The Formation of Hydrogen-Bond Facilitated Salts with Tunable Optical Properties: An Experimental and Theoretical Study of 2,4,5-Triphenylimidazole

Adjusting and modifying the optical properties of organic
fluorophores
are of importance for the development of the next generation of luminescent
materials. Herein, we report the tunable fluorescence of 2,4,5-triphenylimidazole
(TPI) chromophore by the formation of multicomponent crystals with
the supramolecular building blocks, 4-bromotetrafluorobenzene carboxylic
acid and tetrafluorosuccinic acid, by means of hydrogen bonding. A
change in packing fashions between two adjacent TPI molecules is observed
from a staggered pattern in the pure TPI crystal to an antisymmetric
parallel arrangement in the multicomponent crystals. Moreover, the
obtained organic salts show red-shift emission and enhanced fluorescence
lifetime compared with the pure TPI crystal. Periodic density functional
theoretical (DFT) calculations suggest that the introduction of the
coformers can influence the energy level structures and orbital distributions
of the TPI chromophore in the multicomponent crystals. Therefore,
by the combination of experimental and theoretical studies on the
multicomponent organic solids, this work not only reports the supramolecular
assembly of new types of photoactive solid-state materials but also
provides a detailed understanding of the electronic structures of
the luminescent materials.