The
structural, thermal, linear, and femtosecond third-order nonlinear
optical (NLO) properties of two pyridine-based anthracene chalcones,
(2E)-1-(anthracen-9-yl)-3-(pyridin-2-yl)prop-2-en-1-one
(2PANC) and (2E)-1-(anthracen-9-yl)-3-(pyridin-3-yl)prop-2-en-1-one
(3PANC), were investigated. These two chalcones were
synthesized following the Claisen–Schmidt condensation method.
Optically transparent single crystals were achieved using a slow evaporation
solution growth technique. The presence of functional groups in these
molecules was established by Fourier transform infrared and NMR spectroscopic
data. The detailed solid-state structure of both chalcones was determined
from the single-crystal X-ray diffraction data. Both crystals crystallized
in the centrosymmetric triclinic space group P1̅
with the nuance of unit cell parameters. The crystals (labeled as 2PANC and 3PANC) have been found to be transparent
optically [in the entire visible spectral region] and were found to
be thermally stable up to 169 and 194 °C, respectively. The intermolecular
interactions were investigated using the Hirshfeld surface analysis,
and the band structures (highest occupied molecular orbital–lowest
unoccupied molecular orbital, excited-state energies, global chemical
reactivity descriptors, and molecular electrostatic potentials) were
studied using density functional theory (DFT) techniques. The ultrafast
third-order NLO properties were investigated using (a) Z-scan and (b) degenerate four-wave mixing (DFWM) techniques using
∼50 fs pulses at 800 nm (1 kHz, ∼4 mJ) from a Ti:sapphire
laser amplifier. Two-photon-assisted reverse saturable absorption,
self-focusing nonlinear refraction, optical limiting, and optical
switching behaviors were witnessed from the Z-scan
data. 3PANC demonstrated a stronger two-photon absorption
coefficient, while 2PANC depicted a stronger nonlinear refractive
index among the two. The time-resolved DFWM data demonstrated that
the decay times of 2PANC and 3PANC were
∼162 and ∼180 fs, respectively. The second hyperpolarizability
(γ) values determined by DFT, Z-scan, and DFWM
were found to be in good correlation (with a magnitude of ∼10–34 esu). The ultrafast third-order NLO response, significant
NLO properties, and thermal stability of these chalcones brands them
as potential candidates for optical power limiting and switching applications.