Stability Of Charge-transfer Complexes Research Articles

Donor-acceptor complex of 1-benzoylpiperazine with p-chloranil: Synthesis, spectroscopic, thermodynamic and computational DFT gas phase/PCM analysis

A new charge transfer (CT) complex is formed between the n- and π-donor 1-Benzoylpiperazine (1-BNZP) with π- acceptor p-chloranil (CHL). The CT-interaction is characterized in the defined polar solvent (acetonitile: ACN) at different temperatures. The 1:1 composition of the CT complex is proved. Benesi-Hildebrand method is used to find the stability constant (KCT) and molar extinction coefficient (ε). The more stability of CT complex is suggested from observed results. The thermodynamic parameters (ΔH° and ΔS°) were calculated by using Van't Hoff plot. From these values, CT complex formation process is found to be endothermic and spontaneous. FT-IR study gives information about stretching frequencies of mono substituted product of CT complex. TGA-DTA study is used for thermal stability of product. Morphology study is used to estimate the size and structure of the product. EDX spectrum is used for elemental analysis in the stoichiometric ratio. Theoretical investigation of the CT complex using DFT and TD-DFT also supports the experimental work. The C=O bond length of CHL increases on complexation with 1-BNZP along with significant amount of charge transfer from donor to acceptor. The HOMO-LUMO computation for protonated form of complex suggests a mono substituted product is formed via inner sigma (σ) complex.

C-terminal residues of ferredoxin-NAD(P)+ reductase from Chlorobaculum tepidum are responsible for reaction dynamics in the hydride transfer and redox equilibria with NADP+/NADPH.

Ferredoxin-NAD(P)+ reductase ([EC 1.18.1.2], [EC 1.18.1.3]) from Chlorobaculum tepidum (CtFNR) is structurally homologous to the bacterial NADPH-thioredoxin reductase (TrxR), but possesses a unique C-terminal extension relative to TrxR that interacts with the isoalloxazine ring moiety of the flavin adenine dinucleotide prosthetic group. In this study, we introduce truncations to the C-terminal residues to examine their role in the reactions of CtFNR with NADP+ and NADPH by spectroscopic and kinetic analyses. The truncation of the residues from Tyr326 to Glu360 (the whole C-terminal extension region), from Phe337 to Glu360 (omitting Phe337 on the re-face of the isoalloxazine ring) and from Ser338 to Glu360 (leaving Phe337 intact) resulted in a blue-shift of the flavin absorption bands. The truncations caused a slight increase in the dissociation constant toward NADP+ and a slight decrease in the Michaelis constant toward NADPH in steady-state assays. Pre-steady-state studies of the redox reaction with NADPH demonstrated that deletions of Tyr326-Glu360 decreased the hydride transfer rate, and the amount of reduced enzyme increased at equilibrium relative to wild-type CtFNR. In contrast, the deletions of Phe337-Glu360 and Ser338-Glu360 resulted in only slight changes in the reaction kinetics and redox equilibrium. These results suggest that the C-terminal region of CtFNR is responsible for the formation and stability of charge-transfer complexes, leading to changes in redox properties and reactivity toward NADP+/NADPH.

Interfacial Charge Transfer between Zinc Oxide Nanoparticles and Methyl Viologen: Influence of Size

AbstractThe fundamental understanding of photoinduced electron transfer (PET) between semiconductor nanocrystals and dye molecules is very important to design efficient light harvesting system based on inorganic‐organic hybrid system. Here, we have investigated the photoluminescence quenching and charge transfer process from ZnO NPs to methyl viologen (MV2+) by using steady state and time resolved spectroscopy. Absorption spectroscopic studies reveal that the charge‐transfer (CT) complex is formed between ZnO NPs and MV2+ which gives distinct size dependent CT bands. The defect emission of ZnO NPs is found to be quenched significantly after adding MV2+ molecule. The charge transfer process between ZnO NPs and MV2+ is confirmed by using laser flash photolysis and the stability of CT complexes is found to be more prominent for 6.3 nm ZnO NPs with MV2+ than 4.2 nm ZnO NPs with MV2+. The study of the electronic interaction of ZnO NPs with MV2+ is very important for further applications in organic/inorganic hybrid optoelectronic materials.

