Lasing Properties Activation by Constitutional Isomerism of an Electron-Accepting Group

Materials engineering
plays a pivotal role considering its manifold
applications, i.e., in medicine as individualized drug carriers or
in advanced technologies such as optoelectronic devices and others.
Recently, increasing interest in the pyrazoline derivatives family
of compounds was noticed. In this paper, we report on the constitutional
isomerism influence on photophysical properties of low molecular,
push–pull type of pyrazole-based organic chromophores. Particularly,
we show the ability of optical properties tailoring by changing the
substitution of phenyl ring extended by effective electron-accepting
moiety in ortho and para positions.
Such a structural change in molecule results in a shift of photoluminescence
spectra as well as the activation or deactivation of gain mechanism
for multimode laser emission. In order to confirm ground state molecular
structures for both isomers we performed time-dependent DFT calculations
in a solvent environment. In addition, structural analysis of spontaneously
grown single crystals was carried out using X-ray spectroscopy. The
above-mentioned studies allowed us to define the isomer’s molecular
geometries and charge distribution in excited and ground states and
to distinguish the significant differences in crystallographic structures.
Combined experimental and theoretical research have resulted in a
hypothesis of the molecular mechanism standing behind observed differences
in optical properties of both isomers. Importantly, such an approach
can be useful for materials engineering, allowing us to predict the
features of novel materials for optoelectronics and photonics.