A Novel Carbazolophane: A Comparison of the Performance of Two Planar Chiral CP-TADF Emitters

The prototypical example of a (cyclo)phane, [2.2]paracyclophane (PCP), has proven to be a versatile stereogenic moiety within the design of circularly polarized thermally activated delayed fluorescence (CP-TADF) emitters; however, the exploration of other cyclophanes within CP-TADF emitter design has been largely neglected. Here, a comparative study of the photophysical and optoelectronic properties of two cyclophane emitters, (1,7)tBuCzpPhTrz and its isomer (1,4)tBuCzpPhTrz, is presented. The carbazolophane-triazine compound (1,7)tBuCzpPhTrz, obtained via an unprecedented intramolecular rearrangement, is the first example of a planar chiral TADF emitter deviating from the PCP scaffold. Significant geometrical change of the enclosed carbazole in (1,7)tBuCzp results in an attenuation of the donor strength, while the merits of rigidity and steric bulk remain. In particular, the full width at half maximum (FWHM) of the photoluminescence spectrum in toluene of (1,7)tBuCzpPhTrz is reduced by 34% and blue-shifted by 20 nm compared to that of (1,4)tBuCzpPhTrz. In doped films, the compounds reach high photoluminescence quantum yields (Phi PL) of 91 and 81%, respectively. The chiroptical properties reveal dissymmetry factors |gPL| of up to 5 x 10-4. These results demonstrate the impact of the cyclophane for the development of CP-TADF materials and add to the currently limited scope of available planar chiral donors. New perspectives for the design of blue thermally activated delayed fluorescence (TADF) emitters exhibiting circularly polarized luminescence (CPL) are outlined. Two emitters (1,7)tBuCzpPhTrz and (1,4)tBuCzpPhTrz with modified planar chiral donor structures show the use of a novel cyclophane donor design, featuring a bowl-like geometry with strong rigidity, circularly polarized luminescence, and narrowed emission profile in comparison to its regioisomer. image