Supramolecular fullerene/porphyrin charge transfer interaction studied by absorption spectrophotometric method

A detailed UV–Vis spectrometric and thermodynamic studies were done to look insight into the nature of molecular interactions of the electron donor–acceptor complexes of C₆₀ and C₇₀ with 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (1) in chloroform and toluene. Charge transfer (CT) absorption bands were located in the visible region and vertical ionization potential of 1 was determined utilizing CT transition energy. Low values of oscillator and transition dipole strengths suggested that the complexes were almost of neutral character in ground states. The high binding constant value for the C₇₀–1 complex indicated high selectivity of 1 molecule towards C₇₀. Experimental as well as theoretically determined of enthalpies of formation value substantiated the trend in K values for fullerene–1 complexes.     

Spectrophotometric and spectroscopic studies of complexation of 8-hydroxyquinoline with π acceptor metadinitrobenzene in different polar solvents

The complexation of electron donor–acceptor complexes of 8-hydroxyquinoline (8HQ) and metadinitrobenzene (MNB) have been studied spectrophotometrically and thermodynamically in different polar solvent at room temperature. A new absorption band due to charge transfer (CT) transition is observed in the visible region. A new theoretical model has been developed which take into account the interaction between electronic subsystem of 8HQ and MNB. The results indicate the extent of charge transfer complexes (CTCs) formation to be more in less polar solvents. Stoichiometry of the complex was found to be 1:1 by straight line method and ¹H NMR between donor and acceptor at the maximum absorption bands. Ionization potential (I_D) and resonance energy (R_N) were determined from the CT transition energy in different solvents. The formation constants of the complexes were determined in different polar solvents from which ΔG° formation of the complexes was estimated and also extinction coefficient of the charge transfer complex (CTC) was calculated. Oscillator strength, transition dipole strengths and maximum wavelength of the CTC (λ_CT) in various solvents and IR spectra of the CTC have also been discussed. It has been observed that all parameters described above changed with change in polarity and concentration of donor.     

Theoretical studies on the structural and optical properties of a series of Os(II) diimine complexes [Os(NN)(CO)2I2] (NN = 2,2′-bipyridine(bpy), 4,4′-di-tert-butyl-2,2′-bipyridine(dbubpy), 4,4′-dichlorine-2,2′-bipyridine(dclbpy))

The ground- and excited-state structures for a series of Os(II) diimine complexes [Os(NN)(CO)₂I₂] (NN = 2,2′-bipyridine (bpy) (1), 4,4′-di-tert-butyl-2,2′-bipyridine (dbubpy) (2), and 4,4′-dichlorine-2,2′-bipyridine (dclbpy) (3)) were optimized by the MP2 and CIS methods, respectively. The spectroscopic properties in dichloromethane solution were predicted at the time-dependent density functional theory (TD-DFT, B3LYP) level associated with the PCM solvent effect model. It was shown that the lowest-energy absorptions at 488, 469 and 539 nm for 1–3, respectively, were attributed to the admixture of the [d_xy (Os) → π^*(bpy)] (metal-to-ligand charge transfer, MLCT) and [p(I) → π^*(bpy)] (interligand charge transfer, LLCT) transitions; their lowest-energy phosphorescent emissions at 610, 537 and 687 nm also have the ³MLCT/³LLCT transition characters. These results agree well with the experimental reports. The present investigation revealed that the variation of the substituents from H → t-Bu → Cl on the bipyridine ligand changes the emission energies by altering the energy level of HOMO and LUMO but does not change the transition natures.     

In situ measurements of emission transition dipole moment of individual ordered microdomain of diprotonated tetraphenylporphine aggregate formed at dodecane/aqueous H<Subscript>2</Subscript>SO<Subscript>4</Subscript> interface

Rhombic-ordered microdomains of diprotonated 5,10,15,20-tetraphenylporphine aggregate, whose sizes were 10–200 μm, were formed at dodecane/aqueous H₂SO₄ interfaces. The light excitation of their two absorption bands (410 and 473 nm for H- and J-bands, respectively) led to one fluorescence band at longer wavelength (723 nm). The direction of the emission transition dipole moment (μ _e) of individual rhombic microdomains, determined with an in situ optical microscope and a linear polarizer, was almost parallel to the major axis, which was also almost parallel to the direction of the absorption transition dipole moment of their J-bands. Their absorption and emission transition scheme was proposed.     

