Synthesis of Quinolino[4,3‐ j]phenanthridines and their Photophysical Characterization

Quinolino[4,3-j]phenanthridines were synthesized from para-terphenyl-2,2′′-diamines, which were obtained by cross-coupling reactions. The diamines were converted into amides and ortho-cyclized to quinolino[4,3-j]phenanthridines using Morgan-Walls reactions. Prolonged reaction times were required in these electrophilic substitution reactions to overcome the respective deactivated intermediates formed after the first ortho fusion. Optophysical properties were determined by UV/Vis and fluorescence spectroscopy and calculated by quantum chemical calculations. The compounds exhibit rather small HOMO/LUMO gaps and a remarkable bathochromic shift of luminescence upon protonation, what makes these compounds promising candidates for optoelectronic applications.