Substituent Effects in Buta-1,3-diene Photochemistry: A CAS-SCF Study of 2,3-Dimethylbutadiene and 2-Cyanobutadiene Excited-State Reaction Paths (original) (raw)
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Photolysis of n-butene and isobutene at 174.3 – 174.5 nm (7.10 eV)
Journal of Photochemistry, 1978
The photolysis of n-butene and isobutene was carried out in a static system using nitrogen resonance lines at 174.3 -174.5 nm (7.11 -7.10 eV). The main fragmentation process of the photoexcited n-butene molecule is the C-C split in the fl position to the double bond. The primary quantum yield Cp is 0.66. The Q, value for the (x C-C split of isobutene is equal to 0.78.
Phys. Chem. Chem. Phys., 2015
Excited-state chemistry is usually ascribed to photo-induced processes, such as fluorescence, phosphorescence, and photochemistry, or to bio-and chemiluminescence, in which light emission originates from a chemical reaction. A third class of excited-state chemistry is, however, possible. It corresponds to the photochemical phenomena produced by chemienergizing certain chemical groups without light -chemiexcitation. By studying Dewar dioxetane, which can be viewed as the combination of 1,2-dioxetane and 1,3-butadiene, we show here how the photo-isomerization channel of 1,3-butadiene can be reached at a later stage after the thermal decomposition of the dioxetane moiety.
Ab Initio Multiple Spawning Dynamics of Excited Butadiene: Role of Charge Transfer
The Journal of Physical Chemistry a, 2009
Ab initio multiple spawning simulations of the photochemical reaction dynamics of s-trans-1,3-butadiene were performed. It is found that nonadiabatic events involving two low-lying excited states begin as early as 10 fs after excitation, resulting in the population being split between the bright 1 1 B u state and the dark 2 1 A g state. The molecule subsequently twists about a terminal carbon-carbon bond regardless of whether it is on the 1 1 B u or 2 1 A g electronic state. This twisting motion leads to conical intersections between S 1 and S 0. Several regions of the intersection seam involving states of differing character are accessed. The regions of the seam involving intersection between a state of charge-transfer character and a state of covalent character dominate the quenching dynamics, but intersections between two covalent states are also accessed a small percentage of the time. The existence and relative energies of these intersections are validated by optimization at the multistate complete active space second-order perturbation level of theory (MS-CASPT2). Our results point to a new mechanism for photoisomerization of butadiene that emphasizes the role of charge-transfer states.
Journal of the American Chemical Society, 1997
The [4 + 4] photocycloaddition of butadiene + butadiene has been studied at the CASSCF /4-31G level, as a prototype for a class of photochromic systems. For this model system, minima and transition structures are characterized by analytic frequency calculations, and conical intersections are located. Our results indicate that the standard model for the [4 + 4] addition (based on H 4 ) needs to be revised. The reorganization of all 8π electrons is crucial (i.e., it is not always the same 4π electrons that are important). Efficient nonradiative decay of butadiene + butadiene can be explained by the presence of two distinct S 1 /S 0 conical intersections. The first-the lowestenergy point on S 1 overall-is preceded by a barrier for the formation of a new σ bond. The resulting structure is similar to those previously characterized for methyl migration in but-1-ene and the addition of ethylene to benzene. A higher-energy barrier leads to a second crossing which resembles the rhomboidal funnel for the [2 + 2] addition of ethylene + ethylene, but which involves only one double bond from each butadiene. Both reaction paths commence at a true pericyclic minimum, at which the (S 0 -S 1 ) energy gap of ∼37 kcal mol -1 prohibits decay.
Photochemistry of the 1,4-Diphenyl-1,3-butadienes in Ethanol. Trapping Conical Intersections
The journal of physical chemistry. A, 2016
We report photoisomerization and photoaddition quantum yields in ethanol starting from each 1,4-diphenyl-1,3-butadiene, DPB, isomer. Despite the fact that the trans,trans isomer, tt-DPB, has a significant fluorescence quantum yield and lifetime, whereas no fluorescence is observed from the cis isomers, ether formation occurs with similar efficiency from tt-DPB and ct-DPB and less efficiently from cc-DPB. Photoaddition is about 72 times slower than photoisomerization to the ct- and tt-DPB isomers starting from tt- and ct-DPB, respectively. The results are consistent with addition of alcohol to the common zwitterionic trans-phenallyl cation/benzyl anion intermediate that leads to photoisomerization through a conical intersection. Ether formation from cc-DPB tracks inefficient formation of tt-DPB indicating that the small bicycle pedal cc-DPB → tt-DPB component proceeds stepwise through the same zwitterionic trans-phenallyl cation/benzyl anion intermediate. Previous results concerning ...
