pH dependent one-/two-photon fluorescence emission properties and mechanism of the dendrimer PAMAM triphenylamine imine†
Dendrimer PTS-G0, based on poly-amidoamine (PAMAM) functionalized by triphenylamine imine (CN), and reference compound ETS, based on ethylenediamine triphenylamine imine, were both synthesized. PTS-G0's one-/two-photon (2PA σ2 = 75 GM) fluorescence emission increased at low pH and remained high at high pH, showing emission ranges that were different from those of NH2- or HO-terminated PAMAM as previously reported. The pH related fluorescence emissions of PTS-G0 and ETS were compared. The emission properties of the independent chemical groups were calculated by quantum chemical theory methods. The imidic acid (HO–CN), imine (CN), and tertiary ammonium groups fluoresce in different pH ranges. The possible fluorescence emission mechanisms of PTS-G0 were discussed, which can help to explain the fluorescence emission of PAMAM and benefit the understanding of intrinsic fluorescence phenomena.