Synthesis, characterization, photophysics and electrophosphorescent applications of phosphorescent platinum cyclometalated complexes with 9-arylcarbazole moieties

A series of cyclometalating platinum(II) complexes with substituted 9-arylcarbazolyl chromophores have been synthesized and characterized. These complexes are thermally stable and most of them have been characterized by X-ray crystallography. The phosphorescence emissions of the complexes are dominated by (MLCT)-M-3 excited states. The excited state properties of these complexes can be modulated by varying the electronic characteristics of the cyclometalating ligands via substituent effects, thus allowing the emission to be tuned from bright green to yellow, orange and red light. The correlation between the functional properties of these metallophosphors and the results of density functional theory calculations was made. Because of the propensity of the electron-rich carbazolyl group to facilitate hole injection/transport, the presence of such moiety can increase the highest occupied molecular orbital levels and improve the charge balance in the resulting complexes relative to the parent platinum(II) phosphor with 2-phenylpyridine ligand.

Phosphorescence Color Tuning by Ligand, and Substituent Effects of Multifunctional Iridium(III) Cyclometalates with 9-Arylcarbazole Moieties

The synthesis, isomeric studies, and photophysical characterization of a series of multifunctional cyclometalated iridium(III) complexes containing a fluoro- or methyl-substituted 2[3-(N-plienylcarbazolyl)]pyridine molecular framework are presented. All of the complexes are thermally stable solids and highly efficient electrophosphors. The optical, electrochemical, photo-, and electrophosphorescence traits of these iridium phosphors have been studied in terms of the electronic nature and coordinating site of the aryl or pyridyl ring substituents. The correlation between the functional properties of these phosphors and the results of density functional theory calculations was made. Arising from the propensity of the electron-rich carbazolyl group to facilitate hole injection/transport, the presence of such a moiety can increase the highest-occupied molecular orbital levels and improve the charge balance in the resulting complexes relative to the parent phosphor with 2-phenylpyridine ligands. Remarkably, the excited-state properties can be manipulated through ligand and substituent effects that allow the tuning of phosphorescence energies from bluish green to deep red.

Luminescent properties of RE3+-activated CaAl2B2O7 (RE = Tb, Ce) in VUV-visible region

RE3+-activated alpha- and beta-CaAl2B2O7 (RE = Tb, Ce) were synthesized with the method of high-temperature solid-state reaction. Their VUV excitation and VUV-excited emission spectra are measured and discussed in the present article. The charge transfer band of Tb3+ and Ce3+ is respectively calculated to be at 151 +/- 2 and 159 +/- 3 nm. All the samples show an activator-independent excitation peak at about 175 nm and an emission peak at 350-360 nm ascribed to the host absorption and emission band, respectively.

Crystallization of mechanically alloyed amorphous W-Mg alloy under high pressure

Pure metal powder mixtures of W and Mg at the desired composition were milled in conventional high-energy ball mill, and amorphous alloy W50Mg50 was obtained after milling for 20 h. The structure evolution of elemental powder mixtures was studied following milling and subsequent high pressure and high temperature treatment. The amorphous alloy transform into a nanocrystalline material below 1050 degreesC at 4.0 GPa. On increasing the temperature, it transforms into a mixture of several new crystal phases under high-pressure condition. It also found that both mechanical alloying and high pressure treatment are the two necessary processes to form the nanocrystalline and the new phases.

Synthesis and properties of polyquinolines and polyanthrazolines containing pyrrole units in the main chain

A series of eight new polyquinolines and polyanthrazolines with pyrrole isomeric units in main chain were synthesized and characterized. The new polymers showed high glass transition temperatures (T-g = 242-339 degreesC) and excellent thermal stability (T-5% = 398-536 degreesC in air, TGA). Compared to the series of polyanthrazolines, the series of polyquinolines exhibited higher thermal stability, better solubility in common organic solvents, and lower maximum absorption wavelengths (lambda(max)(a)). Polyanthrazolines with 2,5-pyrrole linkage showed an unusually high lambda(max)(a) (565 nm) and small band gap (2.02 eV). All polymers in solution had low photoluminescence quantum yields between 10(-2%) and 10(-5%) and excited-state lifetimes of 0.28-1.29 ns. The effects of molecular structure, especially pyrrole linkage structures, on the electronic structure, thermodynamics, and some of the optical properties of the polymers were explored. A model of hydrogen bonds in the main chain of the polymers was suggested to explain the difference in the properties of the isomer polymers. In addition, a polyquinoline (PBM) was chosen to examine the proton conductivity; the result indicated that the PBM/H3PO4 complex exhibited a high conductivity of 1.5 x 10(-3) S cm(-1) at 157 degreesC.

