O–H bond fission in 4-substituted phenols: S1 state predissociation viewed in a Hammett-like framework

Karsili, Tolga N. V.; Wenge, Andreas M.; Harris, Stephanie J.; Murdock, Daniel; Harvey, Jeremy N.; Dixon, Richard N.; Ashfold, Michael N. R.

doi:10.1039/c3sc50296a

Cited by 48 publications

(70 citation statements)

References 74 publications

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“…41 Tunnelling estimates for a range of phenols suggest that deuterating the O-H bond should result in a ~1000-fold reduction in the barrier penetration rate. 6 Thus the available experimental data reinforces the expectation that tunnelling under the S1/S2 CI makes negligible contribution to the decay of S1 state PhOD (and FPhOD) molecules, but that the rate of this tunnelling process is competitive with that for fluorescence and other (slow) IC pathways in the fully hydrogenated analogues.…”

Section: Summary Discussionsupporting

confidence: 75%

“…The open points in panels (a) and (d) depict cuts along ROH -arguably the most studied dissociation pathway from the S1 state of phenol and substituted phenols 4,6 -with all atoms constrained to lie in the plane. O-H bond fission from the S1 state of either isomer under such circumstances would require the molecule to tunnel under the S1/S2 CI.…”

Section: Radiationless Transfer To the S0 Pesmentioning

confidence: 99%

“…4,6,7 Excitation at shorter wavelengths within the S1-S0 absorption system populates higher S1(v) levels. This vibrational excitation tends to be in Franck-Condon active parent modes that are orthogonal to the dissociation coordinate; such excitation contributes relatively little to the tunnelling process and tends to map through into product vibration.…”

Section: Introductionmentioning

confidence: 99%

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A Multipronged Comparative Study of the Ultraviolet Photochemistry of 2-, 3-, and 4-Chlorophenol in the Gas Phase

et al. 2015

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The S1( 1 *) state of the (dominant) syn-conformer of 2-chlorophenol (2-ClPhOH) in the gas phase has a sub-picosecond lifetime, whereas the corresponding S1 states of 3-and 4-ClPhOH have lifetimes that are, respectively, ~2 and ~3-orders of magnitude longer. A range of experimental techniques -electronic spectroscopy, ultrafast time-resolved photoion and photoelectron spectroscopies, H Rydberg atom photofragment translational spectroscopy, velocity map imaging and time-resolved Fourier transform infrared emission spectroscopyas well as electronic structure calculations (of key regions of the multidimensional ground (S0) state potential energy surface (PES) and selected cuts through the first few excited singlet PESs) have been used in the quest to explain these striking differences in excited state lifetime. The intramolecular OH ---Cl hydrogen bond specific to syn-2-ClPhOH is key. It encourages partial charge transfer and preferential stabilisation of the diabatic 1 * potential (relative to that of the 1 * state) upon stretching the C-Cl bond, with the result that initial C-Cl bond extension on the adiabatic S1 PES offers an essentially barrierless internal conversion pathway via regions of conical intersection with the S0 PES. Intramolecular hydrogen bonding is thus seen to facilitate the type of heterolytic dissociation more typically encountered in solution studies.3

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Section: Summary Discussionsupporting

confidence: 75%

Section: Radiationless Transfer To the S0 Pesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Multipronged Comparative Study of the Ultraviolet Photochemistry of 2-, 3-, and 4-Chlorophenol in the Gas Phase

et al. 2015

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“…Such fragmentation dynamics have been demonstrated in phenol [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] and thiophenol, [24][25][26][27][28][29][30] in a range of substituted phenols [31][32][33][34][35][36] and thiophenols, [37][38][39] and in the methylated analogues anisole 40,41 and thioanisole, [42][43][44][45][46] in both the gas and condensed [47][48][49][50] phase. The present study focusses on thiophenols and, particularly, how the much-studied S-H bond fission process is affected by asymmetric substitution (i.e., in the 2-and 3-positions) of the aromatic ring.…”

Section: Introductionmentioning

confidence: 99%

The near ultraviolet photodissociation dynamics of 2- and 3-substituted thiophenols: Geometric vs. electronic structure effects

