Conformations in the solid state are typically fixed during crystallization. Transference of \"frozen\" C=C conformations in 3,5-bis((E)-2-(pyridin-4-yl)vinyl)methylbenzene (CH3-3,5-bpeb) by photodimerization selectively yielded cyclobutane and dicyclobutane isomers, one of which (Isomer 2) exhibited excellent in vitro anti-cancer activity towards T-24, 7402, MGC803, HepG-2, and HeLa cells.

Aryl-maleimides undergo a novel [2+4]-photodimerization instead of the expected [2+2]-photodimerization under both direct irradiation with visible light and under sensitized energy transfer conditions. This new excited state reactivity in aryl-maleimides is deciphered through photochemical, photophysical, and spectroscopic studies. The stereochemistry of the photodimer depends on the type of non-bonding interactions prevalent during photodimerization which is in turn dictated by the substituents on the maleimide ring. More importantly, the stereochemistry of the photodimer formed is complementary to the product observed under thermal conditions.

In this study, an efficient synthetic strategy and potential route to obtain a photo-reactive silver-containing cytosine-functionalized polypropylene glycol polymer (Ag-Cy-PPG) was developed by combining a hydrophilic oligomeric polypropylene glycol (PPG) backbone with dual pH-sensitive/photo-reactive cytosine-silver-cytosine (Cy-Ag-Cy) linkages. The resulting photo-responsive Ag-Cy-PPG holds great promise as a multifunctional biomedical material that generates spherical-like nanogels in water; the nanogels exhibit high antibacterial activity and thus may significantly enhance the efficacy of antibacterial treatment. Due to the formation of photo-dimerized Cy-Ag-Cy cross-linkages after UV irradiation, Ag-Cy-PPG converts into water-soluble cross-linked nanogels that possess a series of interesting chemical and physical properties, such as intense and stable fluorescence behavior, highly sensitive pH-responsive characteristics, on/off switchable phase transition behavior, and well-controlled release of silver ions (Ag+) in mildly acidic aqueous solution. Importantly, antibacterial tests clearly demonstrated that irradiated Ag-Cy-PPG nanogels exhibited strong antibacterial activity at low doses (MIC values of < 50 μg/mL) against gram-positive and gram-negative bacterial pathogens, whereas non-irradiated Ag-Cy-PPG nanogels did not inhibit the viability of bacterial pathogens. These results indicate that irradiated Ag-Cy-PPG nanogels undergo a highly sensitive structural change in the bacterial microenvironment due to their relatively unstable π-conjugated structures (compared to non-irradiated nanogels); this change results in a rapid structural response that promotes intracellular release of Ag+ and induces potent antibacterial ability. Overall, this newly created metallo-supramolecular system may potentially provide an efficient route to dramatically enhance the therapeutic effectiveness of antibacterial treatments.

Poly(vinyl alcohol) (PVA)-based hydrogels have attracted great attention and been widely used in biological tissue engineering. With the development of modern medicine, precision medicine requires the customization of medical materials. However, lacking of photocurable functional groups or the performance of rapid phase transition makes PVA-based hydrogels difficult to be customizable molded through photocuring 3D printing technique. In this research, customizable PVA-based hydrogels with high performance through 3D photocurable printing and freezing-thawing (F-T) process are obtained. The ability of 3D-printable is endowed by the introduction of polyvinyl alcohol-styrylpyridine (PVA-SBQ), which can be photo-crosslinked quickly without photoinitiator. Meanwhile, the tunable mechanical properties are achieved by adjusting the mass ratio of PVA-SBQ to PVA, and PVA can offer the physical crosslinking points through freezing-thawing (F-T) process. The hydrogels with high resolution are prepared by digital light procession 3D printing with the mass ratio 1:1 of PVA-SBQ to PVA solution. Attributed to the absence of initiator, and no small molecule residues inside the hydrogels, the hydrogels have good biocompatibility and have the potential to be applicated in the field of biological tissue engineering.

Dihydropyridine drugs are well known as photodegradable pharmaceuticals. Herein, we evaluate the photostability of felodipine (FL) medicine (Splendil® (SPL) tablets) and its altered forms (powders and suspensions). FL is a type of dihydropyridine drug, but its photochemical behavior is unknown. FL contents after ultraviolet light (UV) irradiation for 24 h were monitored using high-performance liquid chromatography (HPLC). Values of the residual amounts of FL in UV-irradiated SPL powders and suspensions were 32.76 ± 4.88% and 0.79 ± 0.74%, respectively, with the generation of two photoproducts (FL photoproduct 1 and 2). To identify the chemical structures of these photoproducts, electrospray ionization liquid chromatography mass spectrometry (ESI-LC/MS/MS) analysis was performed. Based on their mass-to-charge ratio values and fragment patterns, it was proposed that FL photoproduct 1 was a pyridine derivative and FL photoproduct 2 was an FL dimer. Interestingly, generation rates of FL photoproduct 1 and 2 were dependent on the presence of the aqueous media. The photodimerization of FL was induced in UV-irradiated SPL suspensions. This is the first report evaluating the photostability of SPL tablets and its altered forms and estimating FL photoproducts induced by UV irradiation in the formulation of SPL.