Pink light emitting long-lasting phosphorescence in Sm3+-doped CdSiO3

Novel pink light emitting long-lasting afterglow CdSiO3:SM3+ phosphors are prepared by the conventional high-temperature solid-state method and their luminescent properties are investigated. XRD and photolurflinescence (PL) spectra are used to characterize the synthesized phosphors. The phosphors are well crystallized by calcinations at 1050degreesC for 5 h. These phosphors emit pink light and show long-lasting phosphorescence after they are excited with 254 nm ultraviolet light. The phosphorescence lasts for nearly 5 h in the light perception of the dark-adapted human eye (0.32mcd/m(2)). The phosphorescence mechanism is also investigated. All the results indicate that these phosphors have promising potential practical applications.

Luminescence properties of rare earth ions in cadmium metasilicate

The luminescence properties of CdSio(3):RE3+ phosphors doped with various rare earth ions are reported. The series of rare earth ions doped CdSiO3 phosphors are prepared by the conventional high-temperature solid-state method, and characterized by XRD and photoluminescence (PL) spectra. The results of XRD measurement indicate that the products fired under 1050 degreesC for 3 h have a good crystallization without any detectable amount of impure phase. The PL spectra measurement results show that CdSiO3 is a novel self-activated luminescent matrix. When rare earth ions such as Y3+, La3+, Gds(3+), Lus(3+), Ce3+, Nd3+, Ho3+, Era(3+), Tm3+ and Yb3+ are introduced into the CdSi03 host, one broadband centered at about 420 nm resulted from traps can be observed. In the case of other earth ions which show emissions at the visible spectrum region, such as Pr3+, Sm3+, Eu3+, Tb3+ and Dy3+, the mixture of their characteristic line emissions with the similar to 420 nm strong broadband luminescence results in various emitting colors. As a consequence, different emitting colors can be attairied via introducing certain appropriate active ions into the CdSiO3 matrix. In additional, this kind of phosphors shows good long-lasting properties when excited by UV light. All the results show that CdSiO3 is a potential luminance matrix.

Synthesis, structure, electrochemistry, photophysics and electroluminescence of 1,3,4-oxadiazole-based ortho-metalated iridium(III) complexes

Four new iridium(III) complexes 1-4, with 1,3,4-oxadiazole derivative as cyclometalated ligand for the first time, have been synthesized and structurally characterized by NMR, EA, MS and X-ray diffraction analysis (except 1). The stronger ligand field strength of the dithiolate ancillary ligands results in higher oxidation potentials and lower HOMO energy levels of complexes than acetylacetone. The absorption spectra of these complexes display low-energy metal-to-ligand charge transfer transition ranging from 350 to 500 nm. Complexes with dithiolate ancillary ligand emit at maximum wavelengths of ca. 500 nm, blue shifting 17 and 11 nm with respect to their counterpart with acetylacetone ligand. The electrophosphorescent devices with 2-4 as phosphorescent dopant in emitting layer have been fabricated. All devices have a low turn-on voltage in the range of 4.5 and 4.9 V. A high-efficiency green emission with maximum luminous efficiency of 5.28 cd/A at current density of 1.37 mA/cm(2) and a maximum brightness of 2592 cd/m(2) at 15.2 V has been achieved in device using 2 as emitter.

Highly efficient phosphorescent bis-cyclometalated iridium complexes based on quinoline ligands

The synthesis and electrochemical and photophysical study of a series of bis-cyclometalated iridium(III) complexes based on quinoline ligands have been carried out. These complexes are found to emit red-orange to deep red phosphorescence with high quantum yield and short lifetime. The red organic light-emitting diodes (OLEDs) with the external quantum efficiency up to 11.3% were demonstrated. Slow decay of efficiency with increasing current density was observed. These indicate that quinoline-based iridium complexes are promising candidates for efficient red emitters.

Substitution effect of nitrogen atoms with carbon atoms in porphyrin on the electronic structure and excited states properties

Density functional theory (DFT) electronic structure calculations were carried out to predict the structures and the absorption and emission spectra for porphyrin and a series of carbaporphyrins-carbaporphyrin, adj-dicarbaporphyrin, opp-dicarbaporphyrin, tricarbaporphyrin and tetracarbaporphyrin. The ground- and excited-state geometries were optimized at the B3LYP/6-31g(d) and CIS/6-31g(d) level, respectively. The optimized ground-state geometry and absorption spectra of porphyrin, calculated by DFT and time-dependent DFT (TDDFT), are comparable with the available experimental values. Based on the optimized excited-state geometries obtained by CIS/6-31g(d) method, the emission properties are calculated using TDDFT method at the B3LYP/6-31g(d) level. The effects of the substitution of nitrogen atoms with carbon atoms at the center positions of porphyrin are discussed. The results indicate that the two-pyrrole nitrogens are important to the chemical and physical properties for porphyrin.

