Heterocyclic Quinol-Type Fluorophores: Synthesis, X-ray Crystal Structures, and Solid-State Photophysical Properties of Novel 5-Hydroxy-5-substituent-benzo[b]naphtho[1,2-d]furan-6-one and 3-Hydroxy-3-substituent-benzo[kl]xanthen-2-one Derivatives

Novel heterocyclic quinol‐type fluorophores (4 a–c) and (5 a–c) that contain substituents (R = Me, Bu, Ph) with nonconjugated linkages to the chromophore skeleton have been synthesized and their photophysical properties have been investigated in solution and in the solid state. Considerable differences in the absorption and fluorescence spectra were observed between the two states. Quinols 4 a–c and 5 a–c exhibited almost the same absorption and fluorescence spectra in solution; however, their solid‐state fluorescence excitation and emission spectra in the crystalline state were quite different. We performed X‐ray crystallographic analyses to elucidate the dramatic effect of the substituents of the nonconjugated linkage on the solid‐state fluorescence excitation and emission spectra. The relationships between the solid‐state photophysical properties and the chemical and crystal structures of 4 a–c and 5 a–c are discussed on the basis of the X‐ray crystal structures. Dramatic substituent effects on the solid‐state photophysical properties of novel heterocyclic quinols, 5‐hydroxy‐5‐substituent‐benzo[b]naphtho[1,2‐d]furan‐6‐one (1 a–c) and 3‐hydroxy‐3‐substituent‐benzo[kl]xanthen‐2‐one (2 a–c) fluorophores, are discussed on the basis of their X‐ray crystal structures.