Ethanol Glass Research Articles

Spectroscopic and redox properties of Rh IIIRu II and Ru IIRu II complexes derived from 2,2 ′-bipyridine, pyrazole-3,5-bis(benzimidazole) and 1,2,4-triazole-3,5-dicarboxylic acid as bridging ligands

The heterovalent heterodinuclear complex [(bpy) 2Ru II(H 2pzbzim)Rh III(bpy) 2](ClO 4) 4 · 3H 2O ( 1) and the isovalent homodinuclear complex [(bpy) 2Ru II(trzdc)Ru II(bpy) 2](ClO 4) · 5H 2O ( 2), where H 3pzbzim=pyrazole-3,5-bis(benzimidazole), H 3trzdc=1,2,4-triazole-3,5-dicarboxylic acid and bpy=2,2 ′-bipyridine, have been synthesized and spectroscopically characterized. Complex 1 undergoes one electron oxidation at 1.20 V (versus Ag/AgCl) in acetonitrile, while for complex 2, two stepwise oxidations occur at 0.63 and 0.81 V with the comproportionation constant K c, for the equilibrium Ru IIRu II + Ru IIIRu III ⇌ 2Ru IIRu III, equal to 1.11 × 10 3 at 298 K. The acid dissociation constants of the benzimidazole moieties of complex 1 have been determined in acetonitrile–water (3:2) by spectrophotometric titrations. Both complexes 1 and 2 exhibit luminescence spectra and the quantum yields obtained for methanol–ethanol (1:4) glass (at 77 K) are ϕ=3.1×10 −2 for 1 and 3.5 × 10 −2 for 2.

Photoluminescence properties of four-coordinate gold(I)-phosphine complexes of the types [Au(diphos)2]PF6 and [Au2(tetraphos)2](PF6)2.

Numerous reports describe the photoluminescence of two- and three-coordinate gold(I)-phosphine complexes, but emission in their analogous four-coordinate complexes is almost unknown. This work examines the luminescence of tetrahedral gold(I) complexes of the types [Au(diphos)(2)]PF(6) (diphos = 1,2-bis(diphenylphosphino)ethane, 1) and [Au(2)(tetraphos)(2)](PF(6))(2) (tetraphos = (R,R)-(+/-)/(R,S)-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane, (R,R)-(+/-)/(R,S)-2). Although nonemitting in solution, these complexes luminesce with an intense yellow color (lambda(max) 580-620 nm) at 293 K in the solid state or when immobilized as molecular dispersions within solid matrixes. The excited-state lifetimes of the emissions (tau 4.1-9.4 micros) are markedly dependent on the inter- and intramolecular phenyl-phenyl pairing interactions present. At 77 K in an ethanol glass, two transitions are observed: a minor emission at lambda(max) 415-450 nm and a major emission at lambda(max) 520-595 nm. For [Au(1)(2)]PF(6), lifetimes of tau 251.0 +/- 20.5 micros were determined for the former transition and tau 14.9 +/- 4.6 micros for the latter. Density functional theory (DFT) calculations and comparative studies indicate that the former of these emissions involves triplet LMCT pi(Ph) --> Au(d)-P(p) transitions associated with individual P-phenyl groups. The latter emissions, which are the only ones observed at 293 K, are assigned to LMCT pi(Ph-Ph) --> Au(d)-P(p) transitions associated with excited P-phenyl dimers. Other tetrahedral gold(I)-phosphine complexes containing paired P-Ph substituents display similar emissions. The corresponding phosphine ligands, whether free, protonated, or bound to Ag(I), do not exhibit comparable emissions. Far from being rare, luminescence in four-coordinate Au(I)-phosphine complexes appears to be general when stacked P-phenyl groups are present.

Synthesis, electrochemistry, spectroscopy and photophysical properties of a series of meso-phenylpyridylporphyrins with one to four pyridyl rings coordinated to [Ru(bipy)2Cl]+ groups

A series of meso-phenylpyridylporphyrins and their respective supermolecular species obtained by the coordination of [ Ru ( bipy )2 Cl ]+ groups to the pyridyl substituents was synthesized and characterized. Their spectroscopic and electrochemical behavior were similar to that observed for the meso-tetra(4-pyridyl)porphyrin derivative, but the redox potential of the Ru (III/II) redox pair was about 70 mV more negative. The porphyrin centered fluorescence quantum yield exhibited a linear decrease as a function of the number of pyridyl substituents on the porphyrin ring. Efficient intramolecular energy transfer processes from the 3 MLCT state of the ruthenium complexes to the porphyrin center were observed at 77K in ethanol glass.

