Synthesis and optical properties of a series of thermally stable diphenylanthrazolines

A series of diphenylanthrazolines were synthesized by Friedländer condensation of 2,5-dibenzoyl-1,4-phenylenediamine and acetyl-functionalized compounds in the presence of polyphosphoric acid as catalyst, in yields ranging from 61% to 88%. The diphenylanthrazolines are thermally robust with high decomposition temperatures (>380.0 °C) and high melt transitions (317-462 °C). All of them show the lowest energy absorption bands (λ_max^Abs: 394-433 nm) from the π-π^* transitions by virtue of their large molar extinction coefficients (ε ≈ 10⁴ M^-1 cm^-1), revealing low optical band gaps (2.59-2.80 eV). The compounds emit blue fluorescence with λ_max^Em ranging from 430 to 466 nm in dilute toluene solution.