Unlocking Phthalonitrile-Based Type I Photosensitizer Through D-A Modulation to Promote Electron Transfer

Area of Science:

• Photodynamic Therapy
• Organic Chemistry
• Materials Science

Background:

• Type I photosensitizers (PSs) are crucial for photodynamic therapy (PDT) due to their oxygen-independent mechanism, offering a solution for hypoxic tumors.
• Rational design of Type I PSs is hindered by incomplete understanding of structure-property relationships.

Purpose of the Study:

• To develop a molecular design strategy for phthalonitrile-based Type I PSs using donor-π bridge-acceptor (D-π-A) modulation.
• To optimize PS properties including singlet-triplet energy gap (ΔE_ST), T₁ energy level, redox potential, and steric hindrance for efficient electron transfer and ROS generation.

Main Methods:

• Systematic modulation of four critical parameters in D-π-A phthalonitrile-based PSs.
• Investigation of aggregate-induced Type I reactive oxygen species (ROS) generation.
• Encapsulation of the lead PS (DTPCH₃) into F127 polymer to form nanoparticles (DTPCH₃_NPs).

Main Results:

• The DTPCH₃ PS exhibited the highest Type I ROS production due to minimal ΔE_S1-T2 and effective intermolecular electron transfer.
• DTPCH₃_NPs demonstrated sustained O₂^•- and HO• generation, leading to effective cancer cell killing and hypoxia tolerance.
• In vivo studies confirmed significant tumor suppression by DTPCH₃_NPs.

Conclusions:

• A rational molecular design strategy for Type I PSs based on D-π-A modulation was established.
• This strategy enables the optimization of PS properties for efficient ROS generation and improved PDT outcomes.
• The developed DTPCH₃_NPs show promise as next-generation PDT agents for hypoxic tumor treatment.