A Raman study of lattice vibrations in II–VI semiconductors doped with 3<Emphasis Type="Italic">d</Emphasis> elements

Room-temperature Raman spectra were obtained for powder samples of Zn_1?xNixSe and Zn_1?yCr_ySe compounds and for a single-crystal Zn_1?xNi_xSe (x = 0.0025) sample in the temperature range 5–140 K. The results obtained are interpreted in terms of large-scale lattice shear strains induced by 3d elements in these solid solutions.     

Alkylimidazolium Protic Ionic Liquids: Structural Features and Physicochemical Properties

We focus on a series of protic ionic liquids (PILs) with imidazolium and alkylimidazolium (1R3HIm, R=methyl, ethyl, propyl, and butyl) cations. Using the literature data and our experimental results on the thermal and transport properties, we analyze the effects of the anion nature and the alkyl radical length in the cation structure on the above properties. DFT calculations in gas and solvent phase provide further microscopic insights into the structure and cation-anion binding in these PILs. We show that the higher thermodynamic stability of an ion pair raises the PIL decomposition temperature. The melting points of the salts with the same cation decrease as the hydrocarbon radical in the cation becomes longer, which correlates with the weaker ion-ion interaction inthe ion pairs. A comparative analysis of the protic ILs and corresponding ILs (1R3MeIm) with the same radical (R) in the cation structure and the same anion has been performed. The lower melting points of the ILs with 1R3MeIm cations are assumed to result from the weakening of both the ion-ion interaction and the hydrogen bond.     

Red Light-Emitting Thermally-Activated Delayed Fluorescence of Naphthalimide-Phenoxazine Electron Donor-Acceptor Dyad: Time-Resolved Optical and Magnetic Spectroscopic Studies

We prepared an orthogonal compact electron-donor (phenoxazine, PXZ)-acceptor (naphthalimide, NI) dyad ( NI-PXZ ), to study the photophysics of the thermally-activated delayed fluorescence (TADF), which has a luminescence lifetime of 16.4 ns (99.2 %)/17.0 μs (0.80 %). A weak charge transfer (CT) absorption band was observed for the dyad, indicating non-negligible electronic coupling between the donor and acceptor at the ground state. Femtosecond transient absorption spectroscopy shows a fast charge separation (CS) (ca. 2.02∼2.72 ps), the majority of the singlet CS state is short-lived, especially in polar solvents (τ_CR = 10.3 ps in acetonitrile, vs. 1.83 ns in toluene, 7.81 ns in n-hexane). Nanosecond transient absorption spectroscopy detects a long-lived transient species in n-hexane, which is with a mixed triplet local excited state (³LE) and charge separated state (³CS), the lifetime is 15.4 μs. In polar solvents, such as tetrahydrofuran and acetonitrile, a neat ³CS state was observed, whose lifetimes are 226 ns and 142 ns, respectively. Time-resolved electron paramagnetic resonance (TREPR) spectra indicate the existence of strongly spin exchanged ³LE/³CT states, with the effective zero field splitting (ZFS) |D| and |E| parameters of 1484 MHz and 109 MHz, respectively, much smaller than that of the native ³NI state (2475 and 135 MHz). It is rare but solid experimental evidence that a closely-lying ³LE state is crucial for occurrence of TADF and this ³LE state is an essential intermediate state to facilitate reverse intersystem crossing in TADF systems.     

Methanethiosulfonate Derivative of OX063 Trityl: A Promising and Efficient Reagent for Side-Directed Spin Labeling of Proteins

Trityl radicals (TAMs) have recently appeared as an alternative source of spin labels for measuring long distances in biological systems. Finland trityl radical (FTAM) served as the basis for this new generation of spin labels, but FTAM is rather lipophilic and susceptible to self-aggregation, noncovalent binding with lipophilic sites of proteins, and noncovalent docking at the termini of duplex DNA. In this paper the very hydrophilic OX063 TAM with very low toxicity and little tendency for aggregation is used as the basis for a spin label. Human serum albumin (HSA) labeled with OX063 has an intense narrow line typical of TAM radicals in solution, whereas HSA labeled with FTAM shows broad lines and extensive aggregation. In pulse EPR measurements, the measured phase memory time T_M for HSA labeled with OX063 is 6.3 μs at 50 K, the longest yet obtained with a TAM-based spin label. The lowered lipophilicity also decreases side products in the labeling reaction.     

