FIGURE 1.

(A) Photographs of D1 and D2 pyrimidine derivative solutions in solvents with an increasing dielectric constant from hexane (left) to DMSO (right) under UV irradiation (365 nm). Normalized steady-state absorption and fluorescence spectra of D1 (B) and D2 (C) in the solvents shown previously under anaerobic conditions. From top to bottom, solvents are ordered by decreasing dielectric constant (DMSO, ACN, DMF, MeOH, EtOH, DCM, EtOAc, CHCl₃, Tol, Bz, and Hx). For fluorescence measurements, an excitation wavelength of 365 nm was used. Lippert–Mataga plot for D1 (D) and D2 (E).