New Triphenylphosphonium Salts of Spiropyrans: Synthesis and Photochromic Properties

The most important area of modern pharmacology is the targeted delivery of drugs, and one of the most promising classes of chemical compounds for creating drugs of this kind are the photochromic spiropyrans, capable of light-controlled biological activity. This work is devoted to the synthesis and study of the photochromic properties of new triphenylphosphonium salts of spiropyrans. It was found that all the synthesized cationic spiropyrans have high photosensitivity, increased resistance to photodegradation and the ability for photoluminescence.

Photoluminescence and mechanoluminescence of solid-state zirconocene dichlorides

Spectral-luminescence properties of 23 samples of zirconium complexes were studied. Mechanoluminescence spectra of 10 complexes were obtained. The solid-state component of the mechanoluminescence spectrum, that is the luminescence of the crystal itself, coincided with the photoluminescence spectra of these complexes, which indicated identical emission from the same excited states in mechanoluminescence and photoluminescence, despite the different ways of excitation. The luminescence maximum was red shifted as substituents appeared in the ligand, in particular in the presence of a bridging group connecting π-ligands (ansa-complexes) and also for a substituted bis-indenyl complex rac-Me₂ Si(2-Me-4-Ph-5-OMe-6-Bu^t -Ind)₂ ZrCl₂ ). It was found that mechanical destruction of the rac-isomer of complex Mе₂ С(2-Me-4-Bu^t -C₅ H₂ )₂ ZrCl₂ , unlike that of the meso-isomer, was accompanied by a more than a 10-fold increase in intensity and by a shift in the mechanoluminescence spectrum to longer wavelengths.

Luminescence of aromatic hydrocarbon molecules in the sonication of terbium sulfate suspensions

The sonication of terbium sulfate suspensions in benzene, toluene, and p-xylene induces intense UV luminescence (260-320 nm). The luminescence bands coincide with the fluorescence spectra of these aromatic hydrocarbons, but it is not observed in their sonoluminescence spectra. Furthermore, the spectra of ultrasound-initiated luminescence of the suspensions defined as sonotriboluminescence, which is 10³ times more intense than the sonoluminescence of hydrocarbons, exhibit also emission from the ^∗Tb³⁺ ion. The luminescence of ^∗N₂, which is observed during traditional triboluminescence of terbium sulfate in air, is hardly detectable in the case of sonolysis of terbium sulfate suspensions in aromatic hydrocarbons, but can be observed on decreasing the temperature of the suspensions, which decreases the saturated vapor pressure of the liquids. A possible mechanism of excitation of aromatic hydrocarbon molecules during sonotriboluminescence is discussed.

Mechanoluminescence of Ce/Tb inorganic salts in methane-acetylene mixtures with inert gases

The mechanoluminescence of cerium (Ce) and terbium (Tb) lanthanide salts is studied in hydrocarbon [methane (CH₄ ) and acetylene (C₂ H₂ )] and inert [helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe)] gaseous mixtures. The lines of *N₂ , *Ln³⁺ , inert gases, *CH, and *C₂ radicals resulted from the mechanochemical decomposition of CH₄ and C₂ H₂ are observed in the emission spectrum. The luminescence intensity of the inert gases decreases with the hydrocarbon gas concentration in the mixture. The intensities of the *CH or *C₂ bands remains almost unchanged within 15-100 vol% of CH₄ or C₂ H₂ in the mixture. When the concentration of CH₄ or C₂ H₂ is lower than 15%, the intensities of the CH or C₂ bands increase achieving their maxima at 0.5-3% of the hydrocarbon. This is probably due to the optimal compositions of the mixtures with the most efficient generation of electrical discharges responsible for mechanoluminescence.

Quenching of electronically excited N2 molecules and Tb3+ /Eu3+ ions by polyatomic sulfur-containing gases upon triboluminescence of inorganic lanthanide salts

The triboluminescence of Eu₂ (SO₄ )₃ ·8H₂ O and Tb₂ (SO₄ )₃ ·8H₂ O crystals in an atmosphere of sulfur dioxide (SO₂ ) or sulfur hexafluoride (SF₆ ) was studied. Quenching of the gaseous (emitter N₂ ) and solid-state (emitter Ln³⁺ ) components of the triboluminescence (TL) emission spectrum was seen when compared with the TL spectra of the crystals in air. One reason for the quenching is a reduction in the effective charge both on the crystal surface and in micro-cracks under an SO₂ or SF₆ atmosphere, leading to a decrease in the probability of electrical breakdown and a reduction in electric field strength responsible for the electroluminescence excitation of lanthanide ions in TL. In an SO₂ atmosphere, there is an additional mode of quenching, as confirmed by quenching of the crystal photoluminescence (emitter Ln³⁺ ). It is supposed that this quenching is due to an exchange of energy on electronic excitation of the lanthanide ions to the vibrational sublevels of the SO₂ molecules adsorbed on the crystal surface. Another additional channel of TL quenching originates from non-radiative transfer of excitation energy during collisions between the *N₂ and SO₂ molecules in the gaseous phase.