Conclusion
In this work, we investigated the crystal structure, electronic
structure and charge transport properties of two pyrazole derivatives
through density functional theory and interpreted via Marcus Electron
Theory. The optimized geometry structures, reorganization energy,
absorption spectra, frontier orbitals, ionization potential (IP) and
electronic affinity (EA) of both compounds were calculated to perform
the relationship between the structure and property taking their crystal
geometry, noncovalent interactions and aggregation modes in solid phase
into account. According to SCXRD results the molecule AB1 andAB2 aggregate J type and antiparallel H type stacking modes in
their solid phases which are favourable stacking modes to obtain high
charge transfer rate due to high transfer integral. The incorporation of
the NO2 group to the molecule skeleton result in
different crystal structure and packing arrangement therefore different
charge transport property in terms of their reorganization energy. The
hole reorganization energies of the both molecules are smaller than that
of electron indicating that they can be used as p -type
semiconductors. Since AB2 exhibits lower hole reogranization
energy than that of AB1 , the charge transfer rate can be
predicted high for AB2 . In terms of its crystallographic data,
it aggregates in strong antiparallel H type \(\pi\cdots\pi\) stacking
type with the small perpendicular distance between the adjacent rings.
Therefore, this result consolidated that the molecule AB2 can
have high charge transport rate when it is used as an optoelectronic
device. In addition, low-lying HOMOs, and high IPs of the AB2indicate the its better redox stability than AB1 . Although this
is case, beside the AB2, AB1 shows prefferred stacking mode in solid
phase and low reorganization energy which is benefical for device
application. Accordingly, both molecules are suggested to be quite
suitable for p type semiconducting materials with small reorganization
energy and preferred stacking modes in solid phase.