72610-88-9Relevant articles and documents
Time-Resolved Photochemistry of Stiffened Stilbenes
Krohn, Olivia A.,Quick, Martin,Ioffe, Ilya N.,Mazaleva, Olga N.,Lenoir, Dieter,Detert, Heiner,Kovalenko, Sergey A.
, p. 4291 - 4300 (2019/05/24)
Broadband transient absorption spectroscopy is used to study the photoisomerization of stiffened stilbenes in solution, specifically E/Z mixtures of bis(benzocyclobutylidene) (t4, c4) and (E)-1-(2,2-dimethyltetralinylidene)-2-2-dimethyltetraline (t6). Upon excitation to S1, all evolve to perpendicular molecular conformation P, followed by decay to S0, while the spectra and the kinetic behavior crucially depend on the size of the stiffening ring. In 4, contrary to all previously studied stilbenes, the trans and cis absorption and excited-state spectra are nearly indistinguishable, while the corresponding isomerization times are comparable: τi = 166 ps for t4 and τi = 64 ps for c4 in n-hexane, as opposed to 114 and 45 ps in acetonitrile, respectively. Faster isomerization in polar solvents agrees with the zwitterionic character of the P state. In t6, torsion to P is effectively barrier-less and completes within 0.3 ps, the S1 → P evolution being directly traceable through the transient spectra of stimulated emission and that of excited-state absorption. In n-hexane, the P state is remarkably long-lived, τP = 1840 ps, but the lifetime drops down to 35 ps in acetonitrile. The trans-to-cis photoisomerization yield for t6 is measured to be 20%, while for t4, it remains uncertain. We discuss the effects of stiffening and substitution on the formation and lifetime of the intermediate states through which the stilbene molecules evolve on the S1 energy surface.
Cyclic trans-stilbenes: Synthesis, structural and spectroscopic characterization, photophysical and photochemical properties
Oelgemoeller, Michael,Brem, Bernhard,Frank, Rudolf,Schneider, Siegfried,Lenoir, Dieter,Hertkorn, Norbert,Origane, Yumi,Lemmen, Peter,Lex, Johann,Inoue, Yoshihisa
, p. 1760 - 1771 (2007/10/03)
trans-Stilbene and several cyclic derivatives with hindered free rotation around the C(vinyl)-C(phenyl) single bond were studied by various spectroscopic techniques. Those derivatives which contain 6- or 7-membered aliphatic rings do not exhibit any measurable S1 → S0 fluorescence. The introduction of two methoxy groups into the 6-membered aliphatic ring derivative accelerates its photoreactivity to such an extent that fluorescence or resonance Raman spectroscopy investigations become impossible. The introduction of aliphatic rings has only a little effect on the frequency of the phenyl-ring stretching vibrations, but pronounced ones on the IR and Raman intensities. The frequency of the vinylic stretching mode is downshifted between 5 and 100 cm-1 except in the case of the derivative with the 4-membered ring, which experiences a hypsochromic shift of 80 cm-1. Only trans-stilbene and its 4-membered cyclic analogues were amenable to fluorescence lifetime measurements. Analysis of VT-NMR spectra of stilbene 7 reveals a barrier of 15.9 kcal mol-1 for equilibration of aliphatic equatorial and axial H-atoms.
Radical-Stabilization-Energy - the MMEVBH Force Field
Roth, Wolfgang R.,Staemmler, Volker,Neumann, Martin,Schmuck, Carsten
, p. 1061 - 1118 (2007/10/02)
Making use of the VB method of Malrieu et al. a force field has been developed, which allows to calculate heats of formation of hydrocarbons (conjugated and non-conjugated olefins, radicals and diradicals) with high accuracy.With this method radical stabilization energies (RSE) for a great number of delocalized radicals are calculated and compared with experimental values, derived from shock-tube measurements of dissociation energies or from rotational barriers of substituted olefins.A detailed analysis of the RSE with respect to structure, substituents, strain, and aromaticity is presented. - Key Words: Resonance energy / Heats of formation / Single pulse shock tube / Intrisic rotational barrier
