Interconversions of Z‐1,3,5‐hexatriene conformers: A theoretical study

Henseler, Debora; Rebentisch, Rupert; Hohlneicher, Georg

doi:10.1002/(sici)1097-461x(1999)72:4<295::aid-qua12>3.3.co;2-l

Cited by 5 publications

(14 citation statements)

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“…For the energy differences between the conformers and for the barrier heights, we took the ab initio values of Pullen et al (Table ). They well agree with previous calculations. , Slightly higher values were found in very recent density-functional calculations 1 Energies of the Less Stable Conformers and Transition States (TS) (see Figure ) Relative to the Ground State of tZt- Hexatriene as Calculated by Pullen et al The Barrier Heights Are Not far from Those in Butadiene 48 and Octatetraene 49 cZc -HTTS between cZc and cZt cZt -HTTS between cZt and tZt tZt -HT energy/cm -1 2956 3370 1088 1809 0 …”

Section: Resultssupporting

confidence: 90%

“…17 This is consistent with the 15 ps time constant for cZt f tZt predicted on the bases of two-dimensional surfaces calculated by density-functional theory. 47 Recent time-resolved investigations by means of IR spectroscopy only found an upper bound for this time: It showed that Z-hexatriene produced by the ring opening of 1,3-cyclohexadiene isomerizes completely to the tZt conformer in less than 20 ns. 58 In the case of exciting tZt-hexatriene, the high temperature of the molecules after the internal conversion leads to an increase of the concentrations of the high-energy conformers during the first 2.5 ps.…”

Section: Ts Between Czt and Tzt Tzt-ht Energy/cmmentioning

confidence: 99%

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Electronic Relaxation and Ground-State Dynamics of 1,3-Cyclohexadiene andcis-Hexatriene in Ethanol

et al. 1998

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The transient absorption induced by UV excitation of 1,3-cyclohexadiene and Z-hexatriene dissolved in ethanol was measured in the wavelength range 255−450 nm. Repopulation of the ground state takes 470 fs in tZt-hexatriene. The same process in 1,3-cyclohexadiene, accompanied by ring opening to Z-hexatriene, occurs in less than 300 fs. The analysis of the long-wavelength wings of the ground-state spectra reveals a cooling time constant of 7 ps for the hot product Z-hexatriene. The transient absorption in the UV furthermore reflects the single-bond isomerizations of this product to different conformers. The evolution of their concentrations was simulated by rate equations using temperature-dependent isomerization rates calculated with the Arrhenius law. In this model, the concentrations of the conformers reach thermal equilibrium in a few picoseconds; during the first 10−20 ps, the concentrations follow the cooling of the molecule by the solvent, staying near thermal equilibrium; and a small quantity of cZt-hexatriene is trapped in its potential well on a time scale of 100 ps at the final temperature (300 K). At this temperature, equilibration takes longer. This model well reproduces the time dependence of the integrated spectra in solution and recent experimental results in gas phase. In addition it allows a consistent interpretation of previous, time-resolved resonance−Raman experiments. The fact that single-bond isomerization in the hot product was not suppressed by contact with the cold solvent suggests that this could also be the case for photorhodopsin, the postulated primary conformer of the photoproduct of rhodopsin which always eluded trapping even at cryogenic temperatures.

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Section: Resultssupporting

confidence: 90%

Section: Ts Between Czt and Tzt Tzt-ht Energy/cmmentioning

confidence: 99%

Electronic Relaxation and Ground-State Dynamics of 1,3-Cyclohexadiene andcis-Hexatriene in Ethanol

et al. 1998

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“…Previous studies confirm our distributions; the ∅ 1 / ∅ 3 -map of HT (Fig. 2) is similar to the map reported by Henseler et al 54 and the dihedral angle conformations of some minimum energy structures of 2,5-IMHT previously determined by DFT 25 are consistent with the high-density regions in Fig. 3 C.…”

Section: Resultssupporting

confidence: 91%

Tuning the photoreactivity of Z-hexatriene photoswitches by substituents – a non-adiabatic molecular dynamics study

Tapavicza

Thompson

Redd

et al. 2018

Phys. Chem. Chem. Phys.