Influence of fused aromatic ring on the stability of charge transfer complex between iodine and some five membered heterocyclic molecules through ultrasonic and spectral studies

The charge transfer (CT) interaction between two fused heterocyclic compounds with basic pyrrole group as donors, viz., indole (IND) and carbazole (CAR), and iodine (acceptor) in DMSO medium is investigated by ultrasonic and UV–visible spectral methods at 303 K. The formation of CT complex in these systems is established from the trend in acoustical and excess thermo acoustical properties with molar concentration. The frequency acoustic spectra (FAS) is also carried out on these two systems for two fixed concentrations 0.002 M and 0.02 M, and in the frequency range 1 MHz-10 MHz to justify the frequency chosen for ultrasonic study. The absorption coefficient values in solution are computed and discussed. The formation constants of these complexes are determined using Kannappan equation in ultrasonic method. The formation of 1:1 complexes between iodine and IND, CAR was established by the theory of Benesi – Hildebrand in the UV–visible spectroscopic method. The stability constants of the CT complexes determined by spectroscopic and ultrasonic methods show a similar trend. These values also indicate that the presence of fused aromatic ring influences significantly when compared with K values of similar CT complexes of parent five membered heterocyclic compound (pyrrole) reported by us earlier.

Spectroscopic and ultrasonic studies on the molecular interaction of certain aromatic amines with p-chloranil

Ultrasonic investigation has been carried out on five binary and four ternary liquid mixtures to identify the dominance of solute–solute interactions. p-Chloranil is used as acceptor and four aromatic amines are used as donors. Primary, secondary and tertiary amines were used mainly to determine the difference in the site of complex formation. The study was made in DMSO at 303K and at atmospheric pressure. The trend in acoustical and excess thermo acoustical parameters of mixtures containing p-chloranil and amines is used to identify the existence of intermolecular interaction, probably through hydrogen bonded or charge transfer complex formation. The formation of 1:1 complexes between p-chloranil and aromatic amines was established by UV–visible spectroscopic methods at 303K. The formation constants of the charge transfer complexes were computed by spectroscopic and ultrasonic methods which show similar trends and well establish the influence of structural aspect of the amine (donor) on the stability of charge transfer complexes.

Effects of the acceptor conjugation length and composition on the electrical memory characteristics of random copolyimides

AbstractResistive‐switching memories based on copolyimides (coPIs), PI‐NTCDIX and PI‐BTCDIX, with different compositions of 4,4′‐diamino‐4″‐methyltriphenylamine (AMTPA), 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, and N,N′‐bis‐(4‐aminophenyl)‐1,8:4,5‐naphthalenetetracarboxydiimide (NTCDI) or N,N′‐bis‐(4‐aminophenyl)‐1,2:4,5‐benzenetetracarboxydiimide (BTCDI) have been developed. By varying the feed ratio of monomers, PI‐NTCDIX and PI‐BTCDIX showed tunable optical and electronic properties through the charge transfer (CT) between AMTPA and NTCDI or BTCDI. The memory devices based on PI‐NTCDIX exhibited the tunable electrical bistability from the volatile dynamic random access memory to nonvolatile write once read many memory characteristics as the NTCDI composition increased. The OFF/ON electrical switching transition was mainly attributed to the CT mechanism for the charge separated high conductance, based on the analysis of model compounds and density functional theory calculation. Also, the volatility of the memory device depended on the stability of CT complex. The long conjugation and high electron affinity of the NTCDI moiety stabilized the radical anion generated in the CT complex and prevented the recombination of segregated radical species even through applying the high positive or negative voltage. On the other hand, the memory devices based on PI‐BTCDIX showed a rather unique behavior compared with those based on PI‐NTCDIX. At the low BTCDI composition, the device exhibited volatile memory property. However, no switching behavior was observed at the high BTCDI composition due to the low highest occupied molecular orbital energy level of BTCDI. Combining these results and our previous study on perylenebisimide (PBI), we concluded that memory characteristics could be tailored by changing the conjugation length (PBI > NTCDI > BTCDI) and the acceptor composition in random coPIs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Tuning the Electrical Memory Characteristics from Volatile to Nonvolatile by Perylene Imide Composition in Random Copolyimides

