Dual Solvatochromism of Neutral Red (original) (raw)
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ChemPhysChem, 2003
Using the density-functional vertical self-consistent reaction field (VSCRF) solvation model, incorporated with the conductor-like screening model (COSMO) and the self-consistent reaction field (SCRF) methods, we have studied the solvatochromic shifts of both the absorption and emission bands of four solvent-sensitive dyes in different solutions. The dye molecules studied here are: S-TBA merocyanine, Abdel-Halim's merocyanine, the rigidified aminocoumarin C153, and Nile red. These dyes were selected because they exemplify different structural features likely to impact the solvent-sensitive fluorescence of ™push-pull∫, or merocyanine, fluorophores. All trends of the blue or red shifts were correctly predicted, comparing with the experimental observations. Explicit H-bonding interactions were also considered in several protic solutions like H 2 O, methanol and ethanol, showing that including explicit H-bonding solvent molecule(s) in the calculations is important to obtain the correct order of the excitation and emission energies. The geometries, electronic structures, dipole moments, and intra-and intermolecular charge transfers of the dyes in different solvents are also discussed.
Photophysical Properties of the Cationic Form of Neutral Red
Photochemistry and Photobiology, 1999
Photophysical properties of the cationic form of neutral red (NRH'), a phenazine-based dye of biological importance, have been investigated in several protic and aprotic solvents using optical absorption, steady-state and time-resolved fluorescence and picosecond laser flash photolysis techniques. Absorption and fluorescence characteristics of the dye in protic solvents indicate the existence of intermolecular hydrogen bonding between the NRH+ and solvent molecules in the ground state as well as in the excited state. Measurements of the fluorescence lifetime in normal and heavy water also support the formation of intermolecular hydrogen bonding. Time-resolved transient absorption spectra obtained in the picosecond laser flash photolysis experiments show only the absorption band due to the S, t S1 absorption. The picosecond transient absorption results do not indicate any spectral shifts attributable to the hydrogen bond formation dynamics between the excited NRH+ and the protic solvent molecules. It is inferred that the hydrogen bonding dynamics are much faster than the time resolution of our picosecond setup (-35 ps).
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1995
Electronic absorption and fluorescence excitation and emission spectra of four acridines (acridine, Acridine Yellow, 9-aminoacridine and proflavine) and three phenazines (phenazine, neutral Red and safranine) are determined at room temperature (298 K) in several solvents of various polarities (dioxane, chloroform, ethyl ether, ethyl acetate, 1-butanol, 2-propanol, ethanol, methanol, dimethylformamide, acetonitrile and dimethyl sulfoxide). The effect of the solvent upon the spectral characteristics of the above compounds, is studied. In combination with the ground-state dipole moments of these compounds, the spectral data are used to evaluate their first excited singlet-state dipole moments by means of the solvatochromic shift method (Bakhshiev's and Kawski-Chamma-Viallet's correlations). The theoretical ground and excited singlet-state dipole moments for acridines and phenazines are also calculated as a vector sum of the ztcomponent (obtained by the PPP method) and the o-component (obtained from o-bond moments). For most acridines and phenazines under study, the experimental excited singlet-state dipole moments are found to be higher than their ground state counterpart. The application of the Kamlet-Abboud-Taft solvatochromic parameters to the solvent effect on spectral properties of acridine and phenazine derivatives is discussed.
2010
Solvent polarity effect on the photophysical properties of two newly synthesized aminostyryl-thiazoloquinoxaline dyes, one with a flexible diphenylamino group, namely, N,N-diphenyl-4-[2-(thiazolo[4,5-b]quinoxalin-2-yl)vinyl]aniline (TQ1), and the other with a rigid julolidinylamino group, namely, (9-[2-(thiazolo[4,5b]quinoxalin-2-yl)vinyl]julolidine) (TQ2), have been investigated in different aprotic solvents and solvent mixtures. From the polarity dependent changes in the absorption and fluorescence spectral properties, it is indicated that the fluorescent states of the dyes are of intramolecular charge transfer (ICT) character. For both the dyes, the photophysical properties like fluorescence quantum yields (Φ f ), fluorescence lifetimes (τ f ), radiative rate constants (k f ) Φ f /τ f ), and nonradiative rate constants (k nr ) 1/τ f -Φ f /τ f ) show clearly contrasting solvent polarity effects in the lower and in the higher solvent polarity region, causing an interesting reversal in the properties below and above an intermediate solvent polarity. It is inferred that the domination of the cis-trans isomerization in the lower solvent polarity region and that of the twisted intramolecular charge transfer (TICT) state formation in the higher solvent polarity region are responsible for the observed contrasting solvent polarity effects on the photophysical properties of the two dyes. As both isomerization and TICT state formation causes an enhancement in the nonradiative decay rate of the excited dyes and both the processes become less significant at the intermediate solvent polarity region, the two dyes show their largest Φ f and τ f values at intermediate solvent polarities. Suitable mechanistic schemes have been proposed and qualitative potential energy diagrams have been presented to explain the observed results with the changes in the polarity of the solvents used.
