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UV–Vis spectral investigations of electron donor–acceptor complexes of laser dye 2,6-Diethyl-4,4-difluoro-1,3,5,7-tetramethyl-8-(4′-hydroxyphenyl)-4-bora-3a,4a-diaza-s-indecene ( 1c ) with chloranils and fullerenes are reported in toluene medium. Well defined charge transfer (CT) absorption bands have been located in the visible region. Oscillator strengths, transition dipole and resonance energies of the CT complexes have been estimated. Vertical ionization potential of 1c has been determined utilizing Mulliken’s equation. A possible mechanism for the interaction between electronic subsystems of chloranils, [60]- and [70]fullerenes with three different BODIPY dyes ( 1a , 1b and 1c shown in Fig. 1 ) have been discussed in comparing the parameters like degree of charge transfer and binding constant in nonpolar toluene. Comparison of 1c complexes is done with DFT/B3LYP/6-31G optimized gas phase geometries. [ABSTRACT FROM AUTHOR]

Abstract: The interactions of FeIIPc and FeIIIPc with π-acceptor 2,3,5,6-tetrachloro-1,4-benzoquinone (p-chloranil, p-CHL) have been investigated spectroscopically (UV/vis and FT-IR) and spectrofluorimetrically at three different temperatures. The stoichiometry of the complexes was found to be 1:1. The results of electronic spectral studies indicated that the formation constant for FeIIPc-p-CHL system is found to be higher than that for FeIIIPc-p-CHL system. This observation is well supported by the results of fluorescence quenching studies and the association constants calculated for FeIIPc-p-CHL system is 4.2×103 molL−1 and that for FeIIIPc-p-CHL system is 2.2×103 molL−1. The data are discussed in terms of physico-chemical parameters viz. molar extinction coefficient, oscillator strength, dipole moment, ionization potential, dissociation energy and thermodynamic parameters. The results indicated that the formation of π–π CT complex is spontaneous and endothermic. Preliminary studies indicated that the CT complex can effectively be used as a colorimetric agent for sensing amino acids and amines. [Copyright &y& Elsevier]

Abstract: The molecular complexes of the donors ketaconazole (KTZ) and oxatomide (OXA) drugs with 2,3,5,6-tetrachloro-1,4-benzoquinone (p-chloranil, p-CHL) have been investigated spectroscopically (UV–vis, FT-IR and 1H NMR) and spectrofluorimetrically in different solvents and temperatures. The stoichiometry of the complexes was found to be 1:1. The data are discussed in terms of formation constant, molar extinction coefficient, oscillator strength, dipole moment, ionization potential, dissociation energy and thermodynamic parameters. The results indicated that the formation of molecular complex is spontaneous and endothermic. The fluorescence quenching studies indicated that the interaction of the donors is spontaneous and the fluorescence quenching increased with an increase in the intensity of complexation with the acceptor. [Copyright &y& Elsevier]

Abstract: Series of 1,n-dicarbazolylalkanes and 1,n-di(3-methylcarbazolyl)alkanes (where n =1–5) were synthesized and the molar extinction coefficients, equilibrium constants, enthalpies, and entropies of their charge-transfer (CT) complexes with the π-acceptors p-chloranil, tetracyanoethylene, and tetracyanoquinodimethane were investigated. 1,n-Di(3-methylcarbazolyl)alkanes formed CT complexes with higher equilibrium constants, more negative enthalpies and entropies than 1,n-dicarbazolylalkanes. Vibrational spectra of CT complexes of one of the donor molecules (1,4-dicarbazolylbutane) with all three acceptors were compared. [Copyright &y& Elsevier]

Abstract: Electron donor acceptor complexes (EDA) of the 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) as a rich donor were spectrophotometrically discussed and synthesized in solid form according the interactions with different nine of usual π-acceptors like 2,3,5,6-tetrachlorocyclohexa-2,5-diene-1,4-dione (p-chloranil; p-CHL), tetrachloro-1,2-benzoquinone (o-chloranil; o-CHL), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetracyanoquinodimethane (TCNQ), 2,6-dichloroquinone-4-chloroimide (DCQ), 2,6-dibromoquinone-4-chloroimide (DBQ), 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid; CLA), N-bromosuccinimide (NBS), 2,4,6-trinitrophenol (picric acid; PA). Spectroscopic and physical data such as formation constant (K CT), molar extinction coefficient (ɛ CT), standard free energy (ΔG°), oscillator strength (f), transition dipole moment (μ), resonance energy (R N) and ionization potential (I p) were estimated in chloroform or methanol at 25°C. Based on the elemental analysis and photometric titrations the CT-complexes were formed indicated the formation of 1:1 charge-transfer complexes for the o-CHL, TCNQ, DCQ, DBQ and NBS acceptors but 1:3 ratio for p-CHL, DDQ, CLA and PA, respectively. The charge-transfer interactions were interpretative according to the formation of dative ion pairs [18C6 +, A −], where A is acceptor. All of the resulting charge transfer complexes were isolated in amorphous form and the complexes formations on IR and 1H NMR spectra were discussed. [Copyright &y& Elsevier]

