Synthesis, X-ray crystal structure, and solid-state blue fluorescence of dialkylbenzo[b]naphtho[2,1-d]furan-6-one-type fluorophores

Novel solid-emissive benzo[b]naphtho[2,1-d]furan-6-one-type fluorophores 2a–2c constructed with a π-planar chromophore skeleton and with sterically hindered dialkyl substituents (R=butyl, octyl, and benzyl) were designed and easily synthesized. Both in cyclohexane and in solid state, the fluorescence quantum yields (Φ) are almost the same among 2a–2c (Φsolution=∼0.5 and Φsolid=∼0.4). Interestingly, the fluorophore 2a exhibits strong blue fluorescence emission both in solution and in crystalline state. To elucidate the effects of the dialkyl substituents on solid-state photophysical properties, we performed time-resolved fluorescence spectroscopic measurement, semi-empirical molecular orbital calculations (AM1 and INDO/S), and X-ray crystallographic analysis.

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