Influence of Alkyl Chain Length on the Solid-State Packing and Fluorescence of 1,4,5,8-Tetra(alkyl)anthracenes

Abstract

1,4,5,8-Tetra(alkyl)anthracenes (alkyl = methyl, ethyl, n-propyl, and n-hexyl) were prepared by a sequence of reactions of 1,2,4,5-tetrabromobenzene and 2,5-dialkylfurans in the presence of n-BuLi, hydrogenation, and treatment with acid. The influence of alkyl chain length on the packing patterns in the crystals and the fluorescent properties in the solid state was investigated. X-ray analysis revealed that the molecular structures can be classified into plane, semi-chair, and chair forms and that the packing patterns can be categorized into two-dimensional (herringbone) and one-dimensional (slipped-parallel) arrangements, in both of which there is no π–π stacking. In the case of the methyl, ethyl, and n-propyl derivatives, the wave shapes of the fluorescence spectra in the solid state resemble each other; on the other hand, the n-hexyl derivative displayed a slightly red-shifted and broader spectrum. The absolute quantum yield depended on the transition dipole moments because of the packing patterns and crystal rigidity. The n-propyl derivative demonstrated the highest quantum yield of Φf = 0.85 among the tetra(alkyl)anthracenes.