Naphthalene Phosphorescence Research Articles

Phosphorescence Decay Kinetics in the Presence of Statistical Distribution of Molecules Over the Rates of Radiative and Nonradiative Deactivation of Triplet Excitations

Approximate formulas of the phosphorescence decay kinetics have been obtained for the statistical distribution of molecules over the rate constants of radiative and non-radiative deactivations of triplet excitations. It is shown that the characters of the phosphorescence decay differ for these two cases. The obtained difference in the kinetics has been used to establish a reason for the deviation from the exponential law and a faster decay of the sensitized phosphorescence of naphthalene and diphenyl in n-paraffin matrices (at T = 77 K) in the presence of heavy dibromo-diphenylene sulfide atoms in the donor.

Low-temperature sensibilization of naphthalene phosphorescence using ortho-bromobenzophenone

The standard approach involving the sensibilization of naphthalene phosphorescence is employed to study the mono-substituted ortho-bromobenzophenone (2-BrBP). A new feature of the approach is the use of octane as the passive neutral matrix. This matrix is chosen due to the absence of the triplet-excitation mobility in pure 2-BrBP crystal. The problem of common phosphorescence kinetics of 2-BrBP and naphthalene is solved in analytic form. Unlike in the classical problem involving unsubstituted benzophenone, the relevant phosphorescence measurements have been performed at low temperatures (as low as 1.6 K). A new approach is suggested to account for the large difference between the typical experimental pulse-delay time and the slow naphthalene phosphorescence. Relevant computations allow us to explain the nature of the two sets of phosphorescence lines of 2-BrBP.

Кинетика затухания фосфоресценции при наличии статистического распределения молекул по скоростям излучательной и безызлучательной дезактивации триплетных возбуждений

Approximate formulas of phosphorescence decay kinetics under the conditions of the statistical scatter of molecules over rate constants of radiative or non-radiative deactivation of triplet excitation have been obtained. It is shown that the phosphorescence decay function has different form for these two cases. The obtained difference in kinetics was used to establish the reason for the deviation from the exponential law and faster decay of the sensitized phosphorescence of naphthalene and diphenyl in n-paraffin matrices ( T = 77 K) in the presence of heavy atoms in the donor.

Spectroscopic Properties of Naphthalene on the Surface of Ice Grains Revisited: A Combined Experimental-Computational Approach.

An experimental-computational method is used to investigate the spectroscopic behavior of naphthalene on the surface of ice grains. UV-vis diffuse reflectance and fluorescence spectroscopies of naphthalene combined with DFT and ADC(2) calculations provide evidence for the occurrence of excited-state associates. The measured and calculated bathochromic shifts of the S0 → S1 electronic transitions related to naphthalene dimers or naphthalene-ice interactions do not exceed 3 nm. The bands observed in the emission spectrum of frozen naphthalene solutions are assigned to excited dimers of different mutual orientations, naphthalene phosphorescence, and fluorescence of anthracene present as a trace impurity and populated by the energy transfer from excited naphthalene. Photochemical reactivity in/on ice and snow is dependent on the absorption properties and speciation of the compounds present in these media. Hence, within this study, we exploit frozen solutions of naphthalene to demonstrate both the absence of considerable bathochromic shift and a strong tendency to aggregate.

Thermodynamic energies of donor and acceptor triplet states

Thermodynamic energies ( E T) of lowest triplet states (T 1) have been measured for 60 triplet energy donors and acceptors. Laser flash photolysis procedures were used to monitor the equilibration between the triplet–triplet absorptions of reference and unknown compounds in ethyl acetate at 295 K. These measurements provide triplet free energies that reflect both enthalpy and entropy differences between T 1 and the ground state (S 0). These thermodynamic energies are the basis of quantitative models for triplet energy transfer kinetics in solution. For comparison, T 1 energies were also measured via phosphorescence at 295 K for most of the donors and many of the acceptors of this study. The phosphorescence of naphthalene at 295 K served as a reference for relating the thermodynamic and phosphorescent triplet energies ( E P). For most rigid molecules the E T and E P values are nearly identical. However, for molecules with considerable rotational or conformational freedom, such as ketocoumarin and α-diketone donors and polyphenyl acceptors, E T values tend to be substantially greater than E P values. This difference partially reflects the tendency for reduced rotational freedom in T 1 relative to S 0, which leads to a reduction in entropy and a corresponding increase in free energy (from − TΔ S) in T 1. For nonrigid chromophores triplet energies obtained from low-temperature measurements tend to approximate E T values in some cases, because the energy increases associated with emission from unrelaxed triplets tend to parallel the positive contributions of decreased T 1 entropy to E T. Triplet–triplet absorption maxima and extinction coefficients are provided for all of the donors and acceptors. Intersystem crossing quantum yields, also measured by laser flash photolysis, are provided for the triplet energy donors.