A Model of Inhomogeneous Broadening and Pressure Induced Hole Shifts in the Optical Spectra of Organic Chromophores in Glasses

Zero phonon holes were burned in the S1rS0 absorption bands of organic compounds in ethanol glass at 6 K. The application of He gas pressure (P) leads to the shift of holes with a frequency coefficient d O/dP. The linear dependence of dO/dP on hole position (O) within the inhomogeneous band is of considerable interest, since it can provide the S1rS0 energies of nonsolvated chromophores and the (local) compressibility of the surrounding matrix. However, the extrapolated frequencies O0(P) at which pressure shift should vanish deviate from the actual 0-0 energies of free solutes in a vacuum. The slope (a) of the plot of dO/dP vs O varies between 1.5 10 -5 and 6.2 10 -5 bar -1 for different dyes, and therefore cannot be directly associated with the isothermal compressibility of the matrix. To account for these facts, a model was developed based on the assumption that the solvent shift is a superposition of repulsive, dispersive, electrostatic, and other possible interactions. Each interaction has a specific intermolecular distance ( r) dependence (e.g. r -6 for dispersive and r -12 for repulsive interactions) and is assigned a Gaussian frequency distribution function. It follows from the model that the observed slope a depends on, in addition to the volume compressibility of the matrix, the widths of the constituent Gaussians and the respective power coefficients of r. Both the measured bandwidth and the slope a are also sensitive to the type of correlation between different solvent shift mechanisms. In rhodamine dyes a dipole moment change between the ground and the excited state is responsible for a strong broadening and a shallow slope a. The conformational flexibility of a dicarbocyanine dye HIDCI has similar consequences. The mechanisms leading to a matrix polarity dependent hypsochromism in open chain cyanine dyes, free base tetrapyrroles, and s-tetrazine correspond to a distance dependence of r -6 and are deemed to be of multipolar nature. The magnitude of the hypsochromic solvent shift owing to repulsive forces is probably small, although their contribution to the slope a and the inhomogeneous bandwidth may be relatively large.

Acute inhibitory effect of alcohol on fibrinolysis.

In contrast to a reduced risk of coronary heart disease (CHD) with light to moderate alcohol consumption, heavy alcohol intake and binge drinking are associated with increased cardiovascular mortality. Alcohol has an acute and profound effect on fibrinolysis that may be relevant to the pathogenesis of CHD. The short-term effects of a low (two glasses, 250 mL, 20 g ethanol) and a high (six glasses, 750 mL, 60 g ethanol) intake of red wine were studied in male volunteers and compared to the intake of mineral water. To find a threshold for inhibition of fibrinolysis and to study a binge effect, a second experiment was performed comparing the intake of four (500 mL, 40 g ethanol) and eight (1000 mL, 80 g ethanol) glasses of red wine with mineral water. Plasminogen activator inhibitor-1 (PAI-1), tissue-type plasminogen activator (t-PA), plasmin-antiplasmin (PAP) complexes and clot lysis time were measured. In contrast to the circadian rhythm with an enhanced fibrinolysis in the evening that was found in the mineral water group, an intake above four glasses of wine inhibited fibrinolysis significantly. After the intake of two glasses no significant disturbance of the circadian rhythm was observed. Five hours after the consumption of six glasses of wine, a dramatic increase occurred of PAI-1 antigen (77 +/- 42 microg L-1 vs. - 5 +/- 10 microg L-1 in the mineral water controls; P < 0.001) and PAI-1 activity (27 +/- 15 U mL-1 vs. - 2 +/- 3 U mL-1 in mineral water controls; P < 0.001). Despite a rise in t-PA antigen, t-PA activity dropped (- 0.5 +/- 0.2 U mL-1 vs. - 0.1 +/- 0.2 in controls; P < 0.001) as did PAP complexes (- 103 +/- 55 microg L-1 vs. - 26 +/- 57 microg L-1 in controls; P < 0.01). After the consumption of eight glasses of wine, the clot lysis assay indicated continued inhibition of fibrinolysis the following morning. Drinking a large amount of alcohol in the evening results in an acute inhibition of fibrinolysis, persisting the following morning. This may predispose to accelerated atherosclerosis and set the stage for thrombotic coronary events, explaining the higher cardiovascular mortality risk in binge drinkers.

