Guest-Driven Light-Induced Spin Change in an Azobenzene Loaded Metal-Organic Framework

Stimuli-responsive materials that can be reversibly switched by light are of immense interest. Among them, photo-responsive spin crossover (SCO) complexes have great promises to combine the photoactive inputs with multifaceted outputs into switchable materials and devices. However, the reversible control the spin-state change by photochromic guests is still challenging. Herein, we report an unprecedented guest-driven light-induced spin change (GD-LISC) in a Hofmann-type metal-organic framework (MOF), [Fe(bpn){Ag(CN)₂ }₂ ]⋅azobenzene. (1, bpn=1,4-bis(4-pyridyl)naphthalene). The reversible trans-cis photoisomerization of azobenzene guest upon UV/Vis irradiation in the solid-state results in the remarkable magnetic changes in a wide temperature range of 10-180 K. This finding not only establishes a new switching mechanism for SCO complexes, but also paves the way toward the development of new generation of photo-responsive magnetic materials.

Influence of the interaction with DNA on the spectral-fluorescent and photochemical properties of some meso-substituted polymethine dyes

Spectral-fluorescent and photochemical properties of meso-substituted thiacarbocyanine dyes 3,3'-dimethyl-9-phenylthiacarbocyanine and 3,3'-diethyl-9-(2-hydroxy-4-methoxyphenyl)thiacarbocyanine in solutions and their interaction with DNA were studied. The dyes form noncovalent complexes with DNA, which is accompanied by changes in the absorption spectra and an increase in the fluorescence intensity of the dyes. The data obtained suggest that the dyes are in the form of trans-isomers both in solvents of different polarity and in complexes with DNA. It was shown that the interaction of the dyes with DNA is a complex process involving monomeric dye molecules and aggregates of the dyes. The primary photochemical processes of the dyes in solutions and in complexes with DNA were studied by flash photolysis technique. Upon flash photoexcitation in solutions, the formation and decay of the photoisomers of the dyes were observed, with no generation of the triplet states. In the complex with DNA, no signal of photoisomers was detected; in the absence of oxygen, the formation of the triplet state of the dyes was observed. The decay kinetics of the triplet state of the dyes were two-exponential. The process of quenching of the triplet state of the dyes by oxygen in a complex with DNA was studied, the respective quenching rate constants were estimated, being lower than the diffusion-controlled value.