Bimolecular gas-phase processes with the participation of vibrationally excited triplet molecules of aromatic ketones

Time-resolved moderated luminescence of aromatic ketones (benzophenone, aceptophenone) in the presence of neutral and reactive hydrogeneous foreign gases (ethylene, pentane, triethylamine) is investigated. It is shown that the addition of hydrogeneous foreign gases leads to strong quenching of the triplet molecules of aromatic ketones. Effectivenesses of such bimolecular processes as the collision detachment of a hydrogen atom and establishment of vibrational and thermal equilibrium are compared. It is concluded that the vibrational degrees of freedom of the acceptors, the aromatic ketones, are inactive in the photochemical process of collision detachment of a hydrogen atom that takes place after the establishment of vibrational equilibrium. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 73–77, January–February, 1999.     

Syntheses and Photophysical Properties of N‐Pyridylimidazol‐2‐ylidene Tetracyanoruthenates(II) and Photochromic Studies of Their Dithienylethene‐Containing Derivatives

A series of tetracyanoruthenate(II) with chelating pyridyl N‐heterocyclic carbene ligands (NHC‐py) was synthesized and characterized. Their photophysical and electrochemical properties as well as the photochromic behavior of their dithienylethene‐containing complexes were studied. Photocyclization was found to take place upon irradiation into the metal‐to‐ligand charge transfer (MLCT) absorption bands of these complexes, and evidence is provided to support the triplet‐sensitizing reaction pathway.     

钠双原子分子2~3∏_u→1~3∑~＋_g跃迁近红外发射光谱

用紫外激光泵浦Ｎａ２分子高位电子态，观察到了位于０．９８１．０４μｍ谱区峰值在１．０μｍ附近的近红外发射谱，判断其来源于单三重态分子间能量转移后的２３∏ｕ→１３∑＋ｇ跃迁。     

Mechanism of formation and spectral characteristics of triplet excimers of Pd-porphyrins in liquid solutions

Concentration quenching of the triplet state (CQTS) of a number of Pd-porphyrins in toluene is investigated. Based on an analysis of experimental results, a conclusion is drawn that such quenching proceeds via formation of exciting complexes from molecules in the ground and triplet states (TS). From a small value of decay rate constants of the complexes it follows that these complexes are triplet excimers but not complexes due to collision. It is established that by increasing the concentration of porphyrins the maxima of their phosphorescence bands shift toward large wavelengths by a value of up to 3 nm and the bands, as a consequence, broaden by 5–7 nm. The formation of excimers is explained by enhancement of solvophobic dispersion interactions of molecules in the TS. Relatively small changes in the phosphorescence spectra upon formation of excimers are attributable to these interactions. The magnitude of dipole-dipole interaction of molecules in the TS is insignificant since the dipole moment of the T↭S transition is small. On the basis of consideration of the oxidation-reduction and energy characteristics of the compounds, it is shown that the interaction with charge transfer in the case of the CQTS of Pd-porphyrins is inefficient. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 857–863, November–December, 1998.     

Conjugated Polymer Nanoparticle‐Triplet Emitter Hybrids in Aqueous Dispersion: Fabrication and Fluorescence Quenching Behavior

Conjugated polymer nanoparticles based on poly[9,9‐bis(2‐ethylhexyl)fluorene] and poly[N‐(2,4,6‐trimethylphenyl)‐N,N‐diphenylamine)‐4,4′‐diyl] are fabricated using anionic surfactant sodium dodecylsulphate in water by miniemulsion technique. Average diameters of polyfluorene and polytriarylamine nanoparticles range from 70 to 100 and 100 to 140 nm, respectively. The surface of the nanoparticles is decorated with triplet emitting dye, tris(2,2′‐bipyridyl)ruthenium(II) chloride. Intriguing photophysics of aqueous dispersions of these hybrid nanoparticles is investigated. Nearly 50% quenching of fluorescence is observed in the case of dye‐coated polyfluorene nanoparticles; excitation energy transfer is found to be the dominant quenching mechanism. On the other hand, nearly complete quenching of emission is noticed in polytriarylamine nanoparticle‐dye hybrids. It is proposed that the excited state electron transfer from the electron‐rich polytriarylamine donor polymer to Ru complex leads to the complete quenching of emission of polytriarylamine nanoparticles. The current study offers promising avenues for developing aqueous solution processed‐electroluminescent devices involving a conjugated polymer nanoparticle host and Ru or Ir‐based triplet emitting dye as the guest.

     

白藜芦醇顺反异构体及第一三重激发态结构的理论研究

在B3LYP/6-311++G(d,p)水平对白藜芦醇顺反异构体及第一三重激发态进行了结构优化、频率计算和自然键轨道(Natural Bond Orbital,NBO)分析.在MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p)水平比较了白藜芦醇顺反异构体的能量.反式白藜芦醇整个分子呈平面结构,顺式白藜芦醇两苯环之间存在约30o扭角.第一三重激发态中两苯环几乎处于互相垂直的关系,C7-H5与C8-H6键也是几乎互相垂直的关系.顺式和反式白藜芦醇C7-C8的σ键成键情况分别为sp1.53-sp1.53和sp1.59-sp1.60,C7与C8各自提供p轨道形成π键,即形成C7=C8双键.三重态中,C7-C8的成键情况为sp1.92-sp1.89,没有p-pπ键,C7、C8均还有一个2p轨道未参与杂化,NBO分析证实C7、C8的各自剩下的2p轨道均几乎独立形成了高能量的反键轨道,分别垂直于单羟基和双羟基苯环,C7-C8键长明显长于白藜芦醇顺反异构体.顺式白藜芦醇比反式白藜芦醇的自由能高约1.3-2.5 kcal/mol,反式构型是热力学稳定构型.含时密度泛函方法(Time-Dependent Density Functional Theory,TD-DFT)方法,B3LYP/6-311++G(d,p)水平计算得反式和顺式白藜芦醇最强紫外吸收峰分别在330 nm和319 nm.     

Energy up-conversion by low-power excitation: new applications of an old concept

Energy up-conversion is the process by which two absorbed photons are converted in one photon of higher energy. Such a process can be conveniently performed by low-power excitation through sensitized triplet-triplet annihilation and it is now an emerging technique with possible applications in different fields, including photovoltaic devices and bioimaging.