they match the 5D0 energy level of Eu3+ and the 5D4 energy level of Tb3+; thus, the energy transfer efficiency from antenna to Eu3+ and Tb3+ is improved, and the Eu3+ and Tb3+ emission intensity is enhanced. This concept can be applied towards improving the luminescent properties of Ln3+ complexes by the modification of coordinating ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Red-edge and inhomogeneous broadening effects of the electronic spectra of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate

Fluorescence excitation, fluorescence and phosphorescence spectra of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate (EAADCy) were recorded in tetrahydrofuran (THF) at room (293 K) and low-temperature (77 K). In our previous publication [M. Józefowicz, M. Aleksiejew, J.R. Heldt, A. Bajorek, J. Pączkowski, J. Heldt, Chem. Phys. 338 (2007) 53], it was shown that at room temperature, the fluorescence spectrum of EAADCy in THF consists of two bands. The short-wavelength emission corresponds to the molecular conformation in which the donor and acceptor moieties are orthogonal to each other, on the other hand, the long-wavelength emission is assumed to originate from a singlet excited state of molecule in which two moieties are coplanar. In present communication, the fluorescence and phosphorescence behavior of the EAADCy has been studied as a function of the excitation wavelength. The luminescence spectra of the molecule under study in THF glass at 77 K show considerable dependence on the excitation wavelengths. Such dependence of the wavelength of maximum intensity of luminescence (fluorescence and phosphorescence) spectrum and the full width at half maximum of phosphorescence spectrum ( Δ ν ˜ 1 / 2 ph ) on the excitation wavelength is a characteristic demonstration of the red-edge effect. These results along our previous studies [M. Józefowicz, M. Aleksiejew, J.R. Heldt, A. Bajorek, J. Pączkowski, J. Heldt, Chem. Phys. 338 (2007) 53] indicate that EAADCy forms a typically spectrally inhomogeneous system.

Exploring 9‐arylcarbazole moiety as the building block for the synthesis of photoluminescent group 10–12 heavy metal diynes and polyynes with high‐energy triplet states

AbstractA new series of organic‐soluble and thermally stable group 10 platinum(II) polyyne polymers functionalized with 9‐arylcarbazole moiety trans‐[Pt(PBu3)2CCRCC]n (R = 9‐arylcarbazole‐3,6‐diyl; aryl = phenyl, p‐methylphenyl, p‐fluorophenyl) were prepared in good yields by Hagihara's dehydrohalogenative polymerization of trans‐[PtCl2(PBu3)2] with HCCRCCH under ambient conditions. The regiochemical structures of the polymers were characterized by multinuclear NMR spectroscopy. We discuss the optical spectroscopy of these polymetallaynes and compare the results with their bimetallic molecular model complexes trans‐[Pt(Ph)(PEt3)2CCRCCPt(Ph)(PEt3)2] as well as its group 11 gold(I) and group 12 mercury(II) congeners [(PPh3)AuCCRCCAu(PPh3)] and [MeHgCCRCCHgMe]. The structural properties of several model complexes were studied by X‐ray crystallography. The influence of the heavy metal atom and the 9‐aryl substituent of carbazole on the phosphorescence behavior and the spatial distribution of the lowest singlet (S1) and triplet (T1) excitons in these metalated alkynyl systems are comprehensively elucidated. The present work indicates that the efficiency of organic triplet emissions harnessed through the heavy‐atom effect of group 10–12 transition metals in the main chain generally follows the order Pt > Au > Hg but the optical properties of the materials are relatively insensitive to the nature of the 9‐aryl group on the carbazolyl ring. All of these metallaynyl‐carbazole materials with high‐energy T1 states of 2.68 eV or higher show high phosphorescence efficiencies at low temperatures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5588–5607, 2006

Phosphorescent-sensitized triplet-triplet annihilation in tris(8-hydroxyquinoline) aluminum

We characterized the photoluminescence properties of an amorphous tris(8-hydroxyquinoline) aluminum (Alq3) thin film heavily doped with fac tris(2-phenylpyridine) iridium [Ir(ppy)3] at 8 K. Not only green fluorescence but also red phosphorescence from Alq3 was clearly observed, where Ir(ppy)3 plays the important role as a phosphorescent sensitizer for Alq3. The triplet energy of Alq3 was estimated to be 2.03 eV from the highest energy peak of the phosphorescence spectrum. The fluorescence intensity was proportional to the excitation power. On the other hand, the deviation from the linearity of the phosphorescence intensity to the excitation power was observed above ∼0.01W∕cm2. This nonlinear phosphorescence behavior is well explained by the simple triplet-triplet annihilation theory. It was demonstrated that the efficient triplet energy transfer from Ir(ppy)3 enables us to observe triplet-triplet annihilation in Alq3.

