Phosphorescence lifetime data

Phosphorescence Lifetime Data The lifetime, , of the triplet state is related to the rate coefficients of radiative (kp ) and nonradiative (kp ) decay by the relation... 

Solid-surface room-temperature phosphorescence (RTF) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTF are only partly understood. To clarify some of the interactions required for strong RTF, organic compounds adsorbed on several surfaces are being studied. Fluorescence quantum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodiiun acetate-sodium chloride mixtures and on a-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet formation efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTF from organic compounds adsorbed on sodium acetate-sodium chloride and a-cyclodextrin-sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid-surface luminescence analysis. 

Chen and coworkers have developed two new phosphorescent blue emitters, which have two identical 2-(2,4-difluorophenyl)pyridine ligands and are derivatives of the Firpic compound, iridium(III) bis(4,6-difluorophenylpyridinato)-3-(trifluoromethyl)-5-(pyridin-2-yl)-1, 2,4-triazolate (Firtaz) and iridium(III) bis(4,6-difluorophenylpyridinato)-5-(pyridin-2-yl)-l//-tetrazolate (FirN4) (Scheme 3.90) [314]. Both these two blue emitters show a 10-nm blue-shift of the emission compared with Firpic. Unfortunately, the efficiency of such blue emitters is inferior to those of Firpic and Fir6. There is no lifetime data reported for such devices. 

Explanation of Table ET = triplet energy in kcal/mole from O—O phosphorescence band. Je = intersystem crossing yield from sensitized olefin isomerization method. tp - phosphorescence lifetime in a rigid glass at —196° (sec). Repetition of the data compiled by Arnold63 has in general been avoided. 

In order to tune the phosphorescence color of [Ir(ppy)3 ], Watts et al. synthesized several substituted ppy-based neutral Ir complexes [96-98]. Table 1 shows the list of complexes that show strong phosphorescence from a3 MLCT excited state. The phosphorescence lifetime of these complexes is in the range of 2-3 ps in nitrogen-saturated acetonitrile at room temperature [97]. The photophysical and electrochemical data (see Table 1) demonstrate the influence of ligands bearing electron-withdrawing and the electron-donating... 

It is in the nature of steady-state kinetic calculations that ratios of rate constants are obtained for example, the expressions for the intensity in Eq. 25, or the parameters extracted from the Stern-Volmer treatment, involve ratios of rate constants to the Einstein A factor for emission. Individual rate constants can often be determined from a comparison of kinetic data obtained under stationary conditions with those obtained under nonstationary conditions. For the present purposes, the nonstationary experiment often involves determination of fluorescence or phosphorescence lifetimes (tf, rp). If a process follows first-order kinetics described by a rate constant k, the mean lifetime, r (the time taken for the reactant concentration to fall to 1/e of its initial value), is given by... 

Some emission lifetime data are presented in Table 14. Particularly of note are the lifetimes in frozen inert gas solutions, reflecting the enhancement of T -> Sq transition with increasing atomic number of the solvent an effect also noted by other authors. The important results of Haaland and Nieman (222) show a marked solvent effect on phosphorescence lifetimes. Per-fluorocarbons are the least perturbing solvents on phosphorescence, an effect consistent with results obtained in liquid solution (72,91). 

An early prediction by El-Sayed [588b] that the halogen atoms should have a negligible influence upon the t —>n phosphorescent lifetimes of these compoimds (relative to COHj) has, in more recent work [337], been refuted. A marked dependence in the predicted lifetimes is revealed in the data in Table 17.14, and this has been attributed [337] to mixing between the halogen and the oxygen atomic orbitals. 

Fig. 7 Phosphorescence intensity as a function of time for a PSBF thin film after pulsed optical excitation and for two temperatures as indicated. The solid lines are exponential fits to the late part of the data sets yielding an estimate for the phosphorescence lifetime...

There remain, however, some questions about the real meaning of these data and the correctness of the evaluation procedure. First of all, the data presented in Table II suggest efficient trapping of the triplet excitons by intrinsic, not exclmeric traps of unknown structure. This is corroborated by reports of all authors who performed quenching and phosphoresence decay measurements that the phosphorescence lifetime is not shortened by adding the quencher. This is a clear proof that it is primarily not the free triplet which is observed in phosphorescence but rather a trapped species, since otherwise Equation (5) should apply. 

The DFT/MRCI approach reproduces excitation energies and other spin-independent properties of experimentally known electronic states of pyranthione and dithio-succinimide excellently. As far as phosphorescence lifetimes of dithiosuccinimide are concerned, calculations have not yet been completed. For the T] state of pyranthione we find that phosphorescence and nonradiative decay via intersystem-crossing to the So state are concurrent processes occurring at approximately equal rates in the range of 104 s-1, in good accord with experimental data. The Ti - So radiative transition borrows its intensity from two sources ... 

Separate measurements of the phosphorescence lifetimes t and reaction quantum yields d>A and <1>X as functions of pressure allowed Weber et al. [77,78] to determine the activation volumes of ammine and halide labilization and of nonradiative deactivation from the 3ELEES of Rh(NH3)5X2 + (X — Cl or Br) for several solvent systems. These AEf values of the key individual ES rate constants are summarized in Table 3. Immediately apparent from these data are the large positive AEX values for ammine photosubstitution and the large negative AEx values for halide photosubstitution in all solvents. 