Ethanol Glass Dynamics: Logarithmic Line Broadening and Optically Induced Dephasing

The TLS model has been quite successful in the description of the anomalous low-temperature properties of glasses. It also predicts that these properties are time dependent, which has indeed been shown to be the case. 5,6 This effect has been attributed to the existence of a broad distribution of rates in the glass at which the tunneling processes occur. The optical properties of a chromophore dissolved in a glass are dependent on dynamical processes in the direct vicinity of the chromophore. Therefore, these optical properties will also be time dependent. A number of optical techniques have been employed to explore the dynamics of the chromophores on different time scales and thus probe the distribution of rates of tunneling processes. Most notably hole burning, photon echo, and singlemolecule spectroscopy have been employed to probe glass dynamics on a range of time scales spanning up to 18 orders of magnitude. This allows for the investigation of the particular nature of the TLS’s. These so-called optical line-narrowing experiments provide a pivotal test for the adequacy of the TLS model in describing glass dynamics. However, the interpretation of chromophore dynamics in amorphous solids is frustrated by qualitative and quantitative discrepancies between the results rendered by different techniques. Thus, although separate results are in qualitative agreement with the TLS model, the quantitative discrepancies between results rendered by different techniques indicated the need for further refinement of the TLS model. Notwithstanding these problems, the concept of low-energy excitations being accountable for the properties of amorphous solids is well accepted. At the same time it is clear that the interpretation of experimental results has to be done with great caution. Indeed the optical dynamical properties can be influenced by various inconspicuous parameters in the experiments. Examples are the cooling history of the sample, the particular subset of chromophores selected in an experiment, 7,8 and also, as was recently pointed out, 9,10 laser fluence. In this paper we revisit the effect of laser fluence on the observed optical dynamics and confirm earlier conclusions regarding its importance in optical dephasing experiments. We further show that optically induced spectral diffusion, an effect unrelated to laser fluence, is of significant importance to the interpretation of all optical line-narrowing techniques. This finding points at the inadequacy of the currently used weakcoupling chromophore-TLS model for a complete description of glass dynamics.

Isotope effect in reactions of CH3 and CD3 radicals in glassy solutions of CH3OH and C2H5OH in methanol-d3 at 77 K

The decay kinetics of methyl radical isotopomers has been studied at 77 K in glassy mixtures xR′HOH+(1−x)CD3OH, where R′HOH is either CH3OH or C2H5OH. In matrices with a small fraction of H component (x⩽0.02) the CD3 radicals decay twice as quickly as the CH3 radicals. As the H content in the mixture increases, the difference in the decay rates of the methyl radical isotopomers first gradually decreases to zero, and for x>0.2 CH3 decays faster than CD3 . A comparison is made with previous results for ethanol glass.

Photophysics of dimethylamino-substituted polymethine dye in polymeric media

The photophysical mechanism responsible for the large Stokes shift in dimethylamino-substituted polymethine dye (DMA-PD) has been studied by steady-state and time-resolved fluorescence spectroscopy. Experiments in low-temperature ethanol glass and in polymer polyurethane acrylate (PUA) in glassy and elastic states allow us to conclude that the emission occurs mainly from two excited states with lifetimes of 2–3 and 6–7 ns, respectively. The excited-state dynamics includes fast subnanosecond rotation of the DMA group around the carbon–dimethylamino bond of the dye molecule and stabilization of this form due to environmental rearrangement. The large Stokes shift remains for this dye in solid media. This process is dynamic even in polymeric media, where it occurs in the subnanosecond–nanosecond time scale. The major spectral shift can be described as an intramolecular excited-state reaction affecting either or both emissive species. We suggest a model in which the twisting of the small dimethylamino group modulates the effective length of the polymethine chromophore, producing the spectral shift. In addition, time-resolved fluorescence anisotropy decays show a slow rotational motion (about 40 ns) of the dye inside the polymer microcavities. These interesting features of the spectral behavior of the PUA matrix doped by DMA-PD may find various applications.

