Modification of optical properties in helicenes via construction of phosphine oxide-based push-pull systems

Six [6]helicene based push-pull systems combining three diarylamines as donors and two phosphine-oxides as acceptors were designed and synthesized in order to modify optical properties of the helicene skeleton. The properties of the target compounds were studied by DFT calculations and spectroscopic methods in both solution and solid film and compared to those of purposely synthesized reference compounds. It was found that the optical properties change substantially upon formation of the push-pull system and show dependence on the withdrawing ability of the acceptor. Furthermore, the introduction of the diphenylaminophenylene group as a donor led to significant increase of fluorescence quantum yield and also a significant dependence of the fluo-rescence maxima on the polarity of solvent - solvatochromism. The Lippert-Mataga plots were used to estimate the change in dipole moments (Delta mu).