Dibenzobarrelene‐Based Azaacenes: Emitters in Organic Light‐Emitting Diodes

Abstract

The synthesis of soluble dibenzobarrelene-substituted azaacenes either by condensation reactions in solution or, more effectively, in the solid state by using a ball mill is reported herein. We relate their optical properties in thin films to their packing in the solid state. The targets are characterized by cyclic voltammetry, X-ray crystallography and UV/Vis and fluorescence analysis. Three highly fluorescent, amorphous azaacenes were processed into organic light-emitting diodes, and their improved performance (luminance, efficiency and efficacy) was compared with that of structurally related iptycene-based azaacenes.

Donor–Acceptor Iptycenes with Thermally Activated Delayed Fluorescence

“…The derivative of 2 without carbazole moieties has recently been published by Bunz and coworkers, and exhibits a similar absorption and emission profile with a weaker charge‐transfer character and slightly lower quantum yield …”

Synthesis of Anthracene Derivatives with Azaacene‐Containing Iptycene Wings and the Utilization as a Dopant for Solution‐Processed Organic Light‐Emitting Diodes

“…Here, even though no π–π stacking of the central anthracene unit was observed in the single‐crystal X‐ray structures, the molecules showed lower Φ F in the solid state compared with those in solution. This result indicates that the interaction between the azaacene moieties in the iptycene units of neighboring molecules does not contribute to improve the Φ solid / Φ solution ratio in spite of the degree of the azaacene size, even though the interaction might prevent the central anthracene units from being stacked. Interestingly, Ant‐Py displayed the shortest fluorescence maximum at 478 nm.…”

“…Therefore, iptycene units act as a steric shield to isolate fluorescent materials. Indeed, iptycene units were fused to different acene cores for the purpose of tuning fluorescence properties, acting as steric blocks . For example, an iptycene‐fused diazatetracene has successfully demonstrated the effective suppression of the aggregation, resulting in the improved luminance of 322 cd m −2 compared to the one without iptycene units .…”

“…Importantly, the intrinsic fluorescence property is promising (1000 cd m −2 at 10 V) . Furthermore, the combination with iptycene and TIPS‐ethynyl groups is expected to reduce aggregation in the solid state . Finally, the performance of the simple solution‐processed OLEDs was evaluated.…”

Azaacene Dimers: Acceptor Materials with a Twist

“…Azaacenes are tailor‐made and electronically modulated by substitution, yet their strong tendency to π‐stack results in crystalline domains in the solid‐state and has hindered their widespread use as active layer acceptors in bulk‐heterojunction OPV. Balancing acceptor character, charge transport and aggregation/morphology is challenging, but can be resolved for azaacenes either by incorporation of morphology‐dominating units, such as iptycenes which also enhance solubility or even simple oligomer formation, for example, the azaphene‐dimer shown in Figure …”