Spectral investigations on 2,3-bis(chloromethyl)-1,4- anthraquinone: solvent effects and host–guest interactions

Two solvent-induced variable host-guest two-dimensional binary frameworks mediated by hydrogen bonding

Two-dimensional binary hydrogen-bonded organic frameworks constructed from 1,3,5-benzenetricarboxylic acid (TMA) and 4,4'-biphenyldicarboxylic acid (BDA) on highly oriented pyrolytic graphite (HOPG) were investigated by scanning tunneling microscopy (STM) in heptanoic acid and octanoic acid solvents. High-resolution STM observations demonstrated that various assemblies of hydrogen-bonded networks are strongly dependent on the nature of the solvent. Well-ordered porous rectangular flowerlike networks were revealed at the heptanoic acid/HOPG interface, whereas two different coexisting densely packed guest-host BDA/TMA structures were observed at the octanoic acid/HOPG interface. It is suggested that the stabilization of the binary networks is possibly associated with the solvent chain length, and longer-chain solvents favored the formation of porous polymorphic networks.

Excited-state proton coupled charge transfer modulated by molecular structure and media polarization

Charge and proton transfer reactions in the excited states of organic dyes can be coupled in many different ways. Despite the complementarity of charges, they can occur on different time scales and in different directions of the molecular framework. In certain cases, excited-state equilibrium can be established between the charge-transfer and proton-transfer species. The interplay of these reactions can be modulated and even reversed by variations in dye molecular structures and changes of the surrounding media. With knowledge of the mechanisms of these processes, desired rates and directions can be achieved, and thus the multiple emission spectral features can be harnessed. These features have found versatile applications in a number of cutting-edge technological areas, particularly in fluorescence sensing and imaging.

Tuning photoinduced intramolecular electron transfer by electron accepting and donating substituents in oxazolones

The solvatochromic and spectral properties of oxazolone derivatives in various solvents were reported. Fluorescence spectra clearly showed positive and negative solvatochromism depending on substituents. The solvatochromic plots and quantum chemical computations at DFT-B3LYP/6-31 + G(d,p) level were used to assess dipole moment changes between the ground and the first excited singlet-states. The electron accepting nitro substituent at the para-position increased the π-electron mobility, however, the 3,5-dinitro substituent decreased the π-electron mobility as a result of inverse accumulation of the electronic density as compared with that of its ground state. Experimental and computational studies proved that the photoinduced intramolecular electron transfer (PIET) is responsible for the observed solvatochromic effects. We demonstrate that PIET can be finely tailored by the position of the electron accepting and donating substituents in the phenyl ring of the oxazolone derivatives. We propose that the photoactive CPO derivatives are new molecular class of conjugated push-pull structures using azlactone moiety as the π-conjugated linker and may find applications in photovoltaic cells and light emitting diodes.

Comments on the determination of excited state dipole moment of molecules using the method of solvatochromism

The present note comments on several publications which appeared in different journals containing many inaccurate statements and lacking honest citations of basic papers dealing with the application of solvatochromism to determine excited state dipole moments.

Solvent-controlled 2D host-guest (2,7,12-trihexyloxytruxene/coronene) molecular nanostructures at organic liquid/solid interface investigated by scanning tunneling microscopy

The two-dimensional (2D) self-assembled networks of 2,7,12-trihexyloxytruxene (Tr) are shown to accommodate coronene guest molecules on highly oriented pyrolytic graphite (HOPG) surfaces. The host-guest structures are revealed by scanning tunneling microscopy (STM) at liquid/solid interfaces. The effect of solvents on the host-guest structures is intensively investigated in different solvents such as 1,2,4-trichlorobenzene (TCB), 1-phenyloctane, 1-octanol, and tetradecane. In contrast to the similar 2D hexagonal self-assembly of Tr host template on HOPG in different solvents, the formation of host-guest nanostructures of coronene in Tr 2D network strongly depend on the polarity of the solvents. The thermodynamic equilibrium during the host-guest assembly process is discussed, and the solvent-guest interaction is proposed as a main contributor for the observed solvent effect in the 2D host-guest self-assembly process. The results are significant to surface host-guest chemistry and nanopatterning.

Molecular recognition of 1,5 diamino anthraquinone by p-tert-butyl-calix(8)arene

The molecular recognition properties of p-tert-butyl-calix(8)arene with 1,5 -diamino anthraquinone (1,5 DAAQ) were studied by using UV-Visible and Fluorescence spectroscopic techniques. The binding constant was determined by using the Benesi-Hilde brand expression. It was found that the host-guest complex was formed between 1,5 DAAQ and p-tert-butyl- calix(8)arene in the 1:2 Stoichiometry ratio.