Charge-transfer biexciton annihilation in a donor–acceptor co-crystal yields high-energy long-lived charge carriers

Organic donor–acceptor (D–A) co-crystals have attracted much interest due to their important optical and electronic properties. Co-crystals having ⋯DADA⋯ π-stacked morphologies are especially interesting because photoexcitation produces a charge-transfer (CT) exciton, D˙⁺–A˙⁻, between adjacent D–A molecules. Although several studies have reported on the steady-state optical properties of this type of CT exciton, very few have measured the dynamics of its formation and decay in a single D–A co-crystal. We have co-crystallized a peri-xanthenoxanthene (PXX) donor with a N,N-bis(3-pentyl)-2,5,8,11-tetraphenylperylene-3,4:9,10-bis(dicarboximide) (Ph4PDI) acceptor to give an orthorhombic PXX–Ph4PDI ⋯DADA⋯ π-stacked co-crystal with a CT transition dipole moment that is perpendicular to the transition moments for S_n ← S₀ excitation of PXX and Ph4PDI. Using polarized, broadband, femtosecond pump–probe microscopy, we have determined that selective photoexcitation of Ph4PDI in the single co-crystal results in CT exciton formation within the 300 fs instrument response time. At early times (0.3 ≤ t ≤ 500 ps), the CT excitons decay with a t^−1/2 dependence, which is attributed to CT biexciton annihilation within the one-dimensional ⋯DADA⋯ π-stacks producing high-energy, long-lived (>8 ns) electron–hole pairs in the crystal. These energetic charge carriers may prove useful in applications ranging from photovoltaics and opto-electronics to photocatalysis.

Femtosecond transient absorption microscopy of donor–acceptor single co-crystals shows that photogenerated charge transfer excitons in one-dimensional donor–acceptor π stacks annihilate to produce high-energy, long-lived electrons and holes.     

Tafel Slopes in Relation to the Replacement of Adsorbed Water by Organic Molecules

Abstract

In the lecture presented by Prof. Reddy the role of water in determining the potential dependence of electrosorption of neutral organic molecules has been discussed. The process one considers is that of the replacement of a number of water molecules n by each organic molecule adsorbed. The dipole moments of the adsorbed water molecules interact with the electrical field in the double layer and hence cause a potential (or charge) dependent adsorption of the neutral organic molecule, even if the latter possesses no permanent dipole moment. The theory of this phenomenon has been worked out by Bockris, Devanathan and Muller. Corrections for lateral interactions between the adsorbed water molecules and for the permanent dipole moment of the electrosorbed neutral organic molecule have been made.^1,2     

吩噻嗪给体受体衍生物激发态的电荷转移

A series of N-bonded donor-acceptor derivatives of phenothiazine containing phenyl （PHPZ）, anisyl （ANPZ）, pyridyl （PYPZ）, naphthyl （NAPZ）, acetylphenyl （APPZ）, and cyanophenyl （CPPZ） as an electron acceptor have been synthesized. Their photophysical properties were investigated in solvents of different polarities by absorption and emission techniques. These studies clearly revealed the existence of an intramolecular charge transfer （ICT） excited state in the latter four compounds. The solvent dependent Stokes shift values were analyzed by the modified Lippert-Mataga equation to obtain the excited state dipole moment values. The large excited state dipole moment suggests that the full （or nearly full） electron transfer take place in the A-D systems. In the system of A-D phenothiazine derivatives, the transition dipole moments Mflu were determined mainly by direct interactions between the solvent-equilibrated fluorescence ^1CT state and ground state because of their lack of significant change with increase of the solvent polarity. The electron structure and molecular conformation of phenothiazine derivatives will be significantly changed with the increase of the electron affinity of the N-10 substituent.     

