Kakali Datta

Ground state EDA complex formation between [60]fullerene and a series of polynuclear aromatic hydrocarbons

Formation constants of 1∶1 adducts of [60]fullerene with naphthalene, phenanthrene, anthracene, pyrene and chrysene have been determined in CCl4 medium. Ionisation potentials of donor molecules and charge transfer (CT) transition energies of the [60]fullerene adducts have been found to correlate in accordance with the Mulliken equation. From such correlation the electron affinity of [60]fullerene has been calculated to be 2.32 eV in solution. A good estimate for the sp2C–sp2C resonance integral β in benzenoid hydrocarbons has also been obtained from the observed CT transition energies.

A PASCAL'S TRIANGLE-LIKE APPROACH FOR THE DETERMINATION OF CHARACTERISTIC POLYNOMIAL COEFFICIENTS OF RECIPROCAL GRAPHS

Characteristic polynomial coefficients of three classes of graph, namely Ln + n(p), Cn + n(p) and K 1,n-1 + n(p), which are known to have reciprocal pairs of eigenvalues, have been shown to be generated by simple manipulation of the Pascals triangle.

Studies on labile chargetransfer complexes between o-chloranil and a series of phenols

Abstract The electron donor–acceptor (EDA) interactions between o -chloranil and a series of phenols have been studied in dioxan medium. Except for resorcinol, the EDA complexes are formed instantaneously on mixing the donor and the acceptor solutions and then they decay slowly into secondary products. In case of resorcinol, formation and decay of the EDA complex are slow and simultaneous. The kinetics of all these reactions have been studied spectrophotometrically and the formation constants of EDA complexes have been determined from kinetic data. The hν CT values change systematically as the number and position of the –OH groups change in the aromatic ring of the phenol moiety. From the trends in the hν CT values, the Huckel parameters ( h O and k C–O ) for the –OH group, required for a PMO calculation on phenols, have been obtained in a straightforward way and the values so obtained, viz., 1.8 and 1.0 respectively, are close to the ones (1.8 and 0.8) recommended by Streitwieser on the basis of other evidences.

Spectroscopic and thermodynamic study of charge transfer interaction between vitamin B6 and p-chloranil in aqueous ethanol mixtures of varying composition.

Charge transfer complexes of 1:1 stoichiometry have been found to form between vitamin B(6) (pyridoxine hydrochloride) and a series of electron acceptors including p-chloranil. Since vitamin B(6) is soluble in water while the electron acceptors are insoluble in water but soluble in ethanol, the medium chosen for study is water-ethanol mixture. From the trends in the CT absorption bands the vertical ionization potential of vitamin B(6) has been determined to be 8.12 eV. The enthalpy and entropy of formation of the complex between p-chloranil and vitamin B(6) have been determined by estimating the formation constant (K) spectroscopically at four different temperatures in 75% ethanol-water mixture. Again, the magnitude of K has been found to decrease noticeably with decrease in dielectric constant of the medium (as the percentage of ethanol in the aqueous-ethanol mixture is increased). A plausible explanation for this has been given in terms of hydrolysis of pyridoxine hydrochloride.

Strongly subspectral pairs in C50+10n and C60+12n fullerenes via a common generic graph

A convenient scheme has been developed for drawing the Schlegel digrams (graphs) of C50+10n and C60+12n (n=integer) fullerenes maintaining five-fold and six-fold rotational symmetry, respectively. It has been found that after symmetry-factorisation, 10+2n eigenvalues common to C50+10n and C60+12n fullerenes can be obtained from a generic graph and for this reason (C60, C72), (C70, C84), (C80, C96) ... , corresponding to n=1, 2, 3, ... respectively, are strongly subspectral pairs having 12, 14, 16, ... common eigenvalues respectively. Of the 10+2n common eigenvalues, n+3 can be expressed in the analytic form: λj= -1+2 cos[jπ/(n+4)], j=1, 2, ... n+3. The other n+7 common eigenvalues can be obtained from a weighted linear chain whose characteristic polynomial can be easily derived by means of a recently developed scheme; a sample calculation for n=1 has been shown. Results for a number of subspectral pairs have been tabulated.

Characteristic polynomials of linear polyacenes and their subspectrality

Coefficients of characteristic polynomials (CP) of linear polyacenes (LP) have been shown to be obtainable from Pascal’s triangle by using a graph factorisation and squaring technique. Strong subspectrality existing among the members of the linear polyacene series has been shown from the derivation of the CP’s. Thus it has been shown that the entire eigenspectrum of ann-ring LP is included in that of (2n + 1)-ring LP. Correspondence between the eigenspectra of linear chains and LP’s is brought out by a recently developed vertex-alternation and squaring algorithm.

Aggregation of [70]fullerene in presence of acetonitrile: A chemical kinetic experiment

[70]fullerene solutions in carbon tetrachloride and o-xylene exhibit a noteworthy spectral variation with time when acetonitrile is added. This has been ascribed to self-aggregation of [70]fullerene caused by the repulsion between polar acetonitrile and hydrophobic [70]fullerene, and the aggregation numbers have been determined from a kinetic scheme and also from a scanning electron microscopic study. The numbers thus obtained follow a cuboctahedral stacking pattern proposed recently and also agree with the magic formula n=55+3m (m=1 to 14) proposed by Branz et al. for [60]fullerene clusters [Phys. Rev. B. 66, 094107 (2002)].

Study of a novel reaction between N,N′-diphenylthiourea and p-chloranil through a charge-transfer intermediate

The well-known electron acceptor, p-chloranil (A) and donor, N,N′-diphenylthiourea (B) have been observed to form a labile charge-transfer (CT) complex (AB), which decays slowly into two products viz. 2,3,5-trichloro-6-(N,N′-diphenylthioureido)benzo-1,4-quinone (P) and 5,6-dichloro-2,3-(N,N′-diphenylthioureylene)benzo-1,4-quinone (Q). The final products have been isolated in pure form and one of them, P, has been shown to exhibit sensitive solvatochromism. A detailed kinetic study of the decay process of the CT complex has been carried out and based on kinetic data, the following steps have been suggested for the decay process.