Photoluminescence mechanisms of BF2-formazanate dye sensitizers: a theoretical study.

Photodynamic therapy (PDT) is an alternative, minimally invasive treatment for human diseases such as cancer. PDT uses a photosensitizer to transfer photon energy directly to cellular 3O2 to generate 1O2 (Type II), the toxicity of which leads to cancer cell death. In this work, the photoluminescence mechanisms of a BF2-formazanate dye sensitizer (BF2-FORM) and its iodinated derivative (BF2-FORM-D) were studied using complementary theoretical approaches; the photoluminescence pathways in the S1 and T1 states were studied using density functional theory (DFT) and time-dependent (TD)-DFT methods, the kinetic and thermodynamic properties of the pathways using the transition state theory (TST), and the time evolution and dynamics of key processes using non-adiabatic microcanonical molecular dynamics simulations with surface-hopping dynamics (NVE-MDSH). Evaluation of the potential energy surfaces (PESs) in terms of the rotations of the phenyl rings suggested a pathway for the S1 → S0 transition for the perpendicular structure, whereas two pathways were anticipated for the T1 → S0 transition, namely, [T1 → S0]1 occurring immediately after the S1/T1 intersystem crossing (ISC) and [T1 → S0]2 occurring after the S1/T1 ISC and T1 equilibrium structure relaxation, with the T1 → S0 energy gap being comparable to the energy required for 3O2 → 1O2. The PESs also showed that because of the heavy-atom effect, BF2-FORM-D possessed a significantly smaller S1/T1 energy gap than BF2-FORM. The TST results revealed that at room temperature, BF2-FORM-D was thermodynamically more favorable than the parent molecule. Analysis of the NVE-MDSH results suggested that the librational motions of the phenyl rings play an important role in the internal conversion (IC) and ISC, and the S1/T1 ISC and T1 → S0 transitions could be enhanced by varying the irradiation wavelength and controlling the temperature. These findings can be used as guidelines to improve and/or design photosensitizers for PDT.

Development of a new series of thioacetal based fluorescence chemosensors for highly sensitive determination of Hg2+ in environmental samples and cell imaging.

Mercury ion is one of the most harmful metal ions with significant hazards to the environment and human health. Thus, the development of innovative, sensitive, and selective sensors to help address the detrimental impacts of heavy metal contamination is necessary. In this work, we present three new chemosensors based on the deprotection reaction of the thioacetal group for distinguishing Hg2+ in environmental samples. These chemosensors show good photophysical properties with high quantum yield in aqueous medium. These prepared chemosensors were employed as fluorometric sensors for the determination of Hg2+ through the quenching of fluorescence emission due to the Hg2+-induced hydrolysis of the thioacetal to the aldehyde group. In the presence of Hg2+, chemosensors showed an emissive color transformation from blue fluorescence to non-fluorescence under UV light, which was readily seen by the visual eye. These chemosensors also exhibited highly distinctive selectivity toward Hg2+ over other interfering metal ions, with detection limits of 1.1 ppb, 13.4 ppb, and 12.7 ppb. Moreover, the practical applicability of chemosensor was successfully demonstrated in real water samples and herb extract samples.

Aza-BODIPY-based polymeric nanoparticles for photothermal cancer therapy in a chicken egg tumor model.

A new push-pull aza-BODIPY (AZB-CF3) derivative comprised of dimethylamino groups and trifluoromethyl moieties was successfully synthesized. This derivative exhibited broad absorption in the near-infrared region in the range from 798 to 832 nm. It also exhibited significant near-infrared (NIR) signals in low-polar solvents with emission peaks around 835-940 nm, while non-fluorescence in high-polar environments due to the twisted intramolecular charge transfer (TICT) phenomenon. The nanoprecipitation of this compound with phospholipid-based polyethylene glycol (DSPE-PEG) yielded AZB-CF3@DSPE-PEG nanoparticles (NPs) with a hydrodynamic size of 70 nm. The NPs exhibited good photostability, colloidal stability, biocompatibility, and excellent photothermal (PTT) competence with a conversion efficiency (η) of 44.9%. These NPs were evaluated in vitro and in ovo in a 4T1 breast cancer cell line for NIR light-trigger photothermal therapy. Proven in the chicken egg tumor model, AZB-CF3@DSPE-PEG NPs induced severe vascular damage (∼40% vascular destruction), showed great anticancer efficacy (∼75% tumor growth inhibition), and effectively inhibited distant metastasis via photothermal treatment. As such, this PTT-based nanocarrier system could be a potential candidate for a clinical cancer therapy approach.

