Star-shaped hexaaryltriindoles small molecules: Tuning molecular properties towards solution processed organic light emitting devices
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2012
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Elsevier
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We present a series of differently substituted star-shaped hexaaryltriindoles with tunable
light-emitting properties. The deep blue emission is unchanged by donor peripheral substituents
while an increasing acceptor character produces a reduction of the optical gap,
an increased Stokes shift and eventually leads to the appearance of a new electronic level
and to the simultaneous deep blue (413 nm) and green (552 nm) emission in solution.
Quenching by concentration increases with the acceptor character but is lower as the tendency
of these compounds to aggregate is stronger. Solution processed thin films present
optical and morphological qualities adequate for device fabrication and similar electronic
structure compared to solutions with an emission range from 423 nm up to 657 nm
(red), demonstrating the possibility of tuning the energy levels by chemical functionalization.
We have fabricated and characterized single-layer solution processed organic light
emitting diodes (OLED) to investigate the influence on transport and emission properties
of the substituting species. We analyzed the I¿V response using a single-carrier numerical
model that includes injection barriers and non-uniform electric-field across the layer. As a
result, we obtained the electric field dependence of the mobility for each device. Best
results are obtained on the most electron rich derivative functionalized with six donor
methoxy groups. This material shows the highest emission efficiency in solid state, due
to aggregation-induced enhancement, and better transport properties with the highest
mobility and a very low turn-on voltage of 2.8 V. The solution processed OLED devices produce
stable deep blue (CIE coordinates (0.16, 0.16)) to white (CIE coordinates (0.33, 0.3))
emission with similar luminous efficiencies.
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Star-shaped hexaaryltriindoles small molecules: Tuning molecular properties towards solution processed organic light emitting devices
Coya C., Ruiz C., Alvarez A.L., Alvarez-Garcia S., Garcia-Frutos E.M., Gomez-Lor B., De Andres A.
(2012) Organic Electronics: physics, materials, applications, 13 (10) , pp. 2138-2148.
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