Coumarin-Rhodamine Hybrids—Novel Probes for the Optical Measurement of Viscosity and Polarity

Polarity-based fluorescence probes: properties and applications

Local polarity can affect the physical or chemical behaviors of surrounding molecules, especially in organisms. Cell polarity is the ultimate feedback of cellular status and regulation mechanisms. Hence, the abnormal alteration of polarity in organisms is closely linked with functional disorders and many diseases. It is incredibly significant to monitor and detect local polarity to explain the biological processes and diagnoses of some diseases. Because of their in vivo safe and real-time monitoring, several polarity-sensitive fluorophores and fluorescent probes have gradually emerged and been used in modern research. This review summarizes the fluorescence properties and applications of several representative polarity-sensitive fluorescent probes.

Fluorescent styryl chromophores with rigid (pyrazole) donor and rigid (benzothiophenedioxide) acceptor – complete density functional theory (DFT), TDDFT and nonlinear optical study

Density functional theory (DFT) and time-dependent DFT computations were employed to examine linear and nonlinear optical (NLO) characteristics of (E)-4-((1,1-dioxido-3-oxobenzo[b]thiophen-2(3H)-ylidene) ethyl)-1-phenyl-1H-pyrazol-5(4H)-one derived styryl dyes. NLO properties were computed using the two different global hybrid functionals B3LYP, BHandHLYP and three range separated hybrid functionals CAM B3LYP, wB97, wB97X and wB97XD with the basis sets 6–311++G(d,p), cc-pVDZ and cc-pVTZ. The compounds shows higher values of dipole moment around 8–9 Debye than the other compounds. They show higher values of α 0, ß 0 and γ 0 values. The values of γ 0 are around 204–544 × 10−36 e.s.u. with the method, B3LYP/6–311++G(d, p). We have calculated the mean absolute error (MAE) for dipole moment, α 0, ß 0 and γ 0 values. It is observed that MAE is less (0.89) for wB97/6–311++G(d,p) which indicates that wB97 is the most suited functional for all three compounds. Chemical stability and reactivity of these dyes were studied using electrophilicity index and chemical hardness and hyperhardness.

A Xanthene Dye-based Sensor for Viscosity and Cell Imaging

A new xanthene dye, namely ImX, has been facilely prepared by reaction of 4-(1H-Imidazol-1-yl)benzaldehyde with N, N-diethyl-3-aminophenol in concentrated propionic acid, and then treated by p-chloranil. ImX presents the maximum absorption and emission band centered at 562 nm and 583 nm in water, respectively. Fluorescent spectra investigations demonstrate that ImX shows viscosity-selective fluorescent response and emission enhancement when the solvent viscosity increases from 1.1 cp. (water) to 1248 cp. (98 % glycerol). In addition, this viscosity-selective fluorescence response covers a wide pH range from 2.5 to 10.0. More significantly, ImX demonstrates low cytotoxicity and can be employed as tracer for the detection of Monensin-triggered viscosity enhancement by cell imaging.

A Theoretical and Experimental Study on the Potential Luminescent and Biological Activities of Diaminodicyanoquinodimethane Derivatives

Recently, several studies have demonstrated that diaminodicyanoquinone derivatives (DADQs) could present interesting fluorescence properties. Furthermore, some DADQs under the solid state are capable of showing quantum yields that can reach values of 90%. Besides, the diaminodiacyanoquinone core represents a versatile building block propense either to modification or integration into different systems to obtain and provide them unique photophysical features. Herein, we carried out a theoretical study on the fluorescence properties of three different diaminodicyanoquinodimethane systems. Therefore, time-dependent density functional theory (TD-DFT) was used to obtain the values associated with the dipole moments, oscillator strengths, and the conformational energies between the ground and the first excited states of each molecule. The results suggest that only two of the three studied systems possess significant luminescent properties. In a further stage, the theoretical insights were confirmed by means of experimental measurements, which not only retrieved the photoluminescence of the DADQs, but also suggest a preliminary and promising antibacterial activity of these systems.

Ready Access to Molecular Rotors Based on Boron Dipyrromethene Dyes-Coumarin Dyads Featuring Broadband Absorption

Herein we report on a straightforward access method for boron dipyrromethene dyes (BODIPYs)-coumarin hybrids linked through their respective 8- and 6- positions, with wide functionalization of the coumarin fragment, using salicylaldehyde as a versatile building block. The computationally-assisted photophysical study unveils broadband absorption upon proper functionalization of the coumarin, as well as the key role of the conformational freedom of the coumarin appended at the meso position of the BODIPY. Such free motion almost suppresses the fluorescence signal, but enables us to apply these dyads as molecular rotors to monitor the surrounding microviscosity.

Diaminodicyanoquinones: Fluorescent Dyes with High Dipole Moments and Electron-Acceptor Properties

Fluorescent dyes are applied in various fields of research, including solar cells and light-emitting devices, and as reporters for assays and bioimaging studies. Fluorescent dyes with an added high dipole moment pave the way to nonlinear optics and polarity sensitivity. Redox activity makes it possible to switch the molecule's photophysical properties. Diaminodicyanoquinone derivatives possess high dipole moments, yet only low fluorescence quantum yields, and have therefore been neglected as fluorescent dyes. Here we investigate the fluorescence properties of diaminodicyanoquinones using a combined theoretical and experimental approach and derive molecules with a fluorescence quantum yield exceeding 90 %. The diaminodicyanoquinone core moiety provides chemical versatility and can be integrated into novel molecular architectures with unique photophysical features.

Rational design of NIR fluorescence probes for sensitive detection of viscosity in living cells

Developing near-infrared (NIR) fluorescence probes for detection of intracellular viscosity is still sufficiently challenging. In this work, three kinds of D-A-D type naphthyl and 2,1,3‑benzoxadiazol hybrid NIR dyes functionalized with amino (NY1), N‑methylamino (NY2) and N,N‑dimethylamino (NY3) groups for intracellular micro-viscosity detection were designed and synthesized. All the probes exhibited very weak NIR emission in low viscosity environment and obvious fluorescence enhancement with the increased viscosity. Different substituent groups had a high impact on the photophysical properties and response sensitive of the probes to viscosity. The structure-property relationships were systematic investigated. The results showed that stronger electron-donating ability and larger steric effect of N,N‑dimethylamino led to a narrower energy gap and more sensitive to viscosity environment. Therefore, NY3 exhibited higher signal noise ratio for viscosity detection and was successfully applied for imaging the changes of intracellular micro-viscosity. This work provides an efficient way to design powerful NIR fluorescence probes for viscosity detection.