Stunning tricolored crystals with distinct regions of green, yellow, and orange luminescence are deposited in solutions of potassium hydrogen phthalate that contain proflavin. The dye serves as a fluorescent probe of surface charge while identifying the polar crystallographic axis. Optical probes, common in biochemistry, can be used widely to study the specificity of noncovalent chemistry crystal growth from solution
Mixed crystals of potassium hydrogen phthalate containing 3,6-diaminoacridine were photoexcited with visible light and the resulting triplet excited states were analyzed by time resolved EPR spectroscopy. Spectra from discrete growth sectors were compared with powders and polycrystalline glasses prepared at various pHs. The data yield the predominant protonation state and orientation of the triplets in each of a pair of growth sectors bounding the positive and negative ends of the polar crystal.
Two dyes (4-nitrostilbene, NST and 4-N,N-dimethylamino-4'-nitrostilbene, DANS) included in zeolites with nanometric channels and different Si : Al ratios have been photoexcited and their triplet state studied by time resolved EPR (TR-EPR). This is the first time that a TR-EPR spectrum of photoexcited triplet states of dyes in zeolites has been observed. The zeolites used were ZSM-5 and mordenite, with either protons or lithium as charge compensating ions, and the aluminium-free porosil. The ZFS parameters and the polarized spin populations have been obtained, and compared with those obtained in glassy solutions and in the organic nanostructured matrix perhydrotriphenylene (PHTP). For (3)DANS in neutral solvents and in PHTP the dimethylamino group is pi conjugated, whereas only its acid form is detected in all the zeolites. In the latter the spectra of the radical cations formed by spontaneous oxidation have also been observed both by cw-EPR and TR-EPR, the last spectra being spin polarized in emission. The mobility of the triplets is discussed, taking into account the spin polarization of the radical cations indicating a strong radical-triplet interaction.
Dreifarbige Kristalle mit grün, gelb und orange lumineszierenden Bereichen wachsen aus Lösungen von Kaliumhydrogenphthalat in Gegenwart von Proflavin. Die Luminophore fungieren als Fluoreszenzsonden für Oberflächenladungen und können zur Untersuchung des Kristallwachstums genutzt werden.
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