Solvent effects on photophysical properties of merocyanine 540 (original) (raw)
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Journal of Organometallic Chemistry, 2016
The photophysical properties of the complex Bu4N[(4,4′-bpy)Re(CO)3(bpy-5,5′-diCOO)] were studied in protic and aprotic media with the aid of steady-state and time-resolved techniques and TD-DFT calculations. The absorption spectrum as well as the steady state and time resolved luminescence of the Re(I) complex display a marked solvent effect. The highest and lowest energy absorption bands experience a bathochromic shift as the polarity of the solvent decreases. In addition, the lowest energy band broadens. Two luminescence bands were observed around 430 and 600 nm in protic organic solvents like alcohols. The high energy emission is observed solely in aqueous solutions, while in aprotic solvents only the low energy luminescence is detected. TD-DFT calculations allowed us to identify the main electronic transitions in the low energy region as M 1 LLCT Re ( CO ) 3 → 4 , 4 ′ - bpy and M 1 LLCT Re ( CO ) 3 → bpy - 5 , 5 ′ - diCOO . The simulated absorption spectra of the Re(I) complex i...
Solvent Effects on the Photophysical Properties of Dibucaine: A Quinoline Analogue
Photochemistry and Photobiology, 1987
The photophysical properties of the complex Bu 4 N[(4,4′-bpy)Re(CO) 3 (bpy-5,5′-diCOO)] were studied in protic and aprotic media with the aid of steady-state and time-resolved techniques and TD-DFT calculations. The absorption spectrum as well as the steady state and time resolved luminescence of the Re(I) complex display a marked solvent effect. The highest and lowest energy absorption bands experience a bathochromic shift as the polarity of the solvent decreases. In addition, the lowest energy band broadens. Two luminescence bands were observed around 430 and 600 nm in protic organic solvents like alcohols. The high energy emission is observed solely in aqueous solutions, while in aprotic solvents only the low energy luminescence is detected. TD-DFT calculations allowed us to identify the main electronic transitions in the low energy region as 1 MLLCT Re(CO) 3 → 4,4′-bpy and 1 MLLCT Re(CO) 3 → bpy-5,5′-diCOO . The simulated absorption spectra of the Re(I) complex in H 2 O, protic (EtOH, MeOH) and aprotic (CHCl 3 , CH 2 Cl 2 , CH 3 CN) organic solvents follow the experimental absorption spectra with reasonable accuracy both in position and relative intensities. The magnitude of the calculated dipole moment (μ) increases with the dielectric constant of the solvent (ε r ). Besides, the energy of 1 MLLCT Re(CO) 3 → 4,4′-bpy also increases with ε r . However, the energy of the 1 MLLCT Re(CO) 3 → bpy-5,5′-diCOO transition is rather insensitive to ε r . This disparity is attributed to the fact that the 1 MLLCT Re(CO) 3 → 4,4′-bpy transition is nearly parallel to the orientation of μ while the 1 MLLCT Re(CO) 3 → bpy-5,5′-diCOO transition is almost perpendicular to it. Unrestricted TDFT calculations were successfully applied to the triplet species. It is observed that in the triplet state the Re N distances are shortened while Re C distances are elongated relative to the ground state. The calculated emission energy by TD-DFT and/or Δ(SCF) methods was compared to the experimental emission maximum in chloroform. All the experimental results as well as the theoretical calculations indicate that solvent effects on the steady state and time resolved luminescence of the Re(I) complex can be accounted by the coexistence of 3 MLLCT Re(CO) 3 → 4,4′-bpy , 3 MLLCT Re(CO) 3 → bpy-5,5′-diCOO and 1 IL excited states.
Chemical Physics, 2003
The solvaton–CS INDO model, previously successfully used to describe the solvatochromic properties of merocyanines, has been extended to the study of the solvent influence on the fluorescence spectra (fluorosolvatochromism) of these dyes. A ketocyanine (M1) and a stilbazolium betaine (M2) were chosen as representatives of positively and negatively solvatochromic behaviours, respectively. The gap of experimental knowledge concerning the emission properties of M2 was filled by a spectrofluorometric analysis in a set of solvents covering a large range of the ET(30) scale. Solvato- and fluorosolvatochromism were described by calculating the S0(eq.)→S1(Franck–Condon) and S1(eq.)→S0(Franck–Condon) transition energies as a function of a polarity factor related to the static dielectric constant of the solvent, and ranging from 0 to 1. The absorbing S0(eq.) and emitting S1(eq.) units (solute molecule + solvent cage) were approximated using the S0 and S1 geometries of the unsolvated molecule and the respective charge distributions fitted to the current value of k(ε). The calculation results fully confirm that S0 and S1 states of merocyanines can be viewed as a mixture of a neutral and a zwitterionic structure whose composition is controlled by the solvent polarity. The plots of the calculated spectral data (absorption and emission maxima and corresponding Stokes shifts) vs k(ε) are in fairly good agreement with those of the experimental data over almost the entire range of the normalized ETN values, thus showing that specific solvent interactions are at least partly simulated within the solvaton–CS INDO scheme. The methodological prerequisites for a correct prediction of solvatochromic shifts are recalled with reference to previous conflicting theoretical interpretations.
