A pH stable fluoran-triphenylamine photosensitizer with efficient type I and type II ROS generation

Area of Science:

• Materials Science
• Photochemistry
• Organic Chemistry

Background:

• Photosensitizers (PSs) are crucial for applications requiring reactive oxygen species (ROS) generation.
• Developing PSs with enhanced pH stability and dual Type I/II ROS generation is a significant challenge.
• Existing PSs often lack the required stability or efficiency for broad applicability.

Purpose of the Study:

• To design and synthesize a novel fluoran-triphenylamine photosensitizer (Fl-TPA) with improved pH stability and ROS generation.
• To investigate the photophysical properties and ROS generation mechanisms of the synthesized Fl-TPA.
• To evaluate the performance of Fl-TPA against clinically approved photosensitizers.

Main Methods:

• Electron donor-acceptor engineering strategy was employed to synthesize Fl-TPA.
• Absorption, fluorescence spectroscopy, and transient fluorescence measurements were used to characterize photophysical properties.
• Time-dependent density functional theory (TD-DFT) calculations were performed to understand electronic properties and intersystem crossing (ISC).
• Reactive oxygen species (ROS) generation experiments were conducted to assess efficacy.

Main Results:

• Fl-TPA exhibited redshifted absorption and efficient light capture (300-600 nm).
• Fl-TPA demonstrated significantly enhanced Type I, Type II, and total ROS generation compared to the reference compound Fl-H and indocyanine green (ICG).
• Fl-TPA showed excellent pH stability and a lower singlet-triplet energy gap (ΔE_S-T), facilitating intersystem crossing (ISC).
• Transient fluorescence measurements indicated longer-lived excited states in Fl-TPA, contributing to its ROS generation efficiency.

Conclusions:

• The synthesized Fl-TPA is a highly effective photosensitizer with robust pH stability and superior ROS generation capabilities.
• The electron donor-acceptor design strategy successfully enhanced photophysical properties and photochemical activity.
• Fl-TPA presents a promising candidate for various applications, offering a new theoretical basis for designing advanced photosensitizers.