Donor-Acceptor Conjugated Polymers with Efficient Thermally Activated Delayed Fluorescence: Random versus Alternative Polymerization

Random polymerization is newly proposed for the achievement of efficient thermally activated delayed fluorescence (TADF) in donor-acceptor (D-A) conjugated polymers. As a proof of concept, a series of random polymers named Ran-P(Ac-TRZ02) similar to Ran-P(Ac-TRZ20) have been designed and synthesized based on the donor N-alkyl acridine (Ac) and the acceptor triphenyltriazine (TRZ) as the major and minor components, respectively. In this case, an increasing hole delocalization can be expected along the extended Ac oligomers, while the electron distribution is localized on the individual TRZ unit. Ongoing from alternative to random polymers, consequently, the enhanced hole-electron separation leads to a reduced singlet-triplet energy splitting (Delta E-ST ) from 0.39 to 0.26-0.28 eV. Unlike the alternative polymer Alt-P(Ac-TRZ) with no TADF, Ran-P(Ac-TRZ02) similar to Ran-P(Ac-TRZ20) achieves a distinct delayed fluorescence and reveals a maximum external quantum efficiency of 7.2% (22.4 cd A(-1), 27.1 lm W-1). The performance is about 2.8 times that of Alt-P(Ac-TRZ) (2.6%), clearly highlighting the superiority of random polymerization to alternative polymerization.