Solid-state proton transfer studies on phototautomerization of 1-phenyl-3-methyl-4-furoyl-5-pyrazolone 4-methyl thiosemicarbazone

Solid-state photochromic behavior of pyrazolone 4-phenylthiosemicarbazones

Pyrazolone 4-phenylthiosemicarbazones show excellent solid-state photochromic properties, thermal stability and fatigue resistance upon the UV/Vis irradiation.

A metal-organic tetrahedron as a redox vehicle to encapsulate organic dyes for photocatalytic proton reduction

The design of artificial systems that mimic highly evolved and finely tuned natural photosynthetic systems is a subject of intensive research. We report herein a new approach to constructing supramolecular systems for the photocatalytic generation of hydrogen from water by encapsulating an organic dye molecule into the pocket of a redox-active metal-organic polyhedron. The assembled neutral Co4L4 tetrahedron consists of four ligands and four cobalt ions that connect together in alternating fashion. The cobalt ions are coordinated by three thiosemicarbazone NS chelators and exhibit a redox potential suitable for electrochemical proton reduction. The close proximity between the redox site and the photosensitizer encapsulated in the pocket enables photoinduced electron transfer from the excited state of the photosensitizer to the cobalt-based catalytic sites via a powerful pseudo-intramolecular pathway. The modified supramolecular system exhibits TON values comparable to the highest values reported for related cobalt/fluorescein systems. Control experiments based on a smaller tetrahedral analogue of the vehicle with a filled pocket and a mononuclear compound resembling the cobalt corner of the tetrahedron suggest an enzymatic dynamics behavior. The new, well-elucidated reaction pathways and the increased molarity of the reaction within the confined space render these supramolecular systems superior to other relevant systems.

Photochromism and fluorescence modulation of pyrazolone derivatives in the solid state

Two novel photochromic pyrazolones were synthesized, and their photochromic performance was investigated in the solid state.

Vibrational spectroscopy (FT-IR and Laser-Raman) investigation, and computational (M06-2X and B3LYP) analysis on the structure of 4-(3-fluorophenyl)-1-(propan-2-ylidene)-thiosemicarbazone

In this study, the experimental and theoretical vibrational spectral analysis of 4-(3-fluorophenyl)-1-(propan-2-ylidene)-thiosemicarbazone have been carried out. The experimental FT-IR (4000-400 cm(-1)) and Laser-Raman spectra (4000-100 cm(-1)) have been recorded for the solid state samples. The theoretical vibrational frequencies and the optimized geometric parameters (bond lengths and angles) have been calculated for gas phase using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and M06-2X (the highly parametrized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set. The diversity in molecular geometry of fluorophenyl substituted thiosemicarbazones has been discussed based on the X-ray crystal structure reports and theoretical calculation results from the literature. The assignments of the vibrational frequencies have been done on the basis of potential energy distribution (PED) analysis by using VEDA4 software. A good correlation was found between the computed and experimental geometric and vibrational data. In addition, the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbital energy levels and other related molecular energy values of the compound have been determined using the same level of theoretical calculations.

THEORETICAL STUDIES ON THE CONFORMATION AND COORDINATION OFN-(1-PHENYL-3-METHYL-4-PROPENYLIDENE-5-PYRAZOLONE)-SALICYLIDENE

Density functional theory (DFT) calculation has been carried out to investigate the isomers of N -(1-phenyl-3-methyl-4-propenylidene-5-pyrazolone)-salicylidene. Chemical potential, chemical hardness and global electrophilicity, which are considered as global indices, have been calculated to assess the stability and reactivity of the tautomers. The condensed Fukui function is calculated for predicting the most probable sites for electrophilic attack. Molecular electrostatic potential is calculated to predict the regions for electrophilic attack.

Solid-state tautomerism in 2-carboxyindan-1,3-dione

The structure of 2-carboxyindan-1,3-dione was investigated using a combination of quantum-chemical calculations and solid-state NMR and IR spectroscopy. Due to poor solubility of the compound in different solvents, no single crystals could be obtained. Two dimeric structures formed from the tautomers of 2-carboxyindan-1,3-dione are likely to coexist in the solid state. The dimers interconvert via intramolecular proton transfer in one of the tautomeric forms constituting the dimers. The energy barrier of the intramolecular proton transfer reaction is calculated as 5.82 kcal mol(-1) at the MP2/6-31++G level of theory.

Study of fluorescence properties of several 4-acyl pyrazolone derivatives and their Zn (II) complexes

Fluorescence properties of four 4-acyl pyrazolone derivatives (H(2)L(1)=N-(1,3-diphenyl-4-propylene-5-pyrazolone)-salicylidene hydrazone (1), H(2)L(2)=N-(1,3-diphenyl-4-ethylene-5-pyrazolone)-salicylidene hydrazone (2), H(2)L(3)=N-(1,3-diphenyl-4-benzylidene-5-pyrazolone)-salicylidene hydrazone (3), H(2)L(4)=N-(1,3-diphenyl-4-phenylethylene-5-pyrazolone)-salicylidene hydrazone (4), and their Zn (II) complexes: (Zn(H(2)L(1))(2) (5), Zn(H(2)L(2))(2).3CH(3)OH (6), Zn(H(2)L(3))(2).2CH(3)OH (7), and Zn(4)(H(2)L(4))(4) (8)) were studied at room temperature. It was revealed that these compounds show different fluorescence properties both in the solid state and in solution. Density functional theory (DFT) calculations on ligands 1-4 were also performed to further understand their emission properties. The calculation results indicate that the energy gaps between the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) of these ligands are in the following order 1>2>3, which is consistent with the redshift of the emission spectra.

Synthesis and Solid-State Photochromism of 1,3-Diphenyl-4- (2-chlorobenzal)-5-hydroxypyrazole 4-Methylthiosemicarbazone

A new photochromic compound containing a pyrazole-ring unit, 1,3-diphenyl-4-(2-chlorobenzal)-5-hydroxypyrazole 4-methylthiosemicarbazone, was synthesized. Its structure, photochromic properties, and photochemical kinetics were characterized. The results show that the title compound exhibits reversible enol-keto photoisomerization, excellent photostability, and high fatigue resistance. An intra- and intermolecular proton-transfer mechanism is proposed.