Excited state kinetics in crystalline solids: self-quenching in nanocrystals of 4,4'-disubstituted benzophenone triplets occurs by a reductive quenching mechanism

We report an efficient triplet state self-quenching mechanism in crystals of eight benzophenones, which included the parent structure (1), six 4,4'-disubstituted compounds with NH(2) (2), NMe(2) (3), OH (4), OMe (5), COOH (6), and COOMe (7), and benzophenone-3,3',4,4'-tetracarboxylic dianhydride (8). Self-quenching effects were determined by measuring their triplet-triplet lifetimes and spectra using femtosecond and nanosecond transient absorption measurements with nanocrystalline suspensions. When possible, triplet lifetimes were confirmed by measuring the phosphorescence lifetimes and with the help of diffusion-limited quenching with iodide ions. We were surprised to discover that the triplet lifetimes of substituted benzophenones in crystals vary over 9 orders of magnitude from ca. 62 ps to 1 ms. In contrast to nanocrystalline suspensions, the lifetimes in solution only vary over 3 orders of magnitude (1-1000 μs). Analysis of the rate constants of quenching show that the more electron-rich benzophenones are the most efficiently deactivated such that there is an excellent correlation, ρ = -2.85, between the triplet quenching rate constants and the Hammet σ(+) values for the 4,4' substituents. Several crystal structures indicate the existence of near-neighbor arrangements that deviate from the proposed ideal for "n-type" quenching, suggesting that charge transfer quenching is mediated by a relatively loose arrangement.     

Photoexcitation of benzophenone triplets: a two-photon pathway for ground state repopulation

Room temperature laser excitation of benzophenone triplets in their visible absorption band in benzene solvent leads to their deactivation with concomitant ground state repopulation.     

Nitrogen extrusion from pyrazoline-substituted porphyrins and chlorins using long wavelength visible light

Protoporphyrin reacts with diazomethane to give pyrazolines which at long wavelength (approximately 630 nm) extrude nitrogen to give the corresponding cyclopropyl derivatives.     

Visible light photocatalysis with benzophenone for radical thiol-ene reactions

We report herein a simple, metal- and oxidant-free visible light promoted strategy for an anti-Markovnikov hydrothiolation of unactivated olefins using benzophenone as an inexpensive photocatalyst at room temperature. Anti-Markovnikov adducts of a wide variety of olefins and thiols are formed in highly regioselective manner and good to excellent yields. The present radical thiol-ene reaction is operationally simple and well tolerates a variety of functional groups.     

Interaction of triplet-excited benzophenone with hindered amines and amino ethers A laser flash photolysis study employing photoconductivity and light emission measurements

Hindered amines such as 2,2,6,6-tetramethyl piperidines and N-methyl-2,2,6,6-tetramethyl piperidines and hindered amino ethers such as N-methoxy-2,2,6,6-tetramethyl piperidines were examined with respect to their reactivity towards triplet-excited benzophenone (³BP^*) in Ar-saturated acetonitrile solution at room temperature. Upon measuring phosphorescence decay rates in the absence and presence of quencher it was found that the amines are two to three orders of magnitude more reactive than the amino ethers. For all amine/BP systems examined the generation of free ions was inferred from an increase in the electrical conductivity. This indicates that a charge transfer (CT) mechanism is operative in these cases. Notably, tertiary amines were found to be more reactive towards ³BP^* and give higher free ion yields than secondary amines. In the case of amino ether/BP systems evidence for a CT mechanism was not obtained in spite of an increase in the electrical conductivity indicating the generation of free ions. The latter are formed much faster than the phosphorescence decays and very likely originate from triplet–triplet annihilation (³BP^*+³BP^*→BP√⁺+BP√⁻).     

Structure of crystalline polymers with unbranched long side chains

The structure and thermodynamic properties of atactic and isotactic acrylic and methacrylic polymers containing 16–18 carbon atoms in the n-aliphatic side chains, and of copolymers of hexadecyl acrylate with isopropyl acrylate were studied by means of x-ray and differential thermal analysis. The crystallization of branched acrylic and methacrylic polymers and of acrylic copolymers proceeds in the form of a hexagonal crystal, regardless of the configuration of the backbone chain. Methods of ordering branched macromolecules are proposed, and the melting points, heats and entropies of fusion determined. The role of flexibility of the backbone chains in ordering and the crystallization processes was determined. In the case of poly(n-alkyl acrylates) the backbone chain is involved in the crystalline lattice; this is not the case in methacrylates and copolymers of hexadecyl acrylate with isopropyl acrylate. Some similarity was assumed between the structure of biopolymers and synthetic branched polymers.     

