A. T. Oza

Dc and ac conductivity of barium hydrogen phosphate (BaHPO4)

D.C. conductivity of the ferroelectric BaHPO 4 is measured and is found to lie between usual conductivities of semiconductor and insulator. Its temperature dependence shows intrinsic conduetion in defwctive crystals due to H + ions. The a.c. conductivity calculated from the measured dielectric constant follows σ-ω 1.54 , a power law. Frequency of 20 kHz resolves the resistivity peak of a.c. conduction into two Gaussians. The Inσ vs f plots at different temperatures show an exponential dependence and existence of a focal point.

Electrical Conductivity of Phenoxazine-Iodine (2:3) and Phenothiazine-Iodine (2:3) Crystals

Abstract Single crystals of phenoxazine-iodine (2 : 3) and phenothiazine-iodine (2 : 3) salts are found to be highly conducting ([sgrave] R.T. = 5–20 ohm−1 cm−1). The observed deviation from the exponential temperature dependence of the conductivities is ascribed to the degenerate semiconducting phases or alternatively to the metallic phases with impurities. However, phenoxazine-iodine and phenothiazine-iodine are perfect semiconductors below 220° K with activation energies of 0.12 eV and 0.14 eV, respectively. The absorption features related with (phenoxazine)+ 2 and (phenothiazine); cations are observed in the infrared spectra of the salts.

Spectroscopic Study of Ternary CT Complexes Based on the Organometallic Donor – Bis(Diphenylglyoximato)NiII

The infrared spectra of the ternary complexes based on the organometallic chelate, namely, bis(N-diphenylglyoximato) NiII working as an electron donor with standard organic acceptors like TCNQ, TCNE, chloranil, and DDQ have been studied for the first time keeping iodine as common acceptor for the four complexes. It is found that binary complexes of Ni (Hdpg)2 are semiconductors while the four ternary complexes exhibit semimetallic behavior. However, in chloranil and DDQ complexes, this modification is not as pronounced as observed in TCNQ and TCNE complexes.

Kuhn Periodicity in Oligoanilines and Oligoaniline–Iodine Complexes

ABSTRACT Spectroscopic work on eight-ring oligoanilines, namely emeraldine, nigraniline, and pernigraniline, has been performed. Infrared spectra are obtained with and without iodine to study the effect of complexation with iodine. Spectra of these even-numbered systems show Kuhn periodicity (paired rings). The number of Gaussian curves shows the delocalized charge between two or more consecutive rings. Thus, emeraldine shows three Gaussian curves. As the quinonoid resonance is established, it electronically shorts two neighboring rings. This leads to two Gaussian curves in nigraniline and one Gaussian curve in pernigraniline. Thus, the quinonoid resonance suppresses Kuhn periodicity and establishes long-range order.

FTIR Spectroscopy of Hydrogen-Bonded Cu(N-R-Salim)2 Dye Complexes

Some of bis(N-R-salicylaldiminato)CuII where R = H, CH3, C2H5, and C6H5 are found to have copper chains in one direction of the crystals. These 1-d systems are hydrogen bonded with six highly polarizable dyes namely Para red, Congo red, Direct red, Bismark brown, Evans blue, and Trypan blue. The Fourier transform infrared (FTIR) spectra reveal infrared absorption edge and its modification with exciton-phonon coupling. Threshold energies for the formation of excitons with phonon emissions are observed. When exciton-phonon coupling is weak, a large number of phonon bands are observed in the edge spectrum. Free excitons are strongly bound and bound excitons are weakly bound to phonons.

Spectroscopy of Charge Transfer Complexes of Aniline Blue

Charge transfer (CT) complexes of aniline blue (AB) were prepared with standard organic acceptors such as TCNQ, TCNE, DDQ, and chloranil and studied with UV-VIS-NIR spectra showing σ→π* and π→π* transitions along with free-carrier absorption due to scattering of light particles which has been found involving phonon–photon, electron–photon, and electron–electron scattering. Infrared spectra contain half power beta density due to hopping conduction and an asymmetric band corresponding to A(k) = A0k exp(−bk) as absorption associated with diffraction of IR light from the crystalline particles.

Infrared Spectroscopy of Charge Transfer Complexes of D-Luciferin

D-luciferin, the luminescent material of firefly, forms charge transfer complexes with organic acceptors such as TCNQ, TCNE, chloranil, DDQ, and iodine. The infrared spectra reveal indirect allowed transition across a single particle gap in the IR range and guassian background absorption. TCNE complex shows triangular distribution due to imperfect nesting. Chloranil complex shows oscillations in the density of states without much dampingthe.

FTIR Spectra of Hydrogen-Bonded Inclusion Compounds of Iodine

The inclusion compounds of iodine such as α-cyclodextrin-KI-I2-4H2O, β-cyclodextrin-KI-I2-H2O, and amylose-iodine are hydrogen bonded with dyes such as Para red, Congo red, Direct red, Bismark brown, Trypan blue, and Evans blue. Hydrogen bonding of these with dyes containing O–H and N–H occurs in glucosidic oxygen atoms or O–H groups of the polysaccharides. Excitons are emitted and absorbed by the electrons along the iodine chains as revealed by the analysis, which reduces band gap along the polyiodide chains.

Spectroscopic Study of Charge Transfer Complexes of Biphenyl

Biphenyl is a well-known photoconductor with a band gap of 0.16 eV lying in the infrared range. In the present work, the charge transfer complexes of biphenyl with the acceptors such as 7,7,8,8-tetracyano-p-quinodimethane, N,N,N′,N′-tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), Chloranil, and iodine have been studied with ultraviolet-visible near infrared and infrared spectroscopy. Biphenyl-TCNE and biphenyl-DDQ show spin-orbit splitting of valence band and consequently show three optical transitions. Biphenyl-iodine and biphenyl-chloranil show nondegenerate semiconducting nature. The charge transfer complexes (CTCs) show an asymmetric Gaussian band associated with small polaron model. Many of the CTCs also show a scattering of charge carriers by light particles as expected in photoconductors.

Infrared Spectra of Charge Transfer Complexes of Biocytin With Organic Acceptors

The infrared (IR) spectra of the well-known biomolecules called biocytin and their charge transfer complexes with standard organic acceptors such as TCNQ (7,7,8,8-tetracyano-p-quinodimethane), TCNE (tetracyano-p-ethylene), DDQ (2,3- dichloro-5,6-dicyano-p-benzoquinone), chloranil, and iodine have been studied in the present work. The spectrum of biocytin contains a beta density at high frequency and a slightly asymmetric triangular distribution as well as a U-shaped distribution at low frequency, the latter being associated with anisotropic disorder. Weak charge transfer from TCNE and iodine reduces the width of U-shaped distribution and makes the triangular peak more asymmetric. Strong CT interactions with TCNQ and DDQ make the triangular peak in absorption become a Gaussian distribution. The strongest interaction with chloranil leads to oscillations in the density of states with square-root singularities. Toward the high frequency side, the interband transition do occur but with either spin-orbit splitting or exciton-phonon coupling. There is correlated hopping in biocytin-iodine complex.