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 (λmaxAbs: 394–433 nm) from the π–π∗ transitions by virtue of their large molar extinction coefficients (ɛ ≈ 104 M−1 cm−1), revealing low optical band gaps (2.59–2.80 eV). The compounds emit blue fluorescence with λmaxEm ranging from 430 to 466 nm in dilute toluene solution.