Fig. 3. Chemical structures, (b) fluorescence spectra, and (c) spectroscopic data of A1–A5, B1–B5, and C1–C5. λabs, peak UV-vis absorption wavelength; λem, peak emission wavelength; Δλ, Stokes shift; ε, the maximum molecular absorption coefficient. The ground state pre-twisting angles θ0 were calculated at the ωB97XD/Def2SVP level in the water and are labelled in the inset. In addition, the quantum yields measured in glycerol are also labelled in the inset of (a). Note that the quantum yields of A2/B2/C2 are not accurate, due to the partial protonation of A1/B1/C1 during the formation of A2/B2/C2, respectively.