Solvatofluorochromism and twisted intramolecular charge-transfer state of the nile red dye
International Journal of Quantum Chemistry, 2012
Profiles of the S 1 potential energy surface of the Nile Red dye along the rotational coordinate of the amino group are computed using time-dependent density functional theory (TDDFT) and XMCQDPT2/CASSCF. The calculated profiles exhibit two minima corresponding to a planar locally excited (LE) state and a twisted intramolecular charge transfer (TICT) state. The profiles calculated by time-dependent density functional theory (TDDFT) depend on the weight of the hartree-fock (HF) exchange in the functional: at 0% exchange, only the TICT minimum exists, whereas at 50% exchange and more there is only the LE minimum. The profiles obtained by TDDFT at 20-25% HF exchange are in qualitative agreement with that obtained by XMCQDPT2/CASSCF calculations. The energy of the charge transfer state is lowered due to the participation of doubly excited configurations and dynamic correlations, which is implicitly included in the density functionals. The solvent effects on the relative energies of the LE and TICT states and on the barrier height are studied using the polarizable continuum model. The effect of hydrogen bonds is studied for a complex of Nile Red with two water molecules. The solvatochromism of Nile Red fluorescence in aprotic polar solvents is explained by nonspecific solvation, which stabilizes the LE state and causes Nile Red fluorescence solvatochromism; in water and alcohols, it is explained by the formation of hydrogen bonds, which stabilize the TICT state and facilitate the LE-to-TICT transition.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017
The present work describes about the photophysical properties of two newly synthesized compounds namely (E)-10-butyl-3-(2-(thiazolo[4,5-b]quinoxalin-2-yl)vinyl)-10Hphenothiazine (PTQ) and (E)-10-butyl-3-(2-(1,1-dimethyl-1H-benzo[e]indol-2-yl)vinyl)-10H-phenothiazine (PBI). A strong Intramolecular Charge Transfer (ICT) is observed in both dyes as indicated from absorption and emission studies on varying the solvent polarity. This can be concluded from the large Stoke shifts among these dyes as PTQ exhibits large Stoke shift with more than 270 nm and PBI around 200 nm. The effect of increasing polarity caused drastic increase in the charge transfer process leading to Twisted Intramolecular Charge Transfer (TICT) process in both the dyes PTQ and PBI. Time resolved emission studies and non-radiative decay rate constant indicates that excited states of both the dyes behaves differently with respect to solvent polarity. The non-radiative decay constant increases dramatically with the solvent polarity specifying change of ICT emissive states in non-polar solvent while TICT emitting states in highly polar solvent. On the other hand, PBI follows a general trend initially exhibiting higher Highlights
Zenodo (CERN European Organization for Nuclear Research), 2022
The ground state () and the excited state () dipole moments of two styryl dyes were studied at room temperature in various organic solvents. The dipole moments () were estimated from solvatochromic shifts of absorption and emission spectra as function of the refractive index (n) and dielectric constant () using Bilot-Kawski, Bakshiev, Lippert Mataga, Kawaski-Chamma-Viallet and Reichardt Methods. Then in order to estimate a theoretical investigation, the dipole moments were calculated in the respective organic solvents with computational method (TDDFT/B3LYP). Intramolecular charge-transfer (ICT) and twisted intramolecular charge transfer (TICT) have been observed due to higher values of excited state dipole moment than ground state dipole moment. The results show that excited state dipole moments of dyes are higher than ground state dipole moments of styryl dyes. The small change in the dipole moments was found after the introduction of sulphar and methoxy group in the styryl dyes are observed. It is observed that dipole moment value of excited state (μe) is higher than that of the ground state in both the styryl dyes indicating that these dyes are more polar in nature in the excited state than in the ground state.