Angewandte Chemie International Edition, 2009
Merocyanines are of widespread interest for different applications [5] and have attracted considerable attention owing to their intense absorption bands and the outstanding sensitivity of these bands to solvents. The solvent sensitivity of the absorption bands is discussed in terms of a simple valence bond (VB) model, which assumes that the electronic ground (S 0 ) and excited state (S 1 ) of merocyanines can be approximated as a linear combination of a non-charge-separated polyene-like and a charge-separated polyene-like limiting form. [5] The net balance is influenced by the nature of the solvent, passing through the "cyanine limit". Several parameters have been suggested for quantifying the contribution of the two limiting forms to the equilibrium structure of the ground state. The concepts of the average bond-length alternation (BLA), [7] and the closely related average p-bond order alternation (BOA), between adjacent bonds in the hydrocarbon chain are most popular. Surprisingly, within the same concept merocyanines have been described by two quite different models, namely Equations (1), [7a,c, 8b,c] and , [7b, 8a] in which A (electron acceptor) and D (electron donor) are capable of charge exchange. Polymethines are characterized by a chain of conjugated double bonds with an odd number n of p centers and (n + 1) p electrons, whereas polyenes are characterized by an even number of p centers and the same number of p electrons. Therefore, polyenes and polymethines differ considerably in electronic structure and light absorption, [5] and, consequently, polymethines cannot be viewed as acceptor/donor-substituted polyenes. Equation (1) describes two possible limiting forms of acceptor/ donor-substituted polyenes and, therefore, cannot be used for merocyanines. Equation represents polymethines; A = N (+) and D = N corresponds to a cyanine [Eq. (3)], A = O and D = O (À) to an oxonole, and A = N (+) and D = O (À) or A = N (+) and D = C (À) to merocyanines [Eqs. (4) and (5)]. The structure labeled b in Equations and do not represent polyene-like forms as often claimed, but are equivalent to structure b in Equation for cyanines and are polymethines.
Absorption, fluorescence, and semiempirical ASED-MO studies on a typical Brooker's merocyanine dye
Journal of Molecular Structure, 2005
Solvatochromism and Solvatofluorchromism of Brooker's merocyanine 1-methyl-4-(4 0-hydroxystyryl) pyridinium betaine, M, were studied in twelve polar protic and aprotic solvents. Moderate hypsochromic fluorescence energy shifts are 4.57 kcal mole K1 while strong hypsochromic absorption energy shifts are 16.63 kcal mole K1. Decreasing of the dipole moment of M upon excitation is the factor, which is responsible for the difference between the two energy shifts. The change of both energies rectilinearly with solvent acidity scale shows the importance of oxygen atom of M as a strong basic center. The application of the atom superposition and electron delocalization molecular orbital (ASED-MO) theory reproduces geometrical and electronic structures for M, which agree well with the experimental observations. The calculations suggest strongly that the dye has a benzenoid valence structure in the ground state and shifts towards a quinonoid one upon excitation with an observed decreasing of the dipole moment. The changing of the dipole moment is explained clearly depending upon the calculated charge distribution over the whole skeleton of the molecule. The formation of a H-bond between the water molecule and the highly negative oxycyclic oxygen atom of M has slightly effect on its dipole moment in the ground state. This leads to suggest that this kind of interaction could be represented as attacking of water with acidic character on the basic site of M. Also, the calculations predict that the formation of monohydrated complex is an exothermic, down hill reaction, which is confirmed from the stabilization of the frontier molecular orbitals, oxygen lone-pair and the HOMO levels.