The influence of temperature on the migration-accelerated quenching of phosphorescence of naphthalene in glassy toluene

The efficiency of migration-accelerated quenching of triplet excitations of naphthalene by oxygen molecules in an undegassed solution of glassy toluene is investigated as a function of temperature. The temperature dependence of the rate constant of the migration-accelerated quenching is established experimentally, and the activation energy of this process is determined. It is demonstrated that the enhancement of the migration-accelerated quenching with increasing temperature is caused by the reverse migration, i.e., by the increase in the probability of transfer of excitations in the process of their migration to higher energy levels of naphthalene within the limits of the statistical scatter.

The dependence of photoinduced energy transfer on the orientation of the acceptor with respect to the π-plane of the donor in naphthalene-linked crown ether–Tb3+ complexes

Abstract The photoinduced energy transfer (ET) from naphthalene (N) to Tb 3+ has been studied in the complexes of Tb 3+ ion with 2,3-naphtho-17-crown-5 ether(I), 2,3-naphtho-20-crown-6 ether(II), 1,8-naphtho-21-crown-6 ether(III) and 1,5-naphtho-22-crown-6 ether(IV), respectively, using nitrate (NO 3 − ) ion as the counter anion in EtOH glass at 77 K. The ligands are so designed that the Tb 3+ ion can be complexed with a predetermined orientation with respect to the naphthalene molecular plane. In systems I and II, the Tb 3+ ion is along the Z -axis; in system III, it is along the Y -axis and in IV, it is along the X -axis, where Z - and Y - are the molecular in-plane long and short axes of the naphthalene molecular plane respectively and X - is the out-of plane axis perpendicular to the naphthalene molecular plane. Present studies indicate that the efficiency of energy transfer (ET) and the quenching of naphthalene phosphorescence show a strong dependence on the orientation of the acceptor metal ion (Tb 3+ ) with respect to the π-plane of the donor naphthalene moiety. The ET studies suggest that an exchange mechanism involving the lowest (ππ * ) triplet state of N and the 5 D 4 state of Tb 3+ ion is predominantly operating. Our observation further indicates that for a given orientation in a complex the emission intensity of the various transitions ( 5 D 4 → 7 F J , J =2–6) for Tb 3+ , vis-a-vis ET efficiency varies considerably with Δ J values (=0, +1 and +2).

Influence of Temperature on the Concentration Quenching of Sensitized Phosphorescence of Organic Molecules in n-Paraffin Solutions

The sensitized phosphorescence of naphthalene and acenaphthene in frozen n-paraffin solutions (n-octane and n-decane) before and after their heating has been investigated. It has been established that heating of the frozen solution leads to an increase in the sensitized phosphorescence intensity. The influence of the solvent concentration on the above phenomenon has been analyzed. On the basis of the results obtained it has been concluded that the nonmonotone character of the temperature dependence of the sensitized phosphorescence intensity and its increase upon the sample heating are due to the removal of the concentration quenching in the process of solution annealing. It has been shown that in this case the intensity increases owing to the increase in the number of acceptor molecules participating in the radiation. The possible mechanisms of this phenomenon are discussed.

Site effects on the electronic relaxation of aromatic molecules in van der Waals solids

Fluorescence and phosphorescence of naphthalene and aniline molecules trapped in cryogenic matrices present site-dependent features. The isolation in solid argon has been especially investigated. Experimental results for naphthalene are summarized and related to the site geometries obtained from molecular dynamics calculations. In the case of aniline, site effects are mainly revealed through the phosphorescence spectra. In particular sites, the measurement of the inversion frequency can be directly extracted.