Dipole moments,transition moments,oscillator strengths,radiative lifetimes,and overtone intensities for CH and CH+ as computed by quasi-degenerate many-body perturbation theory

The correlated, size-consistent, ab initio effective valence-shell dipole operator (μ^v) method is used to calculate dipole moments and transition dipole moments of the CH molecule and transition dipole moments of the CH⁺ ion as a function of internuclear distance. The dipole and transition dipole moments computed here compare well with those of other accurate ab initio methods. The transition dipole moments are then used to calculate oscillator strengths and radiative lifetimes for the A → X and B → A transitions of the CH⁺ ion and the A → X transition of the CH molecule. Comparisons are made with the best available theoretical and experimental lifetimes. Finally, the CH ground-state dipole moment function is used to evaluate overtone intensities and to examine simple models of the CH overtone intensities in polyatomic molecules.     

On the conformation of 6-ketononanolide and 1,4-cyclohexanedione in solution by dipole moment studies

The dipole moments of 6-ketononanolide (1) and its 2,4,7 and 8-Me derivatives (2–5) are found to be 1·8 – 1·9±0·2 D. Utilizing the known solid-state geometry of 1, a dipole moment of 1·6 D is calculated by the INDO quantum mechanical method. Thus the conformation of 1 in solution does not differ much from its solid-state conformation which is diamond-lattice derived with the CO groups 174° apart and in “Type III” positions. However, the IR spectrum of 1 in solution shows differences from that in the solid state (Nujol or KBr).The dipole moment of 1,4-cyclohexanedione (10) is calculated to be 1·2 D for the experimental 156° twist boat conformation (found in the solid-state). This is in excellent agreement with the experimental value found by several groups. 1,6-Cyclodecanedione (6), however, is found to have an experimental dipole moment of 0·7 D, as contrasted with a calculated value of 0 D for 180° opposed carbonyls.     

Charge transfer associated with the physical process of hardness equalization and the chemical event of the molecule formation and the dipole moments

In this article, we have basically launched a search whether the dipole charge and dipole moment of heteronuclear diatomics can be justifiably evaluated in terms of charge transfer kernel using the hardness equalization principle as basis. We have derived a formula for computing dipole charge (q) on the basis of hardness equalization principle as q = aδ + b, where “a” and “b” are the constants and “δ” is the kernel of charge transfer from less hard atom to more hard atom during the rearrangement of charge on molecule formation. We have computed the dipole charges and dipole moments of as many as six different sets of compounds of widely diverse physicochemical behavior in terms of the algorithm derived in the present work. The computed dipole charge nicely reveals the known chemicophysical behavior of such compounds as are brought under the study. A comparative study of the nature of variation of theoretically evaluated and experimentally determined dipole moments reveals that there is an excellent agreement between the two sets of dipole data. Thus, the new algorithm derived for the calculation of the dipole charge using the hardness equalization principle as a basis is efficacious in computing the distribution and rearrangement of charge associated with the chemical event of molecule formation. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Fluorescence properties of a potential antitumoral benzothieno[3,2-b]pyrrole in solution and lipid membranes

Fluorescence properties of the antitumoral methyl 3-(benzo[b]thien-2-yl)-benzothieno[3,2-b]pyrrole-2-carboxylate (BTP) were studied in solution and in lipid bilayers of dipalmitoyl phosphatidylcholine (DPPC), dioleoyl phosphatidylethanolamine (DOPE) and egg yolk phosphatidylcholine (Egg-PC). BTP presents good fluorescence quantum yields in all solvents studied (0.20 ≤ Φ_F ≤ 0.32) and a bathochromic shift in polar solvents. The results indicate an ICT character of the excited state, with an estimated dipole moment of μ_e = 7.38 D.Fluorescence (steady-state) anisotropy measurements of BTP incorporated in lipid membranes of DPPC, DOPE and Egg-PC indicate that this compound is deeply located in the lipid bilayer, feeling the difference between the rigid gel phase and fluid phases.BTP inhibits the growth of three human tumour cell lines, MCF-7 (breast adenocarcinoma), SF-268 (glioma) and NCI-H460 (non-small cell lung cancer), being significantly more potent against the NCI-H460 tumour cells.     

