Browsing by Author "Turro, Nicholas J."
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- Aggregates of cucurbituril complexes in the gas phasePublication . Silva, José P. da; Jayaraj, Nithyanandhan; Jockusch, Steffen; Turro, Nicholas J.; Ramamurthy, V.The self-organization of cucurbit[n]uril (n = 7 and 8, CBs) complexes was probed by electrospray mass spectrometry. The self-association of CB complexes is a general phenomenon but shows some dependence on the absence, presence, and type of included guest molecules.
- Benzoin type photoinitiator for free radical polymerizationPublication . Esen, Duygu Sevinc; Arsu, Nergis; Silva, José P. da; Jockusch, Steffen; Turro, Nicholas J.Benzoin, a popular photoinitiator for free radical polymerization of vinyl monomers, was improved by introduction of two methyl thioether substituents. This new benzoin derivative showed an about 50 times higher light absorption in the near-UV spectral region and performed better than the unsubstituted benzoin in polymerization experiments in bulk solutions or films of acrylate monomers when low initiator concentrations are used. Laser flash photolysis, low temperature luminescence experiments and photoproduct studies by mass spectrometry suggest that a slow -cleavage mechanism (k = 2.2 x 105 s1) from the electronic triplet state with a quantum yield of 0.1 is the primary photoreaction to generate the initiating free radicals. (c) 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 1865-1871
- Capsular complexes of nonpolar guests with octa amine host detected in the gas phasePublication . Silva, José P. da; Kulasekharan, Revathy; Cordeiro, Carlos; Jockusch, Steffen; Turro, Nicholas J.; Ramamurthy, V.Nanocapsules, made up of the deep cavitand octa amine and several guests, were prepared in aqueous acidic solution and were found to be stable in the gas phase as detected by electrospray ionization mass spectrometry (ESI-MS). The observed gas phase host-guest complexes contained five positive charges and were associated with several acid molecules (HCI or HBr).
- Photochemistry of 4-chlorophenol and 4-chloroanisole adsorbed on MFI zeolites: supramolecular control of chemoselectivity and reactive intermediate dynamicsPublication . Silva, José P. da; Jockusch, Steffen; Martinho, José M. G.; Ottaviani, M. Francesca; Turro, Nicholas J.The phototransformation of aryl chlorides adsorbed on MFI zeolites is markedly different from that observed in solution and other solid surfaces such as silica. The formation of radical cations and the constraints imposed by the channels shift the reactivity from the C-CI bond to the O-R bond. Irradiation generates kinetically stabilized intermediates that can be characterized using conventional steady-state spectroscopic techniques, and these intermediates can be used as ordinary chemical reagents.
- Probing the photoreactivity of aryl chlorides with oxygenPublication . Silva, José P. da; Jockusch, Steffen; Turro, Nicholas J.Molecular oxygen was used to probe the mechanism of the phototransformation of chlorobenzene and 4-chloroanisole in organic solvents. Laser. ash photolysis, electron paramagnetic resonance and product distribution studies clarified the reaction mechanisms of these compounds under a wide range of conditions. The main primary photochemical reaction step is the homolytic cleavage of the C-Cl bond to produce a triplet radical pair in the solvent cage. In non-polar solvents hydrogen abstraction, after radical diffusion, leads to reduction. In polar solvents, in addition to H-abstraction, electron transfer within the caged radical pair occurs and leads to an ion pair (phenyl cation and Cl(-)). In the presence of oxygen, phenyl radicals can form phenylperoxyl radicals which have a bathochromically shifted absorption, thus making the homolytic cleavage visible by. ash photolysis. The peroxyl radicals can couple, leading to more polar compounds, or undergo back reaction to the phenyl radical. For concentrations of the aryl chlorides of higher than 10(-3) M, dimerization becomes an important transformation process and occurs after reaction of the transients with ground state molecules. In addition, excimer formation is postulated to be involved in the dimerization process.
- Supramolecular photocatalysis: insights into cucurbit[8]uril catalyzed photodimerization of 6-methylcoumarinPublication . Pemberton, Barry C.; Singh, Raushan K.; Johnson, Alexander C.; Jockusch, Steffen; Silva, José P. da; Ugrinov, Angel; Turro, Nicholas J.; Srivastava, D. K.; Sivaguru, J.Guest induced shape change of the cucurbit[8]uril cavity is likely rate limiting in the supramolecular photocatalytic cycle for CB8 mediated photodimerization of 6-methylcoumarin.