Multiphoton tea CO2 laser excitation of the triplet state of propynal

Multiple infrared photon excitation of propynal triplet molecules gives rise to a strongly perturbed phosphorescence. Following absorption of a few IR photons per molecule the phosphorescence spectrum extends to higher energy, the intensity increases, the decay — deviating from the original exponential decay — accelerates and the emission quantum yield drops dramatically. These findings are explained in terms of temperature sensitive radiative (T₁ → S₀) and radiationless (T₁ → S₀) processes with the vibrational temperature as the determining factor. During the perturbed triplet decay, the IR excitation initially confined to the vibrational degrees of freedom becomes distributed among all degrees of freedom which results in a decrease in the vibrational temperature and thus a complex phosphorescence decay.     

Spin sublevel-selective and position-dependent isotope effects in T1(ππ*) → S0 intersystem crossing of polycyclic para-diazines

ODMR measurements are combined with phosphorescence quantum yield data to show that deuterium isotope effects on the nonradiative decay rates of quinoxaline and dibenzoquinoxaline are spin sublevel-selective as well as position-dependent.     

Luminescence behavior of the pyridine—BCl3 complex

A phosphorescence and CNDO study of the 1:1 electron donor-acceptor complex formed between pyridine and boron trichloride has been shown to account satisfactorily for the electronic states and induced luminescence of pyridine resulting from complexation. The phosphorescence yield and formation constant of the complex in ethyl alcohol were determined to be 0.38 ± 0.04 and 1.3 × 10⁴ M⁻¹ respectively. CNDO calculations show that the lowest n,π* levels are shifted to significantly higher energies, thereby removing efficient radiationless decay routes available with these states.     

The triplet state decay (T1(nπ*) → S0) of benzaldehydes in the dilute gas phase

The triplet T₁(nπ^*) decay of benzaldehyde (B) and its isotopomers

and

were investigated in the dilute vapour phase (≤0.5 Torr) at room temperature. Following

excitation the quantum yields of the phosphorescence and photodecomposition, and the rate constants of the phosphorescence and the radiationless T₁ → S_o process were determined. Based on these results and in conjunction with theoretical calculations of T₁ → S_o rates and previous data obtained on propynal, the decay mechanism of benzaldehyde was analyzed. It is shown that the important accepting modes of the non-radiative T₁ → S_a decay are the

wagging and the CO stretching modes. In spite of the close vicinity of the T₂(ππ^*) and the T₁(nπ^*) states, the non-adiabatic coupling (communication between ring and carbonyl vibrations is not sufficient to influence the relaxed T₁(nπ^*) decay significantly.     

THE INWARD H+ PATHWAY IN BACTERIORHODOPSIN: THE ROLE OF M412 AND P(N)560 INTERMEDIATES

Abstract
In purple bacteriorhodopsin sheets adsorbed onto the phospholipid-impregnated collodion film, electrogenic stages are identified correlating with decays of the M and N(P)-type intermediates. It is concluded that both M N and N bR transitions are electrogenic.
The M decay is shown to be of a complex kinetics. In purple sheets, the lower the light intensity, the higher the rate of "slow M" decay. Such a dependence, which is absent from monomeric bacteriorhodopsin in proteoliposomes and from Triton X-100-solubilized protein, may be explained by the inhibiting effect of a light-induced conformation change in a bacteriorhodopsin molecule upon the M decay in some other bacteriorhodopsin molecules within the same sheet.
The light intensity-independent "slow M" decay in solubilized bacteriorhodopsin is shown to correlate with the decay of the N intermediate and H⁺ uptake after the flash. In contrast to "fast M", "slow M" is pH dependent, closely resembling in this respect the N intermediate. It is suggested that there is a fast light-independent equilibration between M and N so that "slow M" represents the portion of the M pool that monitors the N concentration. The M N equilibrium is assumed to be involved in the effect of the light-induced electric field on the M decay. No direct effect of light on the equilibrium was found.     

