Charge-Transfer Interaction of Aromatic Thiols with 2,3-Dichloro-5,6-dicyano-p-benzoquinone: Spectral and Quantum Mechanical Studies

Molecular tetrominoes: selective masking of the donor π-face to control the configuration of donor-acceptor complexes

Understanding the doping mechanism in organic semiconductors and generating molecular design rules to control the doping process are crucial for improving the performance of organic electronics. Even though controlling the location and orientation of the dopant along the semiconductor backbone is an important step in the doping mechanism, studies in this direction are scarce as it is a challenging task. To address this, herein, we incorporated π-face masked (strapped) units in 1,4-bis(phenylethynylene)benzene (donor) to control the acceptor (dopant) location along the trimer, donor-acceptor binding strength, and acceptor ionization. Two strapped trimers, PCP and CPC, are synthesized with control over the location of the strapped repeat unit in the trimer. The trimers are complexed with the 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) acceptor in solution. DFT calculations show that DDQ residing on the non-strapped repeat unit (the percentage of this configuration is at least ca. 73%) has the highest binding energy for both PCP and CPC. The percentage of dopant ionization is higher in the case of strapped trimers (PCP and CPC) compared to that of linear control trimers (PLP and LPL) and the completely non-strapped (PPP) trimer. The percentage of dopant ionization increased by 15 and 59% in the case of PCP and CPC respectively compared to that of PPP.

Charge transfer complexes of quinones in aqueous medium: spectroscopic and theoretical studies on interaction of cimetidine with novel substituted 1,4-benzoquinones and its application in colorimetric sensing of anions

For the first time, the charge transfer (CT) complexes of quinones in aqueous medium have been reported. A series of novel water soluble 1,4-benzoquinones possessing variable number of chloro and methoxy substituents has been employed as electron acceptors (MQ1-4) in the CT complexation with cimetidine (CTD) drug. The mechanism of the interaction has been investigated using various spectral techniques such as UV-Vis, (1)H NMR and FT-IR spectra. The rate of the CT interaction was observed to decrease with progressive replacement of chloro by methoxy substituent in the quinone and this variation is well supported by the formation constant and enthalpy of activation values. Ab initio DFT calculations predicted that the variation in the bond lengths of the carbonyl moieties and the charge densities on the carbonyl oxygen atoms depend largely on the nature of the substituent present in the quinone ring. Also, the HOMO(Donor)-LUMO(Acceptor) energy gaps correlate linearly with the formation constants of the CT complex. The equilibrium, kinetic, electrochemical and theoretical investigations of the CT interaction of these quinones indicated that progressive replacement of electron withdrawing chlorine atom (-I effect) by an electron releasing methoxy group (+M effect) makes these acceptors progressively weaker. The charge-transfer complex, formed between CTD and monomethoxy quinone derivative, has been employed as a new class of chromogenic sensor for the colorimetric sensing of fluoride and acetate ions.

Experimental and DFT studies on the vibrational and electronic spectra of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

Vibrational and electronic spectral measurements were made for 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Optimized geometrical structure and harmonic vibrational frequencies were computed by DFT(B3LYP, CAMB3LYP, B3P86, M062X, mPW3PBE and PBE1PBE) using 6-311++G(d,p) basis set. Complete assignments of the observed spectra were proposed. The absorption spectra of the compound were computed both in gas-phase and in CH(2)Cl(2) solution using TDCAMB3LYP/6-311++G(d,p) and PCM-TDCAMB3LYP/6-311++G(d,p) approaches, respectively, the calculated results provide a good description of positions of the bands maxima in the observed electronic spectrum.

Spectroscopic studies on the interaction of cimetidine drug with biologically significant sigma- and pi-acceptors

Spectroscopic studies revealed that the interaction of cimetidine drug with electron acceptors iodine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) resulted through the initial formation of ionic intermediate to charge transfer (CT) complex. The CT-complexes of the interactions have been characterized using UV-vis, (1)H NMR, FT-IR and GC-MS techniques. The formation of triiodide ion, I(3)(-), is further confirmed by the observation of the characteristic bands in the far IR spectrum for non-linear I(3)(-) ion with C(s) symmetry at 156 and 131cm(-1) assigned to nu(as)(I-I) and nu(s)(I-I) of the I-I bond and at 73cm(-1) due to bending delta(I(3)(-)). The rate of formation of the CT-complexes has been measured and discussed as a function of relative permittivity of solvent and temperature. The influence of relative permittivity of the medium on the rate indicated that the intermediate is more polar than the reactants and this observation was further supported by spectral studies. Based on the spectroscopic results plausible mechanisms for the interaction of the drug with the chosen acceptors were proposed and discussed and the point of attachment of the multifunctional cimetidine drug with these acceptors during the formation of CT-complex has been established.

Observation of intermolecular charge transfer in a quasi-one-dimensional molecular alloy system

X-band single-crystal electron paramagnetic resonance (EPR) studies of the molecular alloy [NO 2BzPy][Au 0.57Ni 0.43(mnt) 2] are presented in this paper. At room temperature, EPR spectra show both intense resonance signals (main signals) and weak satellite quartet lines. The characteristics of both intense and weak EPR signals depend on the magnetic field orientation. The main signals arise from two magnetically nonequivalent [Ni(mnt) 2] (-) anions, and their corresponding principal values of the g tensor are ( g x ') 1 = 2.04653, ( g y ') 1 = 2.00096, and ( g z ') 1 = 2.15319 and ( g x ') 2 = 2.04520, ( g y ') 2 = 1.99734, and ( g z ') 2 = 2.15361, respectively. The weak satellite lines, whose patterns strongly depend on the magnetic field direction, can be attributed to the hyperfine coupling of the electron spin with the (197)Au nucleus of the [Au(mnt) 2] (-) species. Density functional theory calculations for the spin and charge distributions of the dimer {[Ni(mnt) 2][Au(mnt) 2]} (2-) indicate that the hyperfine interaction of the electron spin with the (197)Au nuclear spins is caused, in part, by the charge transfer between the [Ni(mnt) 2] (-) and the [Au(mnt) 2] (-) species.