Monosubstituted Dibenzofulvene-Based Luminogens: Aggregation-Induced Emission Enhancement and Dual-State Emission

The
observation of unusual aggregation-induced emission enhancement (AIEE)
phenomenon in the deep red wavelength region, dual state emission,
and intramolecular charge transfer of dibenzofulvene (DBF) derivatives are described. These consist of a series of newly synthesized
donor–acceptor based monosubstituted molecules (DT1, DT2, DP1, and DP2) with
their cores comprising DBF molecules. Two luminogens
with thiophene-substituted at the ninth position of DBF, viz. DT1 and DT2, displayed AIEE with
predominant J-type aggregation due to the effect of intramolecular
planarization and formation of nanoparticles in the aggregated state.
In the DP1 and DP2 luminogens an extra phenyl
ring was inserted at the ninth position of DBFs (between
thiophene and DBF) that resulted in a blueshift (∼60 nm) as
compared to the DT derivatives and exhibited a unique
dual state emission with good quantum yields. This additional phenyl
moiety reduces the effective conjugation length toward 2,1,3-benzothiadiazole
from DBF and simultaneously interrupts the head to tail
interaction and also prevents the J-type aggregation. All the four
luminogens exhibited distinctive solvent-dependent photoluminescence
(PL) behavior (solvatochromism) because of the efficient intramolecular
charge transfer. The DT2 and DP2 luminogens
showed heavy atom effect due to the presence of two bromine atoms.