Theoretical investigation on bisarylselanylbenzo-2,1,3-selenadiazoles as potential photosensitizers in photodynamic therapy

Zwitterionic Photosensitizer-Assembled Nanocluster Produces Efficient Photogenerated Radicals via Autoionization for Superior Antibacterial Photodynamic Therapy

Photodynamic therapy (PDT) holds significant promise for antibacterial treatment, with its potential markedly amplified when using Type I photosensitizers (PSs). However, developing Type I PSs remains a significant challenge due to a lack of reliable design strategy. Herein, a Type I PS nanocluster is developed via self-assembly of zwitterionic small molecule (C3TH) for superior antibacterial PDT in vivo. Mechanism studies demonstrate that unique cross-arranged C3TH within nanocluster not only shortens intermolecular distance but also inhibits intermolecular electronic-vibrational coupling, thus facilitating intermolecular photoinduced electron transfer to form PS radical cation and anion via autoionization reaction. Subsequently, these highly oxidizing or reducing PS radicals engage in cascade photoredox to generate efficient ·OH and O2‾·. As a result, C3TH nanoclusters achieve a 97.6% antibacterial efficacy against MRSA at an ultralow dose, surpassing the efficacy of the commercial antibiotic Vancomycin by more than 8.8-fold. These findings deepen the understanding of Type I PDT, providing a novel strategy for developing Type I PSs.

Orthogonal Geometry Enhancing the Intersystem Crossing and Photosensitive Efficiency of Spiro Organoboron Compounds

Based on the reported spiro organoboron compounds (PS1 and PS2 as potent 1O2 sensitizers), several new organoboron molecules (PS4-PS9) were constructed through structural modification, and their low-lying excited states and photophysical properties have been explored by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The predicted effective intersystem crossing (ISC) processes arise from the S1→T2 transition for PS4-PS6 and the S1→T4 transition for PS1, and corresponding KISC rate constants reach the order of magnitude of 109 (s-1). The organoboron compounds with a (N, N) chelate acceptor are predicted to exhibit relatively higher ISC efficiency than those bearing a (N, O) acceptor, and the planar C3NBN ring and the orthogonal configuration between the donor and acceptor moieties are responsible for the ISC rate enhancement. Importantly, the geometric features of the lowest singlet excited state (S1) for these compounds play a decisive role in their photosensitive efficiency. The present results provide a basis for better understanding of the photosensitivity of these spiro organoboron compounds and the structural modification effect.

Quasi-intrinsic thiobase derivatives as potential targeted photosensitizers in two-photon photodynamic therapy

In this study, a set of potential quasi-intrinsic photosensitizers for two-photon photodynamic therapy (PDT) are proposed based on the unnatural 2-amino-8-(1'-β-ᴅ-2'-deoxyribofuranosyl)-imidazo[1,2-ɑ]-1,3,5-triazin-4(8H)-one (P), which is paired with the 6-amino-5-nitro-3-(1'-β-ᴅ-2'-deoxyribofuranosyl)-2(1H)-pyridone (Z) and can specifically recognize breast and liver cancer cells. Herein, the effects of sulfur substitution and electron-donating/electron-withdrawing groups on the photophysical properties in aqueous solution are systematically investigated. The one- and two-photon absorption spectra evidence that the modifications could result in red-shifted absorption wavelength and large two-photon absorption cross-section, which contributes to selective excitation and provides effective PDT for deep-seated tissues. To ensure the efficient triplet state population, the singlet-triplet energy gaps and spin-orbit coupling constants were examined, which is responsible for a rapid intersystem crossing rate. Furthermore, these thiobase derivatives are characterized by the long-lived T1 state and the large energy gap for radiationless transition to ensure the generation of cytotoxic singlet oxygen.

On the origin of photodynamic activity of hypericin and its iodine-containing derivatives

The main photophysical properties, useful for establishing whether hypericin in anionic form and some of its derivatives containing heavy atoms such as iodine, can be proposed for their use in photodynamic therapy, were determined using density functional based computations. The results showed that in the anionic form and in the iodinated derivatives, the absorption wavelength undergoes a bathochromic shift, the singlet-triplet energy gap assumes values ​that allow to excite the oxygen molecule from its ground to the excited singlet state, and that the spin-orbit couplings between singlet and triplet states significantly increase.