A2B- and A3-Type Boron(III)Subchlorins Derived from meso-Diethoxycarbonyltripyrrane: Synthesis and Photophysical Exploration

The first direct fabrication of A(2)B- and A(3)-type B(III)-subchlorins from meso-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 (6a)- or n-propyl (6b)substituted derivatives could be oxidized to the corresponding B(III)-subporphyrins upon refluxing with DDQ, whereas the triethoxycarbonyl moiety (6c) 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 meso-position. B(III)subchlorins 6a and 6c generate singlet oxygen efficiently (44 and 40%, respectively) and, thus, may find application as potential photosensitizers in photodynamic therapy (PDT).

Automated summary

The study demonstrates the direct fabrication of a series of A(2)B- and A(3)-type B(III)-subchlorins using a novel method, which may have potential applications as photosensitizers in photodynamic therapy (PDT). The results show that the absorption and emission behaviors of the subchlorins can be tuned by introducing different electron-rich or electron-deficient substituents. Furthermore, it was found that certain subchlorins efficiently generate singlet oxygen, highlighting their potential in PDT.