Electron paramagnetic resonance study on the triplet species produced from 2-nitrobiphenyl derivatives by UV irradiation

The photochemical behavior of 2-nitrobiphenyl (NBP) derivatives was extensively studied by the electron paramagnetic resonance (EPR) technique. The molecules studied mainly are methyl-, fluoro-, carboxy-, ethoxycarbonyl-, hydroxymethyl- and methoxymethyl-NBPs and ethers possessing two NBP groups. Most of the triplet species produced were stable in ethanol glasses at 77 K after UV irradiation. The zero-field splittings (ZFSs) of these species are fairly close to those of the stable triplet species produced from NBP. Two sets of EPR signals were observed for the NBP derivatives with a relatively large substituent at the 2′-position of the biphenyl skeleton. The ZFS | D| parameters of the stable triplet species giving strong EPR signals are a little larger than those giving weak signals. On the other hand, the ZFS | E| parameters of the stable triplet species giving strong EPR signals are slightly smaller than those giving weak signals. For 3′-substituted NBPs, the EPR signals of methoxycarbonyl- and carboxy-NBPs were observed only during UV irradiation. These signals are attributed to the lowest excited triplet states of the precursors. For 4′-substituted NBPs studied except the methyl- and fluoro-NBPs, no stable triplet signals could be observed at 77 K in ethanol glasses after UV irradiation. From the precursors possessing two NBP groups, no signals of the quintet state could be observed, although the stable triplet signals were detected. The present study has no contradictions to the previous estimation that the stable triplet species is formed through the abstraction of a hydrogen atom from the 2′-position of the biphenyl skeleton by one of the oxygen atoms of the nitro group. Such a hydrogen-transfer process is inferred to occur for the nonplanar derivatives where the above hydrogen atom can approach one of the oxygen atoms rather easily.

Luminescence properties of salts of the [Pt(4′Ph-terpy)Cl]+ chromophore: crystal structure of the red form of [Pt(4′Ph-terpy)Cl]BF4 (4′Ph-terpy = 4′-phenyl-2,2′∶6′,2″-terpyridine)

The complexes [Pt(4′Ph-terpy)Cl]A (4′Ph-terpy = 4′-phenyl-2,2′:6′,2″-terpyridine; A = SbF6, CF3SO3, or BF4) have been prepared by reaction of [Pt(PhCN)2Cl2] with the appropriate silver salt followed by addition of the 4′-phenyl-2,2′:6′,2″-terpyridyl ligand. The hexafluoroantimonate salt is yellow but, depending on the method of crystallisation, the triflate and tetrafluoroborate salts can be isolated in two forms, one yellow and the other red, the red forms only being stable at low temperatures. The crystal structure of red [Pt(4′Ph-terpy)Cl]BF4·CH3CN has been determined at 153 K by X-ray diffraction methods. The [Pt(4′Ph-terpy)Cl]+ cations are stacked face-to-face in an extended chain of stepped tetramers, with essentially equal Pt· · ·Pt distances of ca. 3.3 A within a tetramer and a Pt· · ·Pt distance of 4.680 A between successive tetramers. The spectroscopic and solid state emission properties of the salts have been recorded. The yellow salts are characterised by emission from an isolated chromophore in an excited state that reflects the admixture of 3MLCT (MLCT = metal-to-ligand charge-transfer) and 3IL (IL = intraligand) character. This assignment is supported by the presence of vibrational structure in the emission band as well as by a lifetime of ca. 1 µs for the emission. The red [Pt(4′Ph-terpy)Cl]BF4·CH3CN salt, in contrast, exhibits emission from a 3MMLCT (MMLCT = metal–metal–ligand charge-transfer) state as a consequence of the strong platinum dz2–dz2 orbital interactions. This assignment is consistent with the observation of a narrow, structureless and asymmetric band as well as an emission lifetime of ca. 0.1 µs. There is a systematic and substantial red-shift of 75 nm in the emission maximum on cooling the red salt from 280 to 80 K, an unexpected result since bathochromic shifts of this kind are normally associated with stacked structures with a uniform Pt· · ·Pt separation. The above assignments are further supported by measurements of the emission spectra of solutions of varying concentrations of the tetrafluoroborate salt in a dimethylformamide–methanol–ethanol glass at 77 K and by lifetime measurements. Interestingly, pressure in the form of grinding the salts modifies their luminescent properties. Thus, crushed samples of the yellow hexafluoroantimonate salt exhibit multiple emission at 80 K from both the 3MMLCT and the mixed parentage 3MLCT/3IL excited states, whereas at room temperature the emission spectrum is dominated by a broad band centred at 644 nm associated entirely with the 3MMLCT emission.