Interaction of triplet excitons with charge carriers in crystalline anthracene

The influence of a magnetic field on photo-enhanced hole and electron injected space charge limited currents in anthracene has shown the current enhancement is predominantly due to triplet-trapped charge carrier interactions. The observed current enhancement is too large to be produced by the production of one detrapped carrier for each annihilated triplet exciton. It is suggested that on detrapping the free carriers are in a quartet state, in which they gain energy from the applied field and then detrap further carriers themselves by scattering processes.     

The application of long wavelength radiation in X-ray analysis

The authors used long wavelength X-ray radiation excited by low energy electrons for analytical purposes. Low energy electron excitation was achieved with an open window tube. The authors used a type that was developed in Philips laboratories. The electron source was a glow discharge from which the electrons ( 15 keV) are extracted and directed towards the anode. A photon spectrum of “Bremsstrahlung” and characteristic peaks is generated at a gold anode. In addition about half of the impinging electrons is reflected and may, thanks to the open window, be used to irradiate a specimen in spite of a partial loss of energy due to the collisions.The authors mention the following attractive characteristics: the tube is simple to operate and may easily be exchanged for a closed tube; no high vacuum is needed, a feature which, however, at the same time inhibits the determination of traces of O, N, C; about 7 cm² of the specimen, which may be an insulator, is irradiated. A discussion of applications illustrates the usefulness of the tube.     

Interaction of amorphous and crystalline nickel nanoparticles with hydrogen

Nickel nanoparticles were deposited on the surface of highly oriented pyrolytical graphite by laser electrodispersion and precipitation from a solution of reverse micelles. The particles were studied using scanning tunneling microscopy and spectroscopy as well as Auger spectroscopy. The elemental composition of the nanoparticles and specific features of the electronic structure of their surface were determined. Adsorption of molecular hydrogen was also studied.     

Iodized BODIPY as a long wavelength light sensitizer for the near-infrared emission of ytterbium(III) ion

Novel 8-HOQ-BODIPY-3I was developed as an efficient sensitizer for the near-infrared emission of ytterbium(III) ion at 980 nm under long wavelength excitation.     

Interaction of arenecarbonylchromium π-complexes with light

Interaction of arenecarbonylchromium π-complexes, XArCr(CO)₂L (L = CO, PPh₃ and X = H, 3(CH₃), OCH₃, COOCH₃ and COCH3) with visible light was investigated by measurement of the electronic absorption spectra. These compounds were shown to interact with visible light via photodecay described by first order kinetics. It was shown that C₆H₆ and Cr(CO)₆ are the products of the photodecay of C₆H₆Cr(CO)₃. The substituents in the benzene ring (X = OCH₃, 3(CH₃), COOCH₃ and COCH₃) had no essential effect upon the rate of decomposition of the complexes investigated, while substitution of a CO group in ArCr(CO)₃ by a PPh₃ ligand increased the rate of reaction by about an order of magnitude. The study of the dependence of the rate of reaction on the intensity of the incident light in the course of photodecomposition enabled us to propose a mechanism for the reaction.     

Progress in long wavelength emission in fluorene-based electroluminescent blue materials

On account of the advantages of organic electroluminescent materials compared with their inorganic counterparts,the development of organic electroluminescent materials is one of the hot areas of the optoelectronic materials.Fluorene and its derivatives,which have an aromatic biphenyl structure with a wide energy gap in the backbones and high luminescent efficiency,have drawn much attention of ma-terial chemists and device physicists.However,one drawback of fluorene-based electroluminescent blue materials is that there is an occurrence of long wavelength emission after annealing the films in air or after operating organic light-emitting diodes for a long time.To clarify the origin of this long wave-length emission,the scientists at home and abroad have put forward all kinds of correlative explana-tions.Among the scientists,some thought it was caused by excimer-related species,while some others claimed that it was caused by the fluorenone of photooxdized fluorene.The corresponding solutions to this problem have also been proposed and the problem has been partially resolved in some degree.The present review summarizes and analyzes the progress made on the origin of long wavelength emission in fluorene-based electroluminescent blue materials at home and abroad in the past few years.Some issues to be addressed and hotspots to be further investigated are also presented and discussed.     

