[structure: see text] Ethynyl-linked benzofuran-naphthyridine compounds show high-yield fluorescence with solvatochromic properties. One of the compounds, ABAN, has successfully formed fluorescent organic nanoparticles (FONs), for which the photophysical properties such as the spectral features and intensity are remarkably different from those at the molecular level (solution) and in bulk material. The results are tentatively rationalized by the FONs inducing coplanarization of the benzofuran-naphthyridine molecule to extend its effective conjugation length and hence increase the oscillator strength.