Chiroptical Helices of N-Terminal Aryl Amino Acids through Orthogonal Noncovalent Interactions

In the solid state, amino acids (alanine and phenylglycine) with appended pyrene segments self-assembled into α-helix-like structures by asymmetrical H-bonds between carboxylic acid and amide segments, further inducing supramolecular tilted chirality of the achiral pyrenes. These structures bind melamine and electron-deficient units through H-bond and charge-transfer interactions, respectively. Charge-transfer interactions enhance the dissymmetry g-factor of absorption (g_abs ; up to 1.4×10^-2 ) with an extended Cotton effect active region (from 250 to 600 nm). Incorporating melamine inverts the handedness of circularly polarized luminescence and boosts the dissymmetry g-factor (g_lum ). Melamine also induces macroscopic chirality at the nanoscale, whereby the 2D lamellar structures are transformed into 1D helices at the nanoscale, leading to giant tubular structures at the microscale.