Random copolyimides, PI–PBIX, with different compositions of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), N,N′-bis(4-aminophenyl)-3,4,9,10-perylenebis(dicarboximide) (PBI), and 4,4′-diamino-4″-methyltriphenylamine (AMTPA) were designed and synthesized for resistive-switching memory device applications. By varying the feeding ratio of monomers, PI–PBIX (where X = 0, 1, 2.5, 5, and 10 for molar composition of repeating units containing PBI) showed tunable optical and electronic properties through the charge transfer between AMTPA and PBI. Also, the memory devices prepared from PI–PBIX sandwiched between ITO and Al electrodes exhibited the tunable electrical bistability from the volatile to nonvolatile write once read many-times (WORM) memory characteristics as the PBI composition increased. The OFF/ON electrical switching transition was mainly attributed to the charge-transfer mechanism for charge-separated high conductance, based on the analysis of density function theory. Also, the volatility of PI–PBIX device depended on the stability of charge-transfer complex and charge trapping sites. The deep LUMO energy level of the PBI moiety increased the back-charge-transfer energy barrier and prevented recombination of segregated charges even through applying the high negative and positive voltage. The study revealed that the memory characteristics could be tailored from the donor–acceptor composition in the random copolyimides.

Ultrasonic and optical studies on charge transfer complexes of p-chloranil with certain aromatic hydrocarbons in DMSO at 303.15 K

Ultrasonic investigation has been carried out on six ternary systems to establish the complex formation between p-chloranil (acceptor) and six aromatic hydrocarbons (donors), namely, benzene, toluene, o-xylene, m-xylene, p-xylene and mesitylene in DMSO medium at 303.15 K and at atmospheric pressure. Studies were carried out in the concentration range of 0.002 to 0.02 M of acceptor and donor with equimolar concentration of the two components in solution. The trend in the acoustical parameters and magnitude of excess thermo acoustical parameters has been used to identify the existence of strong intermolecular interaction through charge transfer complex formation. The formation of 1:1 complex was also confirmed by UV–Visible spectroscopic method at 303.15 K in these systems. It may be pointed out that the formation constants of the charge transfer complexes determined by Benesi–Hildebrand (spectroscopic) and Kannappan (ultrasonic) methods show similar trend and well establish the influence of structural aspect of the donor aromatic compounds on the stability of charge transfer complexes.

Heteroaromatic thioamides: Structure and stability of charge transfer complexes with iodine, antithyroid activity

The review generalizes the structural studies on the products of the interaction of antithyroid preparations (heteroaromatic thioamides) with iodine. The n-σ* adducts of imidazol, thiazol, oxazole, pyridine, uracil derivatives with molecular iodine, iodinium salts, and also disulfides formed as a result of thione oxidation in iodine-coordinating solvents are considered. Based on mainly single crystal X-ray diffraction and Raman spectroscopy data, the structural parameters of iodine molecular complexes are shown to be highly sensitive to changes in the type of a heteroatom and substituents in the heteroring. The effect of the structure of heteroaromatic thioamides on their antithyroid activity is analyzed.

The relationship of charge transfer complexes to frontier orbital energies in QSAR

Frontier orbital energies, calculated by fast and approximate semiempirical methods, are widely used as molecular descriptors in medicinal chemistry. The traditional justification is that they represent measures of the ability of drug molecules to participate in the formation of charge transfer complexes. For both theoretical reasons and as a consequence of the drastic approximations inherent in the semiempirical methods, some doubt exists about the basis of this assumption. A computational study has been made of the stability of charge transfer complexes of benzene and methylated benzenes with four electron acceptors by the semiempirical PM3 method. The results support the traditional view that the energy of the highest occupied molecular orbital of the donor molecule is an indicator of the ability of the donor to form charge transfer complexes with electron acceptors. It was found that the heat of formation of the complex could be calculated, which correlated well with the measured stability constant of the complex, taken from the literature, and with measures of transfer of charge in both the ground state and excited state. The energy of the lowest unoccupied molecular orbital of the complex, calculated by PM3, was an extremely good measure of the ability of the donor-acceptor pair to form such a complex.

Correlation of thermodynamic stabilities of charge transfer complexes of anthracene and chloranil with those of tetra-cyanoethylene

The formation constants of charge-transfer complexes of a number of 9- and 9,10-substituted anthracenes with chloranil have been measured by a spectrophotometric method and the corresponding thermodynamic parameters ΔG° c, ΔH° c and ΔS° c evaluated in various solvents. v max values of the chargetransfer band for chloranil were linearly related to those for tetracyanoethylene (TCNE). Good correlations were also obtained between v max and the corresponding ionisation potentials Ip of the donor molecules. In addition ΔG° c varied linearly with Ip and from these correlations, values of ΔG° c, etc. for the corresponding TCNE complexes could be calculated. These values are otherwise very difficult to obtain due to the high reactivity of TCNE.