Spectrofluorometric studies on the interaction between oxacalix[6]arene-locked trizinc(II)porphyrins and crystal violet

A new fluorogenic oxacalix[6]arene bearing three zinc(II) porphyrin groups (1) was prepared. When crystal violet (CV) was bound to 1, fluorescence intensity of 1 was quenched regularly. This indicates that 1 and CV formed a 1:1 complex and the association constant was calculated. The inclusion mechanism was also discussed. This new fluorometric method was developed for rapid determination of CV with a good linearity in the concentration range of 1.40-37.4 micromolL(-1). The method was applied for the determination of CV in synthetic samples successfully.

Study of preferential solvation of 2,6-diaminoanthraquinone in binary mixtures by absorption and fluorescence studies

The role of solute-solvent and solvent-solvent interaction on the preferential solvation characteristics of 2,6-diaminoanthraquinone (DAAQ) has been analysed by monitoring the optical absorption and fluorescence emission spectra. Binary mixtures consist of dimethylformamide (DMF)-ethanol (EtOH), DMF-dimelthylsulfoxide (DMSO), benzene (BZ)-DMF and acetonitrile (ACN)-DMF. The optical absorption spectra maximum and emission spectra maximum of DAAQ show the changes with varying the solvents and change in the composition in the case of binary mixtures. Non-ideal solvation characteristics are observed in all binary mixtures. It is found that at certain concentrations two mixed solvents interact to form a common structure with a nu(12) (wave number in cm(-1)) value not always intermediate (nu(1) and nu(2)) between the values of the solvents mixed. Synergistic effect is observed in the case of DMF-EtOH mixtures. The preferential solvation parameters local mole fraction X(2)(L), solvation index delta(S2), exchange constant K(12) are calculated in all binary mixtures expect in the case of DMF-BZ mixture and DMF-EtOH mixture in the ground state. We have also monitored excitation wavelength effect on the probe molecule in aprotic polar and protic polar solvents.

Solvatochromic study of 1,2-dihydroxyanthraquinone in neat and binary solvent mixtures

Preferential solvation of a solvatochromic probe has been studied in binary mixtures comprising of a non-protic and a protic solvent. The non-protic solvents employed are carbon tetrachloride (CCl(4)), acetonitrile (AcN) and N,N-dimethyl formamide (DMF) and the protic solvents are methanol (MeOH) and ethanol (EtOH). The probe molecule exhibits different spectroscopic characteristics depending upon the properties of the solubilizing media. The observed spectral features provide an indication of the microenvironment immediately surrounding the probe. Solvatochromic shifts of the ground and excited states of the probe were analysed by monitoring the charge transfer absorption band and the fluorescence emission spectra in terms of the solute-solvent and solvent-solvent interactions. Fluorescence emission spectra show the dual emission due to excited state proton transfer nature of the probe molecule. The effect of solvent and the excitation energy on dual emission are also studied. The observed magnitude of the Stokes shift in the above solvents has been used to deduce experimentally the dipole moment ratio of the probe molecule for the excited state to the ground state. The dipole moment of excited state is higher than the ground state.

Absorption, fluorescence studies and ab initio calculations on binary mixture of p-dimethylaminobenzaldehyde

Absorption as well as fluorescence emission studies of p-dimethylaminobenzaldehyde (DMABA) in solvents with different polarity have been reported by varying the concentration of the solute. Dual fluorescence corresponding to the non-polar (NP) and twisted intramolecular charge transfer (TICT) states has been observed. The optimized geometry of DMABA was evaluated using ab-initio theory at various levels. The optimized geometries of the hydrogen bonded complexes with the solvent molecules were also calculated with the theory Hartree Fock at the basis set 6-31+G (HF/6-31+G). The results have been used to understand the structure of the molecule and the spectral changes in terms of hydrogen bonding and solute-solvent interaction.

Solvatochromism, Preferential Solvation of 2,3-Bis(Chloromethyl)-1,4-Anthraquinone in Binary Mixtures and the Molecular Recognition Towards p-Tert-Butyl-Calix[4]arene

Optical absorption and fluorescence emission spectra of 2,3-bis(chloromethyl)-1,4-anthraquinone (DCMAQ) in single solvents namely, carbon tetrachloride, acetonitrile, chloroform, propan-2-ol and its binary mixtures [carbon tetrachloride/chloroform, chloroform/acetonitrile, chloroform/propan-2-ol] have been investigated. The preferential solvation of DCMAQ in above mixtures has been studied by monitoring the absorption and fluorescence spectra of DCMAQ. The spectral features indicate that DCMAQ is preferentially solvated by CHCl(3) in the above mixtures. This can be elucidated from the local mole fraction, non-linearity in transition energy plot, preferential solvation index (delta (s2)) and (f2/f1) values. Molecular recognition properties of p-tert-butylcalix[4]arene (tBC) to DCMAQ via hydrogen bonding and pi-pi interaction were sensed successfully on the basis of absorption and fluorescence emission spectroscopies, by which the stoichiometry ratio and the binding constant of the tBC-DCMAQ complex were determined.