Mechanism of SO2 adsorption on receptor sites incorporated into porous SiO2 films

SO₂ adsorption on porous SiO₂ films containing alkylamine sites is considered. Alkylamine-SO₂ complexes are modeled using the molecular mechanics method; it is demonstrated that the SO₂ molecule is adsorbed on the amine-containing group of alkylamine. On the basis of these computations, the alkylamine fragment responsible for SO₂ adsorption was determined, and quantum chemical calculations of the electronic structure and complexation energies depending on the number of ethyl substituents in the alkylamine were performed. The dipole moment of the alkylamine-SO₂ complex is shown to differ strongly in its magnitude from the geometric sum of dipole moments of component molecules. The reasons for the difference are charge transfer to SO₂ and charge redistribution in the alkylamine with decreasing electron density on hydrogen atoms.Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 131–134, November–December, 1993.Translated by L. Chernomorskaya     

Dielectric data of binary mixtures of 1,2-butanediol with 2-ethyl-1-hexanol and 1,4-dioxane at T = (298.2, 308.2, and 318.2) K

Relative permittivity measurements were made on binary mixtures of (1,2-butanediol + 2-ethyl-1-hexanol) and (1,2-butanediol + 1,4-dioxane) for various concentrations at T = (298.2, 308.2, and 318.2) K. The molecular dipole moments were determined using Guggenheim–Debye method in the temperature range of (298.2 to 318.2) K. The variations of effective dipole moment and correlation factor, g, with the mole fraction in these materials were investigated using Kirkwood–Frohlich equation. The pure compounds showed a negative and small temperature coefficient of effective dipole moment. In order to obtain valuable information about heterogeneous interaction (interactions between the unlike molecules), the Kirkwood correlation factor, the Bruggeman dielectric factor and the excess permittivity were calculated. In addition, in order to predict the permittivity data of polar-apolar binary mixtures, five mixing rules were applied.     

Croomine- and tuberostemonine-type alkaloids from roots of Stemona tuberosa and their antitussive activity

Three new croomine-type Stemona alkaloids, tuberocrooline (1), 10-hydroxycroomine (2), and dehydrocroomine (3), and four new tuberostemonine-type alkaloids, tuberostemoline (4), tridehydrotuberostemonine (5), 9α-bisdehydrotuberostemonine (6), and 9α-bisdehydrotuberostemonine A (7), along with ten known constituents, were isolated from the roots of Stemona tuberosa collected from Yunnan province. The structures of the new compounds were established on the basis of one- and two-dimensional NMR spectra and other spectroscopic studies. The antitussive activity of the major alkaloids was tested using the citric acid-induced guinea pig cough model. Croomine (8) exhibited a dose-dependent inhibition of coughing with an ID₅₀ value of 0.18 mmol/kg.     

Organotin(IV) 4-nitrophenylethanoates: Synthesis, structural characteristics and intercalative mode of interaction with DNA

Four new organotin(IV) carboxylates, [Bu₂SnL₂] (1), [Et₂SnL₂] (2), [Bu₃SnL]_n (3), [Me₃SnL]_n (4), where L = 4-nitrophenylethanoates, were synthesized and characterized by elemental analysis, FT-IR and multinuclear NMR (¹H and ¹³C). Spectroscopic results authenticated the coordination of ligand to the organotin moiety via COO group while X-ray single crystal analysis revealed bidentate chelating mode of coordination of ligand in complex 2 and a bridging behavior in complexes 3 and 4. Cyclic voltammetric (CV) technique was used to evaluate the electrochemical, kinetic and thermodynamic parameters of complexes 1-4, interacting with DNA. The linearity of the plots between the peak current (I) and the square root of the scan rate (ν^1/2) indicated the electrochemical processes to be diffusion controlled. The diffusion coefficients of the free (D_f) and DNA bound forms (D_b), standard rate constants (ks) and charge transfer coefficients (α) were determined by the application of Randle–Sevcik, Nicholson and Kochi equations. Furthermore, the binding constants evaluated from voltammetric data revealed the following increasing order of binding strength: 2 < 1 < 4 < 3. For 1 and 2, the activity against prostate cancer cell lines (PC-3) was found consistent with the order obtained from voltammetric behavior.     

