Highly Efficient Orange-Red/Red Excimer Fluorescence from Dimeric π–π Stacking of Perylene and Its Nanoparticle Applications

To
achieve high-efficiency red excimer fluorescence, two novel
perylene (PE) derivatives (mTPA-3PE and 2SF-3PE) are designed and
synthesized with different monosubstituent triphenylamine (TPA) and
spirofluorene (SF), respectively. The photophysical investigations
reveal that mTPA-3PE and 2SF-3PE exhibit red/orange-red excimer fluorescence
(637 and 610 nm) with long lifetimes (37.86 and 72.41 ns) in crystals
but significantly different photoluminescence efficiencies (24 and
77%). Both crystal structure and excited-state property emphasize
that the discreteness of the PE dimer with π–π
stacking is essentially responsible for the high-efficiency excimer
emission in the crystal. Using PE as a π–π emissive
core in this work, highly efficient red excimer fluorescence is harvested
in the crystal for the first time. Moreover, their nanoparticles with
the same excimer fluorescence exhibit the advantage of easy processing
and the promising application in cell imaging. Once again, our results
validate the mechanism of excimer-induced enhanced emission (EIEE)
by the discrete dimeric π–π stacking of PE in the
solid state, which opens a new way to develop high-efficiency narrow
band gap (e.g., near-infrared) light-emitting materials using the
EIEE mechanism in the future.