Photophysical Studies of a Hemicyanine Dye (LDS-698) in Dioxane−Water Mixture, in Different Alcohols, and in a Room Temperature Ionic Liquid

Effect of Mixture Composition on the Photophysics of Indoline Dyes in Imidazolium Ionic Liquid-Molecular Solvent Mixtures: A Femtosecond Transient Absorption Study

We conducted a study on the photophysics of three indoline dyes, D102, D149, and D205, in binary mixtures of ionic liquids (IL) and polar aprotic molecular solvents (MS). Specifically, we examined the behavior of these dyes in IL-MS mixtures containing four different imidazolium-based ILs and three different polar aprotic MSs. Our investigation involved several techniques, including stationary absorption and emission measurements, as well as femtosecond transient absorption (TA) spectroscopy. Through our analysis, we discovered a peculiar behavior of several photophysical properties at low IL mole fractions (0 < XIL < 0.2). Indeed, in this range of mixture composition, the absorption maximum wavelength decreases noticeably, while the emission maximum wavelength and the Stokes shift, expressed in wavenumbers, reach a maximum. while a minimum occurs in the relative quantum yield and the excited state lifetime. These results indicate that the solvation of dye undergoes a large change in this range of mixture composition. We found that, at high ionic liquid content, the excited relaxation times are correlated with the high viscosity, while at low content, it is the polarity of the solvent that influences the behavior of the excited relaxation times. At a mixture composition of around 0.10, the behavior of the photophysical properties of the studied IL-MS mixtures indicates a crossover between situations where the solvation is dominated by that of ions and that dominated by the solvent.

Amine-incorporated quinoxaline based fluorescent sensor for detection of trace water: Solvent influenced self-assembly

Polarity is a complex parameter, with important effect in chemistry and biology. In recent years, polarity exploration attracted more and more attention hence, it's of great importance to exploit new methods for polarity determination. A novel class of long, coplanar, and amine incorporated electron-rich quinoxaline scaffold(L₁) furnished maximum solvatochromic effect and large Stokes shift and was chosen to determine water content in organic solvents e.g. acetonitrile, THF, DMF, and methanol through fluorescence spectroscopy. Moreover, the probe was found to perform as an effective fluorescent sensor for the quantitative detection of low-level moisture content in four commonly-used organic solvents with low detection limits (0.018%, 0.027%, 0.012%, and 0.43% respectively). This study also describes the morphological transformation of L₁ form a fibrous network to spherical aggregates upon increasing water content in several organic solvents. Real-life implementation of the probe was successfully employed for the detection of moisture content in commercial food products and building materials such as cement, sand, limestone, salt, wheat, and detergent powder. Furthermore, probe L₁-immersed easy-to-prepare test strips provide a reliable approach for qualitative monitoring of water content in organic solvents by a simple color-changing method under UV irradiation via smartphone-assisted RGB analysis.

Photoinduced intramolecular charge transfer in trans-2-[4'-(N,N-dimethylamino)styryl]imidazo[4,5-b]pyridine: effect of introducing a C[double bond, length as m-dash]C double bond

The spectral characteristics of trans-2-[4'-(N,N-dimethylamino)styryl]imidazo[4,5-b]pyridine (t-DMASIP-b) have been investigated using absorption and fluorescence techniques, and compared with 2-(4'-N,N-dimethylamino)imidazo[4,5-b]pyridine (DMAPIP-b). The study reveals that introduction of a C[double bond, length as m-dash]C double bond strongly perturbs the photophysics of the system. Unlike DMAPIP-b, t-DMASIP-b emits a single emission in aprotic and protic solvents. The emission occurs from the locally excited state in nonpolar solvents and from a planar intramolecular charge transfer (PICT) state in polar solvents. Multiple linear regression analysis suggests that among the different solvent parameters, the dipolar interaction contributes more to the stabilization of the system in both the ground and excited states. Theoretical calculations suggest that, unlike in DMAPIP-b, proton coupled twisted intramolecular charge transfer (TICT) emission does not occur in t-DMASIP-b. The higher quantum yield obtained in the viscous solvent glycerol is attributed to the restriction of the twisting of the olefinic bond. The photoirradiation of t-DMASIP-b shows that isomerization takes place in all solvents, including viscous glycerol. The theoretically simulated potential energy surface shows that isomerization occurs via a phantom state, which is a nonradiative process. The rise in temperature favors the photoisomerization, thus, the fluorescence quantum yield decreases. The prototropic study indicates that, unlike in DMAPIP-b, the protonation takes place at different places to form the monocations.

