Synthesis of C3-fluoroalkylated chlorophyll-a derivatives and fine tuning of their optical properties by the fluorination degree

Methyl pyropheophorbides-a possessing a variety of fluoroalkyl groups at the 3-position were prepared via deoxyfluorination or deoxofluorination from naturally occurring chlorophyll-a. The synthetic C3-fluoroalkylated chlorins exhibited monomeric visible absorption spectra in dichloromethane. Their Qx/Qy absorption bands were red-shifted from those of the nonfluorinated counterparts. The red-shift values were dependent on the fluorination degree in the 3-alkyl group. The redmost Qy absorption and main fluorescence emission maxima gradually moved to longer wavelengths by fluorination and trifluoromethylation at the 3(1)-position: lambda(abs)/lambda(em) = 655/659 nm (3-methyl-chlorin) < 676/679 nm (3-perfluoroethyl-chlorin). The substitutions similarly enhanced their fluorescence emission quantum yields and elongated their lifetimes: Phi(em)/tau(em) = 18.0%/6.1 ns (3-methyl-chlorin) < 21.5%/7.3 ns (3-perfluoroethyl-chlorin). The fluorination in the peripheral 3-substituent could finely tune the optical properties of the core chlorin chromophores.