Covalent Bond Torsion-Enabled Unique Crystal-Phase Transformation of an Organic Semiconductor for Multicolor Light-Emitting Transistors

High-mobility and color-tunable highly emissive organic
semiconductors
(OSCs) are highly promising for various optoelectronic device applications
and novel structure–property relationship investigations. However,
such OSCs have never been reported because of the great trade-off
between mobility, emission color, and emission efficiency. Here, we
report a novel strategy of molecular conformation-induced unique crystalline
polymorphism to realize the high mobility and color-tunable high emission
in a novel OSC, 2,7-di(anthracen-2-yl) naphthalene (2,7-DAN). Interestingly,
2,7-DAN has unique crystalline polymorphism, which has an almost identical
packing motif but slightly different molecular conformation enabled
by the small bond rotation angle variation between anthracene and
naphthalene units. More remarkably, the subtle covalent bond rotation
angle change leads to a big change in color emission (from blue to
green) but does not significantly modify the mobility and emission
efficiency. The carrier mobility of 2,7-DAN crystals can reach up
to a reliable 17 cm2 V–1 s–1, which is rare for the reported high-mobility OSCs. Based on the
unique phenomenon, high-performance light-emitting transistors with
blue to green emission are simultaneously demonstrated in an OSC crystal.
These results open a new way for designing emerging multifunctional
organic semiconductors toward next-generation advanced molecular (atomic)-scale
optoelectronics devices.