Yb3+共掺杂对Zn2GeO4∶Mn2+绿色长余辉发光性能增强研究

利用高温固相法合成了Zn2GeO4∶Mn2+以及Zn2GeO4∶Mn2+,Yb3+绿色发射长余辉发光材料,对样品进行了X射线衍射分析、荧光光谱分析、色坐标、热释发光以及发光寿命测量。分析结果表明,在1 050℃下烧结3 h的Zn2GeO4为单相产物,所得Zn2GeO4∶Mn2+发光材料具有良好的发光性能,在紫外灯激发下发出最强发射位于528 nm的宽带发射并具有优良的长余辉发光特性,其色坐标值分别为x=0.145,y=0.773。Yb3+共掺杂对其长余辉发光性能提高明显。余辉发光在暗场环境下肉眼可观察的持续时间超过2 h。通过热释光谱对陷阱进行了分析。对Yb3+共掺杂的长余辉发光增强机理进行了讨论。     

Energetics of Photoinduced Electron Transfer in the Indole-O2 Cluster in Gas Phase: Possible Consequences for Photoexcited Tryptophan in Solution

Abstract— A direct process for an activationless electron transfer from photoexcited tryptophan to molecular oxygen is proposed. By photodetachment of mass-selected indole-O_2- clusters in gas phase a neutral indole₊ O_2- charge-separated exciplex state is found at 2.25 0.2 eV above the neutral ground state. By theory also, the existence of an excited charge separated state at 3.05 0.2 eV is postulated. In gas phase both charge-separated cluster states are energetically below the first singlet states ₁L_b and ₁L_a and the lower even below the first triplet state T₁ of indole. In gas-phase clusters these energetics imply a very efficient quenching of photoexcited indole by fast electron transfer to oxygen. We discuss a similar mechanism for tryptophan-O₂ in aqueous environment and find it without activation barrier and presumably extremely fast. In the collisional tryptophan_*-O₂ complex the efficiency and the time scale of the charge transfer process should be mostly solvent independent. In polar solvent a complete charge separation and free superoxide formation are expected. We correlate this model with previous fluorescence and phosphorescence quenching data of excited tryptophan by O₂ and propose electron transfer to be the relevant process.     

THE INWARD H+ PATHWAY IN BACTERIORHODOPSIN: THE ROLE OF M412 AND P(N)560 INTERMEDIATES*

Abstract— In purple bacteriorhodopsin sheets adsorbed onto the phospholipid-impregnated collodion film, electrogenic stages are identified correlating with decays of the M and N(P)-type intermediates. It is concluded that both M → N and N → bR transitions are electrogenic.
The M decay is shown to be of a complex kinetics. In purple sheets, the lower the light intensity, the higher the rate of "slow M" decay. Such a dependence, which is absent from monomeric bacteriorhodopsin in proteoliposomes and from Triton X-100-solubilized protein, may be explained by the inhibiting effect of a light-induced conformation change in a bacteriorhodopsin molecule upon the M decay in some other bacteriorhodopsin molecules within the same sheet.
The light intensity-independent "slow M" decay in solubilized bacteriorhodopsin is shown to correlate with the decay of the N intermediate and H⁺ uptake after the flash. In contrast to "fast M", "slow M" is pH dependent, closely resembling in this respect the N intermediate. It is suggested that there is a fast light-independent equilibration between M and N so that "slow M" represents the portion of the M pool that monitors the N concentration. The M → N equilibrium is assumed to be involved in the effect of the light-induced electric field on the M decay. No direct effect of light on the equilibrium was found.     

Intensity and polarization of emission studies on C6H6 and C6D6 in 3-methylpentane glass at 77 K

The phosphorescence polarization of the week b_2g bands must be entirely in-plane for a ³B_1u assignment for the lowest triplet state of benzene. This emission is found to have 15–20% out-of-plane character, a result which parallels the in-plane character found in the e_2g region. Both results require radiative decay via the A_2g spin sublevel, in disagreement with theory and microwave work. The inconsistency is discussed in terms of the possibilities of solvent perturbation and reorientational depolarizations.

