Ab Initio Static and Molecular Dynamics Study of 4‐Styrylpyridine

Abstract

We report an in-depth theoretical study of 4-styrylpyridine in its singlet S(0) ground state. The geometries and the relative stabilities of the trans and cis isomers were investigated within density functional theory (DFT) as well as within Hartree-Fock (HF), second-order Møller-Plesset (MP2), and coupled cluster (CC) theories. The DFT calculations were performed using the B3LYP and PBE functionals, with basis sets of different qualities, and gave results that are very consistent with each other. The molecular structure is thus predicted to be planar at the energy minimum, which is associated with the trans conformation, and to become markedly twisted at the minimum of higher energy, which is associated with the cis conformation. The results of the calculations performed with the post-HF methods approach those obtained with the DFT methods, provided that the level of treatment of the electronic correlation is high enough and that sufficiently flexible basis sets are used. Calculations carried out within DFT also allowed the determination of the geometry and the energy of the molecule at the biradicaloid transition state associated with the thermal cis=trans isomerization and at the transition states associated with the enantiomerization of the cis isomer and with the rotations of the pyridinyl and phenyl groups in the trans and cis isomers. Car-Parrinello molecular dynamics simulations were also performed at 50, 150, and 300 K using the PBE functional. The studies allowed us to evidence the highly flexible nature of the molecule in both conformations. In particular, the trans isomer was found to exist mainly in a nonplanar form at finite temperatures, while the rotation of the pyridinyl ring in the cis isomer was incidentally observed to take place within approximately 1 ps during the simulation carried out at 150 K on this isomer.

Ab initio static and molecular dynamics study of the absorption spectra of the 4-styrylpyridine photoswitch in its cis and trans forms

“…Furthermore, the existence of the twisted trans species has been evidenced by the results of the finite-temperature CPMD simulations reported in ref. 20. For the cis isomer, the S 0 -S 1,2 electronic excitations also involve one-electron transitions into the LUMO, which still presents an antibonding character at the level of the C 1 -C 2 ethylenic moiety.…”

“…20 The trans isomer of planar geometry was shown to be the most stable isomer with a cis-trans zero-point energy difference of DE 0 CT = 1680 cm À1 . Furthermore, ab initio molecular dynamics (AIMD) simulations performed at 50, 150 and 300 K using the CarParrinello (CP) scheme 21 allowed us to evidence the highly flexible nature of the molecule in the two conformations.…”

“…Time dependence of the occupied (filled circles) and virtual (empty circles) frontier KS energy levels of trans-4-styrylpyridine as obtained at the B3LYP(AC)/G 0 level from the CPMD simulation performed at 300 K 20. Molecular orbitals are also shown for some instantaneous configurations (see text).configurations, those at t 0 2 and t 0 3 included, the S 0 -S 1 is mainly contributed by the HOMO[p] -LUMO[p*] excitation with a smaller contribution from the HOMO À 1[n] -LUMO[p*] excitation.…”

Influence of Temperature on the Rotameric Forms of the Propyl Acetate Molecule: Raman and FTIR Spectroscopic Studies Aided by ab Initio and Car–Parrinello Molecular Dynamics Simulations

“…62 S26(79), S17 (8) 53 S14(37), S26(26), S8(11), S7 (7), S13 (7) 75 S35(68), S16(9), S26 (7) 60 S26(49), S35(28), S14 (6) 82 S35(56), S17(12), S14(11), S45(5), S26(5) 90 S35(48), S17(25), S14(6), S45 (5) 91 S17(40), S22(23), S14 (12), S26(8), S31(5) 92 S17(45), S22(17), S14 (14), S35 (6) 113 (vw) 100 S26(68), S17(16), S35 (6) 127 S22(32), S16(32), S31 (23) 124 S35(30), S26(23), S17(18), S45(13), S16 (8) 159 S16(29), S22 (27), S45(15), S12 (7) 187 S17(62), S35 (28) (71), S17 (6) 237 (vvw) 233 S45(39), S16(26), S31(9), S11…”

“…3 The preferential existence of various rotameric forms of the PA molecule at high-, room-, and lowtemperature domains has also been estimated from experimental observations, aided by ab initio quantum chemical and Car−Parrinello molecular dynamics (CPMD) simulation studies. 4,5 …”