Fluorescence and room temperature phosphorescence of 6-bromo-2-naphthol in β-cyclodextrin solution and its selective molecular recognition for cyclohexane

The room temperature phosphorescence (RTP) and fluorescence behavior of 6-bromo-2-naphthol (BN) in water and β-cyclodextrin (β-CD) aerated aqueous solution was investigated. The study of fluorescence behavior at different pH values indicated that three kinds of species of BN (protonated, uncharged and anionic species) formed 1:1 inclusion complexes with β-CD, and RTP and fluorescence emission depended on the pH of the solution. The inclusion complex constants were 430±25 l mol −1 (pH 1.80), 840±25 l mol −1 (pH 5.80), 1850±75 l mol −1 (pH 11.50), respectively. Experimental results elucidated that RTP of the BN/β-CD/cyclohexane solution came from the protonated and uncharged species of BN, but not from the anionic species, though the inclusion constant of the anionic species of BN with β-CD was larger than that of the other two species of BN Selective molecular recognition of BN/β-CD as an RTP sensor for 28 small organic molecules was studied, it was shown that BN/β-CD could be develop as a new RTP sensor with high selectivity molecular recognition ability for cyclohexane.

Luminescence behaviour of rare earth doped alkaline earth aluminates prepared by the halide route

The fluorescence and long persistent phosphorescence behaviour of alkaline earth aluminates of the type MAl 2O 4 (M=Ba, Sr or Ca) doped with rare earth ions has been extensively studied in the literature. These phosphors are usually prepared using their oxides as the starting materials and employing temperatures in excess of 1000 °C. In this paper, we report the possibility of synthesizing the alkaline earth aluminates starting from the alkaline earth halides. The operating temperatures are around 900 °C, yet single-phase materials with high luminescence output have been realized.

Photochemistry and Photophysics of Cr(III) Macrocyclic Complexes

The phosphorescence and photochemical behavior of the macrocyclic complexes (1,4,7,10,13,16-hexaazacyclooctadecane)chromium(III) (Cr([18]-aneN(6))(3+); 1) and (4,4',4''-ethylidynetris(3-azabutan-1-amine)) chromium(III) (Cr(sen)(3+); 2) have been compared to each other and to the complex Cr(en)(3)(3+). For both macrocyclic complexes, phosphorescence from room temperature aqueous solutions is too weak to be observed, contrasting with Cr(en)(3)(3+), though both had somewhat longer 77 K lifetimes than Cr(en)(3)(3+). Phosphorescence lifetimes for these macrocyclics decreased with increasing temperature much faster than for Cr(en)(3)(3+) and a conventional extrapolation based on a fit of reciprocal lifetimes (corrected for the low-temperature contribution) to the Arrhenius equation gave estimated room temperature phosphorescence lifetimes of a few nanoseconds, consistent with the failure to observe room temperature emission. Fitting of the nonlinearity of the data seen in these plots suggested that two high-temperature processes were occurring with estimated activation parameters (E in kJ mol(-1) and A in s(-1)) for Cr([18]-aneN(6))(3+): E(1) = 40, A(1) = 1 x 10(16); E(2) = 24, A(2) = 1 x 10(14): Cr(sen)(3+); E(1) = 45, A(1) = 2 x 10(15); E(2) = 29, A(2) = 7 x 10(11). Cr([18]-aneN(6))(3+) was photochemically inert on irradiation. On irradiation into the lowest quartet ligand field absorption band, Cr(sen)(3+) photolyzes with a quantum yield of 0.098 +/- 0.001 at room temperature. Laser flash photolysis with conductivity detection showed that this photoreaction occurred faster than protonation of the liberated amine ligand at all practical proton concentrations. The quantum yield for irradiation directly into the doublet absorption band of Cr(sen)(3+) was 0.077 +/- 0.003. Photoaquation of Delta-Cr(sen)(3+) led to loss of optical activity and product analysis by capillary electrophoresis showed that both racemic and Delta-Cr(sen)(3+) photoaquate to a single main product, trans-Cr(sen-NH)(H(2)O)(4+). The product stereochemistry is shown to be consistent with predictions based on the angular overlap model for Cr(III) photochemistry, recognizing the additional constraints imposed by the ligand. The abnormally short room temperature solution lifetime of the doublet state is a result of a radiation-less process that competes with other processes depleting the doublet state. However, this doublet-state deactivation process does not lead to photoaquation but competes with BISC and photoaquation via the quartet state, resulting in an unprecedented reduction in photoaquation quantum yield on direct irradiation into the doublet state.

