Design, Synthesis, and Optical Properties of Novel Benzo[ <i>d</i> ]oxazolo[2,3‐ <i>a</i> ]isoquinoliniums

ABSTRACT This paper reports the synthesis of benzo[ d ]oxazolo[2,3‐ a ]isoquinoliniums as a novel ring system, its molecular structure, and spectroscopic properties. The target compounds were synthesized using an Ag‐mediated intramolecular nucleophilic cyclization of 2‐(2‐arylethynylphenyl)benzoxazoles. The X‐ray diffraction results revealed that the tetracyclic cation compound contained mostly planar parent skeletons and interacted via π–π stacking with neighboring molecules. Furthermore, in methanol solution, the benzoxazoloisoquinolines exhibited fluorescence with a large Stokes shift in the 350–550 nm region.