Synthesis, photophysics, and electronic structures of benzene-linked bispyrimidine compounds

Seven multi-dipole and multibranched benzene-linked bispyrimidine derivatives containing a two-layer binary tree structure with different electron donor and acceptor groups were designed, synthesized, and characterized. The influences of substituents and solvents on the optical properties of the compounds were investigated. The UV/vis absorption (λ^abs_max: 311-371nm), PL emission (λ^em_max: 386-527nm), stokes shift (2864-6414cm^-1), and fluorescence quantum yield (Φ_f: 0.01∼0.16) of the compounds in CH₃CN solution are influenced by the electron-donor or accept substituents. The absorption and emission spectra of the compound with the highest Φ_f in various solvents indicate that the solvent has little influence on absorption spectrum but does influence the emission spectrum. Transient absorption spectra exhibiting strong positive absorption bands in the near-IR wavelength means that these compounds could potentially be used as optical limiting materials, which is further confirmed by the quantum chemical calculations.