A novel sky-blue-emitting tripyrenylpyridine
derivative, 2,4,6-tri(1-pyrenyl)pyridine (2,4,6-TPP), has been synthesized
using a Suzuki coupling reaction and compared with three previously
reported isomeric dipyrenylpyridine (DPP) analogues (2,4-di(1-pyrenyl)pyridine
(2,4-DPP), 2,6-di(1-pyrenyl)pyridine (2,6-DPP), and 3,5-di(1-pyrenyl)pyridine
(3,5-DPP)). As revealed by single-crystal X-ray analysis and computational
simulations, all compounds possess highly twisted conformations in
the solid state with interpyrene torsional angles of 42.3°–57.2°.
These solid-state conformations and packing variations of pyrenylpyridines
could be correlated to observed variations in physical characteristics
such as photo/thermal stability and spectral properties, but showed
only marginal influence on electrochemical properties. The novel derivative,
2,4,6-TPP, exhibited the lowest degree of crystallinity as revealed
by powder X-ray diffraction analysis and formed amorphous thin films
as verified using grazing-incidence wide-angle X-ray scattering. This
compound also showed high thermal/photo stability relative to its
disubstituted analogues (DPPs). Thus, a nondoped organic light-emitting
diode (OLED) prototype was fabricated using 2,4,6-TPP as the emissive
layer, which displayed a sky-blue electroluminescence with Commission
Internationale de L’Eclairage (CIE) coordinates of (0.18, 0.34).
This OLED prototype achieved a maximum external quantum efficiency
of 6.0 ± 1.2% at 5 V. The relatively high efficiency for this
simple-architecture device reflects a good balance of electron and
hole transporting ability of 2,4,6-TPP along with efficient exciton
formation in this material and indicates its promise as an emitting
material for design of blue OLED devices.