Dissociative photoionization of 1,3-butadiene: Experimental and theoretical insights
The Journal of Chemical Physics, 2011
The vacuum-ultraviolet photoionization and dissociative photoionization of 1,3-butadiene in a region ∼8.5–17 eV have been investigated with time-of-flight photoionization mass spectrometry using tunable synchrotron radiation. The adiabatic ionization energy of 1,3-butadiene and appearance energies for its fragment ions, C4H5+, C4H4+, C4H3+, C3H3+, C2H4+, C2H3+, and C2H2+, are determined to be 9.09, 11.72, 13.11, 15.20, 11.50, 12.44, 15.15, and 15.14 eV, respectively, by measurements of photoionization efficiency spectra. Ab initio molecular orbital calculations have been performed to investigate the reaction mechanism of dissociative photoionization of 1,3-butadiene. On the basis of experimental and theoretical results, seven dissociative photoionization channels are proposed: C4H5+ + H, C4H4+ + H2, C4H3+ + H2 + H, C3H3+ + CH3, C2H4+ + C2H2, C2H3+ + C2H2 + H, and C2H2+ + C2H2 + H2. Channel C3H3+ + CH3 is found to be the dominant one, followed by C4H5+ + H and C2H4+ + C2H2. The major...
The Journal of Organic Chemistry, 2011
The photochemistry of 1,3-butadiene 1 and 1,3,5-hexatriene 2 derivatives has been studied in detail. The photochemical reactions of 1,4-diphenyl-1,3-butadienes, their photoisomerization reactions, 3À11 and some electrocyclization reactions 12,13 have already been studied. However, the photochemistry of 1-(ovinylphenyl)-4-phenylbutadiene derivative 1 ) was described for the first time by our group. 14 The synthesis and photochemistry of 1, a molecule that combines properties of both butadiene and hexatriene systems, were examined. Previous publications 15À22 on the photochemistry of different heteroarylsubstituted hexatrienes showed interesting intramolecular cycloaddition reactions and formation of bicyclo[3.2.1]octadiene structures. By insertion of an additional double bond into the stilbene-like moiety, we obtained the prolonged conjugated system of 1 that might allow the formation of a new polycyclic structure with the double bond functionality for further transformations. The compound 1 undergoes intramolecular photocycloaddition reaction to benzobicyclo[3.2.1]octadiene derivative 2 in very good yield, giving only the endo-phenyl-benzobicyclo[3.2.1]octadiene isomer (endo-2) due to the stereoselectivity of the photoreaction. The phenyl-benzobicyclo[3.2.1]octadiene derivative (endo-2) undergoes further di-π-methane rearrangement leading to tricyclic structure (endo-3), or it can be used as a suitable substrate for other transformations on the isolated double bond, easily derivatized to new compounds with various functionalities. Moreover, the bicyclo[3.2.1]octane skeleton is found in numerous biologically important active natural products. 23À26 As a part of our increasing interest in the photochemistry of conjugated butadiene systems, we extended our research to new ω,ω 0 -diarylbutadiene derivatives 4À7 ) in order to prepare new polycyclic structures by photochemical methodology as well as to get a deeper understanding of the photoinduced behavior of these conjugated systems. In the continuation of our study of 1-(o-vinylphenyl)-4-phenylbutadienes 1, 14 the synthesis of four novel butadiene derivatives 4À7 (unsubstituted or having one or two methyl groups as substituents on the double bond), their spectral characterization, and the detailed investigation of the photochemical and, to a less extent, photophysical behavior are presented. In these new systems with prolonged conjugation, the influence of the introduced methyl group at the double bond is examined in order to see the possibility of the intramolecular [2 + 2] photocycloaddition followed by formation of the ABSTRACT: Novel butadiene derivatives display diverse photochemistry and photophysics. Excitation of 2-methyl-1-(o-vinylphenyl)-4-phenylbutadiene leads to the dihydronaphthalene derivative, whereas photolysis of the corresponding model o-methyl analogue results in the formation of the naphthalene-like derivative, deviating from the nonmethylated analogue of the prior starting compound and producing benzobiand -tricyclic compounds. The effect of the methyl substituents is even more dramatic in the case of the dibutadienes. The parent unsubstituted compound undergoes photoinduced intramolecular cycloaddition giving benzobicyclo[3.2.1]octadiene, whereas the photochemical reaction of the corresponding dimethylated derivative shows only geometrical isomerization due to the steric effect of the substituents. Methyl groups on the butadiene backbones reduce the extent of conjugation, causing a blue-shift of the characteristic absorption band. The fluorescence efficiency is dramatically decreased, as a consequence of nonplanarity and reduced rigidity of the molecules due to the crowding by the methyl and phenyl groups together. Four molecules of very similar structures show dramatically different photoinduced behavior, revealing how changes of the nature and position of the substituents are valuable in understanding the photophysics and photochemistry of these types of compounds.
