Disubstituted “K-region” arene oxides

The first syntheses of tri- and tetra-cyclic vic-disubstituted arene oxides are described. The general route to 9,10-dimethyl- and 9,10 - bis(p - chlorophenyl) - phenanthrene - 9,10 - oxide, and to 5,6 - diphenylbenzo[c]phenanthrene 5,6 - oxide, includes oxidation of the unsubstituted aromatic hydrocarbon to the K-region quinone followed by reaction with an alkyl- or aryl-magnesium bromide and treatment of the resulting trans-diol with dimethylformamide dimethylacetal. A previous report on the synthesis of a disubstituted chrysene oxide has been proved to be in error.     

Synthesis and spectroscopic studies of isosteviol-calix[4]arene and -calix[6]arene conjugates

Novel calix[4]arene derivatives functionalized with two or four isosteviol units at the upper rim and a new calix[6]arene having six isosteviol moieties at the lower rim have been synthesized. The structures of these compounds have been confirmed by NMR and mass spectrometry data. All ¹H and ¹³C NMR chemical shifts of isosteviol were fully assigned by extensive NMR spectroscopic methods, and used to clarify the structures and conformations of isosteviol-calixarene conjugates.     

Emission spectroscopic and ODMR studies of the lowest excited triplet state of dichlorophenylborane

The triplet state T₁ of dichlorophenylborane (PhBCl₂) has been investigated by optical emission and ODMR spectroscopic methods in order to study the influence of substituents with mesomeric and inductive effects. The zero-field splitting (ZFS) parameters D and E, the selective kinetic rates of radiative and non-radiative deactivation of the triplet sublevels and the phosphorescence spectrum were measured. From the small value of D = 0.1201 cm^?1 a considerable charge transfer admixture to the ³L_a state of benzene has to be assumed. The ratio of the radiative rates shows a distortion of the molecule. Further a heavy atom effect of the chlorine atoms on the in-plane rates of the deactivation of T₁ can be observed.     

Asymptotic quantum yield of triplet sensitized decomposition

The asymptotic quantum yield of triplet energy transfer is found by calculating the fraction of acceptor molecules with energy above the minimum energy for decomposition. This is done by allowing for a statistical energy distribution among the internal modes in the collision complex. It is found that for a monatomic triplet donor most of the triplet energy is transferred to the acceptor molecule, while for a polyatomic donor molecule only a fraction of it is available for future decomposition of the acceptor.     

Time-resolved resonance Raman spectroscopic studies on the triplet excited state of thioxanthone

Thioxanthone has been investigated extensively owing to its unique photochemical and photophysical applications and its solvatochromic behavior. Here, we report the time-resolved resonance Raman studies on the structure of the lowest triplet excited state of thioxanthone in carbon tetrachloride. In addition, FT-IR and FT-Raman techniques have been used to study the vibrational structure in the ground state. To corroborate the experimental findings, density functional theory calculations have been carried out. Isotopic calculations and normal coordinate analysis have been used to help in assigning the observed bands to Raman vibrational modes. Structural information derived from this study is expected to help in better understanding the triplet state photochemistry of thioxanthone.     

Femtosecond and nanosecond laser induced breakdown spectroscopic studies of NTO,HMX, and RDX

We present our results from the laser induced breakdown spectroscopic studies of 5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO), Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) investigated using nanosecond and femtosecond pulses. The presence of C, CN peaks in the spectra, signatures of high energy materials, was confirmed and persistence of emissions has been measured. Some of the Nitrogen peaks in fs LIBS spectra were found to be lower in magnitude (after normalization with N 868.60 nm peak) compared to the ns LIBS spectra. The presence of an additional CN peak in the fs spectra was identified for all samples. The ratio of CN peaks (388.28 nm, 387.08 nm, 386.16 nm) to C peak (247.82 nm), recorded with similar fluences, was discovered to be stronger in the fs case. Some of the possible mechanisms ensuing from our studies towards discrimination of such materials are outlined.     

Laser spectroscopic and theoretical studies of encapsulation complexes of calix[4]arene

The complexes between the host calix[4]arene (C4A) and various guest molecules such as NH(3), N(2), CH(4), and C(2)H(2) have been investigated via experimental and theoretical methods. The S(1)-S(0) electronic spectra of these guest-host complexes are observed by mass-selected resonant two-photon ionization (R2PI) and laser-induced fluorescence (LIF) spectroscopy. The IR spectra of the complexes formed in molecular beams are obtained by IR-UV double resonance (IR-UV DR) and IR photodissociation (IRPD) spectroscopy. The supramolecular structures of the complexes are investigated by electronic structure methods (density functional and second order perturbation theory). The current results for the various molecular guests are put in perspective with the previously reported ones for the C4A-rare gas (Rg) (Phys. Chem. Chem. Phys. 2007, 126, 141101) and C4A-H(2)O complexes (J. Phys. Chem. A, 2010, 114, 2967). The electronic spectra of the complexes of C4A with N(2), CH(4), and C(2)H(2) exhibit red-shifts of similar magnitudes with the ones observed for the C4A-Rg complexes, whereas the complexes of C4A with H(2)O and NH(3) show much larger red-shifts. Most of the IR-UV DR spectra of the complexes, except for C4A-C(2)H(2), show a broad hydrogen-bonded OH stretching band with a peak at ~3160 cm(-1). The analysis of the experimental results, in agreement with the ones resulting from the electronic structure calculations, suggest that C4A preferentially forms endo-complexes (guests inside the host calizarene cavity) with all the guest species reported in this study. We discuss the similarities and differences of the structures, binding energies, and the nature of the interaction between the C4A host and the various guest species.     