Dual phosphorescence from 2,3-naphtho-17-crown-5 ether in ethanol glass at 77 K

2,3-naphtho-17-crown-5 ether (I) shows an unusual dual phosphorescence in EtOH and MeOH glass at 77 K as a function of concentration of I. Compound I exhibits, however, single phosphorescence in 2-methyl tetrahydrofuran glass at 77 K in the same concentration range. Crown ethers containing six oxygen atoms do not show any dual phosphorescence at 77 K in EtOH glass in the same concentration range. The lifetime of the T 1 states of the ethers in various matrices and the phosphorescence and the lifetimes of the complexes of I with Tl +, Cs + and K + are reported. The blue-shifted emission of I in alcohol glass at 77 K at higher concentration is attributed to emission from a dimer of I having a ground state stabilished compared to that of the monomer of I.

Excited State Properties of Myochrysin and Auranofin

Myochrysin (sodium aurothiomalate hydrate) and auranofin [2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranosato-S)(triethylphospine)gold(I)] are luminescent in the solid state and in ethanol glasses at 77 K (myochrysin: λmax = 600 nm; auranofin: 618 nm). Aqueous myochrysin and auranofin in acetonitrile undergo a photodecomposition. It is assumed that the luminecence originates from a metal-centered ds excited state with partial ligand-to-metal charge transfer (LMCT) character while the photodecomposition is induced by LMCT excitation.

Fluorescence-line-narrowing spectroscopy of nile blue in glass and polymer at 5 K: Determination of a single-site line shape function

Fluorescence-line-narrowing (FLN) spectra of the oxazine dye nile blue are obtained at 5 K in both ethanol glass and PVOH polymer. Multiple spectra, each associated with a different excitation wavelength setting, are presented. We analyze these spectra assuming a site-independent molecular response. Excellent agreement obtains in the ethanol glass host.

Electronic spectral diffusion in glasses: The influence of coupling to the medium on experimental observables

The theory of electronic dephasing in low temperature glasses is extended to include the possibility that the strength of coupling of the chromophore to the solvent medium depends on the nature of the bath dynamical processes and the nature of the chromophore and, therefore, the chromophore-bath coupling can vary as a function of the rate of the dynamics of the medium. In the context of the sudden jump two-level system (TLS) model of low temperature glasses, this theory is used to reconcile the apparent contradiction implied by differences observed in spectral diffusion data for cresyl violet and metal-porphyrins in deuterated ethanol glass at 1.5 K. Previously, the coupling strength of a chromophore to the TLS has been assumed to be independent of rate of the transition between TLS states. Within the context of this approximation, spectral diffusion data yield, Pi(R), the intrinsic TLS fluctuation rate distribution. With the inclusion of the rate dependent coupling, C(R), it is shown that the spectral diffusion observables actually yield Pi(R)C(R). Therefore, the observed lack of spectral diffusion for a particular chromophore over some range of times can imply C(R) is zero rather than the current interpretation that Pi(R) is zero. To illustrate the importance of C(R), a hueristic model is analyzed. A fluctuation rate distribution is introduced that consists of the sum of three log-normal functions each associated with a specific class of dynamics occurring over three overlapping ranges of rates. The uncharged and nonpolar metal porphyrins is taken to couple to TLS strain dipoles, while the charged and polar cresyl violet also couples to TLS electric dipoles. By taking one of the types of TLS dynamics to only give rise to electric dipole fluctuations, it is possible to fit all of the experimental data in deuterated ethanol with a single intrinsic distribution of TLS fluctuation rates. This analysis of previously reported data is supported by the presentation of new stimulated photon echo data on both cresyl violet and zinc meso-tetraphenyl porphine in deuterated ethanol.

Photochemical processes of benzyltrimethylsilane at 77 K remarkable solvent effects and reaction mechanism

Photophysical and photochemical processes of benzyltrimethylsilane have been studied in 3-methylpentane and ethanol glass at 77 K. Remarkable solvent effects were observed in the UV photolysis: in ethanol glass, benzyl radicals were produced, while in 3-methylpentane glass α-trimethylsilylbenzyl radicals and benzyltrimethylsilane radical cations were produced. It was confirmed that the α-trimethylsilylbenzyl radicals and benzyltrimethylsilane radical cations were formed via the lowest triplet state and the benzyl radicals via the excited singlet state or higher triplet state. The molecular structure of the excited-state benzyl-trimethylsilane has been studied by MNDO-PM3 calculations. Based on the results, a possible mechanism involving the excited state of radical pair character has been proposed for the photochemical process of benzyltrimethylsilane.

