The excited triplet state of a molecule (T₁) is one of the principal intermediate products in various photochemical processes due to its high reactivity and relatively long lifetime. The T₁ quantum yield (${\phi }_{\mathrm{T}}$) is one of the most important characteristics in the study of photochemical reactions. It is of special interest to determine the ${\phi }_{\mathrm{T}}$ of various photoactive compounds (photosensitizer, PS) used in photodynamic therapy (PDT). PDT is an effective medical technique for the treatment of serious diseases, such as cancer and bacterial, fungal and viral infections. This technique is based on the introduction of a PS to a patient’s organism and its further excitation by visible light, producing reactive oxygen species (ROS) via electron or energy transfer from the PS T₁ state to the biological substrate or molecular oxygen. Therefore, information on the ${\phi }_{\mathrm{T}}$ value is fundamental in the search for new and effective PSs. There are various experimental methods to determine ${\phi }_{\mathrm{T}}$ values; however, these methods demonstrate a high discrepancy between ${\phi }_{\mathrm{T}}$ values. This stimulates the analysis of various factors that can affect the determined ${\phi }_{\mathrm{T}}$. In this study, we analyze the effect of the intensity profile of the exciting laser pulse on the calculation of the ${\phi }_{\mathrm{T}}$ value obtained by the Laser Flash Photolysis technique. The φ_T values were determined by analyzing the variation of a sample transient absorption in the function of the exciting laser pulse intensity, in combination with the spectral and kinetic PS characteristics obtained in nonlinear optical experiments by solving the rate equations of a five-level-energy diagram. Well-studied PSs: meso-tetra(4-sulfonatophenyl) (TPPS₄) porphyrins, its zinc complex (ZnTPPS₄) and the zinc complex of meso-tetrakis(N-methylpyridinium-4-yl) (ZnTMPyP) were chosen as test compounds to evaluate the proposed model. The ${\phi }_{\mathrm{T}}$ values were determined through a comparison with the ${\phi }_{\mathrm{T},\mathrm{T}\mathrm{M}\mathrm{P}\mathrm{y}\mathrm{P}}$ = 0.82 of meso-tetrakis(N-methylpyridinium-4-yl) (TMPyP), used as a standard. The obtained results (${\phi }_{\mathrm{T},{\mathrm{T}\mathrm{P}\mathrm{P}\mathrm{S}}_4}=0.75\pm 0.02$, ${\phi }_{\mathrm{T},\mathrm{Z}\mathrm{n}\mathrm{T}\mathrm{M}\mathrm{P}\mathrm{y}\mathrm{P}}=0.90\pm 0.03)$, and ${\phi }_{\mathrm{T},{\mathrm{Z}\mathrm{n}\mathrm{T}\mathrm{P}\mathrm{P}\mathrm{S}}_4}=0.89\pm 0.03$) are highly compatible with the medium ${\phi }_{\mathrm{T}}$ values obtained using the known methods.

This work studied the effect of different electron-withdrawing and electron-donating groups on the linear and nonlinear optical properties of acetamide-chalcone derivatives. The results showed that the addition of the dimethylamine group led to a large fluorescence emission (71% of fluorescence quantum yield in DMSO solution) that can be triggered by two and three-photon excitations, which is essential for biological applications. Furthermore, dimethylamine also red-shifts the lower energy state by approximately 90 nm, increasing the two-photon absorption cross-section of the lower energy band by more than 100% compared with the other studied compounds. All compounds presented two-electronic states observed through one and two-photon absorption spectroscopy and confirmed by Quantum Chemistry Calculations (QCCs). QCC results were also used to model the experimental two-photon absorption cross-sectional spectrum by the Sum-Over-States (SOS) approach, revealing a dependence between the coupling of the ground state with the first excited state and the transition dipole moment between these states.

Multidrug resistance (MDR) remains a major obstacle to effective cancer chemotherapy, often driven by the overexpression of ABC transporters such as ABCG2. In this study, we identified the synthetic chalcone derivative, B5, as a selective ABCG2 inhibitor. Among the 20 chalcone analogs evaluated, B5, bearing an acetamide group at R1 and an ethoxy substituent at R2, was the only compound that produced more than 50% inhibition of ABCG2-mediated Hoechst 33342 transport at 10 μM, while showing no activity against ABCB1. B5 exhibited an IC50 of 2.7 μM for ABCG2 inhibition, consistent with the low-micromolar potency reported for chalcone-based ABCG2 modulators. Furthermore, B5 effectively reversed ABCG2-mediated resistance to the chemotherapeutic agent SN-38 in ABCG2-overexpressing cells, thereby restoring drug sensitivity. Notably, B5 was noncytotoxic at concentrations up to 5 μM and did not exhibit differential cytotoxicity between parental and ABCG2-overexpressing cells, suggesting that it was not efficiently transported under the experimental conditions. ATPase assays revealed that B5 stimulated, rather than inhibited, ABCG2 ATPase activity, a behavior previously reported for chemically distinct ABCG2 inhibitors. Molecular docking and molecular dynamics simulations suggested that B5 bound within the central inhibitor-binding cavity of ABCG2, forming π–π interactions with Phe439 and hydrophobic contacts with Val546, although with a lower interaction frequency than the reference inhibitor Ko143. This binding mode, together with the physicochemical properties of B5, suggested that the electron-donating acetamide group enhanced its inhibitory activity, potentially by facilitating hydrogen-bonding interactions within the binding pocket. Collectively, these findings identified B5 as a promising lead compound for the development of selective ABCG2 inhibitors and provided structural insights to support the rational design of more potent analogs capable of overcoming MDR in cancer.

The interaction between bovine serum albumin (BSA) and porphyrin photosensitizers, as well as the phototransformation of BSA upon excitation with visible and near infrared light, were investigated using steady state and time resolved absorption and fluorescence spectroscopy. The porphyrins selected for this study were the anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4), cationic 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) and Zn(II)TMPyP complex. Porphyrin excitation by visible and near infrared light leads to a decrease in BSA fluorescence, which is attributed to protein transformation mediated by reactive oxygen species (ROS), such as singlet oxygen (1O2) or superoxide anion radical ([[EQUATION]] which are generated through energy or electron transfer from porphyrin molecules in the excited triplet state to molecular oxygen. The efficiency of BSA transformation depends on the affinity of the porphyrins for BSA. The results show that porphyrins bind effectively to BSA, forming BSA–porphyrin complexes, with the highest binding constant observed for the negatively charged TPPS4 ((1.7 ± 0.1) × 106 M−1). Higher affinity for BSA leads to an increased concentration of protein-bound porphyrin, which, in turn, results in higher ROS concentrations in the vicinity of the protein molecule and increases the probability of reactions between ROS and their targets within the BSA structure. Binding to BSA reduces the singlet oxygen quantum yield (ΦΔ) due to restricted interaction between the bound porphyrin and molecular oxygen. However, after irradiation, the ΦΔ value for TPPS4 bound to BSA exceeds that of the free porphyrin.