Study on micelle stabilized room temperature phosphorescence behaviour of pyrene by laser induced time resolved technique

Room temperature phosphorescence (RTP) decay generally follows a first order exponential law P t= P 0e −t/ τ in the micelle system. The pre-exponential factor (or transient phosphorescence intensity) P 0 and phosphorescence lifetime τ can be used to qualitatively indicate the probability of intersystem crossing ( S 1- T 1) (ISC) and radiationless deactivation ( T 1- S 1) of the phosphors in micelle system. These two factors indirectly reflect the inducing effect of heavy atoms on the probability of ISC of phosphor and the preservation of micelle to phosphor. In this paper, P 0 and τ of pyrene were measured by a laser induced time resolved technique. The effects of the concentration of heavy atom species, surfactant SDS, as well as pH, on the above parameters were studied.

Room temperature phosphorescence optosensing for gadolinium

An optosensing method for gadolinium based on the room-temperature phosphorescence behavior in aqueous solution induced by the transient adsorption of the complex formed by 1,4-bis (1′-phenyl-3′-methyl-5′-pyrazolone-4′-)butanedione (1,4) with Gd (III) on the chelating resin Chelex 100 (packed in a flow cell) is proposed. The proposed optosensing is satisfactory for the determination of the gadolinium ion in the range 8 × 10–7−5 × 10−5M with a correlation coefficient of 0.995. The relative standard deviation was 2.0% for determination of 5× 10−6M gadolinium ion (n = 10). The response mechanism of the optosensing and the interferences of other lanthanide ions were also investigated. The method has been used to determine gadolinium ion in synthetic sample.

Self-Sensitized Photolysis of N-(1-Naphthoyl)-N-phenyl-O-(benzoyl-substituted benzoyl)hydroxylamines

Abstract The mechanism of intramolecular triplet–triplet (T–T) energy transfer and subsequent reaction in N,O-diacylhydroxylamines was investigated using the model compounds N-(1-naphthoyl)-N-phenyl-O-(benzoyl-substituted benzoyl)hydroxylamines (NPB) with self-sensitization abilities. An examination of the UV absorption and phosphorescence behavior as well as of energy-minimized conformations of these relatively flexible model compounds established that T–T energy transfer from the benzophenone chromophore to the naphthoyl chromophore occurs in a nearly unit efficiency exhibiting only phosphorescence derived from the latter chromophore in both methanol–ethanol (1 : 1 v/v) and 2-chlorobutane at 77 K and is more likely to proceed by a “through-space” mechanism than by a “through-bond” mechanism. The self-sensitized photolysis of NPB with 366 nm light in methanol at room temperature was found to give the fragmentation products, N-phenyl-1-naphthalenecarboxamide (PNA), benzophenone (BP), and benzoyl-substituted benzoic acids (BBA), whereas no BBA was detected in the photolysis in 1,2-dichloroethane and acetonitrile. The finding that the reaction of NPB is efficiently quenched by trans-stilbene according to the Stern–Volmer equation in both methanol and 1,2-dichloroethane indicates that all the products come from the first excited triplet state of the naphthoyl chromophore. On the other hand, the enhanced hydrogen bonding ability of the medium resulted in an increase in the quantum yield for the formation of BBA (ΦBBA) accompanied by a decrease in ΦBA holding the magnitude of ΦBBA + ΦBA nearly constant. But neither ΦPNA nor the quantum yield for the disappearance of NPB was subject to such a hydrogen-bonding effect. This intriguing result was explained in terms of a mechanism in which the N–O bond cleavage in triplet NPB gives a vibrationally excited triplet radical pair whose relaxation is very slow compared to decarboxylation of the caged benzoyl-substituted benzoyloxyl radical in 1,2-dichloroethane. Solvation of this vibrationally hot radical pair through hydrogen bonding substantially promotes its relaxation eventually affording BBA.

