Synthesis, X‐ray Crystal Structures and Solid‐State Fluorescence Properties of 3‐Dibutylamino‐6‐alkoxy‐6‐phenylnaphtho[2,3‐b]benzofuran‐11(6H)‐one Derivatives

Abstract

AbstractNovel heterocyclic fluorophores – 6‐alkoxy‐3‐dibutylamino‐6‐phenylnaphtho[2,3‐b]benzofuran‐11(6H)‐ones 2a–2g with different chain lengths in alkoxy substituents non‐conjugatedly linked to the chromophore skeleton – have been derived from the quinol‐type compound 1, and their photophysical properties have been investigated in solution and in the solid state. In solution, the fluorophores 1 and 2a–2g exhibit similar fluorescence properties. In the solid state, however, the fluorophores 2a–2g exhibit stronger fluorescence properties than the quinol 1. Furthermore, the fluorescence quantum yields (Φ) of 2 in the solid state are higher than those of 2 in solution, and considerable differences in the solid‐state fluorescence were observed among the alkoxy derivatives 2a–2g. To elucidate the dramatic effect of the alkoxy substituents we performed semiempirical molecular orbital calculations (AM1 and INDO/S) and X‐ray crystallographic analysis. On the basis of the results of the calculations and the X‐ray crystal structures, the relationships between the solid‐state photophysical properties and the chemical and crystal structures of 1 and 2a–2g are discussed. It was confirmed that the introduction of long alkoxy chains such as butoxy and pentoxy groups in non‐conjugated linkage to the chromophore can efficiently prevent short π–π contacts between the fluorophores in molecular aggregation states and thus cause dramatic solid‐state fluorescence enhancements.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)