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A New type of organic fluorophores exhibiting strong blue and green emission in the solid state has been easily synthesized by an one-step reaction.Leave this area blank for abstract info. 6, 7 However, organic fluorophores exhibiting strong fluorescence both in solution and in the solid state are relatively limited because most fluorophores undergo fluorescence quenching by molecular aggregation in the solid state. In order to develop strong solid-emissive fluorophores, many efforts were made on inhibition of molecular aggregation state causing fluorescence quenching. Fluorescent dyes having non-planar structures with sterical hindered substituents prevent the fluorophores from the close packing causing fluorescence quenching in the solid state and produces intense solid-state fluorescence emission. 5h, 8, 9 In contrast, we have designed novel dialkylbenzo[b]naphtho[2,1-d]furan-6-one-type fluorophores (2a-2c), which consist of π-planar chromophore skeleton with sterical hindered dialkyl substituents prevent the fluorophores from short π-π contacts causing fluorescence quenching in the solid state. In this paper, we report the preparation of 2a-2c by onestep reaction and their photophysical properties in solution and in the solid state. To elucidate the effects of the dialkyl substituents on the solid-state photophysical properties, we have carried out the measurement of the solid-state fluorescence spectra and the X-ray crystallographic analysis of the fluorophores.The starting 1,1-dialkyl-1H-naphthalen-2-one 1a-1c were prepared according to the published procedure.10 Novel dialkylbenzo[b]naphtho[2,1-d]furan-6-one-type fluorophores 2a-2c were easily obtained by the reaction of 1a-1c with m-(dibutylamino)phenol in the presence of FeCl 3 (Scheme 1). However, when metal salt such as NiCl 2 or CuCl 2 instead of FeCl 3 was used, the fluorophores 2 were not obtained. The compounds 2a and 2c were obtained as crystals by recrystallozation from n-hexane, but the compound 2b was obtained as amorphous.The spectroscopic properties of 2a-2c both in solution and in the solid state are summarized in Table 1. 11 The fluorescence spectra of the compounds were recorded by excitation at the wavelengths of the longest absorption maximum. In cyclohexane, the absorption maxima at Pergamon TETRAHEDRON LETTERS Tetrahedron Letters 2 around 394-403 nm and the fluorescence maxima at around 439-449 nm are both red-shifted by conjugation with the substituent (R) in the order of 2a≈2b<2c. From these results, it was considered that π-electron effect of the benzyl group for 2c caused red-shift of the absorption and fluorescence maxima. On the other hand, the fluorescence quantum yields (Φ) are almost the same among 2a-2c (Φ = ca. 0.5). The absorption maxima of 2a-2c show a small bathochromic shift of 7-9 nm from cyclohexane to 1,4-dioxane, while the fluorescence maxima show a large bathochromic shift of 47-49 nm, so that the Stokes shift values in polar solvent become larger than that in nonpolar solvent. Similar spectral changes are genera...

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