The photodimerization of 4-aminothiophenol (PATP) into 4,4\'-dimercaptobenzene (DMAB) has been extensively utilized as a paradigm reaction to probe the role of surface plasmons in nanoparticle-mediated light-driven processes. Here I report the first observation of the PATP-to-DMAB photoreaction in the absence of any plasmonic mediators. The reaction was observed to occur with different kinetics either for PATP adsorbed on non-plasmonic nanoparticles (TiO2 , ZnO, SiO2 ) or deposited as macroscopic droplets. Confocal microRaman spectroscopy enabled to investigate the reaction progress in different plasmon-free contexts, either aerobic or anaerobic, suggesting a new interpretation of the photodimerization process, based on direct laser-induced activation of singlet oxygen species. These results provide new insights in light-driven redox processes, elucidating the role of sample morphology, light and oxygen.

In homogeneous solid-state reactions, the single-crystal nature of the starting material remains unchanged, and the system evolves seamlessly through a series of solid solutions of reactant and product. Among [2+2] photodimerizations of cinnamic acid derivatives in the solid state, those involving salts of the 4-aminocinnamic acid have been recognized to proceed homogeneously in a \"single-crystal-to-single-crystal\" fashion by X-ray diffraction techniques. Here the bromide salt of this compound class is taken as a model system in a Raman spectroscopy study at low wavelengths, to understand how such a mechanism defines the trend of the crystal lattice vibrations during the reaction. Vibrational mode calculations, based on dispersion corrected DFT simulations of the crystal lattices involved in the transformation, have assisted the interpretation of the experiments. Such an approach has allowed us to clarify the spectral signatures and to establish a correlation between the dynamics of the monomer and dimer systems in a process where chemical progress and crystal structural changes are demonstrated to occur simultaneously.

Standard hydrogels prepared by free radical polymerization (FRP) have heterogeneous structures with a wide mesh size distribution, which affect their mechanical and separation properties. Recent research has identified four-armed poly(ethylene glycol) (tetra-PEG) as a solution to this problem. tetra-PEG gels with a homogeneous network can be prepared and applied as high-strength gels and cell-culture substrates by reacting two types of tetra-PEG with different reactive groups at the ends. In this study, we report a photoresponsive tetra-PEG that undergoes a phase transition from a sol to a gel state in response to light. tetra-PEGs containing cinnamoyl and maleimide groups at the ends of the four-armed chains were found to gel when exposed to light. The effects of polymer concentration and light irradiation time on the gelation of tetra-PEG containing photodimerization groups were investigated. The results showed that the elastic modulus of the gel increased with the increase in the light irradiation time.

The ditopic halogen-bond (X-bond) donors 1,2-, 1,3-, and 1,4-diiodotetrafluorobenzene (1,2-, 1,3-, and 1,4-di-I-tFb, respectively) form binary cocrystals with the unsymmetrical ditopic X-bond acceptor trans-1-(2-pyridyl)-2-(4-pyridyl)ethylene (2,4-bpe). The components of each cocrystal (1,2-di-I-tFb)·(2,4-bpe), (1,3-di-I-tFb)·(2,4-bpe), and (1,4-di-I-tFb)·(2,4-bpe) assemble via N···I X-bonds. For (1,2-di-I-tFb)·(2,4-bpe) and (1,3-di-I-tFb)·(2,4-bpe), the X-bond donor supports the C=C bonds of 2,4-bpe to undergo a topochemical [2+2] photodimerization in the solid state: UV-irradiation of each solid resulted in stereospecific, regiospecific, and quantitative photodimerization of 2,4-bpe to the corresponding head-to-tail (ht) or head-to-head (hh) cyclobutane photoproduct, respectively.

Anthracenes are an important class of acenes. They are being utilized more and more often in chemistry and materials sciences, due to their unique rigid molecular structure and photoreactivity. In particular, photodimerization can be harnessed for the fabrication of novel photoresponsive materials. Photodimerization between the same anthracenes have been investigated and utilized in various fields, while reactions between varying anthracenes have barely been investigated. Here, Nuclear Magnetic Resonance (NMR) spectroscopy is employed for the investigation of the photodimerization of two exemplary anthracenes: anthracene (A) and 9-bromoanthracene (B), in the solutions with only A or B, and in the mixture of A and B. Estimated k values, derived from the presented kinetic model, showed that the dimerization of A was 10 times faster in comparison with B when compounds were investigated in separate samples, and 2 times faster when compounds were prepared in the mixture. Notably, the photoreaction in the mixture, apart from AA and BB, additionally yielded a large amount of the AB mixdimer. Another important advantage of investigating a mixture with different anthracenes is the ability to estimate the relative reactivity for all the reactions under the same experimental conditions. This results in a better understanding of the photodimerization processes. Thus, the rational photofabrication of mix-anthracene-based materials can be facilitated, which is of crucial importance in the field of polymer and material sciences.