Influence of Annealing on the Quantum Yield of Sensitized Phosphorescence of Naphthalene in Frozen Solutions of n-Hexane

We revealed and investigated the increase in the quantum yield of sensitized phosphorescence of naphthalene in a frozen solution of n-hexane as a result of annealing of a specimen near the melting point of a solvent. We show that the reason for the rise in the quantum yield is the increase in the number of acceptor molecules that participate in radiation due to the removal of static quenching.

Fluorescence and Phosphorescence Properties of Naphthalene in Aqueous d-Glucose Solutions Containing 6-Deoxy-6-iodo-β-cyclodextrin at Room Temperature

Abstract In aqueous solutions, 6-deoxy-6-iodo-β-cyclodextrin (β-CDI) forms a 1 : 1 inclusion complex with naphthalene. The naphthalene fluorescence is quenched upon the formation of the inclusion complex with β-CDI. The room-temperature phosphorescence of naphthalene has been observed from aqueous naphthalene solutions containing both d-glucose and β-CDI. Although the room-temperature phosphorescence has also been observed from aqueous naphthalene solutions containing both d-glucose (5.0 g/5.0 mL) and β-cyclodextrin (1.0 × 10−2 mol dm−3), its intensity amounts to at most 9% of that containing d-glucose (5.0 g/5.0 mL) and β-CDI (1.0 × 10−3mol dm−3). In addition to the high viscosities of d-glucose solutions, the external heavy atom effects of β-CDI cause the appearance of the room-temperature phosphorescence. The room-temperature phosphorescence quantum yield of naphthalene in d-glucose (5.0 g/5.0 mL) solution containing β-CDI (1.0 × 10−3 mol dm−3) has been estimated to be 2.2 × 10−3, which is around 1.8% of the intrinsic phosphorescence quantum yield of naphthalene in ethanol at 77 K.

Photochemical probe of the conformation of naphthalene triplet excimer: light-induced changes in the phosphorescence of Agosta pinacol dimer in rigid hydrocarbon glasses

The initial monomeric phosphorescence of Agosta pinacol dimer of naphthalene in hydrocarbon glasses at 77 K changes to an excimer-like phosphorescence of the corresponding diketone dimer upon irradiation. The close spectral resemblance between the diketone emission and the room-temperature excimer phosphorescence of naphthalene and 1,n-di-{alpha}-naphthylalkanes (n = 1-4) in fluid solutions provides compelling evidence for the stability of the naphthalene triplet excimer and enables us to address the question of its likely conformation.

The location of organic guests within X-type faujasite zeolites via external heavy-atom induced phosphorescence

Heavy-atom induced phosphorescence of naphthalene and related aromatic guest molecules included in X-type faujasite zeolites (M +X −, M + = Li, + Na, + K +, Rb +, Cs +, Tl +)_has been studied and evidence has been obtained for direct interactions between the heavy-atom cations present within the zeolite supercage and the included organic guest. As expected for an external heavy-atom perturbed excited state, both singlet and triplet excited state lifetimes and emission efficiencies depend upon the identity and accessibility of the cation. The use of photophysical probes to monitor the guest's local environment and approaches to monitoring guest diffusion processes within zeolites via. phosphorescence are discussed.

Modification of photochemical reactivity by zeolites: Location of guests within faujasites by heavy-atom-induced phosphorescence

Heavy-atom-induced phosphorescence of naphthalene included in faujasites has been observed and evidence obtained for the existence of direct interaction between the heavy metal cations present within the zeolite supercage and the included aromatic guest. Naphthalene when included in faujasites exchanged with rubidium and cesium as cations exhibits intense phosphorescence and possesses short singlet and triplet lifetimes. When adsorbed in faujasites exchanged with lithium, sodium and potassium as cations, naphthalene gives intense fluorescence and weak phosphorescence with long singlet and triplet lifetimes.

Phosphorescence of naphthalene and related compounds in fluid media: excimer phosphorescence or phosphorescence from a biacetyl-like impurity?

Molecular excimer phosphorescence observed in fluid media for naphthalene and l, n-di-α-naphthylalkanes has recently been attributed to the sensitized phosphorescence of biacetyl-like impurities. While there is remarkable spectral similarity between the two emissions, experiments in this laboratory indicate that the assignment of the emission to the phosphorescence of excimers is correct.

