Photophysical and photochemical properties of anthraquinones: A DFT study

Bridging D-A type photosensitizers with the azo group to boost intersystem crossing for efficient photodynamic therapy

Photodynamic therapy (PDT) has attracted much attention in disease treatments. However, the exploration of a novel method for the construction of outstanding photosensitizers (PSs) with stimuli-responsiveness remains challenging. In this study, we, for the first time, report a novel and effective strategy to boost reactive oxygen species (ROS) generation by bridging donor-acceptor (D-A) type PSs with the azo group. In contrast to the counterpart without azo-bridging, the azo-bridged PSs exhibit remarkably enhanced ROS generation via both type-I and type-II photochemical reactions. Theoretical calculations suggest that azo-bridging leads to a prominent reduction in ΔE ST, thereby enabling enhanced ROS generation via efficient intersystem crossing (ISC). The resulting azo-bridged PS (denoted as Azo-TPA-Th(+)) exhibits a particularly strong bactericidal effect against clinically relevant drug-resistant bacteria, with the killing efficiency up to 99.999999% upon white light irradiation. Since azo-bridging generates an azobenzene structure, Azo-TPA-Th(+) can undergo trans-to-cis isomerization upon UV irradiation to form emissive aggregates by shutting down the ISC channel. By virtue of the fluorescence turn-on property of unbound Azo-TPA-Th(+), we propose a straightforward method to directly discern the effective photodynamic bactericidal dose without performing the tedious plate-counting assay. This study opens a brand-new avenue for the design of advanced PSs with both strong ROS generation and stimuli-responsiveness, holding great potential in high-quality PDT with rapid prediction of the therapeutic outcome.

Daylight-driven rechargeable antibacterial and antiviral nanofibrous membranes for bioprotective applications

Emerging infectious diseases (EIDs) are a significant burden on global economies and public health. Most present personal protective equipment used to prevent EID transmission and infections is typically devoid of antimicrobial activity. We report on green bioprotective nanofibrous membranes (RNMs) with rechargeable antibacterial and antiviral activities that can effectively produce biocidal reactive oxygen species (ROS) solely driven by the daylight. The premise of the design is that the photoactive RNMs can store the biocidal activity under light irradiation and readily release ROS under dim light or dark conditions, making the biocidal function "always online." The resulting RNMs exhibit integrated properties of fast ROS production, ease of activity storing, long-term durability, robust breathability, interception of fine particles (>99%), and high bactericidal (>99.9999%) and virucidal (>99.999%) efficacy, which enabled to serve as a scalable biocidal layer for protective equipment by providing contact killing against pathogens either in aerosol or in liquid forms. The successful synthesis of these fascinating materials may provide new insights into the development of protection materials in a sustainable, self-recharging, and structurally adaptive form.