Strategies to Enhance the Photosensitization: Polymerization and the Donor-Acceptor Even-Odd Effect.

A particular challenge in the design of organic photosensitizers (PSs) with donor-acceptor (D-A) structures is that it is based on trial and error rather than specific rules. Now these challenges are addressed by proposing two efficient strategies to enhance the photosensitization efficiency: polymerization-facilitated photosensitization and the D-A even-odd effect. Conjugated polymers have been found to exhibit a higher 1 O2 generation efficiency than their small molecular counterparts. Furthermore, PSs with A-D-A structures show enhanced photosensitization efficiency over those with D-A-D structures. Theoretical calculations suggest an enhanced intersystem crossing (ISC) efficiency by these strategies. Both in vitro and in vivo experiments demonstrate that the resulting materials can be used as photosensitizers in image-guided photodynamic anticancer therapy. These guidelines are applicable to other polymers and small molecules to lead to the development of new PSs.

Evoking Photothermy by Capturing Intramolecular Bond Stretching Vibration-Induced Dark-State Energy.

Development of highly effective approaches to desirable photothermal conversion agents is particularly valuable. Herein, we report a concept, namely, bond stretching vibration-induced photothermy, that serves as a mechanism to construct advanced photothermal conversion agents. As a proof-of-concept, two compounds (DCP-TPA and DCP-PTPA) with donor-acceptor (D-A) structures were synthesized. The bond stretching vibration of the pyrazine-containing unit in these molecules is vigorous and insensitive to the external environmental restraint, which efficiently transforms the absorbed photons to dark-state heat energy. The nanoparticles (NPs) of DCP-TPA and DCP-PTPA show rather high photothermal conversion efficiency (52% and 59%) and stronger photoacoustic (PA) signal than commercial methylene blue and reported high-performance semiconducting polymer nanoparticles. The DCP-PTPA NPs perform better than DCP-TPA NPs in terms of photothermal conversion, PA signal production, and in vivo PA tumor imaging because of the increased bond stretching vibration in the former molecule.