Zur Konzentrationsabhängigkeit der Benzophenonsensibilisierten Naphthalin-Phosphoreszenz in einem Kohlenwasserstoff-Glas bei 77 K / On the Concentration Dependence of the Benzophenonesensitized Naphthalene Phosphorescence in a Hydrocarbon Glass at 77 K

The variation of intensity of the benzophenone-sensitized naphthalene phosphorescence with naphthalene concentration is different in a hydrocarbon or ethanol-ether glass, respectively. The naphthalene phosphorescence quenching observed in the hydrocarbon glass at higher naphthalene concentrations is assumed to result from the formation of non-phosphorescent naphthalene aggregates in benzophenone microcrystals.

Spin coherence in crystalline complexes. Naphthalene: 2(1,4-diiodotetrafluorobenzene)

The weak crystalline complex of naphthalene : 2(1,4-diiodotetrafluorobenzene), which exhibits naphthalene phosphorescence with a lifetime in milliseconds, is conveniently investigated by a combination of conventional and pulse techniques of optically detected magnetic resonance. The D + E and D − E resonances, investigated here, reveal no transferred hyperfine interaction, but increased D and E values because of the external spin-orbit coupling which is found to be anisotropic. Measurements are made of T 2, T 2*, and T 2ϱ for this complex. This coherence study finds T 2 to be similar in magnitude to what has been observed for mixed organic crystals. T 2*, when compared with T 2, confirms the earlier suggestion that the crystalline complex is highly ordered. T 2ϱ measurement suggests interaction with the nuclear spins of C 6I 2F 4.

Homofusion and heterofusion of triplet excitons in a ‘‘real’’ organic mixed crystal: Biphenyl host-naphthalene and pyrene guests system

The prompt and delayed emission spectra of a biphenyl host with naphthalene and pyrene both as guests mixed crystal have been studied. The fluorescence of naphthalene and pyrene and the excimer fluorescence of pyrene have been observed. The delayed emissions are observed from pyrene and naphthalene as delayed fluorescence of pyrene, phosphorescence of naphthalene, and pyrene. The investigations of excitation spectra of these emissions have shown to be very useful to understand the mechanism of delayed fluorescence generation. The heterogeneous defect-naphthalene and homogeneous naphthalene–naphthalene triplet–triplet annihilation are responsible for the production of delayed fluorescence of pyrene. The kinetic analyses from the decays and buildups have been made. The delayed luminescence decays at various temperatures have found to be nonexponential. However, in the long time region they are nearly exponential. Even in the long time region, the pyrene delayed fluorescence decays and buildups are nonexponential in the temperature range above 130 K. It has been established from the various Arrhenius plots that in this mixed crystal the temperature dependence of the phosphorescence lifetime is controlled by the thermal processes The kinetic scheme described satisfactorily explains the experimental results.

Luminescence of naphthalene in an argon matrix. Geometry changes and multiplet structures

The stabilization energies of naphthalene in the ground and excited states for various substitutional sites in an argon matrix have been calculated. The major multiplet splittings in the naphthalene phosphorescence depend on the size of the sites The geometry change between the ground and excited states of naphthalene was found to be the important factor which modifies the energies of the multiplet components in S 1 → S o and T 1 → S o transitions.

Active nitrogen induced chemiluminescences of aromatic guests dispersed in benzene polycrystalline hosts at 77 K

Chemiluminescence is emitted during the reaction of active nitrogen with pure or doped benzene polycrystals at 77 K. With a pure benzene (h6 or d6) polycrystal, the active nitrogen induced blue chemiluminescence is the benzonitrile (respectively h5 or d5) phosphorescence. With doped benzene, the chemiluminescence is the guest phosphorescence. With naphthalene as a guest, the intensity of the naphthalene phosphorescence is proportional to the square of the nitrogen atom concentration. All these chemiluminescences can be accounted for by the following two-step mechanism: (i) a three body recombination of the nitrogen atom on the cold hydrocarbon surface, which results in the formation of the nitrogen molecule in a triplet state, probably the A 3Σ + u electronic state; (ii) a subsequent triplet-triplet energy transfer to a guest molecule.