Tetrahydro[5]helicene-based full-color emission dyes in both solution and solid states: synthesis, structures, photophysical properties and optical waveguide applications

A series of tetrahydro[5]helicene-based dye molecules were efficiently synthesized and the helical structural features of their tetrahydro[5]helicene skeletons were confirmed by the crystal structures. The substituent effect of the dyes on their photophysical properties was then investigated. Consequently, it was found that compared with hydroxymethyl and ester groups, the introduction of imide to the tetrahydro[5]helicene skeleton could result in not only red shifts of their absorption and emission bands, but also higher quantum yields and larger Stokes shift. Especially, intense full-color fluorescence emissions in both solution and solid states could be achieved just by changing the substituents with different electron-donating abilities in the tetrahydro[5]helicene imide skeleton. Moreover, a significant solvent-effect on the emissions of the tetrahydro[5]helicene-based organic dyes was also found. The density functional theory calculations further demonstrated that with the increase of the electron-donating ability of the substituents, the energy gaps of the tetrahydro[5]helicene-based dyes gradually decreased, which theoretically elucidated the substituent effect of the dyes on their photophysical properties. Additionally, an optical waveguide application of the tetrahydro[5]helicene-based imide dye is shown as well.