Fig. 3. (A) Absorption and (B) emission spectra of n-H1 and c-H1. (C) Absorption and (D) emission spectra of n-H2 and c-H2. All the absorption and emission spectra were recorded in CHCl3 (4 μM) at 25 °C; excitation wavelength = 440 nm, 455 nm, 430 nm, and 432 nm for c-H1, c-H2, n-H1, and n-H2 respectively. (E) Computed change in the helical pitch values in n-H1 and n-H2 upon protonation, calculated at the B3LYP/6-31g(d,p) level of theory. (F) Acid–base responsive changes in the absorption properties of n-H1. (G) Acid–base responsive changes in the emission properties of n-H1. (H) Acid–base responsive changes in the absorption properties of n-H2. (I) Acid–base responsive changes in the emission properties of n-H2. All the absorption spectra were recorded in CHCl3 (20 μM) at 25 °C. All the emission spectra were recorded in CHCl3 (10 μM) at 25 °C; excitation wavelength = 420 nm (for n-H1), 440 nm (n-H2). Molecular electrostatic potential (MEP) maps of the (J) neutral (n-H1) and the positively charged (alkylated c-H1, and protonated n-H1 + 2H+) helicenes, and (K) neutral (n-H2) and the positively charged (alkylated c-H2, and protonated n-H2 + 2H+) helicenes. (calculated by DFT at the B3LYP/6-31g(d,p) level of theory).
