John Masnovi

Picosecond spectroscopy of charge-transfer processes. Photochemistry of anthracene-tetranitromethane EDA complexes

Abstract The temporal sequence of events that follow 532 nm excitation of electron donor-acceptor, EDA, complexes of several substituted anthracenes with tetranitromethane is monitored by means of picosecond spectroscopy. Excitation of the charge-transfer band of these EDA complexes produces high yields of 1 : 1 adducts. Absorption spectra and kinetics of the transient species involved in these photochemical reactions provide the basis for elucidation of the reaction mechanism following charge-transfer excitation to the ion pairs.

Crystal structure of 9-methacryloylanthracene

In the title compound, the substituted aromatic C atom lies 0.2030 (16) Å out of the anthryl plane, which forms a dihedral angle 88.30 (3)° with the plane of the transoid methacryloyl moiety.

Syntheses, Structures and Properties of Polycarbosilanes Formed Directly by Polymerization of Alkenylsilanes

Vinylsilane polymerizes to form predominantly a carbosilane polymer using dimethyltitanocene catalyst. This is in contrast to alkylsilanes, which afford polysilanes under the same conditions. The mechanism of polymerization of alkenylsilanes has been shown to be fundamentally different from that for the polymerization of alkylsilanes. The silyl substitute apparently activates a double bond to participate in a number of polymerization processes in this system, particularly hydrosilation. Isotopic labeling indicates the involvement of silametallocyclic intermediates, accompanied by extensive nuclear rearrangement. Polymers and copolymers derived from alkenylsilanes have relatively high char yields even for conditions which afford low molecular weight distributions. Formation of crystalline beta-SiC is optimum for a copolymer of an alkylsilane and an alkenylsilane having a silane/carbosilane backbone ratio of 85/15 and a C/Si ratio of 1.3/1.

Gaseous cation chemistry and chain‐length effects in electron ionization and collision‐induced dissociation mass spectraof symmetric 1,n‐bis(9‐anthracenyl)alkanes

The behavior of the gaseous cations resulting from EI (30 and 70 eV) of the bichromophoric title compounds 1-5 (for n = 1-5, respectively) is examined by ion-trap mass spectrometry, including collision-induced dissociation (CID) with variation in collision energy. These results are compared with those from anthracene and 9-methylanthracene and with previously reported mass spectrometric results for 3 and dicarbazolylalkanes. Rather than using the kinetic method to obtain ion energetics where the fragmentation mechanism is clear, as commonly done, the method is used here with relative complementary-ion abundances from CID to test the proposed fragmentation mechanisms using B3LYP calculations of relative ionization energies and optimized geometries of ionic and neutral fragments. Hydrogen migrations are common, and skeletal rearrangements including formation of expanded, fused and spiro rings are proposed in several cases. Of the chain cleavages, α-homolysis giving C(15) H(11) (+) , likely as dibenzotropylium, is most important for each of 1-5 except 3, where β-cleavage to C(16) H(13) (+) dominates with a proposed methyldibenzotropylium structure. α-Cleavage was important also in the dicarbazolylalkanes. A previous inference of a McLafferty rearrangement to explain C(15) H(12) (+•) from 3 is not supported by the present results. The fragmentation behavior of 1-5 depends strongly on n and implies significant interchromophoric interaction between anthracenyl groups.

[2,3:5,6]Dibenzo[2.2.2]octa-2,5,7-triene (C2/c) and [2,3:5,6]dibenzo[2.2.2]octa-2,5-diene

Two barrelene homologs are reported. Strain in the bicyclic framework of [2,3 :5,6]dibenzo[2.2.2]octa-2,5,7-triene, (I) (C 16 H 12 ), which is manifest in the deviations from ideality of the bond angles in the central bicyclic ring system and compression of the double bond [1.312 (3) A], is reduced in the more saturated derivative, [2,3:5,6]dibenzo[2.2.2]octa-2,5-diene, (II) (C 16 H 14 ), with the corresponding single bond being 1.5380 (19) A. The formation of isomorphs of (I) in both chiral (C2) and achiral (C2/c) space groups has implications for asymmetric syntheses involving solid (I) which rely on a non-centrosymmetric space group.

A MECHANISTIC STUDY OF THE PHOTOCHEMISTRY OF CARBOHYDRATE P-TOLUENESULFONATES

Abstract Photolysis of 1,2:3,4-di-O-isopropylidene-6-O-(p-tolylsulfonyl)-α-D-galactopyranose (5) in methanol under nitrogen in the presence of sodium hydroxide or diazabicyclo[2.2.2]octane (3, DABCO) produces toluene and 1,2:3,4-di-O-isopropylidene-α-D-gatactopyranose (6). Electron transfer from DABCO or hydroxide ion to singlet excited 5 to generate a radical anion is the first step in this reaction. The radical anion rapidly fragments to give the p-tolylsulfonyl radical (2) and deprotonated 6, which accepts a proton from the solvent. The p-tolylsulfonyl radical (2) then abstracts a hydrogen atom from the solvent to give p-toluenesulfinic acid, a compound that is converted to the p-toluenesulfinate anion (8) under the basic reaction conditions. Photolysis of 8 completes the reaction sequence by forming toluene.