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To understand how substituents can be used to increase the quantum yield of photochemical electrocyclic ring-closing of the Z-hexa-1,3,5-triene (HT) photoswitch forming cyclohexadiene (CHD), we investigate the S1 photo dynamics of HT and its derivatives 2,5-dimethyl-HT (DMHT), 2-isopropyl-5-methyl-HT (2,5-IMHT), 1-isopropyl-4-methyl-HT (1,4-IMHT), and 2,5-diisopropyl-HT (DIHT) using time-dependent density functional theory surface hopping dynamics. We report detailed photoproduct distributions, formation mechanisms, branching ratios, and wavelength-dependent product quantum yields. Most products have been confirmed experimentally and include all-trans HT derivatives, cyclopropanes, cyclobutenes, cyclopentene, cyclohexadienes, and bicyclic compounds. Regarding CHD formation, we find that for the 2,5-substituted derivatives DMHT, 2,5-IMHT, and DIHT, the branching ratios increase with increasing size of the substituents. In contrast the branching ratios of the E/Z-isomerization decrease with increasing size of the substituents. Due to steric interactions, increasing the size of the substituents increases the amount of gZg rotamers in the ground state, which are prone to CHD formation and have lower E/Z-isomerization probability. Furthermore, we find [1,4], [1,5], and [1,6]-sigmatropic hydrogen shift reactions occurring at large percentages (5% to 15%); for sterical reasons these reactions stem from tZg conformers. DIHT shows the lowest percentage of side product formation among the 2,5-substituted molecules and highest CHD branching ratio; its CHD quantum yield can be increased up to more than 64%, by excitation of DIHT on the red tail of its absorption spectrum, whereas the Z/E-isomerization is reduced below 5% and side reactions practically vanish. This makes DIHT the best candidate for applications in molecular switches.

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“…The ring-opening reaction of 1,3-cyclohexadiene (CHD) and subsequent relaxation of hot 1,3,5- cis -hexatriene (Z-HT) provides an interesting paradigm for the detailed investigation of energy flow in a chemical system. Several groups have investigated both the electrocyclic ring-opening reaction of CHD, − and of the related 7-dehydrocholesterol chromophore responsible for the photoreaction that results in vitamin D formation. − Initial UV excitation of CHD produces a population in the 1 1 B state which decays by internal conversion to an optically forbidden 2 1 A state on a time scale of ca. 10 fs. , The electrocyclic ring-opening reaction of CHD occurs on the 2 1 A state and produces vibrationally hot cis -1,3,5-hexatriene with a quantum yield of 0.40 .…”

Section: Introductionmentioning

confidence: 99%

“…The transition states for cZt f tZt (TS2) and cZc f cZt (TS1) are indicated on the plot, as are approximate reaction coordinates (green dashed line). A more complete energy surface is provided by Hensler et al22…”

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confidence: 99%

Solvent Dependent Conformational Relaxation of cis-1,3,5-Hexatriene

2006

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Ultrafast transient absorption spectroscopy was used to study the conformational relaxation dynamics of 1,3,5-cis-hexatriene (Z-HT) produced in the photochemical ring-opening reaction of 1,3-cyclohexadiene (CHD) in methanol and n-propanol solvents. The results are compared with earlier investigations performed using cyclohexane and hexadecane solvents [Anderson, N. A.; Pullen, S. H.; Walker II, L. A.; Shiang, J. J.; Sension, R. J.; J. Phys. Chem. A 1998, 102, 10588-10598.]. The conformational relaxation between hot cZc-HT, cZt-HT, and tZt-HT, where the labels c and t designate cis and trans configurations about the single bonds, is much faster in alcohol solvents than in alkane solvents. The hot Z-HT produced in the photochemical ring-opening reaction evolves from the conformationally strained cZc-HT form to the more stable cZt-HT form on a time scale of 2 ps in alcohols compared with 6 ps in alkanes. The overall decay of the internal vibrational temperature of the hot Z-HT is faster in alcohols (5-6 ps) than alkanes (12-20 ps) and is weakly dependent on the specific alcohol or alkane solvent. A small population of cZt-HT (5-10%) is trapped as the solute equilibrates with the surrounding solvent following UV excitation of CHD or direct UV excitation of Z-HT. The influence of solvent on conformational relaxation of Z-HT was investigated further by probing the temperature dependence of the decay of this thermally equilibrated cZt-HT population. The apparent barrier for the cZt --> tZt conformational isomerization is lower in alcohols (17.4 kJ/mol) than in alkanes (23.5 kJ/mol). However the equilibrium Arrhenius prefactor (A(h)) is an order of magnitude smaller for alcohols (ca. 4 x 10(12)) than alkanes (ca. 6 x 10(13)) resulting in an absolute rate of decay that is faster in the alkane than in the alcohol solvents. These results are discussed in the context of transition state theory and Kramers' theory for condensed phase reaction dynamics.

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Interconversions of Z‐1,3,5‐hexatriene conformers: A theoretical study

Cited by 5 publications

References 0 publications

Electronic Relaxation and Ground-State Dynamics of 1,3-Cyclohexadiene andcis-Hexatriene in Ethanol

Electronic Relaxation and Ground-State Dynamics of 1,3-Cyclohexadiene andcis-Hexatriene in Ethanol

Tuning the photoreactivity of Z-hexatriene photoswitches by substituents – a non-adiabatic molecular dynamics study

Solvent Dependent Conformational Relaxation of cis-1,3,5-Hexatriene

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