Search Results (9)

Two charge transfer compounds based on pyridazinium ylids were studied by electronic absorption spectroscopy in binary and ternary solutions, with the purpose of evaluating their descriptors of the first singlet excited state and to estimate the strength of the intermolecular interactions in protic solvents. The molecular descriptors of the excited state were comparatively estimated using the variational method and the Abe model of diluted binary solutions. Analysis of electronic properties using density functional theory was performed for several key solvents, in order to understand the solvatochromic behavior. The DFT calculations revealed that, in the polar and strongly interacting solvents, the carbanion and the terminal group become a stronger electron acceptor. The bathochromic shift of the ICT band was confirmed using DFT calculus. The ability of the two ylids to recognize and discriminate the solvents was analyzed with principal component analysis and with cluster analysis. Although the study was performed in 24 solvents, the results showed that the ylids were most sensitive to alcohols, so they can be a useful tool to identify and classify different types of low-alcoholic solvents. Full article

This article contains a comparative spectral analysis corroborated with the quantum mechanical computations of four cycloimmonium ylids. The spectral shift of the visible electronic absorption band of the studied molecules in 20 solvents with different empirical parameters is expressed by linear multi-parametric dependences that emphasize the intramolecular charge transfer (ICT) process. The nature of molecular interactions and their contribution to the spectral shift of the visible ICT band of solutes are also established in this manuscript. The results of the statistical analysis are used to estimate the cycloimmonium ylids’ excited dipole moment by the variational method, using the hypothesis of McRae. The importance of the structure of both the heterocycle and carbanion substituents to the stability and reactivity of the studied cycloimmonium ylids is underlined by the quantum mechanical computations of the molecular descriptors. Full article

The nature and strength of the molecular interactions were established by solvatochromic studies of 22 binary and 42 ternary diluted solutions of pyridinium–carbethoxy–anilidomethylid (PCAnM). The visible absorption band of PCAnM, due to an intramolecular charge transfer (ICT) from the carbanion towards the heterocycle, shows a great sensitivity to the solvent nature. The spectral data are analysed by linear energy relationship (LERS) and the contribution of each type of interaction to the total spectral shift is estimated. The results from the solvatochromic study and those obtained by quantum mechanical computations were correlated in order to estimate the excited state dipole moment of the studied methylid. The decrease of the dipole moment by excitation emphasized in this study corresponds to the ICT nature of the visible absorption band of the solute. The ternary solutions of PCAnM achieved in mixtures of water with primary alcohols (ethanol and methanol) show the dependence of the visible band on the molar fraction of water and give the difference between the interaction energies in molecular pairs of the type water–methylid and alcohol–methylid, computed based on the statistical cell model of ternary solutions. The decrease in strength of the hydrogen bond between PCAnM and the protic solvent molecules was estimated in the following order: water $>$ methanol $>$ ethanol. The results from this study can be utilized in Organic Chemistry to generate knowledge of the interactions with solvents when cycloimmonium methylids are used as precursors to obtain new heterocycles and also in Quantum Chemistry to obtain a better description of their excited electronic states. Full article

Three new tetraphenylethene (TPE) push–pull chromophores exhibiting strong intramolecular charge transfer (ICT) are described. They were obtained via [2 + 2] cycloaddition–retroelectrocyclization (CA-RE) click reactions on an electron-rich alkyne-tetrafunctionalized TPE (TPE-alkyne) using both 1,1,2,2-tetracyanoethene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄-TCNQ) as electron-deficient alkenes. Only the starting TPE-alkyne displayed significant AIE behavior, whereas for TPE-TCNE, a faint effect was observed, and for TPE-TCNQ and TPE-F₄-TCNQ, no fluorescence was observed in any conditions. The main ICT bands that dominate the UV–Visible absorption spectra underwent a pronounced red-shift beyond the near-infrared (NIR) region for TPE-F₄-TCNQ. Based on TD-DFT calculations, it was shown that the ICT character shown by the compounds exclusively originated from the clicked moieties independently of the nature of the central molecular platform. Photothermal (PT) studies conducted on both TPE-TCNQ and TPE-F4-TCNQ in the solid state revealed excellent properties, especially for TPE-F4-TCNQ. These results indicated that CA-RE reaction of TCNQ or F₄-TCNQ with donor-substituted are promising candidates for PT applications. Full article