Precautions were taken to avoid the interference caused by photoproduct formation, an effect that can also distort relative emission quantum yields.     

Comparative sensibility of S1 ←S0 and S2 ←S0 indole electronic transitions to environment perturbations. The positions of the 0—0 bands in polar media

The modifications under environmental perturbations of the well separated two first electronic systems of carbazole are used to demonstrate the possibility of including solute-ether complexes in polyethylene films. The application of this technique to indole allows to differentiate the overlapping ¹L_a and ¹L_b transitions in the spectrum of hydrogen bonded indole. The ground state interactions of indole, 5-methoxyindole and 3-methylindole in several well defined environment conditions (hydrogen bond in a polar cage, hydrogen bond in a nonpolar cage) are investigated through UV absorption spectroscopy between 293 and 88 K. A strong red shift of the ¹L_a bands under the hydrogen bonding occurs with all the indoles investigated. The comparative analysis of the spectra in three types of environment, allows to give the accurate location of the first bands for the two overlapping vibronic systems of these molecules in polar media. Particularly, it is unambiguously shown that the first ¹L_a band and the first ¹L_b band of indole in alcohols are superposed at 288 nm. These results offer reliable new bases for the study of the emission properties of indole and its derivatives.     

The 1,3B 1— 1A 1 systems of the nitrite anion in a NaHCO 2 host crystal

The lower energy electronic transitions of the NO ^?₂ anion in a NaHCO ₂ host crystal at 4 K are reported and analyzea. The ¹B ₁— ¹A ₁ system, whose origin is at 25 649 cm ^?1, is seen in absorption and fluorescence accompanied by a long progression in the symmetric bending mode (ν′ ₂ = 626, ν″ = 820 cm ^?1). The implied change in the ONO bond angle is 9 ± 3 ⁰. The ³B ₁ → ¹A ₁ phosphorescence is quite weak with an extrapolated origin at 18 059 cm ^?1. The ¹B ₁ ← ¹A ₁ absorption linewidths, the lower-resolution fluorescence photoexcitation spectrum, and the relative phosphorescence and fluorescence intensities suggest the involvement of an intermediate state in populating the triplet manifold after excitation of the ¹B ₁ state.     

MATRIX EFFECTS ON THE RADIATIONLESS TRANSITION' S1→T1 AND T1→S0 FOR BENZENE AND N, N, N', N'-TETRAMETHYLPARAPHENYLENE-DIAMINE MOLECULES

Abstract— The present study attempts to correlate the phosphorescence life time τ_p at 77°K of a definite solute: tetramethylparaphenylenediamine (TMPD) with various solvents viscosity and polarity. A few experiments with benzene in the same solvents are also reported. The following results have been obtained:

• 1 The measured τ_p vary regularly with the sample immersion time in liquid N₂, reaching a constant value after a few hours. This effect is related to the glass matrix relaxation. The rate constant K_isc (S, ₁→T₁) is also found to vary during relaxation of the solvent.
• 2 In the expression giving the nonradiative rate constant K_nr (T₁→S₀), the bimolecular quenching term appears negligible for high viscosity matrices i.e. for η= 10⁹ poises for benzene and for TMPD. K_nr is found to vary linearly with log η, as well as the intersystem crossing S₁→T₁ rate constant K^isc.
• 3 Both K_nr (T₁→S₀) and K^isc (S₁→T₁), increase with decreasing polarity of the solvent.
• 4 From our own observations and literature data[6] for C₆H₆ it appears that solvent viscosity does not contribute appreciably to the observed temperature effect on the solute τ_p when only a monomolecular triplet deactivation is operative.

     

Single crystal EPR studies of the T1 states of indene,indole, benzofuran and coumarin; systems with large |E|

Single crystal EPR and phosphorescence studies of indene, indole, benzofuran and coumarin were made using DBB host. It was shown unambiguously that D < 3 |E| for these systems. (Z axis is perpendicular to the molecular plane.) The directions of the magnetic axes were also determined. Spin densities at the 6 and 5 positions in indole were estimated and compared with those of other substituted benzenes. It is concluded that large spin density is located at the CC group.     