0riginal article, 2020
To cite this article: Dereje Fedasa, Dunkana Negussa, Alemu Talema. Effect of Substituents on Electronic Structure and Photophysical Properties of Re(I)(CO) 3 Cl(R-2, 2'-Bipyridine) Complex: DFT/TDDFT Study. Abstract: The electronic structure, absorption and emission spectra, as well as phosphorescence efficiency of Re(I) tricarbonyl complexes of a general formula fac-[Re(I)(CO) 3 (L)(R-N^N)](L = Cl; N^N = 2, 2'-bipyridine; R =-H, 1;-NO 2 , 2;-PhNO 2 , 3;-NH 2 , 4;-TPA (triphenylamine), 5) were investigated by using density functional theory(DFT) and time dependents density functional theory (TDDFT) methods. The calculated results reveal that introductions of the Electron with drawing group (EWG) and Electron donating group (EDG) on the R position of 2, 2'-bipyridine ligand. When EWG (-NO 2 and-PhNO 2) are introduced into complex 2 and 3, the lowest energy absorption and emission bands are red shifted compared with that of complex 1. On the contrary, the introduction of the EDG (-NH 2 and-TPA) in complex 4 and 5 cause corresponding blue shifted. The solvent effect on absorption and emission spectrum indicates that the lowest energy absorption and emission bands have red shifts with the decrease of solvent polarity. The electronic affinity (EA), ionization potential (IP) and reorganization energy (λ) results show that complex 5 is suitable to be used as an emitter in phosphorescence organic light emitting diodes (PHOLEDs). Meanwhile the emission quantum yield of complex 5 is possibly higher than that of other complexes.
International journal of computational and theoretical chemistry, 2020
The electronic structure, absorption and emission spectra, as well as phosphorescence efficiency of Re(I) tricarbonyl complexes of a general formula fac-[Re(I)(CO) 3 (L)(R-N^N)](L = Cl; N^N = 2, 2'-bipyridine; R =-H, 1;-NO 2 , 2;-PhNO 2 , 3;-NH 2 , 4;-TPA (triphenylamine), 5) were investigated by using density functional theory(DFT) and time dependents density functional theory (TDDFT) methods. The calculated results reveal that introductions of the Electron with drawing group (EWG) and Electron donating group (EDG) on the R position of 2, 2'-bipyridine ligand. When EWG (-NO 2 and-PhNO 2) are introduced into complex 2 and 3, the lowest energy absorption and emission bands are red shifted compared with that of complex 1. On the contrary, the introduction of the EDG (-NH 2 and-TPA) in complex 4 and 5 cause corresponding blue shifted. The solvent effect on absorption and emission spectrum indicates that the lowest energy absorption and emission bands have red shifts with the decrease of solvent polarity. The electronic affinity (EA), ionization potential (IP) and reorganization energy (λ) results show that complex 5 is suitable to be used as an emitter in phosphorescence organic light emitting diodes (PHOLEDs). Meanwhile the emission quantum yield of complex 5 is possibly higher than that of other complexes.
Optik - International Journal for Light and Electron Optics, 2017
The physical properties of five different samples of azo merocyanine dyes, each dissolved in three different polar solvents (Acetonitrile, Ethanol and 1-propanol) with three different concentrations (3 x10-5 , 2x10-5 and 1x10-5 mol/L) have been measured experimentally. The refractive indices of the samples have been determined with an accuracy of ±1x10 −4 by using an Abbe Refractometer of measuring range from 1.300 to 1.700. The measurements have been performed at four different wavelengths (435.8, 546.1, 578.0 and 589.3 nm). Other parameters such as Cauchy's dispersion constants, resonance wavelength, molar polarizability, molar refractivity, absorption index and abbe number have been calculated. Also, viscosity, thermal expansivity and the effect of temperature on refractive index have been investigated. The intermolecular interactions between the solute and the solvent have been discussed. The physical characterization of merocyanine dyes provides valuable and important information needed for using them in many applications. Keywords: Merocyanine dyes used for data storage and solid state devices, refractive index and its dispersion, thermo-optic coefficient, Viscosity and thermal expansivity.
Journal of Photochemistry and Photobiology A: Chemistry, 2017
The photophysical behavior of a series of flexible di-2-pyridylaminomethyl substituted ligands systematically substituted on a rigid benzene core and their corresponding mono-metallic Re (I) complexes have been investigated by steady state and time-resolved fluorescence spectroscopy in different composition of DMSO-water binary solvent mixtures. Unusual fluorescence properties in lower DMSO content (X DMSO = 0.1~0.3) solvent mixtures is consistent with fascinating property of DMSO, which is known to perturb the hydrogen bonding ability of water with the solute. Spin allowed inter-ligand ππ * transition is more apparent in (1, 3) substituted systems. The calculated spectroscopic parameters of the complexes are significantly different from the ligands, mainly due to ligand to metal charge transfer. The experimental observations are in very good agreement with the theoretical results obtained at B3LYP/6-31G(d,p)/LANL2DZ level of density functional theory (DFT) calculation. Natural bond orbital (NBO) analysis and examination of frontier molecular orbitals reveal that the basic architecture of the symmetrically substituted multi-chromophoric ligand can induce excitation energy hopping, similar to an artificial antenna system.