The results obtained both in quantum chemical computation and in solvatochromic study of pyridinium di-carbethoxy methylid (PCCM) are correlated in order to estimate the electric dipole moment in the excited state of this molecule. This estimation is made by a variational method in the hypothesis that the molecular polarizability does not change in time of the absorption process. Ternary solutions of PCCM in protic binary solvents are used here, both establishing the contribution of each type of interaction to the spectral shift and to characterize the composition of the first solvation shell of PCCM. Results are compared with those obtained before for other binary solvents. The difference between the interaction energies in molecular pairs of PCCM-active solvent and PCCM-less active solvent was also estimated based on the cell statistical model of the ternary solutions. Full article

A series of ten push-pull chromophores comprising 1H-cyclopenta[b]naphthalene-1,3(2H)-dione as the electron-withdrawing group have been designed, synthesized, and characterized by UV-visible absorption and fluorescence spectroscopy, cyclic voltammetry and theoretical calculations. The solvatochromic behavior of the different dyes has been examined in 23 solvents and a positive solvatochromism has been found for all dyes using the Kamlet-Taft solvatochromic relationship, demonstrating the polar form to be stabilized in polar solvents. To establish the interest of this polyaromatic electron acceptor only synthesizable in a multistep procedure, a comparison with the analog series based on the benchmark indane-1,3-dione (1H-indene-1,3(2H)-dione) has been done. A significant red-shift of the intramolecular charge transfer band has been found for all dyes, at a comparable electron-donating group. Parallel to the examination of the photophysical properties of the different chromophores, a major improvement of the synthetic procedure giving access to 1H-cyclopenta[b]naphthalene-1,3(2H)-dione has been achieved. Full article

Two solution-processable small organic molecules, (E)-6,6′-bis(4-(diphenylamino)phenyl)-1,1′-bis(2-ethylhexyl)-(3,3′-biindolinylidene)-2,2′-dione (coded as S10) and (E)-6,6′-di(9H-carbazol-9-yl)-1,1′-bis(2-ethylhexyl)-(3,3′-biindolinylidene)-2,2′-dione (coded as S11) were successfully designed, synthesized and fully characterized. S10 and S11 are based on a donor-acceptor-donor structural motif and contain a common electron accepting moiety, isoindigo, along with different electron donating functionalities, triphenylamine and carbazole, respectively. Ultraviolet-visible absorption spectra revealed that the use of triphenylamine donor functionality resulted in an enhanced intramolecular charge transfer transition and reduction of optical band gap, when compared with its carbazole analogue. Both of these materials were designed to be donor semiconducting components, exerted excellent solubility in common organic solvents, showed excellent thermal stability, and their promising optoelectronic properties encouraged us to scrutinize charge-carrier mobilities using solution-processable organic field effect transistors. Hole mobilities of the order of 2.2 × 10⁻⁴ cm²/Vs and 7.8 × 10⁻³ cm²/Vs were measured using S10 and S11 as active materials, respectively. Full article

The postfunctionalization of the main chain alkyne moieties of carbazole containing poly(arylenebutadiynylene)s was attempted by using a high yielding addition reaction between electron rich alkynes and a strong acceptor molecule, tetracyanoethylene (TCNE). After successful postfunctionalization, the polymer band gap decreased due to the intramolecular donor-acceptor interactions. The resulting donor-acceptor alternating polymer showed a very broad charge-transfer band in the visible region as well as redox activities in both anodic and cathodic directions. The optical band gap showed good agreement with the electrochemical band gap. Furthermore, the thermal stability was enhanced after postfunctionalization. These features of the donor-acceptor alternating polymer are expected to be useful for high performance activities in organic solar cell applications. Full article

Steady-state and time-resolved emission spectroscopy are valuable tools to probe photochemical processes of metal-ligand, coordination complexes. Ru(II) polyazine light absorbers are efficient light harvesters absorbing in the UV and visible with emissive ³MLCT excited states known to undergo excited state energy and electron transfer. Changes in emission intensity, energy or band-shape, as well as excited state lifetime, provide insight into excited state dynamics. Photophysical processes such as intramolecular electron transfer between electron donor and electron acceptor sub-units may be investigated using these methods. This review investigates the use of steady-state and time-resolved emission spectroscopy to measure excited state intramolecular electron transfer in polyazine bridged Ru(II),Rh(III) supramolecular complexes. Intramolecular electron transfer in these systems provides for conversion of the emissive ³MLCT (metal-to-ligand charge transfer) excited state to a non-emissive, but potentially photoreactive, ³MMCT (metal-to-metal charge transfer) excited state. The details of the photophysics of Ru(II),Rh(III) and Ru(II),Rh(III),Ru(II) systems as probed by steady-state and time-resolved emission spectroscopy will be highlighted. Full article