ELECTRONIC ABSORPTION SPECTRA AND INTERMOLECULAR HYDROGEN BONDING IN MESOGEN–NONMESOGEN SYSTEMS

• Published in: Journal of structural chemistry Vol. 61; no. 10; pp. 1530 - 1540
• Main Authors: Giricheva, N. I., Bubnova, K. E., Chernova, E. M., Fedorov, M. S., Syrbu, S. A., Girichev, G. V.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01-10-2020
• Subjects: Atomic; Atomic/Molecular Structure and Spectra; Chemistry; Chemistry and Materials Science; Inorganic Chemistry; Molecular; Optical and Plasma Physics; Physical Chemistry; Solid State Physics; alkyloxycinnamic acid; 4; electronic absorption spectra; H-complexes; nonmesogens; 4,4′-bipyridine; quantum chemical calculations; liquid crystals; frontier molecular orbitals; hydrogen bond
• ISSN: 0022-4766; 1573-8779
• DOI: 10.1134/S0022476620100054

The TD-DFT/B97-D/6-311G
**
method is used to calculate the electronic absorption spectra of
А
⋯
Х
⋯
А
supramolecules with intermolecular hydrogen bonds (HBs), where
А
is 4-
n
-propoxycinnamic acid,
Х
is a nonmesogen molecule with bifunctional HB acceptors. Nonmesogens
Х
(
B
,
C
,
D
,
E
) consist of two pyridyl fragments connected by bridging groups of different natures: 4,4′-bipyridine (
В
), 1,2-bis(4-pyridyl)ethane (
С
), 1,2-bis(4-pyridyl)ethylene (
D
), 4,4′-azopyridine (
Е
). It is shown that the introduction of bridging groups (–CН
2
–CН
2
–, –CН=СН–, –N=N
–
) significantly affects the energy of frontier orbitals and electronic absorption spectra (EAS) of nonmesogens
Х
in the near-UV region. The EAS of two structural units
A
⋯
В
⋯
A
,
A
⋯
A
, which may be formed due to the self-assembly in two-component mesogen
А
–nonmesogen 
В
systems, are compared. Due to hydrogen bonds (O–H⋯N and O–H⋯O), having different types and strengths in these complexes, the high-intensity band shifts to shorter wavelengths in complex
А
⋯
В
⋯
А
and to longer wavelengths in complex
А
⋯
А
with respect to the λ = 333 nm band of monomer
А
. It is shown that EAS of hydrogen-bonded complexes
А
⋯
Х
⋯
А
are not superpositions of EAS of individual components. The spectra show electronic transitions related to charge transfer between the components of the complexes. Using nonmesogens
Х
of different nature in supramolecules
А
⋯
Х
⋯
А
will allow one to change purposefully their electro-optical properties and to achieve intense absorption in particular regions of UV spectra.