Circular Polarized Luminescence of Hydrogen-Bonded Molecular Assemblies of Chiral Pyrene Derivatives

Abstract

The absorption and fluorescence spectra of chiral alkylamide-substituted pyrene derivatives (R-1 and S-1) in the solution phase were consistent with the formation of N–H···O═ hydrogen-bonded helical π-stacked one-dimensional (1D) supramolecules (R-1)n and (S-1)n in methylcyclohexane (MCH), toluene, chloroform (CHCl3), and tetrahydrofuran (THF); the π-stacked structures and aggregation number (n) were governed by the concentration (c) and solvent polarity. The aggregation of (R-1)n and (S-1)n in MCH and toluene was much greater than that in THF and CHCl3, and excimer emission of excited-state (R-1)n* and (S-1)n* supramolecules with n ≥ 2 was observed in all solvents. Interestingly, the circular polarized luminescence (CPL) spectra of (R-1)n* and (S-1)n* revealed a glum value of 0.03 in MCH at c > 1 × 10–6 M. Circular dichroism and CPL spectra revealed the formation of hydrogen-bonded helical 1D supramolecular assemblies in the ground and excited states. The helicities of the 1D supramolecular assemblies of (R-1)n and (S-1)n in CHCl3 were inverted as compared to those in MCH and THF. The solvent polarity and concentration were sensitive to the π-stacked structure and helical configuration of the N–H···O═ hydrogen-bonded 1D supramolecular assemblies.