Alternating Donor-Acceptor π-Conjugated Macrocycle Exhibiting Efficient Thermally Activated Delayed Fluorescence and Spontaneous Horizontal Molecular Orientation

A versatile design of thermally activated delayed fluorescence (TADF) pi-conjugated macrocycles incorporating electron-donor (D) and acceptor (A) units into a cyclo-meta-phenylene motif with an alternating pattern is presented. The new pi-conjugated macrocycle, which combines three 5-(N-carbazolyl)-phenylen-1,3-diyl as D units and three 6-phenyl-1,3,5-triazin-2,4-diyl as A units, possesses a small singlet-triplet energy gap and hence can emit efficient green TADF both in solution and doped thin films. Comparative experimental and computational investigations of the electronic and photophysical properties of the macrocycle with its analogous noncyclic compound reveal key advantages of the cyclic molecular configuration for actual emitters. Organic light-emitting diodes incorporating the TADF pi-conjugated macrocycle as an emitter demonstrate high external electroluminescence quantum efficiencies of up to 15.7%, outperforming the devices based on the noncyclic emitter. Herein, the importance of geometric design for producing novel organic emitters with fascinating optoelectronic and morphological characteristics is highlighted.

Automated summary

The study introduces a versatile design of thermally activated delayed fluorescence (TADF) pi-conjugated macrocycles, which emit efficient green TADF by incorporating D and A units into a cyclo-meta-phenylene motif. Experimental results show that organic light-emitting diodes utilizing macrocycles as emitters display higher external electroluminescence quantum efficiencies compared to devices based on noncyclic emitters.