Detour to success: photoswitching indirect excitation.

Photoswitchable molecules that undergo nanoscopic changes upon photoisomerisation can be harnessed to control macroscopic properties such as colour, solubility, shape, and motion of the systems they are incorporated into. These molecules find applications in various fields of chemistry, physics, biology, and materials science. Until recently, research efforts have focused on the design of efficient photoswitches responsive to low-energy (red or near-infrared) irradiation, which however may compromise other molecular properties such as thermal stability and robustness.

Triplet sensitization enables bidirectional isomerization of diazocine with 130 nm redshift in excitation wavelengths.

Diazocines are bridged azobenzenes with phenyl rings connected by a CH-CH group. Despite this rather small structural difference, diazocine exhibits improved properties over azobenzene as a photoswitch and most importantly, its configuration is more stable than the isomer. Herein, we reveal yet another unique feature of this emerging class of photoswitches.

Unraveling an Alternative Mechanism in Polymer Self-Assemblies: An Order-Order Transition with Unusual Molecular Interactions between Hydrophilic and Hydrophobic Polymer Blocks.

Polymer self-assembly leading to cooling-induced hydrogel formation is relatively rare for synthetic polymers and typically relies on H-bonding between repeat units. Here, we describe a non-H-bonding mechanism for a cooling-induced reversible order-order (sphere-to-worm) transition and related thermogelation of solutions of polymer self-assemblies. A multitude of complementary analytical tools allowed us to reveal that a significant fraction of the hydrophobic and hydrophilic repeat units of the underlying block copolymer is in close proximity in the gel state.

Expanding excitation wavelengths for azobenzene photoswitching into the near-infrared range endothermic triplet energy transfer.

Developing azobenzene photoswitches capable of selective and efficient photoisomerization by long-wavelength excitation is an enduring challenge. Herein, rapid isomerization from the - to -state of two -functionalized bistable azobenzenes with near-unity photoconversion efficiency was driven by triplet energy transfer upon red and near-infrared (up to 770 nm) excitation of porphyrin photosensitizers in catalytic micromolar concentrations. We show that the process of triplet-sensitized isomerization is efficient even when the sensitizer triplet energy is substantially lower (>200 meV) than that of the azobenzene used.

Endothermic and Exothermic Energy Transfer Made Equally Efficient for Triplet-Triplet Annihilation Upconversion.

Expanding the anti-Stokes shift for triplet-triplet annihilation upconversion (TTA-UC) systems with high quantum yields without compromising power density thresholds () remains a critical challenge in photonics. Our studies reveal that such expansion is possible by using a highly endothermic TTA-UC pair with an enthalpy difference of +80 meV even in a polymer matrix 1000 times more viscous than toluene. Carrying out efficient endothermic triplet-triplet energy transfer (TET) requires suppression of the reverse annihilator-to-sensitizer TET, which was achieved by using sensitizers with high molar extinction coefficients and long triplet state lifetimes as well as optimized annihilator concentrations.

Structure and Dynamics of Thermosensitive pDNA Polyplexes Studied by Time-Resolved Fluorescence Spectroscopy.

Combining multiple stimuli-responsive functionalities into the polymer design is an attractive approach to improve nucleic acid delivery. However, more in-depth fundamental understanding how the multiple functionalities in the polymer structures are influencing polyplex formation and stability is essential for the rational development of such delivery systems. Therefore, in this study the structure and dynamics of thermosensitive polyplexes were investigated by tracking the behavior of labeled plasmid DNA (pDNA) and polymer with time-resolved fluorescence spectroscopy using fluorescence resonance energy transfer (FRET).

Efficient photon upconversion at remarkably low annihilator concentrations in a liquid polymer matrix: when less is more.

A green-to-blue triplet-triplet annihilation upconversion of 24.5% quantum yield was achieved at a remarkably low 600 μM annihilator concentration in a viscous polymer matrix. This was made possible by utilizing a ZnTPP-based photosensitizer with exceptionally long 11 ms phosphorescence lifetime.

Halogen-Bond-Assisted Photoluminescence Modulation in Carbazole-Based Emitter.

Halogen bonding between a carbazole-based, pyridine-substituted organic semiconductor and a common halogen-bond donor (pentafluoroiodobenzene) yields efficient halogen-bond-driven fluorescence modulation in solution. Steady-state, time-resolved emission and absorption spectroscopy as well as density functional theory studies demonstrate that the fluorescence modulation arises from halogen-bond-induced intramolecular charge transfer. Fluorescence modulation offers a range of possibilities both in solution and in the solid state, for instance providing a potential pathway for the design of tunable luminescent materials for light-emitting devices.

Quantitative parameters of complexes of tris(1-alkylindol-3-yl)methylium salts with serum albumin: Relevance for the design of drug candidates.

Triarylmethane derivatives are extensively investigated as antitumor and antibacterial drug candidates alone and as photoactivatable compounds. In the series of tris(1-alkylindol-3-yl)methylium salts (TIMs) these two activities differed depending on the length of N-alkyl chain, with C4-5 derivatives being the most potent compared to the shorter or longer chain analogs and to the natural compound turbomycin A (no N-substituent). Given that the human serum albumin (HSA) is a major transporter protein with which TIMs can form stable complexes, and that the formation of these complexes might be advantageous for phototoxicity of TIMs we determined the quantitative parameters of TIMs-HSA binding using spectroscopic methods and molecular docking.

Microphase mechanism of "superquenching" of luminescent probes in aqueous solutions of DNA and some other polyelectrolytes.

A new approach in terms of microphase model of aqueous solutions of polyelectrolytes is proposed for explanation of a very strong quenching of luminescent probes ("superquenching") in these solutions. This phenomenon is used in literature for creation of extremely sensitive chemical and biosensors and was attributed predominantly to efficient energy or electron transfer. Microphase approach considers this phenomenon in terms of local concentrations of both the luminescent compound and of the quencher in microphase, formed by DNA and other polyelectrolytes, which can be several (4-10) orders of magnitude greater than their apparent concentrations in solution.

Role of the acyl groups in carbohydrate chains in cytotoxic properties of olivomycin A.

A series of olivomycin A derivatives containing different combinations of the acyl residues in the carbohydrate chains was obtained. The formation of complexes of Mg(2+)-coordinated dimers of these compounds with double-stranded DNA was studied using spectral methods such as absorption, fluorescence and circular dichroism (CD) spectral analyses. There was a good correlation of the values of binding constants of complexes (antibiotic)2Mg(2+)-DNA, the quantum yields of fluorescence and changes of the induced CD spectra with topoisomerase I inhibition and cytotoxicity.

Modification of olivomycin A at the side chain of the aglycon yields the derivative with perspective antitumor characteristics.

A novel way of chemical modification of the antibiotic olivomycin A (1) at the side chain of the aglycon moiety was developed. Interaction of olivomycin A with the sodium periodate produced the key acid derivative olivomycin SA (2) in 86% yield. This acid was used in the reactions with different amines in the presence of benzotriazol-1-yl-oxy-trispyrrolidino-phosphonium hexafluorophosphate (PyBOP) or diphenylphosphoryl azide (DPPA) to give corresponding amides.