Abstract:
Density functional theory (DFT) calculations have been performed for a series of
supramolecular assemblies containing azobenzene (Azo-X where X=I, Br and H) and
alkoxystilbazole subunits to evaluate their electronic, linear and nonlinear optical
properties. These assemblies are derivatives of azobenzene, obtained by the substitution
of electron-withdrawing and electron-donating groups onto the molecular skeleton. The
interaction energies (Eint) of all the designed supramolecular complexes (IA-IF, IIA
IIF and IIIA-IIIF) range from -1.02 kcal/mol to -7.70 kcal/mol. Electronic properties
of these hydrogen/halogen bond driven supramolecular assemblies such as, vertical
ionization energies (VIE), HOMO-LUMO energy gap (GH-L), excitation energies,
density of states (DOS) and natural bond orbital (NBO) analyses were also computed.
The non-covalent interaction index (NCI) and quantum theory of atoms in molecules
(QTAIM) analyses have also been performed to validate the nature of inter- and intra
molecular interactions in these complexes. A substantial enhancement in the first
hyperpolarizability (βₒ) values of the designed supramolecular complexes has been
observed driven by the charge transfer from the pyridyl moiety of alkoxystilbazole to
Azo-X. The highest first hyperpolarizability (βₒ) value of 1.3×104 au is observed for
supramolecular complex of p-nitro substituted azobenzene with alkoxystilbazole (ID
complex). It was confirmed on a purely theoretical basis that both the type of
noncovalent interactions present and the substituent group incorporated influence the
nonlinear optical response (NLO) of the systems.
