Studies On The Synthesis, Crystal Structures And Photochemical Photochemical Properties Of Pyrazolone Thiosemicarbazones

Photochromism is defined as a reversible transformation between two isomers having different absorption spectra by photoirradiation, and these materials are of great interest due to their applications in ophthalmic lenses, display and communications systems, and optical storage and memory devices. Although many photochromic compounds have been so far reported, compounds which show photochromic reactivity in the crystalline phase are rare. Typical photochromic compounds, such as azobenzenes, spirobenzopyrans, and spirooxazines, require large geometrical structure or molecular volume changes in the photochromic reaction process. Therefore, the reactivity is lost in the rigid crystalline lattice. Hydrogen transfers or reversible radical formations are possible mechanism for the crystalline photochromism, the former plays a role in the photochromism of N-salicylideneanilines. On the basis of our laboratory previous work, several new thiosemicarbazones compounds containing pyrazolone-ring have been synthesized. The photochromic mechanism was analyzed and presumed by studying the properties and crystal strutures of the photochromic compounds. The relation between the structure and properties has been obtained.In the first part, five new 4-acyl pyrazolone 4-ethyl-thiosemicarbazones compounds: 1-Phenyl-3-methyl-4-(4-bromo)benzal-pyrazol-5-one N(4)-ethyl-thiosemicarbazone (PM4Br BP-ETSC), 1-Phenyl-3-methyl-4-(4-methyl)benzal-pyrazol-5-one N(4)-ethyl-thiosemicarbaz -one (PM4MBP-ETSC), 1-Phenyl-3-methyl-4-benzal-pyrazol-5-one N(4)-ethyl-thiosemicarba -zone (PMBP–ETSC), 1,3-diphenyl-4-benzal-pyrazol-5-one N(4)-ethyl-thiosemicarbazone (DPBP-ETSC) and 1-Phenyl-3-methyl-4-phenylacetyl-pyrazol-5-one N(4)-ethyl-thiosemi -carbazone (PMPaP-ETSC) have been synthesized and characterized by elemental analyses, IR, 1H NMR spectra and single-crystal XRD. The photochromic properties and photochemical kinetics of the former four compounds also have been studied by solid-state time-dependent UV-vis absorption spectra under irradiation of 365 nm light. The crystal structures of them show the photochromism is due to the photoisomerization only from enol form to keto form. According to the results of structure analyses, the intermolecular proton transfer mechanism is proposed for photochromism. We also observed their acidichromism in solution. On the basis of acidic solution absorption spectral changes and acidic solution emission spectral changes, we analyzed their probable chemical conformation under the addition of acidic solution and explained the phenomenon.In the second part, the derivatives of 1-phenyl-3-methyl-4-(4-methyl)benzal-5-pyrazol -one (PM4MBP) have been prepared. The configuration of 1-phenyl-3-methyl-4-(4–methy -l)benzal-pyrazol-5-one thiosemicarbazone (PM4MBP-TSC) and 1-phenyl-3-methyl-4-(4-m -ethyl)benzal-pyrazol-5-one N(4)-methyl-thiosemicarbazone (PM4MBP-MTSC) were determined by X-ray crystallography, other molecular structures of the derivatives were obtained by the techniques of elemental analyses, IR, 1H NMR and 13C NMR spectra. We have envisioned the reason of non-photochromism for these compounds by analyzing their structure, and then acquired the conclusion that, if the 4-position of pyrazolone-ring is the conjugate group of electron contributing, for example, phenyl and other substituted phenyl, the compounds synthesized possess the properties of photochromism, on the contrary, there is no photochromism. In the other words, their process of photochromism have been completed in solution, and the structures of compounds precipitated from solution are stable, and their conformation cannot be changed even though the energy (e.g. Uv-visible light) was added, so, the photochromism cannot be observed. Like the former part, we also gave the acidic absorption and emission spectral changes in solution about the two photochromic compounds, and discussed the possible consideration leading to the emission spectra changes by adding aicid and base solution.In the third part, two novel heterocyclic compounds PMCP-E...