Pseudo Jahn-Teller origin of instability of planar configurations of hexa-heterocycles. Application to compounds with 1,2- and 1,4-C4X2 skeletons (X = O, S, Se, Te)

Pseudo Jahn-Teller Effect in Puckering and Planarization of Heterocyclic Compounds

“…The values of the PJT parameters we obtained are: K 0 = 0.37 eV/Å 2 , ∆ = 6.77 eV, and F = 1.32 eV/Å. They agree rather well with those calculated in [10]. At small distortions, the resulting value of the curvature of the AP along the b 1u puckering coordinate is negative, K = −0.14 eV/Å 2 .…”

“…Solving for the 3×3 secular determinant, one can get the following equation for the energies of the three states (1 ground state and 2 excited states) along the distortion coordinate: A similar equation can also be obtained for the four-level PJT problem. The procedure for estimating the vibronic constants in these cases can be found in N. Gorinchoy International Journal of Organic Chemistry the works [10] [13].…”

“…Knowledge of the mechanism of puckering of cyclic molecules provides the key to understanding how one can influence the system to suppress this effect and to flatten the system. In a recent review of Bersuker [12] The first group of compounds includes 1,4-dithiine molecules C 4 S 2 L 4 [10] with a variety of the ligands (L = H, F, Cl, Br), S-oxygenated derivatives of 1,4-dithiine, two tricyclic systems (thianthrene [11] and C 6 S 8 with two S-atoms in the 1,4-position of the central six-membered ring [13]), and 1,4-dihydropyrazine and its derivatives C 4 N 2 H 4 L 2 [15] in which two imide hydrogen atoms are replaced with halogens (L = F, Cl, Br). All these compounds are unstable in the high-symmetry planar nuclear configuration of D 2h symmetry, in the equilibrium configuration of C 2v symmetry they are bent at the S-S axis.…”

“…The next group of molecules includes 1,2-dichalcogenins, 1,2-C 4 X 2 L 4 , with X = O, S, Se, Te and L = H, F [10], two tricyclic species C 6 S 8 and with L = H, F, Cl, Br [17]. The planar configuration of these systems is unstable with respect to the twisting coordinate of a 2 symmetry that leads to a puckered equilibrium structure of C 2 symmetry.…”

Color‐Change Photoswitching of an Alkynylpyrene Excimer Dye

“…Based on the data, we posited a possible mechanism for O 2 -dependent bleaching involving photoexcitation of ambient dioxygen to its singlet state [10] , followed by formal [2+2+2] cycloaddition to two adjacent alkynes, generating an unstable 1,2-dioxin intermediate (Figure 4). Although 1,2-dioxins have not been isolated, they have been analyzed in computational studies, [11] are implicated in the generation of benzodioxins, [12] and they are postulated to rapidly isomerize to stable enediones. [13] We suggest, in analogy to the work by Block et al ., that after reaction with oxygen, our bis - pyrene 1,2-dioxin cyclic intermediate rapidly isomerizes to the corresponding stable enedione product (Figure 4).…”