The problem of planarization of organic components in electronic devices is
widely discussed in the literature (see, e.g. [1] for thiophene-based
heterodimers). As any deviation from the high-symmetry nuclear configurations
of polyatomic systems in non-degenerate electronic states is induced by the
pseudo Jahn-Teller effect (PJTE) [2], the restoration of such symmetry
configurations can be achieved via suppression of the PJTE by external
influence [3, 4]. In the present work we discuss this problem using the 2,2'-
bithiophene and the 2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]-thiophene
(BTTT-H) molecules as examples. For example, we show that torsion motion of
a2 symmetry in cis-2,2'-bithiophene molecule is induced by the (1A1+1A2)a2
PJTE, where the excited 1A2 state is formed by one-electron excitation
a2(HOMO)→a1(LUMO+1). It follows that removal of one electron from the
HOMO by oxidation reduces by-half the vibronic coupling constant, thereby
suppressing the PJTE and restoring the planar configuration. Addition of one
electron to the LUMO b1 by reduction increases the energy gap between the
mixing states, which, too, leads to the suppression of the PJTE and to
restoration of the planar nuclear configuration of the molecule (see the Figure
below).

[1] J. B. Lin, Yu Jin, et.al; Chem. Theory Comput. 13 5624 (2017).
[2] I. B. Bersuker; Chem. Rev. 113 1351 (2013).
[3] I. B. Bersuker; FlatChem 6 11 (2017).
[4] N. Gorinchoy; Intern. J. Org. Chem. 8 142 (2018).