Phenanthrene-Fused BN-Acenaphth(yl)ene: Synthesis, Structures, and Photophysical Studies

Two novel BN-doped CP-PAHs, <b>BN-ANH-TPh</b> and <b>BN-AN-TPh</b>, were synthesized in a straightforward manner. <b>BN-ANH-TPh</b> features a localized C-C bond in the five-membered ring, whereas <b>BN-AN-TPh</b> features a localized C═C bond. Notably, <b>BN-AN-TPh</b> was obtained via the dehydrogenation of <b>BN-ANH-TPh</b>. Both compounds were unambiguously characterized by single-crystal X-ray diffraction analysis. A subtle structural alteration from C-C to C═C bonding resulted in significant modulation of their electronic structures and photophysical properties. Compared to <b>BN-ANH-TPh</b>, <b>BN-AN-TPh</b> exhibits lower LUMO and HOMO energy levels, accompanied by a narrower HOMO-LUMO energy gap. <b>BN-AN-TPh</b> exhibits red-shifted absorption and emission spectra relative to those of <b>BN-ANH-TPh</b>. Both compounds emit strongly in solution, with quantum yields of 73% and 71%, respectively. Furthermore, organic light-emitting diodes (OLEDs) were fabricated by using <b>BN-AN-TPh</b> and <b>BN-ANH-TPh</b> as emissive layers. The OLED device based on <b>BN-AN-TPh</b> achieved a maximum current efficiency of 2.41 cd/A and a maximum luminance of 1556 cd/m².