Room-Temperature Phosphorescence Studies of Epoxy Resin Cured by an Aromatic Diamine

The applicability of phosphorescence spectroscopy is investigated for cure characterization of epoxy resin cured by an aromatic diamine. By using a time-resolved method to separate fluorescence from phosphorescence, the room-temperature phosphorescence (RTP) behavior of a commonly used curing agent, bis(p-aminophenyl) sulfone (DDS), is studied. RTP emission spectra with a maximum around 500 nm are obtained. Both RTP emission and excitation intensity increase very sharply with cure time due to the increase in the rigidity of the cured epoxy. They can be correlated to the extent of cure of epoxy, when properly calibrated. The triplet lifetime (τ T ) obtained by monitoring RTP emission decay at 500 nm increases from zero to about 40 ms following cure at 160 °C for 180 min. Correlation curves of τ T with the extent of cure and the glass transition temperature are also obtained. Thus, τ T provides a way to estimate the cure extent without the need to calibrate the RTP emission intensity. While these RTP characteristics cannot be used for in-situ cure monitoring, they can be used as a sensitive cure estimate technique in lightly cured prepregs for composites or after a cure cycle.

Luminescence studies of polymer matrices: 1. Phosphorescence of benzophenone dispersed in poly(methyl methacrylate)

The photophysical behaviour of benzophenone (BP) in poly(methyl methacrylate) (PMMA) has been studied as a function of temperature. Time-resolved phosphorescence data reveal that at no temperature between 77 and 420K can the decay behaviour of the triplet state of BP in PMMA be described adequately by a single exponential function. This contrasts with the phosphorescence behaviour of BP in low temperature, low molecular mass, glassy matrices and that reported previously for BP dissolved in PMMA at temperatures below the onset of the β relaxation of the polymer. The complexity of the phosphorescence decay kinetics of the BP/PMMA system increases at temperatures greater than that of the β transition of the polymer host. This has been rationalized in terms of the onset of enhanced energy transfer interactions between the BP triplet excited state and the PMMA solvent, as proposed earlier. However, the function derived previously on the basis of diffusion-controlled quenching of the triplet state of BP by the PMMA host, did not model, adequately, the time-resolved phosphorescence data obtained in the current study. In this respect, the form of the quenching influence exerted by the polymer matrix upon the photophysical behaviour of the BP solute remains to be explained. Notwithstanding the absence of a complete rationalization of the influence of the PMMA host upon the photophysical behaviour of the BP guest, it has been shown that both the intensity of phosphorescence emitted by the BP and its mean decay time provide means whereby transitions within the polymer matrix can be detected. In this respect the data are not equivalent: the lifetime data ‘sense’ the presence of the α′ transition (at ∼345 K) of the PMMA. This transition is not apparent in the temperature dependence of intensity data which, in common with the lifetime data, are sensitive to the onset of both the γ and β transitions of the polymer. The relevance of the data in respect of establishing phosphor/polymer combinations for application as phosphorescent coding media is discussed.

Determination of europium with solid-surface room-temperature phosphorescence optosensing

Immobilization of the complex formed by thenoyltrifluoroacetone (TAA) with EuIII on the chelating resin Chelex 100 packed in a flow cell can induce the phosphor to have room-temperature phosphorescence behaviour in aqueous solution. Based on this phenomenon, a new room-temperature phosphorescence optosensing method in an aqueous flow system has been established to determine europium ions at 2.0 × 10–9–1.0 × 10–7 mol dm–3. Using a response time of 60 s, the detection limit was 1.0 × 10–9 mol dm–3 Eu3+. Using 0.5 mol dm–3 HCl solution, the sensing layer, coordinated by the Eu-TTA complex, can be regenerated quickly and completely. The response mechanism of the optosensing was also studied in detail. The present method has been applied to the determination of europium ions in three synthetic samples.

Excited state protonation of phenylpyridines

Abstract A study of the excited state behavior of 2-, 3- and 4-phenylpyridines indicates that their fluorescence in water is due to excited state protonation, with a relative efficiency of 0.17:0.62:1.0 respectively, which decreases with the pKa value of the phenylpyridinium ion. No fluorescence is observed for the neutral molecule in organic solvents nor in basic medium. 2-Phenylpyridine, which has the smallest torsional energy and ground state pKa value, undergoes a sixfold increase in fluorescence as the phenylpyridinium ion in acidic medium relative to that in water. Results are consistent with pKa*=9.0±0.5 for the phenylpyridinium ion of the three molecules. Fluorescence and phosphorescence data support the view that these molecules become increasingly planar in the triplet state: their fluorescence behavior is similar to that of nitrogen heterocyclic (substituted pyridine), but their phosphorescence behavior is similar to that of substituted benzene, biphenyl. CNDO/S semi-empirical calculations for 3-phenylpyridine satisfactorily predict an inversion of n,π and π,π states upon protonation.

