Chiral binol-[4]helicene hybrids: Strong solid-state organic emitters with aggregation-enhanced emission and chiroptical properties

Abstract

Chiral organic fluorescent materials have attracted broad attention for their application in various chiroptical devices. Helicenes possess special helical structure and unique optical properties, and have been utilized to develop chiral organic fluorescent materials with excellent chiroptical performance. However, the low luminescence efficiency of helicene-based chiral fluorescent materials in solid state limits their practical applications. In this work, chiral organic fluorescent emitters with helicene moiety have been developed from binaphthanol structure. These BINOL [4]helicene compounds display aggregation-enhanced emission properties, and have strong blue emission in solid state with fluorescent quantum yield up to 0.67. The DFT calculation reveals that these compounds have highly twisted molecular structures. Thus, the excellent fluorescent properties in solid state could be aroused by the highly contorted molecular structures, which could limit the π-π stacking of adjacent molecules in solid state. The enantiomers of these compounds show strong Cotton effects in circular dichroism spectra, and the molecules with 4-methoxy phenyl moiety exhibit circularly polarized luminescence properties.