Heavy atom enhanced generation of singlet oxygen in novel indenofluorene-based two-photon absorbing chromophores for photodynamic therapy

• Five two-photon photosensitizers have been synthesized and characterized.
• The photosensitizers with heavy atoms show enhanced 1O2 generation efficiencies.
• A maximum TPA cross-section value up to 2707 GM is achieved.

A series of indenofluorene-based two-photon absorbing chromophores (FL0, FL-2BrN, FL-1IN, FL-2IN, and FL-2IS) have been designed and synthesized for photodynamic therapy (PDT). Two-photon absorption (TPA) properties of these chromophores are determined and their structure-property relationship has been established. By incorporating electron withdrawing halogen atoms (such as Br, I) into the π-conjugation backbone of the chromophores, enhanced TPA cross-section values up to 2707 GM were achieved due to the formation of a donor-acceptor-donor (D-A-D) motif. At the same time, upon excitation at 430 nm, 2.2–4.1 times of enhancement in the singlet oxygen generation yield was observed for the photosensitizers with the heavy atoms incorporated. The photosensitizers with heavy atoms also show increased singlet oxygen generation efficiencies upon two-photon excitation at 808 nm, compared to those photosensitizers without heavy atoms. Photocytotoxicity of FL-2IN against cancer cells via two-photon excitation (808 nm) demonstrated that the indenofluorene-based chromophores are effective singlet oxygen donors for two-photon PDT.

A series of novel indenofluorene-based chromophores have been designed as singlet oxygen (1O2) generators for two-photon photodynamic therapy (PDT). Both the 1O2 generation efficiencies and two-photon absorption are enhanced by incorporating heavy atoms (such as Br, I) into the π-conjugation backbone of the chromophores.Figure optionsDownload as PowerPoint slide