0000000000671267
AUTHOR
I. Zabala
Molecular orbital studies on the mechanism of catalytic isomerization of xylenes II. The photochemical process
Abstract The feasibility of an intermediate step in the mechanism of photochemical isomerization of xylenes in acidic media is explored by using CNDO molecular orbital methods. Along the reaction path from 2,6-dimethylbenzenium ion to dimethylbicyclo[3.1.0]hexenyl cation, the energy surfaces for this intermediate step have been drawn both for the first singlet S1 and triplet T1 excited states. The energies of these excited states have been calculated by adding to the ground-state energy calculated by CNDO/2 method the excitation energy calculated by CNDO/S-CI method. An optimization of the saddle point energy is achieved by introducing the angle between methyl groups and the ring plane as a…
Photophysical behavior of 3-methylquinoline and 3-bromoquinoline
Abstract The phosphorescence emission and excitation spectra and their polarizations have been studied for 3-methylquinoline and 3-bromoquinoline in methylcyclohexane and ethanol glasses at 77 K. From the results obtained in 3-methylquinoline (τp = 1.30 s in ethanol, τp = 1.05 s in methylcyclohexane and the out-of-plane polarization) it is concluded that the emission originates from a triplet state of 3ππ∗ character. In 3-bromoquinoline, the phosphorescence lifetimes (ca. 8 ms in a non-polar solvent and 15 ms in a polar solvent) and the negative degree of polarization indicate an emitting state of ππ∗ character that is strongly coupled to a higher-lying triplet state of the nπ∗ type. The mo…
Photophysical behavior of norharmane related to proximity effect
Abstract Solvent and temperature effects of fluorescence and its polarization characteristics for norharmane were studied. From the results obtained it is concluded that the fluorescent state changes from the φφ ∗ -type in a polar solvent (EPA) to nφ ∗ -type in a nonpolar solvent (MC), and also that lowest singlet excited states (φφ ∗ -type and nφ ∗ -type) interact by vibronic coupling. In the nonpolar solvent (MC) the lowest singlet excited states are very close in energy and consequently the vibronic coupling is stronger. At high temperatures, in a nonpolar solvent (MC), the emission is from both the φφ ∗ - and nφ ∗ -states due to thermal equilibration, while at low temperatures the emiss…
Phosphorescence emission and polarization of quinoline 3-carbonitrile
Abstract The phosphorescence emission and excitation spectra and their polarization have been studied for quinoline 3-carbonitrile in methylcyclohexane and ethanol glasses at 77 K. From the results obtained in this molecule (τ=1.15 sec in ethanol, τ=1.04 sec in methylcyclohexane and out-of-plane polarization) it is concluded that the emission is orginated from a triplet state of 3 ππ * character. The two major spin-orbit coupling mechanisms through which the ππ * state of quinoline 3-carbonitrile acquires dipole-allowed character via nπ * states are: 1. In ethanol glass: 2. In methylcyclohexane glass: