Excited state dynamics with the direct trajectory surface hopping method: azobenzene and its derivatives as a case study (original) (raw)
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The Journal of Chemical Physics, 2005
We have studied the cis→ trans and trans→ cis photoisomerization of azobenzene after n → * excitation using the full multiple spawning ͑FMS͒ method for nonadiabatic wave-packet dynamics with potential-energy surfaces and couplings determined "on the fly" from a reparametrized multiconfigurational semiempirical method. We compare the FMS results with a previous direct dynamics treatment using the same potential-energy surfaces and couplings, but with the nonadiabatic dynamics modeled using a semiclassical surface hopping ͑SH͒ method. We concentrate on the dynamical effects that determine the photoisomerization quantum yields, namely, the rate of radiationless electronic relaxation and the character of motion along the reaction coordinate. The quantal and semiclassical results are in good general agreement, confirming our previous analysis of the photodynamics. The SH method slightly overestimates the rate of excited state decay, leading in this case to lower quantum yields.
The Photoisomerization Mechanism of Azobenzene: A Semiclassical Simulation of Nonadiabatic Dynamics
Chemistry-a European Journal, 2004
We have simulated the photoisomerization dynamics of azobenzene, taking into account internal conversion and geometrical relaxation processes, by means of a semiclassical surface hopping approach. Both n→π* and π→π* excitations and both cis→trans and trans→cis conversions have been considered. We show that in all cases the torsion around the NN double bond is the preferred mechanism. The quantum yields measured are correctly reproduced and the observed differences are explained as a result of the competition between the inertia of the torsional motion and the premature deactivation of the excited state. Recent time-resolved spectroscopic experiments are interpreted in the light of the simulated dynamics.
Journal of Computational Chemistry, 2019
Within three functionals (TD-B3LYP, TD-BHandHLYP, and TD-CAM-B3LYP) in combination with four basis sets (3-21g, 6-31g, 6-31g(d), and cc-pvdz), global switching (GS) trajectory surface hopping molecular dynamics has been performed for cis-to-trans azobenzene photoisomerization up to the S 1 (nπ*) excitation. Although all the combinations show artificial doublecone structure of conical intersection between ground and first excited states, simulated quantum yields and lifetimes are in good agreement with one another; 0.6 (AE5%) and 40.5 fs (AE10%) by TD-B3LYP, 0.5 (AE10%) and 35.5 fs (AE4%) by TD-BHandHLYP, and 0.44 (AE9%) and 35.2 fs (AE10%) by TD-CAM-B3LYP. By analyzing distributions of excited-state population decays, hopping spots, and typical trajectories with performance of 12 functional/basis set combinations, it has been concluded that functional dependence for given basis set is slightly more sensitive than basis set dependence for given functional. The present GS on-the-fly time-dependent density functional theory (TDDFT) trajectory surface hopping simulation can provide practical benchmark guidelines for conical intersection driven excited-state molecular dynamics simulation involving in large complex system within ordinary TDDFT framework.
Computational simulation of the excited states dynamics of azobenzene in solution
2009
Azobenzene and its derivatives are molecules very often used to construct photomodulable materials and molecular devices. The main characteristic of this kind of molecules is the efficient and reversible trans → cis photoisomerization, that occurs in either sense, without secondary processes. Using the appropriate wavelength, one can convert either isomer into the other one. The photoisomerization mechanism of azobenzene has been debated, during the last decades, because of the peculiar wavelength dependence of the quantum yields and because at least two standard possibilities exist: N=N double bond torsion and N inversion. Our research group has performed simulations of the photodynamics of azobenzene molecule by mixed quantum-classical methods. Such simulations have been successful in explaining the dependence of the quantum yield on the excitation wavelength. However, these simulations have been conducted on the isolated azobenzene molecule, while almost all the experimental data...
Physical chemistry chemical physics : PCCP, 2014
We develop a novel method to simulate analytical nonadiabatic switching probability based on effective coupling and effective collision energy by using only electronic adiabatic potential energy surfaces and its gradients in the case of avoided crossing types of nonadiabatic transitions. In addition, the present method can keep the same time step for computing both on-the-fly trajectory and nonadiabatic transitions accurately. The present method is most useful for localized nonadiabatic transitions induced by conical intersection. We employ the on-the-fly surface hopping algorithm with an ab initio quantum chemistry calculation to demonstrate a dynamic simulation for photoisomerization in azobenzene. Simulated quantum yield and lifetime converge to 0.39 and 53 femtosecond, respectively (0.33 and 0.81 picosecond) for cis-to-trans (trans-to-cis) photoisomerization with up to 800 (600) sampling trajectories. The present results agree well with those of the experiment, as well as result...
Dynamics of Azobenzene Dimer Photoisomerization: Electronic and Steric Effects
The journal of physical chemistry letters, 2016
While azobenzenes readily photoswitch in solution, their photoisomerization in densely packed self-assembled monolayers (SAMs) can be suppressed. Reasons for this can be steric hindrance and/or electronic quenching, e.g., by exciton coupling. We address these possibilities by means of nonadiabatic molecular dynamics with trajectory surface hopping calculations, investigating the trans → cis isomerization of azobenzene after excitation into the ππ* absorption band. We consider a free monomer, an isolated dimer and a dimer embedded in a SAM-like environment of additional azobenzene molecules, imitating in this way the gradual transition from an unconstrained over an electronically coupled to an electronically coupled and sterically hindered, molecular switch. Our simulations reveal that in comparison to the single molecule the quantum yield of the trans → cis photoisomerization is similar for the isolated dimer, but greatly reduced in the sterically constrained situation. Other implic...
Chemical Physics, 2008
The aim of this work is to investigate the mechanism of photoisomerization of an azobenzenic chromophore in a supramolecular environment, where the primary photochemical act produces important changes in the whole system. We have chosen a derivative of azobenzene, with two cyclopeptides attached in the para positions, linked by hydrogen bonds when the chromophore is in the cis geometry. We have run computational simulations of the cis ? trans photoisomerization of such derivative of azobenzene, by means of a surface hopping method. The potential energy surfaces and nonadiabatic couplings are computed ''on the fly" with a hybrid QM/MM strategy, in which the quantum mechanical subsystem is treated semiempirically. The simulations show that the photoisomerization is fast (about 200 fs) and occurs with high quantum yields, as in free azobenzene. However, the two cyclopeptides are not promptly separated, and the breaking of the hydrogen bonds requires longer times (at least several picoseconds), with the intervention of the solvent molecules (water). As a consequence, the resulting trans-azobenzene is severely distorted, and we show how its approach to the equilibrium geometry could be monitored by time-resolved absorption spectroscopy.
Nature Communications, 2015
Azobenzene, a versatile and polymorphic molecule, has been extensively and successfully used for photoswitching applications. The debate over its photoisomerization mechanism leveraged on the computational scrutiny with ever-increasing levels of theory. However, the most resolved absorption spectrum for the transition to S 1 (np*) has not followed the computational advances and is more than half a century old. Here, using jet-cooled molecular beam and multiphoton ionization techniques we report the first high-resolution spectra of S 1 (np*) and S 2 (pp*). The photophysical characterization reveals directly the structural changes upon excitation and the timescales of dynamical processes. For S 1 (np*), we find that changes in the hybridization of the nitrogen atoms are the driving force that triggers isomerization. In combination with quantum chemical calculations we conclude that photoisomerization occurs along an inversion-assisted torsional pathway with a barrier of B2 kcal mol À 1. This methodology can be extended to photoresponsive molecular systems so far deemed non-accessible to high-resolution spectroscopy.