Study of energy transfer in KMgF3 : Eu-X (X = Gd, Cr, Ce) by the decay model of P-6(7/2) exited state of Eu2+

Energy transfer processes between Eu2+ and Gd3+, Cr3+, Ce3+ ions in KMgF3, which are difficult to study spectroscopically, have been investigated by using the proposed four-level decay model of the P-6(7/2) excited state of the Eu2+ ion. Gd3+ and Ce3+ transfer its energy to the vibronic transition of the P-6(7/2) --> S-8(7/2) transition of Eu2+, whereas Cr3+ receive energy from Eu2+ via the d-d interaction. The energy transfer from the Eu2+ 4f(6)5d level to the Ce3+ 4f5d state is observed spectroscopically, and the energy transfer mechanism is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

A rule to design high spin molecules with hetero-spin centers

The series of biradicals with m-phenylene coupling unit and hetero-spin centers were calculated compared with those possessing home-spin centers using AM1-CI method. A simple rule was proposed to design high spin molecules with ferromagnetic coupling unit and hetero-spin centers. Two neutral (or charged) hetero-spin centers resulted in high spin ground state, one neutral and another charged hetero-spin centers correspond to low spin ground state. The latter was ascribed to the huge splitting of two partially occupied molecular orbitals.

The intermolecular coupling through space for stacked high spin molecules

Intermolecular ferromagnetic interactions in two stacking models for the dimer of high spin molecules are investigated by means of AM1-CI approach. It is shown that the stability of high spin ground state versus low spin state can be simply traced back to the number and the extent of atoms with reversed signs of pi-spin density in neighboring molecules coupled to each other in shortest distance.

Time-dependent wavepacket approach to the influence of intense fields on the population of molecular excited states

The influence of laser-field parameters, such as intensity and pulse width, on the population of molecular excited state is investigated by using the time-dependent wavepacket method. For a two-state system in intense laser fields, the populations in the upper and lower states are given by the wavefunctions obtained by solving the Schrodinger equation through split-operator scheme. The calculation shows that both the laser intensity and the pulse width have a strong effect on the population in molecular excited state, and that as the common feature of light-matter interaction (LMI), the periodic changing of the population with the evolution time in each state can be interpreted by Rabi oscillation and area-theorem. The results illustrate that by controlling these two parameters, the needed population in excited state of interest can be obtained, which provides the foundation of light manipulation of molecular processes. (C) 2005 Elsevier B.V. All rights reserved.

Electronic spectroscopy of thiones

The phosphorescence excitation spectra of two thiones, 4-H-1-xanthione (XT) and 4-H-1-pyrane-4-thione (PT), cooled in a supersonic jet were investigated. The vibronic lineshape of the T1z origin of PT measured by cavity ring-down spectroscopy is considered and the excited state rotational constants are calculated. For XT the 3A2(nπ* ) → X1A1 phosphorescence excitation spectrum was investigated in the region 14900-17600 cm-1. The structure observed is shown to be due to the T1← S0 absorption and an assignment in terms of the vibronic structure of the band is proposed. A previous assignment of the S1 ← S0 origin is considered and the transition involved is shown to be most probably due to the absorption of a vibronic tiplet state T1z,v7. An alternative but tentative assignment of the S1,0 ←S0,0 transition is suggested. In the case of PT the phosphorescence excitation spectrum was investigated in the region of the 1A2(ππ*) ← X1A1 absorption band between 27300 and 28800 cm-1. The spectrum exhibits complex features which are typical for the strong vibronic coupling case of two adjacent electronic states. The observed intermediate level structure was attributed to the coupling with a lower lying dark electronic state 1B1(nπ*2), whose origin was estimated to be ~ 825 - 1025 cm-1 below the origin of 1A2(ππ*)0. Consequences of the vibronic coupling on the decay dynamics of 1A2(ππ*) as well as tentative assignments of vibronic transitions 1A2(ππ*)v ← X1A1 are also discussed. In the T1z ← S0 cavity ring-down absorption spectrum of PT, the vibronic lineshape of the T1z origin is analysed. As the T1z line is separated from the T1x,1y lines by a large zero-field splitting it is possible to use an Asyrot-like program to calculate the vibrational-rotational parameters determining the lineshape. It is shown that PT is non-planar in the first excited triplet state and the lineshape is composed of a mixture of A-type and C-type bandshapes. The non-planarity of PT is discussed.