Preparation, photophysical characterization, and modeling of LDS722/Laponite 2D-ordered hybrid films

A novel hybrid material with promising optical properties for nonlinear optical applications is presented, as formed by LDS 722 organic dye confined in Laponite clay. Thin films of the hybrid material with different dye loadings have been prepared. The film thickness, the dye and water content, and the clay swelling due to guest molecule incorporation have been characterized. Then, the photophysical properties of the thin films have been studied in detail using experimental methods and molecular simulation. As the dye load increases, the hybrid films present a hypsochromic shift in absorption and a bathochromic shift in emission. The former is attributed to the increasing strength of solvation of the dye donor group, while the latter is ascribed to a switch from an intramolecular to an intermolecular charge-transfer process as the dye load increases. The LDS 722 molecules are preferentially oriented in the host clay almost in parallel to the platelet surfaces, inducing macroscopic order that makes the material responsive to polarized light.

Optical properties of hemicyanines with terminal amino groups and their applications in near-infrared fluorescent imaging of nucleoli

A cellular dye with properties of long-wave emission, large Stokes shift, water solubility, low cytotoxicity, and good photostability is reported.

Photophysical properties of 7-(diethylamino)coumarin-3-carboxylic acid in the nanocage of cyclodextrins and in different solvents and solvent mixtures

The photophysical properties of 7-(diethylamino) coumarin-3-carboxylic acid (7-DCCA) were studied in cyclodextrins (α, β, γ,-CDs), different neat solvents and solvent mixtures by using steady state absorption, emission and time-resolved fluorescence spectroscopy. We have observed that with gradual increase in concentration of β-CD the fluorescence quantum yield and lifetime decreased in a regular pattern whereas with gradual increase in concentration of γ-CD the fluorescence quantum yield and lifetime gradually increased. With addition of urea, the fluorescence quantum yield and lifetime of 7-DCCA in CDs increased. Binding constant calculation shows that 7-DDCA forms 1:1 complex with β-CD and with γ-CD it forms 1:1 and 1:2 (guest:host) inclusion complex. We proposed that the dye molecule formed capping complex with β-CD by means of hydrogen bonding and after addition of urea the hydrogen bonding network broke down and part of dye molecule entered inside the cavity of β-CD. The photophysics of 7-DCCA was studied in dioxane-water mixture and ethylene glycol-acetonitrile mixture to know the effect of polarity and viscosity of the media. The photophysics of 7-DCCA was also studied in different neat solvents. It was found that the photophysics of 7-DCCA depended on the structural feature of the solvents and solvent mixtures.

Origin of strong synergism in weakly perturbed binary solvent system: a case study of primary alcohols and chlorinated methanes

A strong synergistic solvation was observed for the mixtures of hydrogen bond donating and accepting solvent pairs. The nature of the interactions between two solvent pairs was investigated with different dye molecules viz. coumarin 480, coumarin 153, 4-aminophthalimide, and p-nitroaniline. Coumarin 480 in differenet alcohols-CHCl(3) (alcohols: MeOH, EtOH, BuOH) binary mixture shows a strong synergism, which is explained in the backdrop of solvent-solvent interactions. Fluorescence quenching of C480 by 1,2-phenylenediamine in the binary solvent mixture exhibited the maximum deviation in quenching constant corresponding to ~0.45 mol fraction of MeOH in MeOH-CHCl(3) binary mixture and hence suggested the maximum extent of hydrogen-bonding interactions prevailing at this proportion of mixture. The solvation behavior of MeOH-CHCl(3) mixture shows strong probe dependence with no synergism observed in p-nitroaniline, which is ascribed to its higher ground state dipole moment (8.8 D) relative to C480 (6.3 D). Interestingly, the strong synergistic signature observed through spectrophotometric measurement of C480 in alcohol-CHCl(3) binary mixture is absent when studied by fluorescence measurement. The higher excited state dipole moment of coumarin 480 (13.1 D) is considered to be the driving force for the absence of synergism in the excited state. In such strongly perturbed systems (due to high dipole moment values) the dominant phenomenon is preferential solvation. Analysis of proton NMR of MeOH-CHCl(3) binary solvent mixture indicates the existence of MeOH-CHCl(3) clusters in the stoichiometric ratio of 1:2.15. Refractive index measurement also infers the existence of hydrogen bonded network structure between MeOH and CHCl(3). A modified Bosch solvent exchange model has been used to determine the feasibility of synergistic behavior and polarity parameter of the mixed solvent structure of MeOH-CHCl(3) binary solvent mixture.