Theoretical studies upon the electronic structures and spectroscopic properties for a series of luminescent terpyridyl platinum(II) phenylacetylide complexes

A comprehensive calculations were carried out to get a deep insight into the ground- and excited-state electronic structures and the spectroscopic properties for a series of [Pt(4-X–trpy)CCC₆H₄R]⁺ complexes (trpy = 2,2′,6′,2″-terpyridine; X = H, R = NO₂ (1), Cl (2), C₆H₅ (3) and CH₃ (4); R = Cl, X = CH₃ (5) and C₆H₅ (6)). MP2 (second-order Møller–Plesset perturbation) and CIS (single-excitation configuration interaction) methods were employed to optimize the structures of 1–6 in the ground and excited states, respectively. The investigation showed that substituted phenylacetylide and trpy ligands only give rise to a small variation in geometrical structures but lead to a sizable difference in the electronic structures for 1–6 in the ground and excited states. The introduction of electron-rich groups into the phenylacetylide and/or terpyridyl ligands produces two different low-lying absorptions for 1 and 2–6, i.e., Pt(5d) → π^*(trpy) metal-to-ligand charge transfer (MLCT) mixed with π → π^*(CCPh) intraligand charge transfer (ILCT) for 1 and Pt(5d)/π(CCPh) → π^*(trpy) charge transfer (MLCT and LLCT) for 2–6. Remarkable electronic resonance on the whole Pt–CCPh–NO₂ moiety for 1 may be responsible for the difference. Solvatochromism calculation revealed that only LLCT/MLCT transitions showed the solvent dependence, consistent with the experimental observations.     

A charge–charge flux–dipole flux decomposition of the dipole moment derivatives and infrared intensities of the AB3 (A = N,P; B = H,F) molecules

The quantum theory of atoms in molecules (AIM) has been used to decompose dipole moment derivatives and fundamental infrared intensities of the AB₃ (A = N,P; B = H,F) molecules into charge–charge flux–dipole flux (CCFDF) contributions. Calculations were carried out at the MP2(FC)/6-311++G(3d,3p) level. Infrared intensities calculated from the AIM atomic charges and atomic dipoles are within 13.8 km mol⁻¹ of the experimental values not considering the NH₃ and PH₃ stretching vibrations for which the experimental bands are severely overlapped. Group V atomic dipoles are very important in determining the molecular dipole moments of NF₃, PH₃ and PF₃ although the atomic charges account for almost all of the NH₃ molecular moment. Dipole fluxes on the Group V atom are important in determining the stretching band intensities of all molecules whereas they make small contributions to the bending mode intensities. Consideration of dipole flux contributions from the terminal atoms must also be made for accurately describing the intensities of all these molecules. As expected from a simple bond moment model, charge contributions dominate for most of the NH₃, NF₃, and PF₃ dipole moment derivatives and intensities. Charge flux and dipole flux contributions are very substantial for all the PH₃ vibrations, cancelling each other for the stretching modes and reinforcing one another for the bending modes.     

Density functional and molecular orbital study of physical process of inversion of nitrogen trifluoride (NF3) molecule

