Acetylene bridged D-(π-A)2 type dyes containing benzophenone moieties: Photophysical properties, and the potential application as photoinitiators

Acetylene bridged acceptor-'t-bridge-donor-'t-bridge-acceptor (A-pi-D-pi-A) dyes (DBPs) based on benzophenone were designed and synthesized via Sonogashira coupling reaction utilizing carbazole/phenothiazine/triphenyl-amine as electron donating groups. The photophysical properties, photochemistry characteristics, as well as the two-photon absorption properties were studied. All dyes exhibited excellent intra-/intermolecular charge transfer properties upon excitation, and large two photon absorption cross sections in the wavelength range of 720-860 nm. Significant differences in fluorescence and photochemistry properties were found depending on the electron donating groups. The rigid carbazole favored hybridization of benzophenone like local excited state and intramolecular charge transfer excited state, which resulted in abnormal changes in fluorescence quantum yield, poor photostability, and good initiating ability both as Norrish II initiator and as sensitizer for iodonium salt. However, the butterfly-shaped phenothiazine and propeller-shaped triphenylamine facilitated intramolecular charge transfer excited states, which resulted in typical positive solvatochromism effect, good photostabilities, and lacking of initiating ability as Norrish II initiator.

Automated summary

DBPs dyes based on benzophenone were synthesized using different electron donating groups, resulting in varying photophysical and photochemistry properties. Carbazole favored abnormal fluorescence changes and good initiation ability, while phenothiazine and triphenylamine facilitated good photostability and positive solvatochromism effect.