Naphthalimide-Annulated [n]Helicenes: Red Circularly Polarized Light Emitters

Two [n]heliceno-bis(naphthalimides) 1 and 2 (n = 5 and 6, respectively) where two electron-accepting naphthalimide moieties are attached at both ends of helicene core were synthesized by effective two-step strategy, and their enantiomers could be resolved by chiral stationary-phase high-performance liquid chromatography (HPLC). The single-crystal X-ray diffraction analysis of enantiopure fractions of 1 and 2 confirmed their helical structure, and together with experimental and calculated circular dichroism (CD) spectra, the absolute configuration was unambiguously assigned. Both 1 and 2 exhibit high molar extinction coefficients for the S-0-S-1 transition and high fluorescence quantum yields (73% for 1 and 69% for 2), both being outstanding for helicene derivatives. The red circularly polarized luminescence (CPL) emission up to 615 nm for 2 with CPL brightness (BCPL) up to 66.5 M(-1 )cm(-1) demonstrates its potential for applications in chiral optoelectronics. Time-dependent density functional theory (TD-DFT) calculations unambiguously showed that the large transition magnetic dipole moment |m| of 2 is responsible for its high absorbance dissymmetry (g(abs)) and luminescence dissymmetry (g(lum)) factor.

Automated summary

Two heliceno-bis(naphthalimides) compounds with electron-accepting naphthalimide moieties attached at both ends of helicene core were synthesized by an effective two-step strategy. Their enantiomers were successfully resolved using chiral stationary-phase high-performance liquid chromatography (HPLC). The helical structure and absolute configuration of the compounds were confirmed through single-crystal X-ray diffraction analysis and experimental and calculated circular dichroism (CD) spectra. Both compounds exhibited high molar extinction coefficients and fluorescence quantum yields, and compound 2 demonstrated potential for applications in chiral optoelectronics due to its red circularly polarized luminescence emission and high brightness.