The triplet sensitized reaction of singlet oxygen with 2,5-ditertiarybutylfuran: yield evidence for inefficient triplet energy transfer from benzophenone to oxygen

The reaction of 2,5-ditertiarybutylfuran with singlet oxygen has been used as a monitor to show that the quenching of triplet benzophenone by oxygen gives singlet oxygen with considerably less than unit efficiency.     

Alkali metal mediated conversion of arene oxides and arene imines into aromatic hydrocarbons

K-Region oxides and imines of phenanthrene, chrysene benz[a]anthracene, and dibenz[a,h]anthracene react in tetrahydrofuran with lithium and sodium to give the parent hydrocarbons. In the presence of excessive metal, the latter are converted into dianions from which the parent compounds can be regenerated upon quenching with oxygen. Metalate derivatives of the oxides and imines are proposed to be the corresponding reaction intermediates in the deoxygenation and deamination processes.     

Synthesis,electrochemical and spectroscopic studies of highly extended tetraaryl-m-phenylenediamines as precursors of ground-state triplet dications

Two types of iodinated tetraaryl-1,3-phenylenediamine were designed and synthesized as useful building blocks for synthons in organic syntheses. Various highly π-extended tetraaryl-1,3-phenylenediamines for charged high-spin molecular systems were successfully synthesized from the precursors using Sonogashira coupling. Their electrochemical and spectroscopic properties were also examined. The dications derived from highly π-extended tetraaryl-1,3-phenylenediamines were generated and characterized by electron transfer stopped-flow method. Some of the monocation radicals were short-lived.     

Chiral alpha-branched benzylic carbocations: diastereoselective intermolecular reactions with arene nucleophiles and NMR spectroscopic studies

The chiral benzylic alcohols 1-6 were prepared and subjected to S(N)1-type displacement reactions with various arene nucleophiles in acidic medium. Under optimized conditions (HBF(4).OEt(2), CH(2)Cl(2), -78 degrees C --> r.t.) the corresponding 1,1-diarylalkanes 11-18 and 20 were obtained in good chemical yields (48-99%). The facial diastereoselectivity of the reaction is high (d.r. = 91/9-97/3) when the substrate bears a stereogenic carbon center -CHtBuMe in the alpha-position to the electrophilic carbon atom. If the starting material was enantiomerically pure, no significant racemization was observed (94% ee --> 92% ee). The reactions proceed stereoconvergently as demonstrated by the conversion of the separated diastereoisomers syn-1a and anti-1a in separate reactions to the same product syn-11 (d.r. = 97/3). Further evidence for long-lived chiral benzylic carbocations as reaction intermediates was obtained from NMR studies in superacidic medium. The chiral cation 24 was generated in SO(2)ClF as the solvent at -70 degrees C employing SbF(5) as the Lewis acid and characterized by its (1)H and (13)C NMR spectra. NOE measurements suggest a preferred conformation in which the diastereotopic faces of the cation are differentiated by the two carbon substituents R and Me at the stereogenic carbon center in the alpha-position. The hypothesis is further supported by the observation that the diastereoselectivity of the substitution reaction decreases if the bulky tert-butyl (R = tBu) substituent in the substrate 1a is replaced by a smaller ethyl group (2a, R = Et).     

Far-red triplet sensitized Z-to-E photoswitching of azobenzene in bioplastics

We report the first example of direct far-red triplet sensitized molecular photoswitching in a condensed phase wherein a liquid azobenzene derivative (Azo1) co-assembled within a liquid surfactant–protein film undergoes triplet sensitized Z-to-E photoswitching upon far-red/red light excitation in air. The role of triplet sensitization in photoswitching has been confirmed by quenching of sensitizer phosphorescence by Z-Azo1 and temperature-dependent photoswitching experiments. Herein, we demonstrate new biosustainable fabrication designs to address key challenges in solid-state photoswitching, effectively mitigating chromophore aggregation and requirement of high energy excitations by dispersing the photoswitch in the trapped liquid inside the solid framework and by shifting the action spectrum from blue-green light (450–560 nm) to the far-red/red light (740/640 nm) region.

We report the first example of direct far-red endothermic triplet sensitized Z-to-E photoswitching of azobenzene derivative (Azo1) in a condensed phase of a liquid Azo1 co-assembled within a liquid surfactant-protein bioplastic film in air.     

Kinetic studies on the reaction of methylcobalamin with metal oxides

Aqueous solutions of methylcobalamin (CH₃B₁₂) react with various water-insoluble metal oxides. The decomposition of methylcobalamin follows a kinetic pattern of two parallel first-order reactions. A proposed reaction mechanism involves the attachment of methylcobalamin to the oxide surface, followed by methyl transfer and dissolution of the oxide.     

p-sulfonatocalix[8]arene and chitosan based vesicle formation studies by spectroscopic and thermal methods

p-sulfonatocalix [8]arene and chitosan based supramolecular amphiphilic vesicles were formed by electrostatic interaction between anionic character of calixarene and cationic chitosan molecules. UV–visible, fluorescence, dynamic light scattering and thermogravimetric analysis were performed for the characterization of p-SCX8 with chitosan. Increase in absorption and enhancement of fluorescence emission intensity attributed to vesicle formation between both calixarene and chitosan in aqueous media. Results obtained from size distribution curve of dynamic light scattering experiment gives clear evidence for vesicle formation at pH 4.98. Positive zeta potential values obtained from dynamic light scattering experiment gives the evidence for vesicle formation. Thermogravimetric analysis gives quantitative results for purity and stability of the vesicles. From overall studies we can conclude that degree of deacetylation as well as pH 4.98 of the solutions and anionic nature of pSCX8 plays important role in electrostatic interaction of vesicle formation.