Heavy Atom Effect on the Intersystem Crossing of a Boron Difluoride Formazanate Complex-Based Photosensitizer: Experimental and Theoretical Studies.

Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves using light to activate photosensitizers (PSs). Attractively, PDT is one of the alternative cancer treatments due to its noninvasive technique. By utilizing the heavy atom effect, this work modified a class of formazan dyes to improve intersystem crossing (ISC) to improve reactive oxygen species (ROS) generation for PDT treatment. Two methods were used to observe the ROS generation enhanced by ISC of the synthesized complexes including, (1) recording DPBF decomposition caused by the ROS, and (2) calculating the potential energy curves for photophysical mechanisms of BF2 -formazanate dyes using the DFT and nudged elastic band (NEB) methods. The photophysical properties of the dyes were studied using spectroscopic techniques and X-ray crystallography, as well as DFT calculations. The experimental and theoretical results and in vitro cellular assays confirmed the potential use of the newly synthesized iodinated BF2 -formazanate dyes in PDT.

Unraveling the photophysical characteristics and biological applications of vinyl sulfones as viscosity sensors.

For the first time, a series of vinyl sulfone-NH2-based push-pull fluorophores (4a-4d) were introduced for their potential use in biological applications. The fluorophores 4a-4d were readily synthesized upon reduction of the corresponding vinyl sulfones-NO2 (3a-3d), which were prepared by sulfonylation of nitrostyrene. Both types of probes can be prepared in high yields through a few steps with minimal cost. In diverse solvents, probes 4a-4d exhibited fluorescence with strong emission peaking around 403-490 nm. Additionally, the fluorescence intensity of probe 4d rose approximately 85-fold with increasing viscosity. The probes 4a-4d demonstrated good stability and photostability in a broad pH range. Moreover, probes 4a-4d showed significantly improved biocompatibility compared to those derived from 3a-3d. For cell imaging applications, the developed probes 4a-4d exhibited much stronger blue fluorescence in cancer cells (HepG2) compared to 3a-3d. In addition, probes 4a-4d exhibited low cytotoxicity within 24 h toward both cancer and normal cells (HEK-293). Interestingly, probe 4d showed great sensitivity to viscosity in cancer cells. As a result, readily prepared vinyl sulfone-NH2-based push-pull fluorophores (4a-4d) offer a promising strategy for further development as cancer cell staining agents.

Cationic styryl dyes for DNA labelling and selectivity toward cancer cells and Gram-negative bacteria.

Fluorescence-based methods are important tools for the analysis of nucleic acids in vitro and in cells. In this study, two cationic cyanine-styryl derivatives were produced using a two-step synthesis. Their optical properties were evaluated in different solvents, and frontier molecular orbital theory was utilized to interpret the findings. The DNA binding of these molecules was investigated to show fluorescence intensification. The molecular docking of both dyes in DNA illustrated the relevance of the electrostatic interaction between the quaternary ammonium of both dyes and the phosphate of the DNA backbone. Last but not least, applications of the synthesized styryl dyes were demonstrated to be selective towards cancer cells and particular kinds of bacteria.

Hemicyanine-based pH-responsive probes for rapid hypoxia detection in cancer cells.

As pH-sensitive and hypoxia-responsive probes, three hemicyanine derivatives based on vanillin and the indole ring (Val-Hcys) were synthesized. The fluorescence of the probes can be activated at acidic pH using the amide functionalized sidechains. Furthermore, when Val-Hcys were incubated with hypoxic cells for 5 min, the fluorescent signals significantly increased when compared to normoxia cells (4-fold enhancement, maximum at 180 min). In addition, Val-Hcys tend to accumulate in lysosomes and mitochondria, two important organelles involved in cell mitophagy. Surprisingly, Val-Hcys improved cell viability in hypoxic conditions. As a result, this study demonstrates the utility of Val-Hcys as pH-responsive probes for detecting hypoxic areas.