ESR and Theoretical Studies of Bis-Benzene-1, 2-Diselenolate Nickel and Related Complexes

Abstract

ESR and theoretical studies of the transition metal complexes of [Co and Ni (Se₂C₆H₄)₂]^? (n-C₄H₉)₄N⁺ are reported and compared with closely related systems. Room temperature single crystal X-ray studies reveal the Nickel complex is orthorhombic. ESR studies of the polycrystalline powders of the Ni complex as a function of temperature from 108 K to room temperature show a series of spectral envelopes which can arise only from a paramagnetic site which possesses axial symmetry. At ca 160 K, there is an abrupt change in the value of the principal components of the anisotropic g-tensor of the Ni complex which is discussed. Low temperature ESR studies of polycrystalline samples of the ground state triplet Cobalt complex which is isomorphous with the Nickel complex reveal an orthorhombic g-tensor. From the field position of the half-field resonance, it is possible to calculate a mean separation, of the two electrons which make up the triplet state, of 4.3 (±0.5) A.     

The Absorption,Fluorescence and Phosphorescence and Phosphorescence of Single Crystals of 1,2,4,5-Tetrachlorobenzene and 1,4-Dichlorobenzene at Low Temperatures

Abstract

The emission spectra of ultra pure single crystals of 1, 2, 4, 5. tetrachlorobenzene (TCB) and 1, 4-dichlorobenzene (DCB) at temperatures from 4.2°K upwards are reported. In addition, by use of the phosphorescence excitation technique the singlet-triplet absorption spectrum at 4.2°K has been obtained.

The phosphorescence emission of TCB at 4.2°K occurs predominantly from a defect origin “X” situated 48 cm^?1 below the triplet exciton band. The triplet exciton energy level is at 26676 cm^?1 from both emission and absorption studies. This is the triplet emission origin when the crystal is above 12°K. The temperature dependence of the emission intensity from the defect has an activation energy of 40±8 cm^?1. This value is consistent with our suggestion of thermal depopulation of the traps.

Single crystals of DCB show strong excimer emission and weak triplet exciton emission. There is no evidence for trapping levels. The triplet exciton emission. There is no evidence for trapping levels. The triplet exciton origin is 27890 cm^?1 from both emission and absorption studies.

Weak fluorescence (φ < 10⁰²) is detected from both TCB and DCB.

Vibrational analyses are reported for the absorption, fluorescence and phosphorescence spectra.     

Analyse de la Raie Zéro-Phonon et des Processus de Relaxation Excitoniques dans le Spectre d'Absorption Singulet-Triplet du Cristal de 4-4′-Dichlorobenzophenone

Abstract

In this paper we discuss the dynamic scattering information which can be obtained from an analysis, at high resolution, of the triplet exciton absorption band in the molecular crystal 4-4′-dichlorobenzophenone. The zero phonon lineshapes, widths and positions are investigated as a function of temperature. At temperatures below 30 K the broadening and the shift are analyzed in terms of exchange theory involving a torsional mode of the molecule. The lifetime in the phonon promoted state is 0.75 ps over the range 5 K-30 K. The difference between the excited and ground state energies of the torsional mode is δω = -8.45 cm^?1. Above 30 K the change on linewidth is discussed in a model which implies a momentarily localization of the exciton by lattice phonons. During the localization time a weak coupling between the trapped excitation and phonons is assumed. At very low temperatures the lineshape is asymmetric, gaussian on the high energy side, lorentzian on the low energy side. This experimental result may be due to the fact that the k = 0 level is at the bottom of the exciton band.     

Electron Transfer and Energy Transfer Reactions in Photoexcited α-Nonathiophene/C60 Films and Solutions

Abstract

Photoexcitation of a nonathiophene in film or solution across the π-π* energy gap produces a metastable triplet state. In the presence of C₆₀, on the other hand, an ultra fast electron transfer from the photoexcited nonathiophene onto C₆₀ is observed in films, whereas in solution C₆₀ is involved in an efficient energy transfer reaction with the triplet-state nonathiophene.     

Assignment of the Lowest Singlet and Triplet States of the Monoaldehyde of Durene

Abstract

The monoaldehyde of durene has been synthesized. It has been shown to be the impurity frequently encountered in spectral studies involving durene crystals. Both the polarized absorption and emission spectra of the protonated and deuterated aldehyde in crystals of durene^h-14 and durene^d-14 have been obtained. Although the lowest excited singlet and triplet states, separated by 2200 cm^?1, are shown to be nπ* a number of features in the phosphorescence spectrum are more characteristic of a ³π* state. The polarization of the absorption spectrum, in particular the 0-0 band and bands involving the excitation of totally symmetric vibrations, is inconsistent with the nπ* nature of the transition. A number of explanations is proposed.     

