Organic spontaneous emission approaching the monochromatic limit

Spontaneous emission is inherently associated with spectral broadening mechanisms, resulting in finite bandwidth in the emitted light. Narrowing this linewidth toward the monochromatic limit has long been a central pursuit in photonics, as it determines the ultimate color purity of nonstimulated light sources. Organic luminescent materials offer facile wavelength tunability but typically exhibit broad emission bands (>40 nanometers). The emergence of multiple-resonance emitters has provided a promising route to overcome this limitation, yet most reported systems remain within 20 to 30 nanometers. We present a molecular design strategy that amplifies the multiple-resonance effect through molecular repetition, yielding fluorescence with linewidths of 6.9 nanometers in toluene, 5.5 nanometers in 3-methylpentane, and 9.1 nanometers in a doped polymer film, placing this molecular framework among the narrowest-band organic luminophores reported.