Bis(9-ethylcarbazol-3-yl)methane

Poly(N-vinylcarbazole) (PVK), renowned as the first organic polymer, has found applications in electrophotography as a hole-transporting material and is among the most studied semi-conducting polymers (Loh et al., 1991; Rocquin & Chevrot, 1997; Li et al., 1998). It is believed that the orientation of the pendant carbazole groups along the polymer chain plays an important role in the photoconduction process (Turner & Pai, 1979). Time-resolved emission studies have been conducted on a number of bis(N-carbazolyl)alkanes and related compounds, the bicromophoric model compounds of PVK, to gain information about the photophysical properties of PVK (Klöpffer, 1969; Masuhara et al., 1983; Cai & Edward, 1994). Single-crystal X-ray studies on several of these dimers have also been reported (Baker et al., 1991). Recently, we have reported the crystal structure of 1,3-bis(9-ethylcarbazol-3yl)propane as a model of poly(3-vinylcarbazole) (P3VK), a structural isomer of PVK (Asker & Masnovi, 2005). We report here the structure of the title compound, (I), another bichromophoric model compound of P3VK.

cis-4,5-Dihydroxy-2,3,4,5-tetraphenylcyclopent-2-enone

The title compound, C 29 H 22 O 3 , was prepared by the oxidation of tetraphenylcyclopentadienone with tetranitromethane. The cyclopentenone ring has a C5-envelope conformation, with an elongated C sp3 -C sp3 bond length of 1.569 (2) A. One hydroxyl group takes part in a bifurcated hydrogen bond involving an intra- and intermolecular bond to adjacent hydroxyl groups [O...O 2.6299 (16) and 2.9279 (15) A], while the second hydroxyl group forms an intermolecular hydrogen bond to an adjacent carbonyl O atom [O...O 2.8441 (18) A].

Structure and Properties of 9,14,15,16,17,18,19,20-Octahydro-9,14[1′,4′]-benzenobenzo[b]triphenylene

The compound 9,14,15,16,17,18,19,20-octahydro-9,14[1′,4′]-benzenobenzo[b]triphenylene, C28H24, was prepared by hydrogenation of the photocycloadduct of dibenz[a,c]anthracene and 1,3-cyclohexadiene with Pt/C in ethyl acetate. The X-ray diffraction analysis shows that the compound crystallizes in the monoclinic space group with the geometric parameters of = 11.0090(17) A, = 13.733(2) A, = 13.091(2) A, and = 109.583(13)°. In addition to several close intramolecular contacts involving hydrogens derived from the dibenzanthracene moiety, long interannular C–C single bonds of about 1.593 A are present. These bonds are shorter by about 0.18 A than the corresponding bonds in the unsaturated precursor, which can be attributed to reduced strain in the more saturated polycyclic ring system. Anisotropic shielding of the four endo-methylene hydrogens in the 1H NMR spectrum is larger for the two hydrogens lying above the phenanthrene unit, which resonate at 1.03 ppm, than those above the benzenoid ring, which resonate at 1.24 ppm. Theoretical calculations reproduce the geometry with good agreement.

(E,E)-1,3-Bis[9,10-dihydro-9-nitro-10-(trinitro­meth­yl)-9-anthr­yl]propane

Aromatic amine compounds are of interest due to their potential uses as photoconductive materials in a wide range of electrophotographic devices (Hara & Omae, 1978; Thelakkat, 2002). One common method for the preparation of aromatic amines is the reduction of the corresponding nitro compounds which are commonly prepared through the reaction of aromatic compounds with concentrated nitric acid in the presence of concentrated sulfuric acid. Nitration through the irradiation of the charge-transfer complexes formed between aromatic compounds and tetranitromethane (TNM) offers an alternative route to the use of concentrated acids (Kochi, 1991; Butts et al., 1996; Cox, 1998; Lehnig & Schürmann, 1998). We have already reported the crystal structure of (E)-9,10dihydro-9-methyl-9-nitro-10-(trinitromethyl)anthracene as the product of the photoreaction between 9-methylanthracene and TNM (Arslan et al., 2005). In the present paper, we report the crystal structure of the title compound, (I), which is a product of the photoreaction between 1,3-di-9-anthrylpropane, a dimeric analogue to 9-methylanthracene, with TNM.