AB- and A-Type Boron(III)Subchlorins Derived from -Diethoxycarbonyltripyrrane: Synthesis and Photophysical Exploration.

The first direct fabrication of AB- and A-type B(III)subchlorins from ethoxycarbonyl-substituted tripyrrane has been realized by condensation with appropriate acid chlorides (benzoyl chloride, butyryl chloride, and ethyl chlorooxoacetate). The aliphatic acid chloride-based annulation reaction is new to subporphyrinoid chemistry. The phenyl ()- or -propyl ()-substituted derivatives could be oxidized to the corresponding B(III)subporphyrins upon refluxing with DDQ, whereas the triethoxycarbonyl moiety () was found to be resistant to oxidation and exhibits the most red-shifted absorption (587 nm) and emission (604 nm). The study indicates that absorption and emission behaviors of the B(III)subchlorin can be tuned by the introduction of electron-rich or electron-deficient substituents at the -position. B(III)subchlorins and generate singlet oxygen efficiently (44 and 40%, respectively) and, thus, may find application as potential photosensitizers in photodynamic therapy (PDT).