Triplet Excitions in Crystalline Trans-Stilbene I. Spectroscopy of the So → T1 Transition

Abstract

The first singlet → triplet absorption of trans-stilbene has been studied between 10 and 300 K. The triplet exciton energy (energy of the lowest 0–0 line) is 17380 cm^?1 at 10 K, and does not change significantly with temperature. Vibrational A_g modes of 206. 1250 and 1570 cm^?1 are active. The Franck-Condon factor of the origin region is small. The low temperature spectra of the 0–0 and 206 cm^?1 regions show a doublet structure with a splitting of 82 ± 1 cm^?1 which is attributed to the site splitting. Further structure shown by the lines is discussed. The lines are approximately lorentzian. From curve fitting, line-widths and exciton-phonon coupling constants, increasing linearly with T, are deduced. Exciton-phonon coupling appears to be different on the two sites. The product of absorption coefficient at 4880 Å, α, by the total triplettriplet interaction rate constant has been measured at 295 K: αγ=2.3 ± 0.3. 10^?15 cm² sec^?1, corresponding for γ_total to a value of a few 10^?12 cm³ sec^?1.     

Thermally activated delayed fluorescence host materials based on triphenylphosphine oxide derivatives

Abstract

Novel thermally activated delayed fluorescence (TADF) host molecules for blue electrophosphorescence were developed by combining the electron donor acridine derivatives with the electron acceptor triphenylphosphine oxide unit in a single molecule based on density functional theory. We obtained the energies of the first excited singlet (S₁) and triplet (T₁) states of the TADF materials by performing procedures in accordance with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to the ground state using dependence on the charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. Using DFT and TD-DFT calculations, the significant separation between the HOMO and LUMO caused a small difference in energy (ΔE_ST) between the S₁ and T₁ states. The host molecules retained high triplet energy and showed great potential for use in blue phosphorescent organic light-emitting diodes. The results also showed that these molecules are promising TADF host materials because they demonstrate a low barrier to hole and electron injection, balanced charge transport for both holes and electrons, and small ΔE_ST.     

Doping behavior of silicon in vapor-grown III–V epitaxial films

An expanded silicon-doping model, applicable for unintentionally doped vapor-grown III–V epitaxial materials, is presented based on additional experimental results of doping-level influences of AsH₃, PH₃, and HCl. This model retains the role of HCl as the silicon generation agent, as suggested in a recently reported silicon-doping model for GaAs. It also includes a surface kinetic factor for the silicon-incorporation efficiency in III–V materials as influenced by the relative vapor-phase concentration of As₂, As₄ and P₂, P₄ species. The present studies indicate a different degree of influence of the HCl and AsH₃ partial pressures on the suppression of the GaAs background doping level. The additive effect of both partial pressures is very similar to that found in the chloride system. Qualitatively, the same sensitivity of GaP doping levels to variations in HCl and PH₃ has been observed; however, the magnitudes of the doping-level changes are different. In all instances, the impurity levels in the epitaxial films are reduced by increases in the partial pressures of the various reactants, with the AsH₃ and PH₃ having a greater influence than the HCl.     

Synthesis and Crystal Structure of 2,13-Bis(acetamido)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0<Superscript>1.18</Superscript>,0<Superscript>7.12</Superscript>]docosane Tetrachlorocobalt(II)dihydrate

Abstract The novel ionic compound [H₂bdtd][CoCl₄] · 2H₂O (1) was prepared by the reaction between CoCl₂ and 2,13-bis(acetamido)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane (bdtd) in adjusted to pH 3.0 by 1.0 M HCl and structurally characterized. The crystals are monoclinic C2/c with a = 18.7777(9), b = 9.7356(4), c = 20.0884(9) ?, β = 109.6340(10)°, V = 3458.9(3) ?³, Z = 4. The dication H₂bdtd occupies a special position about an inversion center. The cobalt(II) atom in the anion is in a distorted tetrahedral environment with four chloride ligands. The crystal structure is stabilized by a variety of hydrogen-bonding contacts involving the dication, chloride anions and solvent water molecules. Cyclic voltammetry of [CoCl₄]²⁻ anion in 1 undergoes irreversible one-electron reduction to the Co^II/Co^I. Graphical abstract The crystal structure of the ionic compound [H₂bdtd][CoCl₄] · 2H₂O (1) consists of [H₂bdtd]²⁺ cation, [CoCl₄]²⁻ anion and water molecules joined together by ionic interaction and hydrogen bonds. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Charge Carrier Transport 1n 1:1 Complexes of Tetracyanobenzene with Naphthalene Anthracene and Durene