Hydrostatic pressure up to 300 MPa had no effect on the absorption and emission spectra (2 = 511 nm) of Pt2(POP)4 in ambient temperature aqueous solution. There was a modest decrease in the phosphorescence lifetime from t = 8.8 ps at 0.1 MPa to 7.6 ps at 300 MPa and a corresponding 13 % decrease in the phosphorescence quantum yield (C>°- = 0.55, 0, = 0.48). Since the intersystem crossing to the LEES was estimated to be unity in both cases, these data demonstrate that pressure has little effect on k, (Eq. 6.9) [22], consistent with the relative insensitivity of the refractive index of water to pressure [23]. 

Simple benzenoid systems have not been as extensively reported as in previous years. West and Miller have studied the fluorescence from dilute solutions of benzene in cyclohexane induced by protons and alpha particles. A model for interpretation of the data involving intratrack quenching by products of the irradiation is not fully adequate. Gibson and Rest have measured quantum yields of fluorescence and phosphorescence in various frozen gas matrices and from these yields and lifetime data have calculated the photophysical rate constants for and at 12 K, which are given in Tables 1, 2, and 3. The... 

The rate of energy transfer from the benzotriazole chromophore to the hydroperoxy groups is controlled by the lifetime of the excited state, as long as it is higher than 1.5 ev approximately. Details of decay mechanisms of the excited states will be published later. Here we will note that the principal feature of the deactivation mechanism involves an intramolecular proton transfer process which may occur before vibrational equilibration of the vertical excited state is completed. The fluorescence has a blue (X-max = 405 nm) and a red (X.max = 585 nm) component, with the blue component only being present at room temperature in dilute solution, and at low temperatures in polar matrices. The red component is present in emission at room temperature from polycrystalline powders and at low temperatures in hydrocarbon matrices. It may be postulated that the blue component arises from a vibra-tionally excited 0-protonated species, while the red component arises from a proton transferred zwitterionic excited state. Phosphorescence is detected from the model compound (II) in polar matrices at 77K. Table II gives some excited state lifetime data on the copolymer and model systems. 

Phosphorescence is not usually observed in fluid solutions near room temperature. One reason for the absence of phosphorescence is the long phosphorescence lifetimes and the presence of dissolved oxygen and other quencb. For instance, recent data for tryptophan revealed a phosphorescence lifetime of 1.2 ms at 20 Suppose that the... 

While various techniques, such as stopped flow, have been used to follow substrate kinetics, many kinetic measurements have involved the photophysical properties of solubilized probes. Because of the luminescent properties of their excited states, the aromatic hydrocarbons provide opportunities for monitoring movement of such probes across the micelle boundary. For example, long-lived phosphorescence of aromatic hydrocarbons has been monitored in micellar solutions containing ionic quenchers that themselves are repelled by the surfactant head groups. Since quenching must take place in the aqueous phase, phosphorescence lifetimes may be interpreted to provide rate constants for exit of the probe from the micelle. Some typical values obtained by this technique are given in Table III. Fluorescence data have also been used to obtain such information. 

A comparison of simulated decays for lattices with 100 and 500 sites under steady state initial conditions with experimental decay profiles of P2VN is shown in Fig. 11. It is evident that the quality features of iDp(f) are consistent with experimental data in the sense that (1) there is a strong L dependence, (2) decays are nonexponential, and (3) first order processes do not dominate the kinetics. Only when first order kinetics dominate is loF t) exponential with a decay time (Tdf) one-half the phosphorescence lifetime (Tp). Unfortunately a direct comparison of lifetime data is difficult since polymer phosphorescence usually arises from shallow traps, e.g. in PIVN Tdf = 0 msec whereas Tp = 1.9 sec (1). 

Quantum yields for fluorescence and phosphorescence from several 1-substituted naphthalenes as well as their observed phosphorescence lifetimes, T, are shown in Table II. The data for halogenated naphthalenes clearly demonstrate the heavy atom effect on intersystem crossing efficiency. Such data strongly suggest that substituent effects on photo-... 

Data on duorescence, phosphorescence, excited-state lifetimes, transient absorption spectra, and dye lasers are tabulated in Ref. 16. The main nonduorescent process in cyanine dyes is the radiationless deactivation Sj — Sg. Maximum singlet-triplet interconversion ( 52 ) methanol for carbocyanines is about 3% (maxLgrp > 0.03), and the sum [Lpj + st] I than 0.10. 

The lifetime of triplet acetone at 25° in the vapor phase, as measured from the rate of decay of phosphorescence, is 0.0002 sec,318 so that the rate of decay is 5 x 103 sec-1. This figure represents the sum of the rates of all decay processes. Since the data at 40° 308 indicate that decomposition and internal conversion of triplet acetone occur approximately 40 times as fast as emission, the radiative lifetime must be on the order of 0.01 sec. Measurements of the rate of phosphorescence decay from solid acetone at 77°K, where all activated fragmentation and most radiationless decay normally disappear, have actually yielded values approximately one-tenth as large as that obtained in the gas phase at room temperature.319 The most recent measurements of the lifetime of triplet acetone at 77°K in frozen glasses does indeed yield an estimate of 0.01 sec for the radiative lifetime of triplet acetone.318... 

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