Puspendu K. Das

Schiff base linked ferrocenyl complexes for second-order nonlinear optics

Abstract A series of substituted ferrocenyl compounds where one of the cyclopentadienyl rings is linked to an aromatic Schiff base, have been synthesized and analyzed for their second-order nonlinearity (β). Two photon fluorescence corrected β, of these complexes correlates well with the electron withdrawing nature of the substituted benzene ring. The well-known two-state model has been invoked to rationalize the observed values of the first hyperpolarizability, β, of these complexes. The metal to ligand charge transfer (MLCT) transition dominates their second-order response. These compounds form charge transfer (CT) complexes with acceptors such as iodine, p-chloranil (CA), 2, 3-dichloro-5, 6-dicyano-1, 4-benzoquinone (DDQ), tetracyanoethylene (TCNE), and 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ). The CT complexes exhibit much higher second-order response. A series of bisferrocenyl complexes where two ferrocene moieties are linked through the same aromatic Schiff base spacer has also been synthesized and characterized. The β values of the bisferrocenyl complexes and their CT counterparts are much higher than the corresponding monoferrocene complexes. In all these compounds there is a strong resonant contribution to β due to the MLCT transition around 532 nm. The dispersion free hyperpolarizability, β0 of these complexes have also been calculated using the two-state model.

Metal-assisted red light-induced efficient DNA cleavage by dipyridoquinoxaline-copper(II) complex.

Complete cleavage of double stranded pUC19 DNA by the complex [Cu(dpq)2(H2O)](ClO4)2 (dpq, dipyridoquinoxaline) has been observed on irradiation at 694 nm from a pulsed ruby laser, assisted by the metal d-band transition as well as the quinoxaline triplet states in the absence of any external additives.

Dynamics of I*(2P1/2) production from fluorinated alkyl iodides at 266, 280, and ∼305 nm

In this paper, we present I*(2P1/2) quantum yield, φ* from the gas phase photodissociation of a series of perfluoroalkyl iodides at three different wavelengths 266, 280, and ∼305 nm. The iodine atoms in the ground I(2P3/2) and spin–orbit excited I*(2P1/2) states were monitored directly by a two photon laser induced fluorescence scheme. The I* quantum yields for the fluorinated alkyl iodides are found to be much higher than their corresponding alkyl iodide analogs over the entire A band. However, φ* remains more or less unchanged as a function of photolysis wavelength for the perfluoroalkyl iodides with the exception of CF3I in which it drops monotonically as a function of wavelength. Unlike in normal alkyl iodides, branching at the α position does not affect the φ* in perfluoroalkyl iodides. The prediction of I* yield using the one dimensional Landau–Zener soft-radical-impulse model is opposite to what is seen from our measurements. In all the fluorinated alkyl iodides, the CF3 in-plane rocking mode which...

First-order hyperpolarizabilities of octupolar aromatic molecules: symmetrically substituted triazines

The first hyperpolarizabilities of some symmetrically substituted triazines have been measured and compared with those of the corresponding symmetrically substituted benzenes. The octupolar triazines have higher quadratic polarizabilities than the corresponding octupolar benzenes. The triazine ring seems to be a better central acceptor than the benzene ring, but if it acts as a donor as in sym-triphenyl triazine, the nonlinearity improves further.

Quadratic nonlinearity of one- and two-electron oxidized metalloporphyrins and their switching in solution.

We report the quadratic nonlinearity of one- and two-electron oxidation products of the first series of transition metal complexes of meso-tetraphenylporphyrin (TPP). Among many MTPP complexes, only CuTPP and ZnTPP show reversible oxidation/reduction cycles as seen from cyclic voltammetry experiments. While centrosymmetric neutral metalloporphyrins have zero first hyperpolarizability, beta, as expected, the cation radicals and dications of CuTPP and ZnTPP have very high beta values. The one- and two-electron oxidation of the MTPPs leads to symmetry-breaking of the metal-porphyrin core, resulting in a large beta value that is perhaps aided in part by contributions from the two-photon resonance enhancement. The calculated static first hyperpolarizabilities, beta0, which are evaluated in the framework of density functional theory by a coupled perturbed Hartree-Fock method, support the experimental trend. The switching of optical nonlinearity has been achieved between the neutral and the one-electron oxidation products but not between the one- and the two-electron oxidation products since dications that are electrochemically reversible are unstable due to the formation of stable isoporphyrins in the presence of nucleophiles such as halides.

A model exact calculation of SHG coefficients in polysubstituted push—pull polyenes☆

We report the model exact second-harmonic generation coefficients

Ferrocenyl donor-organic acceptor complexes for second order nonlinear optics

(\beta^{exact})

Second harmonic generation coefficients in push-pull polyenes: A model exact study☆

in polysubstituted all-trans push—pull polyenes up to ten carbon atoms. The Pariser-Parr-Pople (PPP) model with standard molecular parameters has been used in the calculations. The two-state charge-transfer model in these systems is inadequate and an exact calculation is necessary to obtain reliable SHG coefficients. We find that for a fixed geometry,

Production of I*(2P1/2) in the ultraviolet photodissociation of α ‐branched alkyl iodides

\beta

Environmental and Excitonic Effects on the First Hyperpolarizability of Polar Molecules and Related Dimers

is enhanced if all the electron withdrawing substituents (pull) are successively placed from one end of the polyene chain and all the electron pushing groups (push) from the other. A twisted conformation of the polyene backbone leads to large SHG coefficients at the YAG laser frequency since the system approaches two-photon resonance. For a given chain length, the SHG coefficients increase with increase in the number of the push and pull groups.