Flexible and Continuous Regulation Promoting Remarkably Emission Enhancement of Planar Triphenylene

The photophysical properties of π-conjugated materials
in
aggregate states are heavily dependent on molecular arrangements.
Accordingly, the regulation of molecular packing is an essential issue
for achieving optimized optical properties, especially the related
adjustment of π–π interactions. Herein, triphenylene
(TPhE) with the planar structure was presented as an ideal model,
in which the molecular packing was regulated continuously by the exogenous
stimulation, as monitored by the uncommon and conspicuous emission
enhancement, which should be attributed to the enhanced excimer yielded
by the pressure-induced strengthening π–π interactions.
Additionally, the different fluorescence behaviors of cocrystal based
on TPhE and tetrafluoroterephthalonitrile (TFTP) under high pressure
further illustrated the important role of enhanced excimer formation
in fluorescence enhancement. To the best of knowledge, this research
is the first example with pressure-induced emission enhancement (PIEE)
feature of polycyclic aromatic hydrocarbon (PAH) without heteroatom,
which revealed the evolution of an excimer with its intrinsic photophysical
properties, and provided deep insights into the packing-property of
π-conjugated materials in aggregates.