Abstract

It is well established that crystals of charge transfer (CT) complexes formed between aromatic donors and acceptors are built up of linear stacks of closely packed molecules. There are two main types of CT crystal structure, (i) a parallel arrangement of linear stacks made up of the individual component molecules, AAAA…DDDD… and (ii) a parallel arrangement of linear stacks made up of alternating molecules, ADADA… In each case it is to be expected that the intermolecular forces between the face to face packed molecules in each stack are far greater than those forces between stacks. A considerable anisotropy in physical properties which are a strong function of intermolecular interactions is a natural result of these crystal structures. Such anisotropy has been reported in the few crystals of the ADAD structure which have been examined, for example, in triplet exciton motion in biphenxl² and anthracene tetracyanobenzene (TCNB) complexes³,⁴ and in charge carrier mobilities μ in anthracene⁵ and phenthrene-pyromellitic-acid-dianhydride⁶ as well as anthracene-trinitrobenzene⁷. Carrier mobilities which were reported were all low, < 0.1 cm²/V sec., and though the major interesting questions were posed, such as what is the effect of different donors on μ?; or are there separate conduction and valence bands for acceptors and donors?; the dearth of mobility data on a range of materials leaves these questions unanswered. We have recently measured the mobilities of holes in several TCNB complexes as a first step towards understanding carrier transport in such materials. These are a particularly interesting series of materials in that triplet motion is said to be primarily two dimensional in anthracene TCNB³, and unidimensional in biphenyl TCNB². Since the transport of charge, like triplet exciton motion, is dominated by exchange interactions, and since CT triplet     

Role of diffusing molecular hydrogen on relaxation processes in Ge-doped glass

Temperature dependencies of steady-state and time-resolved photoluminescence (PL) from triplet state at 3.1 eV and singlet state at 4.2 eV ascribed to the twofold-coordinated Ge have been measured in unloaded and H₂-loaded Ge-doped silica samples under 5.0 eV excitation in the 10–310 K range. Experimental evidences indicate that diffusing molecular hydrogen (H₂) depopulates by a collisional mechanism the triplet state, decreasing both its lifetime of about 14% and the associated triplet PL intensity, whereas those of the singlet are insensitive to the presence of H₂.     

EPR Studies of Electron Spin Polarization of Triplet Exciton and its Transfer into Triplet Traps of Naphthalene-TCNQ and Naphthalene-pChloranil Guest Complexes in the Naphthalene-TCNB Host

The EPR spectra of triplet excitons in single crystals of Naphthalene-TCNB (N-TCNB) charge-transfer (CT) complexes show optical electron spin polarization (OEP) which is accounted for by a spin selective populating process from the excited CT singlet into an excited triplet state localized on the acceptor. OEP is also observed for triplet traps in N-TCNB crystals doped with TCNQ and pChloranil. The analysis of the orientation dependence of spin polarization allows one to establish that also selective decay from the trap spin sublevels is important for the onset of the observed OEP features.     

Energy of Pair Interaction of Molecular Systems: Excited State – Ground State of Molecules Pentyl – and Pentyloxy – Cyanobiphenyls

Abstract

The energies of pair interaction of molecular systems: first excited state and ground state of molecules pentyl - and pentyloxy - cyanobiphenyls was calculated and equilibrium configuration of these molecular systems was determinate. Pair orientated destabilization energies evaluation is given at the absorbtion and emission processes.     

Starburst-Type Carbazole Trimers as Host Materials for Solution-Processed Phosphorescent OLEDs

Novel starburst-type carbazole trimers SB-1 and SB-2 were developed as hole-transporting host materials for phosphorescent organic light-emitting diodes (PhOLEDs). The triplet levels (T₁s) of SB-1 and SB-2 were determined as at 2.81 and 2.73 eV, respectively. Also, these compounds afforded stable amorphous thin films upon spin-coating, and thus it was found that they are applicable to solution-processed devices. Indeed, blue PhOLEDs were fabricated by a solution method using SB-1 and SB-2 as host materials, where better device performance was obtained for the SB-1-based device due to its higher-lying T₁.     

The Triplet State in Pyrene

Both emission and excitation spectra of phosphorescence and delayed fluorescence of pyrene single crystals have been investigated between 2 K and 300 K using cw dye laser excitation. The experiments prove that the lowest triplet state is excitonic in nature in the high and low temperature crystalline phases. No evidence for triplet excimer emission could be found. The so-called regular broad band triplet excimer emission was spectrally resolved at low temperature and identified as trap emission. On the basis of polarized high resolution excitation spectra of undoped normal and perdeuterated pyrene (supplemented by Zeeman spectra at helium temperature) and the concentration dependent phosphorescence excitation spectra of isotopically mixed crystals the triplet state symmetry and the excitonic Davydov splitting of the low temperature crystalline phase was determined. The resonance pair interaction between the dimer molecules was found to be an order of magnitude smaller than predicted from calculations reported so far.     