Ion Complexation Induced High-Spin Associations of Spin-Labeled Crown Ethers: A Reevaluation

Abstract Between 1978 and 1989, Mukai and coworkers demonstrated that a series of spin-labeled benzo-15-crown-5 derivatives gave triplet ESR spectra in ethanol glasses in the presence of diamagnetic alkali and alkaline earth ions. They proposed that the high-spin coupling resulted from a pair of radicals being brought into close contact by a 1:2 complexation of metal ions with the crown ether moieties. The work of Mukai and his colleagues represents an early example of high-spin coupling induced in radical pairs that assemble around diamagnetic metal ions. Herein, we describe ion binding experiments with simple stable free radicals such as TEMPO and galvinoxyl that lack the crown moiety. The triplet state species that we observe require the possibility of unforeseen mechanisms for previously reported high-spin associations in spin labeled crown ethers.

Properties of singlet excited N-(pyrimidin-2-one-4-yl)pyridinium chloride and structurally related organic cations

The UV absorption and fluorescence spectra, fluorescence quantum yields and lifetimes of four new fluorescent N-(pyrimidin-2-one-4-yl)pyridinium and N-(pyrimidin-2-one-4-yl)methylimidazolium cations were measured in several solvents at room temperature and in ethanol glasses at 77 K. The spectroscopic studies were supplemented by theoretical calculations of the electronic transition energies, oscillator strengths and dipole moment changes by the INDO/S CI method. It is concluded that the lowest excited singlet state of the compounds studied has charge transfer character. The significantly different charge distribution in the S 1 state and the rotational relaxation of the excited molecules are responsible for the large Stokes shift observed in the spectra of pyridinium cations. N-(Pyrimidin-2-one-4-yl)methylimidazolium cations are more efficient fluorophores than pyridinium cations and this is due to the increased rate of non-radiative decay in the latter compounds.

Nanosecond spectral diffusion and optical dephasing in organic glasses over a wide temperature range: incoherent photon echo study of resorufin in D- and D 6-ethanol

Incoherent photon echoes (IPE) decay curve of two differently deuterated ethanol glasses: resorufin in d-ethanol (r/d-e) and resorufin in d 6-ethanol (r/d 6-e) have been measured in wide temperature interval (1.7–35 K). At low temperatures the difference in decay times between results of IPE and two-pulse picosecond photon echoes (2PE) were observed and attributed to nanosecond spectral diffusion (SD). The T-dependence of the SD contribution in IPE data was defined and analyzed using Bai-Fayer theory. IPE high temperature results have shown that high-temperature dephasing in r/d-e is caused mainly by interaction with single low frequency mode (LFM). LFM dephasing was analyzed using Osad'ko nonperturbative dynamical theory. The difference in temperature dependencies of dephasing time between r/d-e and r/d 6-e was observed: the deuteration influenced both on LFM and two-level systems (TLS) contribution to dephasing.

Spectral diffusion of molecular electronic transitions in amorphous solids: Weak and strong two-level-system phonon coupling.

The two-level-system (TLS) model of glasses is used with nonphenomenological TLS distribution functions [R. Jankowiak et al., J. Phys. Chem. 90, 3896 (1986)] to account for the time-dependent spectral-diffusion data for cresyl violet and zinc porphin in ethanol glasses at low temperatures [K. A. Littau and M. D. Fayer, Chem. Phys. Lett. 176, 551 (1991); H. C. Meijers and D. A. Wiersma, Phys. Rev. Lett. 68, 381 (1992)]. The two distributions of faster and slower TLS relaxation rates required to fit the data are characterized for both weak and strong TLS-phonon coupling. Comparison of the values obtained for the TLS parameters with those determined earlier for specific heat, thermal conductivity, pure dephasing, and spontaneous filling of nonphotochemical holes establishes that the faster and slower distributions are associated with intrinsic and extrinsic TLS. The pronounced effects of strong coupling on the TLS relaxation-rate distributions are discussed.

Phosphorescence emission and polarization of quinoline 3-carbonitrile

The phosphorescence emission and excitation spectra and their polarization have been studied for quinoline 3-carbonitrile in methylcyclohexane and ethanol glasses at 77 K. From the results obtained in this molecule (τ=1.15 sec in ethanol, τ=1.04 sec in methylcyclohexane and out-of-plane polarization) it is concluded that the emission is orginated from a triplet state of 3ππ * character. The two major spin-orbit coupling mechanisms through which the ππ * state of quinoline 3-carbonitrile acquires dipole-allowed character via nπ * states are: 1. In ethanol glass: ▪ 2. In methylcyclohexane glass: ▪