Effects of limited CI on T1 → S0 oscillator strength and phosphorescence lifetime of pyrazine

Using modified CNDO/S/CI wavefunctions, the effects of 10, 20, 30 and no CI on the oscillator strength of the T₁ → S_o transition and phosphorescence lifetime of pyrazine was investigated. From these calculations, it was determined that although the individual numbers varied, the order of magnitude remained fairly constant, approximately 10^?2 s. The closest results to the experimental values for oscillator strength and phosphorescence lifetime was obtained with 20 and 30 CI     

THERMODYNAMIC FUNCTIONS FOR SINGLET MOLECULAR OXYGEN, O2(1△g) and O2 (1σ8+)

Abstract— A correction is offered to the approximate values previously given by Mendenhall (1978) for the enthalpy of formation and entropy of O₂(a₁Δ_g) and O₂(b₁₊) between 298 and 1500 K. Accurate values have been calculated for the functions together with the equilibrium constants for the formation of these species from O₂(X₃σ_g-).     

Deuterium isotope effect in the T1 → S0 radiationless transition of propynal in the gas phase

The phosphorescence lifetimes of propynal-h₁ and propynal-d₁ have been measured at room temperature in the 40 mTorr-1 Torr pressure range The reciprocal of the zero-pressure lifetime (k₀) is (3.10 ± 0.05) × 10³ and (1.70 ± 0.04) × 10³ s^?1 for propynal-h₁ and propynal-d¹ For both compounds the rate constant for self-quenching between triplet and ground-state molecules is k_SQ = (1 2±007) × 10³ Torr^?1 s^?1 The deuterium isotope effect is attributed to the T₁ → S₀ radiationlcss decay, for which k^H_ISC/k^D_ISC = 2 4     

CCl2自由基被无机小分子猝灭的速率常数

对CCl4/Ar混合气体脉冲直流高压放电产生CCl2自由基,用541.52 nm激光将电子基态CCl2激励到A 1B1(0,4,0)振动能级上. 通过检测激发态CCl2时间分辨荧光信号,测得室温下CCl2(A 1B1和a 3B1)被O2、N2、NO、 CO2、 CS2、H2O、SO2,和SF6分子猝灭的实验结果.用我们提出的三能级模型分析处理实验数据,获得了CCl2(A 1B1)态和CCl2(a 3B1)态的碰撞猝灭速率常数kA和ka值.     

The uniqueness of the propyl compound in the series (CnH2n+1NH3)2MnCl4 with n = 1–10

The perovskite-like layer structures of (C_nH_2n+1NH₃)₂MnCl₄ with n = 1–10 have been investigated by X-ray methods to determine their lattice constants and the temperature of transition to the respective zero-tilt phases. It has been found that the propyl compound is distinctive in that it exhibits the highest temperature of transition to a zero-tilt phase, the longest MnCl bond, and the largest difference between the a and b lattice parameters. Furthermore, it undergoes a large number of phase transitions (five), some of which are accompanied by the formation of commensurable or incommensurable superstructures. The special position of this compound is attributed to geometrical peculiarities related to the terminal methyl groups. The propyl compound is the only member of the series in which coupled movements of terminal methyl groups of neighboring strata do not seem to be important below 400°K.     

CCl2(A 1B 1,a3B1)自由基被烷烃类分子猝灭动力学

用放电 LIF实验装置,对CCl4/Ar混合气体放电产生CCl2自由基,再用541.52 nm激光将电子基态CCl2激励到激发态A 1B1(0,4,0)振动能级上,通过检测激发态CCl2时间分辨荧光信号,测得室温下CCl2(A 1B1)被烷烃类分子猝灭的实验结果,用我们提出的三能级模型分析处理实验数据,获得CCl2(A 1B1)态和CCl2(a 3B1)态的碰撞猝灭速率常数kA和ka值.