Journal of Physical Chemistry A, 2019
The photochemistry of organic chromophores generally involves the co-evolution of the electronic and nuclear degrees of freedom. In order to obtain a specific and predetermined photochemical reaction outcome, chemical substitution can be used to selectively alter the underlying electronic potential energy surfaces to favour a particular reaction pathway. We show using ab initio simulation that substitution of s-trans-1,3-butadiene with a cyano group can effectively "direct" a molecular wavepacket to particular regions of the seam of conical intersection and either favour or inhibit photo-initiated cis-trans isomerization. The substituent is able to effect this control due to the formation of transient charge-separated electronic structures that arise during the nonadiabatic dynamical process. The atomic site at which this charge develops can be selectively stabilized (or destabilized) depending on the location of the cyano substituent, and gives rise to a single dominant decay pathway.
Excited state spectra and dynamics of phenyl-substituted butadienes
The Journal of Physical Chemistry, 1994
A combination of steady-state and dynamic spectral measurements are used to provide new insights into the nature of the excited-state processes of all-trans-1,4-diphenyl-1,3-butadiene and several analogs: 1,4-diphenyl-1,3-~yclopentadiene, 1,1,4,4-tetraphenyIbutadiene, 1,2,3,4-tetraphenyl-1,3-cyclopentadiene, and E,E-diindanylidenylethane. Ground-state absorption, fluorescence, and nanosecond transient absorption measurements identify geometry changes upon excitation and provide information regarding the nature of the first excited singlet state. Femtosecond and picosecond transient absorption data indicate that phenyl torsional motion is not important to the excited-state dynamics and reveal alternative excited-state reaction pathways. The results demonstrate how molecular systems that are structually similar can exhibit different electronic properties and excited-state dynamics.
Studies on photodissociation dynamics of butadiene monoxide at 193nm
Journal of Chemical Physics, 2008
Butadiene monoxide ͑BMO͒ undergoes the S 0 → S 1 transition, involving the excitation of both and n electrons to * orbital, at 193 nm. After relaxing to the ground electronic state via internal conversion, BMO molecules undergo intramolecular rearrangement and subsequently dissociate to form unexpected OH radicals, which were detected state selectively by laser-induced fluorescence technique, and the energy state distribution was measured. OH is produced vibrationally cold, OH͑Љ =0,JЉ͒, with the rotational population characterized by a rotational temperature of 456± 70 K. The major portion ͑ϳ60% ͒ of the available energy is partitioned into internal degrees of the photofragments, namely, vibration and rotation. A considerable portion ͑25%-35%͒ also goes to the relative translation of the products. The ⌳ doublet and spin-orbit ratios of OH were measured to be nearly unity, implying statistical distribution of these states and, hence, no preference for any of the ⌳ doublet ͑⌳ + and ⌳ − ͒ and spin-orbit ͑⌸ 3/2 and ⌸ 1/2 ͒ states. Formation time of the nascent OH radical was measured to be Ͻ100 ns. Different products, such as crotonaldehyde and methyl vinyl ketone, were detected by gas chromatography as stable products of photodissociation. A reaction mechanism for the formation of all these photoproducts, transient and stable, is proposed. The multiple pathways by which these products can be formed have been theoretically optimized, and energies have been calculated. Absorption cross section of BMO at 193 nm was measured, and quantum yield of OH generation channel was also determined.