Phenothiazine–BODIPY–Fullerene Triads as Photosynthetic Reaction Center Models: Substitution and Solvent Polarity Effects on Photoinduced Charge Separation and Recombination

Novel photosynthetic reaction center model compounds of the type donor₂–donor₁–acceptor, composed of phenothiazine, BF₂‐chelated dipyrromethene (BODIPY), and fullerene, respectively, have been newly synthesized using multistep synthetic methods. X‐ray structures of three of the phenothiazine‐BODIPY intermediate compounds have been solved to visualize the substitution effect caused by the phenothiazine on the BODIPY macrocycle. Optical absorption and emission, computational, and differential pulse voltammetry studies were systematically performed to establish the molecular integrity of the triads. The N‐substituted phenothiazine was found to be easier to oxidize by 60 mV compared to the C‐substituted analogue. The geometry and electronic structures were obtained by B3LYP/6‐31G(dp) calculations (for H, B, N, and O) and B3LYP/6‐31G(df) calculations (for S) in vacuum, followed by a single‐point calculation in benzonitrile utilizing the polarizable continuum model (PCM). The HOMO?1, HOMO, and LUMO were, respectively, on the BODIPY, phenothiazine and fullerene entities, which agreed well with the site of electron transfer determined from electrochemical studies. The energy‐level diagram deduced from these data helped in elucidating the mechanistic details of the photochemical events. Excitation of BODIPY resulted in ultrafast electron transfer to produce PTZ–BODIPY^.+–C₆₀^.?; subsequent hole shift resulted in PTZ^.+–BODIPY–C₆₀^.? charge‐separated species. The return of the charge‐separated species was found to be solvent dependent. In nonpolar solvents the PTZ^.+–BODIPY–C₆₀^.? species populated the ³C₆₀* prior to returning to the ground state, while in polar solvent no such process was observed due to relative positioning of the energy levels. The ¹BODIPY* generated radical ion‐pair in these triads persisted for few nanoseconds due to electron transfer/hole‐shift mechanism.     

Thermoelectric properties of HPHT sintered In-doped Pb0.5Sn0.5Te

The thermoelectric properties of Pb_0.5Sn_0.5Te doped with In at 1.0, 2.0, and 3.0×10¹⁹/cm³ and sintered at a high pressure and high temperature (HPHT) of 4.0 GPa and 800 or 900 °C, respectively, have been studied. All samples show p-type semiconducting behavior with positive thermopower. We find that HPHT sintering of conventionally synthesized materials improves their thermoelectric properties. The highest power factor is obtained for In doping of 2.0×10¹⁹/cm³ with 13.5 μW/cm K² at 230 °C. The corresponding figure of merit is 1.43×10⁻³/K. This represents a twofold improvement in thermoelectric figure of merit, compared to the conventionally sintered materials reported in the literature. When exposed to 400 °C for 10 days, samples sintered at 900 °C exhibit more stable thermoelectric properties, while the properties of those sintered at 800 °C deteriorated. These results demonstrate that HPHT sintering is a viable and controllable way of tuning the thermoelectric properties of PbTe-based materials.     

A new protecting group for the exocyclic amino groups of nucleosides

A new protecting group has been developed for the exocyclic amino groups of nucleosides that occur in DNA. 3-Phenyl-[{N-(2-trimethylsilyl-ethoxycarbonyl)-2-amino}]-propanoic acid used as the protective agent.     

Reactivity of polyesters in glycolysis reactions: Unexpected effect of the chemical structure of the polyester glycolic unit

Kinetic studies of PET glycolysis by diethylene glycol (DEG), dipropylene glycol (DPG), glycerol (Gly) and mixtures of these glycols have shown, in a previous study, that the order of reactivity of the glycols differs according to the conditions of temperature and catalysis. Indeed, their global reactivity depends both on their chemical reactivity and physico-chemical properties.Glycolysis of model polyesters which are liquid at the reaction temperature, which allows us to overcome the problem of the polyesters' solubility, were studied to compare the chemical reactivity of these glycols. Three oligoesters were synthesized from dimethyl terephthalate and three different glycols namely triethylene glycol, ethylene glycol and hexanediol to form, respectively, PE₃T, OET and PTHD.Results showed that the order of reactivity of the glycols is the same for PET, OET and PTHD but different for PE₃T. Indeed, DPG without catalyst has a particular and unexpected behaviour: its reactivity seems to be strongly influenced by the presence of oxygen atoms in the chain.     

Water substitution on iron centers: from 0D to 1D sandwich type polyoxotungstates

Four novel polyoxotungstates have been synthesized by reaction of the sandwich type compound [Fe (III) 4(H 2O) 10(B-beta-SbW 9O 33) 2] (6-) (noted Fe 4(H 2O) 10Sb 2W 18) with ethylenediamine (en) and/or oxalate (ox) ligands under various conditions. The one-dimensional (1D) compound [enH 2] 3[Fe (III) 4(H 2O) 8(SbW 9O 33) 2].20H 2O ( 1) is isolated at 130 degrees C and results from the elimination of two water molecules and the condensation of the polyoxotungstate precursor. The reaction of Fe 4(H 2O) 10Sb 2W 18 with oxalate ligands affords the molecular complex Na 14[Fe (III) 4(ox) 4(H 2O) 2(SbW 9O 33) 2].60H 2O ( 2) where two organic ligands substitute four water molecules, while the same reaction in the presence of en molecules at 130 degrees C leads to the formation of the functionalized 1D chain [enH 2] 7[Fe (III) 4(ox) 4(SbW 9O 33) 2].14H 2O ( 3) with protonated ethylenediamine counterions. Finally, at 160 degrees C a rearrangement of the Fe 4(H 2O) 10Sb 2W 18 polyoxotungstate is observed, and the sandwich type compound [enH 2] 5[Fe (II) 2Fe (II) 2(enH) 2(Fe (III)W 9O 34) 2].24H 2O ( 4) crystallizes. In 4, the heteroelement is a Fe (III) ion, and the water molecules on the two outer Fe (II) centers are bound to pendant monoprotonated en ligands. The four compounds have been characterized by IR spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. A detailed study of the magnetic properties of the mixed-valent hexanuclear iron complex in 4 shows evidence of an S = 5 ground-state because of spin frustration effects. A quantification of the electronic parameters characterizing the ground state ( D = +1.12 cm (-1), E/ D = 0.15) confirms that polyoxotungstate ligands induce large magnetic anisotropy.     

Asymmetric conjugate addition of thioglycolate to a range of chalcones using tetrahydroisoquinoline (TIQ) N,N′-dioxide ligands

A series of novel TIQ based N,N′-oxide ligands were synthesised and screened for their catalytic activity in the enantioselective conjugate addition of thioglycolate to chalcones. Bulky groups on the side chain of the TIQ backbone provided the highest enantioselectivity of up to 88% with 10 mol % catalyst loading. It was also observed that these reactions proceeded optimally in the presence of dichloromethane as a solvent. Screening of various metals emphasized La(OTf)₃ as the ideal pre-catalyst for this particular reaction.     

THE REACTIONS OF N3P3CL6 AND RELATED COMPOUNDS WITH DIFUNCTIONAL REAGENTS. COMPARISONS AND CONTRASTS

Abstract

The reactions of N₃P₃Cl₆ with a variety of difunctional reagents are discussed. NMR spectroscopic and X-ray crystallographic investigations are presented.     

Reduction of Aryl Trifluoromethyl Oximes

Borane-tetrahydrofuran complex reduces trifluoromethyl oximes to trifluoromethyl hydroxylamines in good yields.