Abstract: A two new charge transfer complexes formed from the interactions between o-tolidine (o-TOL) and picric (PA) or chloranilic (CA) acids, with the compositions, [(o-TOL)(PA)2] and [(o-TOL)(CA)2] have been prepared. The 13C NMR, 1H NMR, 1H-Cosy, and IR show that the charge-transfer chelation occurs via the formation of chain structures O–H⋯N intermolecular hydrogen bond between 2NH2 groups of o-TOL molecule and OH group in each PA or CA units. Photometric titration measurements concerning the two reactions in methanol were performed and the measurements show that the donor–acceptor molar ratio was found to be 1:2 using the modified Benesi–Hildebrand equation. The spectroscopic data were discussed in terms of formation constant, molar extinction coefficient, oscillator strength, dipole moment, standard free energy, and ionization potential. Thermal behavior of both charge transfer complexes showed that the complexes were more stable than their parents. The thermodynamic parameters were estimated from the differential thermogravimetric curves. The results indicated that the formation of molecular charge transfer complexes is spontaneous and endothermic. [Copyright &y& Elsevier]

Abstract: In the present work, we report the synthesis and characterization of novel charge-transfer complexes of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorodicyanoquinone, picric acid and duraquinone). We also evaluated their thermal and electrochemical properties and we conclude that these complexes are frequency dependent. Charge-transfer complex between thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigma acceptors are more conducting than with pi acceptors. [Copyright &y& Elsevier]

Abstract: The interactions of the electron donors 2-aminopyridine (2APY) and 3-aminopyridine (3APY) with the π-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2-chloro-1,3,5-trinitrobenzene (picryl chloride, PC), and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge transfer (CT) complexes were recorded. Photometric titration showed that the stoichiometries of the reactions were fixed and depended on the nature of both the donor and the acceptor. The molecular structures of the CT-complexes were, however, independent of the position of the amino group on the pyridine ring and were formulated as [(APY)(TCNE)], [(APY)(DDQ)], [(APY)(PC)], and [(APY) (chloranil)]. The formation constants (K CT), charge transfer energy (E CT) and molar extinction coefficients (ɛ CT) of the formed CT-complexes were obtained. [Copyright &y& Elsevier]

Abstract: A highly sensitive spectrofluorimetric method was developed for the first time, for the analysis of three fluoroquinolones (FQ) antibacterials, namely enrofloxacin (ENR), levofloxacin (LEV) and ofloxacin (OFL) in pharmaceutical preparations through charge transfer (CT) complex formation with 2,3,5,6-tetrachloro-p-benzoquinone (chloranil,CLA). At the optimum reaction conditions, the FQ–CLA complexes showed excitation maxima ranging from 359 to 363nm and emission maxima ranging from 442 to 488nm. Rectilinear calibration graphs were obtained in the concentration range of 50–1000, 50–1000 and 25–500ngmL−1 for ENR, LEV and OFL, respectively. The detection limit was found to be 17ngmL−1 for ENR, 17ngmL−1 for LEV, 8ngmL−1 for OFL, respectively. Excipients used as additive in commercial formulations did not interfere in the analysis. The method was validated according to the ICH guidelines with respect to specificity, linearity, accuracy, precision and robustness. The proposed method was successfully applied to the analysis of pharmaceutical preparations. The results obtained were in good agreement with those obtained using the official method; no significant difference in the accuracy and precision as revealed by the accepted values of t- and F-tests, respectively. [Copyright &y& Elsevier]

Abstract: The solid charge-transfer complexes formed in the reaction of the electron donor 1,4,7-trimethyl-1,4,7-triazacyclononane (TMTACN) with the acceptors iodine, tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) have been isolated. These were characterized through electronic and infrared spectra as well as thermal and elemental analysis. The results show that the formed solid CT-complexes have the formulas [(TMTACN)I]I3, [(TMTACN)(TCNE)5] and [(TMTACN)(TCNQ)3] in full agreement with the known reaction stoichiometries in solution. The chloranil CT-solid complex cannot be isolated in pure form. [Copyright &y& Elsevier]

Abstract: Charge transfer complexes of 1:1 stoichiometry have been found to form between vitamin B6 (pyridoxine hydrochloride) and a series of electron acceptors including p-chloranil. Since vitamin B6 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 B6 has been determined to be 8.12eV. The enthalpy and entropy of formation of the complex between p-chloranil and vitamin B6 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. [Copyright &y& Elsevier]