The physical process of the umbrella inversion of the nitrogen trifluoride molecule has been studied invoking the formalisms of the density functional theory, the frontier orbital theory, and the molecular orbital theory. An intuitive structure and dynamics of evolution of the transition state for the event of inversion is suggested. The physical process of dynamic evolution of the molecular conformations between the equilibrium (C_3v) shape and the planar (D_3h) transition state has been followed by a number of molecular orbital and density functional parameters like the total energy, the eigenvalues of the frontier orbitals, the highest occupied molecular orbital and lowest unoccupied molecular orbital, the (HOMO–LUMO) gap, the global hardness and softness, and the chemical potential. The molecular conformations are generated by deforming the ∠FNF angle through steps of 2° from its equilibrium value, and the cycle is continued till the planar transition state is reached, and the geometry of each conformation is optimized with respect to the length of the N? F bond. The geometry optimization demonstrates that the structural evolution entails an associated slow decrease in the length of the N? F bond. The dipole moment at the equilibrium form is small and that at the transition state is zero and shows a strange behavior with the evolution of conformations. As the molecular structure begins to distort from its equilibrium shape by opening of the ∠FNF angle, the dipole moment starts increasing very sharply, and the trend continues very near to the transition state but abruptly vanishes at the transition state. A rationale of the strange variation of dipole moment as a function of evolution of conformations could be obtained in terms of quantum mechanical hybridization of the lone pair on the N atom. The pattern of charge density reorganization as a function of geometry evolution is a continuous depletion of charge from the F center and piling up of charge on the N center. The continuous shortening of bond length and the pattern of variation of net charge densities on atomic sites with evolution of molecular conformations predicts that the bond moment would decrease continuously. The quantum mechanical hybridization of the lone pair of the central N atom shows that the percentage of s character of the lone‐pair hybrid on the N atom decreases at a very accelerated rate, and the lone pair at the transition state is accommodated in a pure p orbital. The result of the continued destruction of asymmetry of charge distribution in the lone pair on the central N atom due to the elimination of contribution of the s orbital with evolution of molecular conformations is the sharp decrease in lone‐pair moment. The decrease in bond moment is overcompensated by the sharp fall of its offsetting component, the lone‐pair moment, resulting in a net gain in dipole moment with the evolution of molecular geometry. Since the offsetting component decreases very sharply, the net effect is a sharp rise of dipole moment with the evolution of molecular conformations just before the transition state. The lone‐pair moment is zero by virtue of the symmetry of the pure p orbital, the lone pair of the central atom in the transition state, and the sum of the bond moments is zero by symmetry of the geometry. The barrier height is quite high at ～65.45 kcal/mol, which is close to values computed through more sophisticated methods. It is argued that an earlier suggestion regarding the development of high barrier value of NF₃ system seems to be misleading and confronting with the conclusions of the density functional theory. An analysis and a comparative study of the physical components of the one‐ and two‐center energy terms reveals that the pattern of the charge density reorganization has the principal role in deciding the origin and the magnitude of barrier of inversion of the molecule and the barrier originates not from a particular energetic effect localized in a particular region of the molecule, rather the barrier originates from a subtle interplay of one‐ and two‐center components of the total energy. The decomposed energy components show that the F?F nonbonded interaction and N? F bonded interaction favor the formation of transition state, while the one‐center energy terms prohibit the formation of the transition state. The barrier principally develops from the one‐center energy components. The profile of the HOMO is isomorphic and that of the LUMO is homomorphic with the potential energy curve for the physical process of the event of umbrella inversion of the molecule. The variation of the HOMO–LUMO gap, ?ε, the global hardness, η, and the softness, S, as a function of the reaction coordinates of angular deformation of NF₃ molecule are quite consistent with the predictions of the molecular orbital and the density functional theories in connection with the deformation of molecular geometry. The profiles of ?ε, η, and S, as a function of reaction coordinates, mimic the potential energy curve of the molecule. The eigenvalues of the frontier orbitals, and the ?ε, η, S parameters are found to be equally effective theoretical parameters, like the total energy, to monitor the physical process of the inversion of pyramidal molecules. The nature of the variation of the global hardness parameter between the equilibrium shape and the transition state form for the inversion is in accordance with the principle of maximum hardness (PMH). © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002     

Equilibrium geometry and electronic structure of benzylidene,arylethylidene, and heterocyclic arylidene malononitriles

The equilibrium geometry of some benzylidene, arylethylidene, and heterocyclic arylidene malononitriles has been calculated within the framework of the MNDO –MO formalism. Various structural factors are analyzed and discussed in terms of localized and delocalized MOS and π-interaction between methylene malononitrile (MMN) and aryl moieties. The possibility of charge transfer (CT ) from aryl to MMN moieties has been examined. The presence of a heterocyclic ring introduces a small perturbation into the MMN nuclear frame. p-Substituents have a pronounced effect on the magnitude and direction of the dipole moment. The variation of ionization potentials and bond order with the Hammet σ p are examined and a straight-line relationship is obtained. The correlation between physiological activity and quantum mechanical properties is analyzed in terms of heat of formation, ionization potential, dipole moment, and charge density on the aryl ring. © 1994 John Wiley & Sons, Inc.