| Abstract |
New arylhydrazones of beta-diketones, 2-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl) benzoic acid (1) and (Z)-ethyl-2-(2-(2-nitrophenyl)hydrazono)-3-oxobutanoate (2), have been synthesized by reaction of activated beta-diketones with the corresponding aryldiazonium salts, and characterized by IR, H-1 and C-13 NMR spectroscopies and elemental analysis. In DMSO solution, 1 is stable exclusively in the hydrazone form, while 2 exists in DMSO and H2O solutions as a mixture of enol-azo and hydrazone tautomeric forms. In the latter case, an increase in the solvent polarity shifts the tautomeric balance to the enol-azo form. Solvatochromic, thermal and photoluminescent properties of 1,2 and the known related 2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)benzoic acid (3), (2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)phenyl)arsonic acid (4), (Z)-2-(2-(1,3-dioxo-1-phenylbutan-2-ylidene)hydrazinyl)benzoic acid (5) and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2,3-dihydrophthalazine-1,4-d ione (6) were studied. The obtained UV-vis absorption spectra confirm that epsilon(max) depends on the solvent and on the nature of AHBD, but no clear correlation was found. Upon heating, 1-3,5 and 6 are stable up to 474 K and decompose in two steps whereas 4 decomposes in three steps starting from 343 K. The kinetic parameters of the thermal decomposition were estimated suggesting a low rate of the thermal decomposition. Compounds 2 and 3 exhibit luminescence with intense emission bands with maxima at lambda(em) of 466.0 (lambda(ex) = 318 nm) and 532.5 nm (lambda(ex) = 315 nm), respectively, while compounds 4 and 6 show low-intensity bands at lambda(em) of 501 (lambda(ex) = 396 nm) and 503 nm (lambda(ex) = 389 nm). Compounds 1 and 5 display no photoluminescence. (C) Crown Copyright 2012 Published by Elsevier B.V. All rights reserved. |