Spin–Orbit Charge-Transfer Intersystem Crossing in Anthracene–Perylenebisimide Compact Electron Donor–Acceptor Dyads and Triads and Photochemical Dianion Formation

Perylenebisimide ( PBI )–anthracene ( AN ) donor–acceptor dyads/triad were prepared to investigate spin–orbit charge-transfer intersystem crossing (SOCT-ISC). Molecular conformation was controlled by connecting PBI units to the 2- or 9-position of the AN moiety. Steady-state, time-resolved transient absorption and emission spectroscopy revealed that chromophore orientation, electronic coupling, and dihedral angle between donor and acceptor exert a significant effect on the photophysical property. The dyad PBI-9-AN with orthogonal geometry shows weak ground-state coupling and efficient intersystem crossing (ISC, Φ_Δ=86 %) as compared with PBI-2-AN (Φ_Δ=57 %), which has a more coplanar geometry. By nanosecond transient absorption spectroscopy, a long-lived PBI localized triplet state was observed (τ_T=139 μs). Time-resolved EPR spectroscopy demonstrated that the electron spin polarization pattern of the triplet state is sensitive to the geometry and number of AN units attached to PBI . Reversible and stepwise generation of near-IR-absorbing PBI radical anion ( PBI^−⋅ ) and dianion ( PBI²⁻ ) was observed on photoexcitation in the presence of triethanolamine, and it was confirmed that selective photoexcitation at the near-IR absorption bands of PBI^.− is unable to produce PBI²⁻ .     

Thermodynamics of heteroligand mercury(II) complexes with nitrilotriacetic acid and ethylenediamine in aqueous solution

Formation of heteroligand complexes HgNtaEn⁻ and Hg(Nta)₂En⁴⁻, where Nta³⁻ is nitrilotriacetate ion and En is ethylenediamine, was studied by means of direct calorimetry, potentiometry, and NMR spectroscopy at 298.15 K and ionic strength I = 0.5 (KNO₃).     

Enantiomers of all-cis-5-(4-bromophenyl)-4-tert-butoxycarbonyl-2-methoxycarbonylpyrrolidine: preparative HPLC separation and acylative kinetic resolution of the racemate

The fundamental possibility of acylative kinetic resolution of racemic heterocyclic amines was demonstrated by the example of all-cis-5-(4-bromophenyl)-4-tert-butoxycarbonyl-2-methoxycarbonylpyrrolidine. Individual enantiomers (ee >99%) were obtained in high yields via preparative chiral HPLC.     

Gas-chromatographic identification of chloro- and bromo-substituted anilines by their retention indices

Gas chromatography retention indices were experimentally determined for 27 chloro- and bromo-substituted anilines on the standard non-polar polydimethylsiloxane stationary phase; a procedure for the estimation of retention indices for any other species of the studied class was proposed. The computational algorithm is based on a modified additive scheme equivalent to the assembly of the target structure from simpler molecules characterized by retention indices, using their addition and subtraction.     

Effect of the nature of chiral fragment on mesomorphic properties of triphenylene ethers

A number of new 2,3,6,7,10,11-hexakis(heptyloxy)triphenylenes possessing a chiral substituent in position 1 of the triphenylene ring system and characterized by predictable mesomorphism were synthesized. The effect of the nature of the chiral fragment (dehydrocholic, lipoic, and d-tartaric acid residues) on the mesomorphic properties of triphenlylene ethers was studied. N-[2,3,6,7,10,11-hexakis(heptylozy)triphenylen-1-yl]amides derived from the above acids, unlike initial monomesomorphic amine, exhibit enantiotropic columnar polymorphism and give rise to helical columnar structure at reduced temperature. The newly synthesized amides are characterized by lower thermal stability and broader temperature range of the mesophase. Introduction of two chiral dehydrocholic acid fragments into the triphenylene core favors columnar (including chiral) mesomorphism.