Effect of light wavelength on photooxygenation of hexamethylbenzene

Irradiation of the charge transfer complex of hexamethylbenzene with oxygen at 313 nm in a mixture of methanol and benzene afforded methoxymethylpentamethylbenzene and methoxypentamethylbenzene.     

Synthesis of monomers which are triplets of the “crystalline” part of collagen molecule

Conclusions Triplet monomers were synthesized with the sequences Gly-I-I, Gly-Ala-I, Ala-I-I, and Gly-Pro-R (I=the imino acid proline or hydroxyproline, and R=an amino acid residue).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 392–397, February, 1969.     

A single component ratiometric pH probe with long wavelength excitation of europium emission

Following excitation in the range 370-405 nm, the emission spectrum of a cell permeable macrocyclic Eu(III) complex incorporating an N-methylsulfonamide moiety changes form with pH, allowing ratiometric pH measurements in the range 6 to 8.     

Interaction of dihydrogen with small and light molecules

Second-order M?ller-Plesset (MP2) calculations (using the approximate resolution of the identity, RI-MP2), explicitly correlated MP2 (MP2-R12) calculations, and coupled-cluster calculations including all single and double excitations with a perturbative estimate of triple excitations [CCSD(T)] are performed to study the interaction of molecular hydrogen with the small molecules HF, H2O, NH3, and LiOH. Different adsorption positions are studied. In the cases of H2O and NH3, the most favorable configuration places H2 in an end-on fashion on the O or N atom, respectively. In the cases of HF and LiOH, the H2 molecule takes a side-on position on the H atom of HF or the Li atom. With respect to MP2 calculations in a triple-zeta basis, both the enlargement of the basis set and the extension of the correlation treatment (CCSD(T) vs MP2) increase the interaction energy. The basis set limit CCSD(T) estimates of the interaction energy of H2 with the HF, H2O, NH3, and LiOH molecules amount to 4.40, 2.67, 3.02, and 10.74 kJ mol-1, respectively. The interaction energy for the simultaneous interaction of H2 with two LiOH molecules does not significantly exceed the value obtained for the interaction with a single LiOH molecule. Furthermore, the interaction energies (by MP2) of H2 with glycine, the glycine dimer, and imidazolium chloride amount to 2.78, 5.00, and 6.30 kJ mol-1, respectively.     

Liquid crystalline epoxides with long lateral substituents: Synthesis and curing

A series of liquid crystalline epoxides with long lateral substituent from 4 to 12 carbon atoms was synthesized and characterized by ¹H NMR, FTIR spectroscopy, differential scanning calorimetry (DSC), polarized light optical microscopy (POM). The curing products of the LCE with DDM, was analyzed by POM and WAXS. The cure kinetics of epoxides and aromatic amine was investigated. The curing activation energy about 43.3-53.2 kJ mol⁻¹ was determined and compared for all the LC epoxides through Ozawa method. The change of activation energy suggests that the reaction active depends upon the lateral substituents, because the lateral substituents parallel to the rod-like core and can act as bound solvent.     

Determination of soluble phosphates in water samples using ytterbium(III) and dynamic measurements of light scattering intensity at long wavelength

A selective and fast method has been developed for the determination of phosphates by measuring the formation of ytterbium(III) phosphate through the variation of the light scattering intensity with time. The low solubility of this compound causes an efficient dispersion of the radiation at 490 nm, which is measured at 980 nm using the second-order grating effect. This approach minimizes potential background signals from the sample matrix. The initial rate of the system is automatically obtained in only 0.5 s by stopped-flow mixing technique. The variable optimization study has been carried out using univariate and multivariate methods. The dynamic range of the calibration graph is 0.09–7.9 mmol L⁻¹ (Pearson's correlation coefficient = 0.9999) and the detection limit is 0.03 mmol L⁻¹. The precision of the method, expressed as relative standard deviation, is 2.3%. The study of the potential interference of different inorganic anions showed that arsenate is the main interferent, although it is tolerated in a molar ratio of 5.5. The method has been satisfactorily applied to the determination of soluble phosphates in tap, ground and river water using a previous preconcentration step with a Dowex 1 (1 × 4–400) anionic resin. A 500-fold concentration has been achieved, which has allowed to decrease the detection limit up to 60 mmol L⁻¹. The recovery range is 97.5–102.5%. The results obtained are consistent with those obtained with the standard molybdenum blue method.