THE MECHANISM OF PHOTOSENSITIZATION IN PHOTODYNAMIC THERAPY: PHOSPHORESCENCE BEHAVIOR OF PORPHYRIN DERIVATIVES IN SALINE SOLUTION CONTAINING HUMAN SERUM ALBUMIN

The phosphorescence properties, especially the dynamic behavior of metal free and metal complexed porphyrins, have been studied in phosphate buffered saline (PBS) containing 0-3% human serum albumin (HSA). 6,7-Bisaspartyl-2,4-bis (1-hexyloxyethyl)-deutero- porphyrin (DP) and its gallium(III), zinc(II), and indium(III) complexes are used as photosensitizers. Upon irradiation, a solution of porphyrins containing more than 0.1% HSA shows phosphorescence with a lifetime longer than 1 ms. With an increase in irradiation time, phosphorescence intensities and lifetimes of porphyrins increase, depending upon their concentrations and triplet lifetimes, and approach saturated values close to those under deaerated conditions. The experimental results may be interpreted in terms of hypoxia induced by photosensitization in a local environment surrounding the sensitizer. The hypoxia is caused by the reaction between proteins and singlet molecular oxygen generated by photosensitization of porphyrins. Phosphorescence behavior of sensitizers in HSA PBS solution gives significant information for classifying photosensitizers as to their efficacy for photodynamic therapy.

Thermoluminescence and phosphorescence with a continuous distribution of activation energies

Some theoretical features of phosphorescence decay curves and thermoluminescence (TL) glow curves have been investigated with some select depth distributions. In early studies a t -1 (inverse-time dependence) behaviour for isothermal decay was found assuming a uniform distribution of activation energies ranging from 0 to infinity. Additional studies explored the TL features resulting for Gaussian distributions of activation energies. For broad enough distributions the t -1 behavior for isothermal luminescent decay again followed. It thus appears that broad distributions will quite generally result in t -1 phosphorescence behavior. We have addressed the more mathematically tractable situation of a continuous uniform distribution within a finite range of energies, from E 1 to E 2. The circumstances under which the t -1 law can be accepted as a valid approximation, as well as the deviations from this law, are discussed using numerical calculations. Also, the expected features of TL glow curves under similar conditions for continuous trap distributions are discussed. In particular the effective values of the activation energies one can calculate using different known methods for its evaluation are studied. The relationship of these derived effective values to the distributions actually used in the calculations is discussed. The near- t -1 time dependence of phosphorescence resulting from a model of electrons and holes recombining through tunneling is contrasted to that for the standard first-order kinetics model with a broad excitation energy distribution also giving a near- t -1 dependence. The distinction appears in the curvature of yield curve with time during the onset of phosphorescence.

Tautomerism of 1-hydroxy-2-pyridone and 1-hydroxypyridine-2-thione in the excited triplet state

Both the title compounds show dual phosphorescence depending on the excitation wavelength and the nature of the solvents at 77K. 1-Hydroxy-2-pyridone (HP) gives dual emission only in a nonpolar matrix, whereas dual emission of 1-hydroxypyridine-2-thione (HPT) was observed even in polar and hydrogen-bonding solvents as well as in a nonpolar matrix. From a comparison with the phosphorescence behaviour of 2-ethoxypyridine 1-oxide and 2-ethylthiopyridine 1-oxide, which have structures corresponding to the enol and enethiol isomers of the tautomeric HP and HPT, respectively, it is concluded that tautomerization taking place in the excited triplet state is responsible for the dual phosphorescence of the title compounds. Further supporting evidence for this conclusion is obtained from the measurements of the phosphorescence lifetimes and phosphorescence excitation spectra. HPT is much more subject to tautomerization to its enethiol isomer form than HP. This is explained on the basis of the fact that the thiocarbonyl group is more polar and more polarizable than the carbonyl group.

Enhanced phosphorescence in intramolecular exciplex systems

Phosphorescence behavior of the series of compounds, (carbazole)-(CH 2) n -(terephthalic acid methyl ester), which show intramolecular exciplex emission, has been studied in a rigid medium at 77 K. The phosphorescence of the carbazole moiety is enhanced by electron transfer fluorescence quenching of the carbazole residue in accord with the degree of quenching.