Marchetti

Karsili

Cipriani

et al. 2017

The Journal of Chemical Physics

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The near ultraviolet spectroscopy and photodissociation dynamics of two families of asymmetrically substituted thiophenols (2- and 3-YPhSH, with Y = F and Me) have been investigated experimentally (by H (Rydberg) atom photofragment translational spectroscopy) and by ab initio electronic structure calculations. Photoexcitation in all cases populates the 11ππ* and/or 11πσ* excited states and results in S–H bond fission. Analyses of the experimentally obtained total kinetic energy release (TKER) spectra yield the respective parent S–H bond strengths, estimates of ΔE(A∼−X∼), the energy splitting between the ground (X∼) and first excited (A∼) states of the resulting 2-(3-)YPhS radicals, and reveal a clear propensity for excitation of the C–S in-plane bending vibration in the radical products. The companion theory highlights roles for both geometric (e.g., steric effects and intramolecular H-bonding) and electronic (i.e., π (resonance) and σ (inductive)) effects in determining the respective parent minimum energy geometries, and the observed substituent and position-dependent trends in S–H bond strength and ΔE(A∼−X∼). 2-FPhSH shows some clear spectroscopic and photophysical differences. Intramolecular H-bonding ensures that most 2-FPhSH molecules exist as the syn rotamer, for which the electronic structure calculations return a substantial barrier to tunnelling from the photoexcited 11ππ* state to the 11πσ* continuum. The 11ππ* ← S0 excitation spectrum of syn-2-FPhSH thus exhibits resolved vibronic structure, enabling photolysis studies with a greater parent state selectivity. Structure apparent in the TKER spectrum of the H + 2-FPhS products formed when exciting at the 11ππ* ← S0 origin is interpreted by assuming unintended photoexcitation of an overlapping resonance associated with syn-2-FPhSH(v33 = 1) molecules. The present data offer tantalising hints that such out-of-plane motion influences non-adiabatic coupling in the vicinity of a conical intersection (between the 11πσ* and ground state potentials at extended S–H bond lengths) and thus the electronic branching in the eventual radical products.

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“…This is a general fact that does not rely on any interaction or coupling or condition on the energy gap. A nice illustration of this is the series of BMA [5,5], BMA [6,5] and BMA [6,7] cations, studied in the present work: these molecules exhibit the same charge migration but with diff erent energy gaps between the two electronic eigenstates (and therefore diff erent periods of oscillation). The same was observed in benzene, toluene and para-xylene cations, with the extreme situation where the period of oscillations is in nite in the benzene cation because of the zero energy gap.…”

mentioning

confidence: 71%

Electronic and non-adiabatic dynamics: general discussion

Orr-Ewing¹,

Verlet²,

Penfold³

et al. 2016

Faraday Discuss.

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Miller remarked: How did you damp the mode? Was the parameter based on physically reasonable damping, presumably to the bath (system-bath coupling). The reason I ask is that normally vibrational damping times for relatively high frequency coupling modes are on the order of ps relative to much faster motions to the CI region. This mechanism may not be operative. Maxim Gelin responded:We considered a minimal model of a so-called dissipative conical intersection. Namely, two coupled electronic states and two vibrational modes are considered as the system, which is bilinearly coupled to an environment. The results of our studies demonstrate that the conical intersection induces highly non-linear dynamics which is very sensitive to even weak coupling † Wolfgang Domcke's paper was presented by Maxim Gelin, Technische Universit¨at Munchen,¨ Garching, Germany.to the bath. If the electronic coupling at the conical intersection were set to zero, the weakest system-bath couplings considered in the present work would virtu-ally produce no eff ect on the wavepacket dynamics on a picosecond timescale. The dynamics at the conical intersection, on the contrary, is highly non-linear and chaotic and hence very sensitive to even weak system-bath couplings.Andrew Orr-Ewing asked: Can your results for a conical intersection which is bound along both the tuning and coupling coordinates provide some insights about the role of a dissipative medium on the dynamics of passage through a conical intersection in which the tuning coordinate is dissociative? For example, can we learn something about how a solvent aff ects the non-adiabatic dissocia-tion of heteroaromatic molecules excited to repulsive ps* states?Maxim Gelin answered: The role of vibrational energy relaxation due to the coupling to a vibrational bath in photodissociation reactions driven by repulsive ps* states was explored for a model of the photodissociation of pyrrole by Lan and Domcke. 1 It was shown that sufficiently strong system-bath coupling reduces the dissociation probability and enhances the probability for internal conversion to the electronic ground state. This nding is in qualitative agreement with the experimental observation that H-atom photodetachment via dissociative ps* states is suppressed in larger chromophores with more vibrational degrees of freedom, see e.g., M.-F. Lin et al.2 While H-atom photodetachment is the domi-nant photochemical channel in pyrrole and indole, it is completely quenched in tryptophan and larger chromophores. Dmitrii Shalashilin commented: Is the computational approach you are using generic or can it only be used for speci c types of Hamiltonian?Maxim Gelin replied: The approach assumes that the bath is described by a collection of harmonic oscillators and the system bath coupling is linear in the bath coordinates. The system Hamiltonian may be quite general.Adam Kirrander remarked: Could one adapt your model of a bath to describe a speci c system, for instance, a particular solvent or an anisotropic environment such as a protein em...

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O–H bond fission in 4-substituted phenols: S1 state predissociation viewed in a Hammett-like framework

Cited by 48 publications

References 74 publications

A Multipronged Comparative Study of the Ultraviolet Photochemistry of 2-, 3-, and 4-Chlorophenol in the Gas Phase

A Multipronged Comparative Study of the Ultraviolet Photochemistry of 2-, 3-, and 4-Chlorophenol in the Gas Phase

The near ultraviolet photodissociation dynamics of 2- and 3-substituted thiophenols: Geometric vs. electronic structure effects

Electronic and non-adiabatic dynamics: general discussion

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