Cis-Trans Isomerization of C=C Double Bonds

Saltiel, Jack; Sun, Ya Ping

doi:10.1016/b978-044451322-9/50007-5

Cited by 29 publications

(36 citation statements)

References 295 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Such a mechanism can often compete with the more common (reversible) diabatic mechanism implying S 1 f S 0 internal conversion (IC) or T 1 f S 0 intersystem crossing (ISC) at the perpendicular configuration (p) and relaxation to the groundstate isomers, 1,3 E* f 1,3 p* f 1 p f R 1 Z + (1 -R) 1 E, where the partitioning factor R is assumed to be ∼0.5 in most cases. 36 For the compounds here investigated, only for Z-2-StN a relatively small contribution of adiabatic mechanism to the overall yield of photoisomerization in the Z f E direction has been reported by Saltiel et al 28 and later confirmed in our laboratory. 34,35 Mixed diabatic/adiabatic channels in the opposite direction were also reported for the photoisomerization and photocyclization processes of E-1,2-di(n-naphthyl)ethenes.…”

Section: Introductionsupporting

confidence: 54%

Competition between Photoisomerization and Photocyclization of the Cis Isomers of n-Styrylnaphthalenes and -Phenanthrenes

Mazzucato

Spalletti

2009

J. Phys. Chem. A

View full text Add to dashboard Cite

The isomerization and cyclization photoreactions of the cis (Z) isomers of n-styrylnaphthalenes (n = 1 and 2), n-styrylphenanthrenes (n = 1, 2, 3, 4, and 9), and two related compounds, 3-styrylchrysene and 3-styrylbenzo[c]phenanthrene, were investigated by spectrophotometric and chromatographic techniques. The quantum yields of the two photoreactions were measured in aerated and deaerated nonpolar solvent at room temperature and compared with those reported in the literature for some of the molecules investigated and other related compounds. The combined use of high-performance liquid chromatographic and spectrophotometric techniques made easier the separation of the components of the photoreaction mixtures thus simplifying the study of the isomerization/cyclization competition and the measurement of the UV-vis absorption spectra and the thermal decay kinetics of the dihydrophenanthrene-type intermediates. The conformational equilibria in the ground state and the positional isomerism (n values) notably affect the prevalence of one or the other competitive photoreaction. Oxygen also plays an important role: practically it does not affect the quantum yield of the Z --> E process but has a drastic effect on the formation of the final oxidation product which can proceed even in the presence of traces of air. In three cases, non-negligible formation of a side colorless product was detected. It was assigned to an isomer of the normal photocyclization intermediate (4a,4b-dihydrophenanthrene-type), formed by shift of one or both hydrogen atom(s) to other positions of the rings. Parallel ab initio calculations of the potential energy of the possible conformers helped to explain the structure effects on the competitive photoreactive relaxation pathways. Some correlations between the computed reagent/product energy difference in the ground state and the photocyclization yield and thermal stability of the intermediates were also verified.

show abstract

Section: Introductionsupporting

confidence: 54%

Competition between Photoisomerization and Photocyclization of the Cis Isomers of n-Styrylnaphthalenes and -Phenanthrenes

Mazzucato

Spalletti

2009

J. Phys. Chem. A

View full text Add to dashboard Cite

show abstract

“…Similar values are obtained from Arrhenius plots of the lifetime data. These values of E a are somewhat larger than the value of 3.5 kcal/mol for stilbene, 25 contributing to the longer singlet decay time for 3,4′DS versus stilbene. However, they are sufficiently small to suggest that isomerization of 3,4′DS, unlike that of the other diaminostilbenes, occurs predominantly via a singlet state mechanism (Scheme 1, k tc ).…”

Section: Scheme 1: Simplified Scheme For the Deactivation Channels Ofmentioning

confidence: 90%

“…The values of k isc for 3,5AS and 3,3′AS in MC are 2.4 and 4.6 × 10 7 s -1 , bracketing the value of k isc ) 3.9 × 10 7 estimated by Saltiel for stilbene. 25 The behavior of 3,5AS and 3,3′AS is analogous to that of the monoamines 3AS and 3DS, for which a lower bound of 7 kcal/mol was estimated for the barrier for singlet-state torsion. 2,3 Similar values of E a > 7 kcal/mol can be assumed for 3,5AS and 3,3′AS.…”