Mechanisms of chemical vapor deposition of silicon

The distribution in the silicon epitaxial growth from SiCl₄ and hydrogen are observed in situ by IR absorption spectroscopy. Two methods are used complementarily, one is IR spectroscopy of reactants extracted from the reactor by a fine quartz tube which is not disturbing the reactions, and gives knowledge about the local distribution, the other is direct IR spectroscopy of hot reactants in the reactor which is useful to ascertain the results at the real high temperature situation. The intermediate species are SiHCl₃, SiH₂Cl₂ which is estimated from the induced emission bands at 500 and 570 cm^-1. HCl is a dominant waste product and contributes to reverse reactions. To investigate the reaction, HCl is intentionally injected into the reacting gas. This kind of injection method may also be very effective to analyze the reactions using other reactants such as SiCl₄, SiHCl₃ and SiH₂Cl₂.     

3-D polymeric structure formed by hydrogen bonds of copper (II) complex

A new copper complex trans-Dichlorobis[4-methoxypyridine]copper(II) (1) was synthesized and its crystal structure determined by X-ray diffraction. The close Cu···Cl contacts between the molecular units form bi-bridged dimers. The Copper(II) ion completes its 4 + 2 coordination via interaction with the Cu···Cl close contact. The complex has a polymeric structure of infinite one-dimensional (1D) bi-bridged chains, consisting of six-coordinate copper(II) units. C–H···C l intermolecular interaction connect the 1D-chains in the structure of 1 which form to 3D structure. The π ··· π interactions between the aromatic rings are also observed in the hydrogen bonded assembly of 1.     

Crystal structure of two tricyclic antidepressant drugs: Lofepramine hydrochloride and dothiepin hydrochloride

The structures of lofepramine·HCl (1) [C₂₆H₂₇ClN₂O·HCl, triclinic, space groupP¯1, witha=17.273(8),b=9.451(7),c=7.447(5) Å,=101.88(5),=96.14(6), =96.38(5)°,Z=2] and dothiepin·HCl (2) [C₁₉H₂₁NS·HCl, monoclinic, space groupP2₁/c, witha=14.296(5),b=9.364(3),c=13.724(3) Å,=97.77(3)°,Z=4] were determined by the symbolic-addition procedure and refined by least-squares methods to anR of 0.045 (2253 diffractometer-measured reflections) for (1) and 0.051 (1696 reflections) for (2). The butterfly angle between the two aromatic ring mean planes in the tricyclic system is 123.7° in (1) and 126.2° in (2); the middle seven-membered heteroring shows twist, bow, and stern angles of 18.1, 127.6, and 149.2° for (1) and 14.6, 132.8, and 155.5° for (2). The configuration at the propylamino C(16)-C(17) and C(17)-C(18) bonds of the side chain in (1) is close totrans-trans and in both compounds the only approach less than van der Waals distances is the hydrogen bond between the positively charged dimethylammonium and the chloride ion [3.01 and 2.96 Å for (1) and (2), respectively].     

Complexes of poly-N-vinylpyrrolidone with sulfonated tetraphenylporphins

The interaction of sulfonated tetraphenylporphins H₂ TPPS₄(HCl)₂ and in CuTPPS₄ with poly-N-vinylpyrrolidone (PVP) is studied using small-angle neutron scattering, dynamic light scattering, visible spectrophotometry, and viscometry. It is shown that porphyrin molecules form complexes with PVP, thus charging the polymeric chain.     

Optically Detected Magnetic Resonance (ODMR) Study of Isolated C70 Molecules and C70 Films

Abstract

The X-band ODMR of C₇₀ molecules isolated in a toluene/polystyrene (C₇₀:T/PS) glass and C₇₀ films is compared to that of C₆₀. As C₆₀:T/PS, the C₇₀ glasses exhibit only a triplet pattern at g ? 2, clearly due to an exciton delocalized over the molecule; however, it is strikingly asymmetric and narrower, due to the larger size of C₇₀. The ODMR of both C₆₀ and C₇₀ films includes a narrow photoluminescence-enhancing polaron resonance and full- and half- field narrow and broad triplet exciton patterns. As in the glasses, the narrow pattern is due to the exciton delocalized over the molecule and is narrower in C₇₀ The broad pattern is tentatively assigned to a triplet localized on a face adjacent to a neighboring molecule. In contrast to C₆₀, the ODMR of C₇₀ films is detectable up to 295 K, apparently due to the slower rotation.