Triphenylamine-based pH chemosensor: Synthesis, crystal structure, photophysical properties and computational studies

A triphenylamine-containing pH chemosensor, N,N′-di[3-(diphenylamine)benzyl]-piperazine, was designed and synthesized with Ullmann reaction. The compound crystallize in the monoclinic space group P21/n: a = 9.8004(12) Å, b = 13.3321(17) Å, c = 12.9575(16) Å, β = 103.510(2)°, V = 1646.2(4) Å3, Z = 2 and ρ = 1.212 Mg/m3. The synthesized compound excited by UV light produce intensive emission and a quantum yield of 0.56 relative to quinine sulfate was achieved. The fluorescence intensity of synthesized compound in water/DMF (4:1, v/v) under excitation of 307 nm decreased with the decrease of pH, experimental and computational studies further confirmed that the protonation of N-triphenylamine leads to the fluorescence quenching. The results clearly indicate the potential of synthesized compound as highly efficient “on–off” switcher for protons.