Section: Scheme 1: Simplified Scheme For the Deactivation Channels Ofmentioning

confidence: 99%

Relaxation Pathways of Photoexcited Diaminostilbenes. The meta-Amino Effect

2001

View full text Add to dashboard Cite

The spectroscopy and photochemistry of several 3-substituted trans-diaminostilbenes have been investigated and the results compared with those from previous studies of 4,4′-diaminostilbenes. The excited-state properties of 3,5-diaminostilbene and 3,3′-diaminostilbene are similar to those for the parent 3-aminostilbene. These amines display long, temperature-independent singlet lifetimes and large fluorescence quantum yields. The long singlet lifetimes are a consequence of large barriers for torsion about the central double bond on the singlet state surface and low fluorescence rate constants. Thus, these diaminostilbenes display the "metaamino effect" previously identified for 3-aminostilbene and for some amine-donor-acceptor substituted stilbenes. The 4,4′-diaminostilbenes also have larger torsional barriers in nonpolar solvents but shorter singlet lifetimes as a consequence of larger fluorescence and intersystem crossing rate constants. The photophysical properties of 3,4′-dimethylaminostilbene are similar to those of 4,4′-aminostilbenes; however, it has a lower torsional barrier, similar to that of the parent 4-aminostilbene.

show abstract

“…In the case of azobenzene and its derivatives also a thermally activated cis f trans reaction is possible. In contrast, for stilbenoid compounds the thermal back reaction is unlikely since the activation barrier (E a ) is on the order of 1.9 eV [1][2][3][4] and thus much higher as compared to azobenzenes (E a ≈ 1 eV; see Figure 1b). [4][5][6][7] Recently, increasing interest has been directed toward research on molecular switches at surfaces due to their potential use in nanotechnology ranging from information storage and processing to adaptive surfaces.…”

Section: Introductionmentioning

confidence: 99%

Photoisomerization Ability of Molecular Switches Adsorbed on Au(111): Comparison between Azobenzene and Stilbene Derivatives

et al. 2009

View full text Add to dashboard Cite

High resolution electron energy loss spectroscopy and two-photon photoemission was employed to derive the adsorption geometry, electronic structure, and the photoisomerization ability of the molecular switch tetratert-butyl-stilbene (TBS) on Au(111). The results are compared with the azobenzene analogue, tetra-tertbutyl-azobenzene (TBA), adsorbed on Au(111). TBS was found to adsorb on Au(111) in a planar (trans) configuration similar to TBA. The energetic positions of several TBS-induced electronic states were determined, and in comparison to TBA, the higher occupied molecular states (e.g., the highest occupied molecular orbital, HOMO) are located at similar energetic positions. While surface-bound TBA can be switched with light between its trans and cis configurations, in TBS this switching ability is lost. In TBA on Au(111), the trans f cis isomerization is driven by a substrate-mediated charge transfer process, whereby photogenerated hot holes in the Au d band lead to transient positive ion formation (transfer of the holes to the TBA HOMO level). Even though the energetic positions of the HOMOs in TBA and TBS are almost identical and thus a charge transfer should be feasible, this reaction pathway is obviously not efficient to induce the trans f cis isomerization in TBS on Au(111). Quantum chemical calculations of the potential energy surfaces for the free molecules support this conclusion. They show that cation formation facilitates the isomerization for TBA much more pronounced than for TBS due to the larger gradients at the Franck-Condon point and the much smaller barriers on the potential energy surface in the case of the TBA.

show abstract

Cis-Trans Isomerization of C=C Double Bonds

Cited by 29 publications

References 295 publications

Competition between Photoisomerization and Photocyclization of the Cis Isomers of n-Styrylnaphthalenes and -Phenanthrenes

Competition between Photoisomerization and Photocyclization of the Cis Isomers of n-Styrylnaphthalenes and -Phenanthrenes

Relaxation Pathways of Photoexcited Diaminostilbenes. The meta-Amino Effect

Photoisomerization Ability of Molecular Switches Adsorbed on Au(111): Comparison between Azobenzene and Stilbene Derivatives

Contact Info

Product

Resources

About