Abstract: The interaction of the interesting polynitrogen cyclic base 1,4,7-trimethyl-1,4,7-triazacyclononane (TMTACN) with the σ-acceptor iodine and π-acceptors tetracyanoethylene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetrachloro-p-benzoquinone (chloranil) have been studied spectrophotometrically and cyclic voltametrically in chloroform at 20°C. Based on the obtained data, the formed charge-transfer complexes were formulated as [(TMTACN)I]+·I3 −, [(TMTACN)(TCNE)5], [(TMTACN)(TCNQ)3] and [(TMTACN)(chloranil)3] where the stoichiometry of the reactions, donor:acceptor molar ratios, were shown to equal 1:2 for iodine complex, 1:3 for chloranil and TCNQ complexes and 1:5 for TCNE complex. [Copyright &y& Elsevier]

Abstract: Charge transfer complexes between colchicine as donor and π acceptors such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), p-chloranil (p-CHL) have been studied spectrophotometrically in dichloromethane at 21°C. The stoichiometry of the complexes was found to be 1:1 ratio by the Job method between donor and acceptors with the maximum absorption band at a wavelength of 535, 585 and 515nm. The equilibrium constant and thermodynamic parameters of the complexes were determined by Benesi–Hildebrand and van’t Hoff equations. Colchicine in pure form and in dosage form was applied in this study. The formation constants for the complexes were shown to be dependent on the structure of the electron acceptors used. [Copyright &y& Elsevier]

Abstract: Dimer model compounds of polyvinylcarbazoles (1,n-di(N-carbazolyl)alkanes, when n =1–5) were synthesized to model the effects of distance and orientation between carbazole groups in polymeric systems. Charge-transfer (CT) complexes of carbazole, N-ethylcarbazole and 1,n-di(N-carbazolyl)alkanes with p-chloranil (p-CHL) have been investigated spectrophotometrically in dichloromethane. The colored products are measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptor. The formation constants of the CT complexes were determined by the Benesi–Hildebrand equation. The thermodynamic parameters were calculated by Van’t Hoff equation. Stochiometries of the complexes formed between donors and acceptor were defined by the Job''s method of the continuous variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands. [Copyright &y& Elsevier]

Abstract: Dimer model compounds of polyvinylanthracenes (1,n-di(9-anthryl)alkanes, when n =1–5) were synthesized to model the effects of distance and orientation between anthracene groups in polymeric systems. Charge transfer (CT) complexes of anthracene, 9-methylanthracene and 1,n-di(9-anthryl)alkanes with p-chloranil (p-CHL) have been investigated spectrophotometrically in dichloromethane. The colored products are measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptor. The formation constants of the CT complexes were determined by the Benesi–Hildebrand equation. The thermodynamic parameters were calculated by Van’t Hoff equation. Stochiometries of the complexes formed between donors and acceptor were defined by the Job''s method of the continuous variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands. [Copyright &y& Elsevier]

Abstract: The interaction of the mixed oxygen–nitrogen cyclic base, N,N′-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DD18C6) with π-acceptors such as picric acid (HPA) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) has been studied spectrophotometrically in chloroform at 25°C. The results obtained indicate the formation of 1:4 charge–transfer complexes with the general formula (DD18C6)(acceptor)4. The electronic and infrared spectra of charge–transfer complexes along with the 1H NMR spectra were recorded and discussed. Based on the data obtained, the complexes were formulated as [(DD18C6H2)(HPA)2](PA)2 and [(DD18C6H2)(DDQ)2](DDQH)2. A general mechanism explaining the formation of the DDQ complex has been suggested. [Copyright &y& Elsevier]

The reaction of ferric(III) acetylacetonate (donor), Fe(acac)3, with iodine as a σ-acceptor and with other different π-acceptors have been studied spectrophotometrically at room temperature in chloroform. The π-acceptors used in this investigation are 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), p-chloranil and 7,7′,8,8′-tetracyanoquinodimethane (TCNQ). The results indicate the formation of 1:1 charge-transfer complexes with a general formula, [Fe(acac)3 (acceptors)]. The iodine complex was shown to contain the triiodide species, [Fe(acac)3]2I+I3-, based on the electronic absorptions as well as on the Far-infrared absorption bands characteristic for the non-linear triiodide species, I3-, with C2v symmetry. The proposed structure of this complex is further supported by thermal and middle infrared measurements. [Copyright &y& Elsevier]

o-Chloranil has been shown to form 1:1 molecular complexes with pyridine and 2-, 3- and 4-picolines in CCl4 medium. Isosbestic points have been found but charge-transfer bands could not be detected. The formation constants of the complexes exhibit a very good linear free energy relationship from which the Hammett ρ parameter for the complexation reaction is found to be −3.67. [ABSTRACT FROM AUTHOR]