Influence of polarity of solvents on the spectral properties of bichromophoric coumarins

Photophysical Properties of Sinapic Acid and Ferulic Acid and Their Binding Mechanism with Caffeine

Sinapic acid (SA) and ferulic acid (FA) are bioactive compounds used in the food, pharmaceutical, and cosmetic industries due to their antioxidant properties. In this work, we studied the photophysical properties of SA and FA in different solvents and concentrations and their interactions with caffeine (CF), using ultraviolet-visible (UV-Vis), fluorescence spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The findings show that the quantum yield, fluorescence lifetime, radiative decay rates, and non-radiative decay rates of SA and FA are influenced by the concentrations and solvent polarity. The interaction between SA and FA with CF was also studied using UV-Vis and fluorescence spectroscopy. The results indicate that the CF quenched the fluorescence intensity of SA and FA by static quenching due to the formation of a non-fluorescent complex. The van't Hoff equation suggests that the van der Waals forces and hydrogen bonds force were responsible for the interaction between SA and CF, as indicated by a negative change in enthalpy (Δ H o  < 0) and a negative change in entropy (Δ S o  < 0). On the other hand, the interaction between FA and CF was primarily controlled by electrostatic force, as indicated by a negative change in enthalpy (Δ H o < 0) and a positive change in entropy (Δ S o > 0). The negative change in Gibbs free energy (Δ G o ) indicates that both compounds underwent a spontaneous binding process.

A. E. Albadri A, Patel H, Messaoudi S, Kadri A, M. Al-Hazmy S, Aouadi K. Synthesis, optical properties, DNA, β-cyclodextrin interaction, hydrogen isotope sensor and computational study of new enantiopure isoxazolidine derivative (ISoXD)

A novel isoxazolidine derivative (ISoXD) dye was successfully synthesized and comprehensively characterized. In this study, we conducted a thorough examination of its various properties, including optical characteristics, interactions with DNA and β-cyclodextrin (β-CD), molecular docking, molecular dynamic simulation, and density functional theory (DFT) calculations. Our investigation encompassed a systematic analysis of the absorption and emission spectra of ISoXD in diverse solvents. The observed variations in the spectroscopic data were attributed to the specific solvent's capacity to engage in hydrogen bonding interactions. Remarkably, the most pronounced intensities were observed in glycol, which can establish many hydrogen bonds with ISoXD. Furthermore, our study revealed a significant distinction in the fluorescence behavior of ISoXD when subjected to different solvents, particularly between CHCl3 and CDCl3. Moreover, we explored the fluorescence intensity of the ISoXD complex in the presence of various metals, both in ethanol and water. The ISoXD complex exhibited a substantial increase of fluorescence upon interaction with different metal ions. The utilization of DFT calculations allowed us to propose an intramolecular charge transfer (ICT) mechanism as a plausible explanation for this quenching phenomenon. The interaction of ISoXD with DNA and β-CD was studied using absorption spectra. The binding constant (K) and the standard Gibbs free energy change (ΔGo) for the interaction between DNA and β-CD with ISoXD were determined. In docking study, ISoXD exhibited significant docking scores (-6.511) and MM-GBSA binding free energies (-66.27 kcal/mol) within the PARP-1 binding cavity. Its binding pattern closely resembles to the co-crystal ligand veliparib, and during a 100ns MD simulation, ISoXD displayed strong stability and formed robust hydrogen bonds with key amino acids. These findings suggest ISoXD's potential as a PARP-1 inhibitor for further investigation in therapeutic development.

p-Phenylenediamine-derived carbon nanodots for probing solvent interactions

Carbon nanodots, the luminescent nanoparticles of carbon with size restriction below 10 nm, have attracted inordinate attention in materials science due to their widespread applications in optoelectronic and biological fields. Low toxicity and facile synthesis pathways render them favourites in the above-mentioned areas in the context of green chemistry. This work presents fine applications of p-phenylenediamine-derived carbon nanodots (PD-CNDs) achieved via a facile one-pot hydrothermal method. Adequate characterization using X-ray diffraction and spectroscopic and microscopic studies confirmed spherical particles with an average particle size of 2.8 nm, functionalised with amino, carboxyl, and hydroxyl groups. The carbon framework was functionalised with pyridinic and pyrrolic nitrogens. Upon 365 nm UV light illumination, an aqueous dispersion of PD-CNDs showed red-orange fluorescence. Detailed spectral analysis using UV-visible absorption and fluorescence spectroscopy identified edge states and surface groups as luminescent centres, with a significant contribution arising from the latter. The investigation conducted using a collection of solvents, categorized into polar and nonpolar, indicated the potential of the system for applications based on its solvatochromic nature. The feature enabled the determination of different polarity parameters of the solvents, as well as dielectric constants of solvents and solvent mixtures, with considerable accuracy. The system was potent for predicting the composition of a given pair of solvents. The service of the system is also extended for moisture sensing in organic solvents within an error percentage < 1. High quantum yield values (0.61) combined with solvent composition-dependent optical features ensure broader applications of the system to probe solvent interactions.

Controlled tuning of radiative-nonradiative transition via solvent perturbation: Franck-Condon emission vs. aggregation caused quenching

Organic molecules with tunable fluorescence quantum yield are attractive for opto-electronic applications. A fluorophore with tunable fluorescence quantum yield should be a better choice for a variety of applications that demand fluorophores with different quantum yields. Here organic emitters with a continuous bell-shaped fluorescence yield profile would be promising in view of sustainability and reusability; however, fluorophores with these properties are rarely reported. A bis-indole derivative, 3,3'-bisindolyl(phenyl)methane (BIPM), was synthesised and found to undergo a unique 'rise-and-fall' profile in fluorescence yield with a compositional change of the 1,4-dioxane (DiOx)-H₂O solvent system. A predominant interplay of two contrasting factors, (a) polarity and proticity induced emission enhancement and (b) aggregation caused fluorescence quenching, on either side of a crossover solvent composition (∼50% f_W), resulted in a continuous bell-patterned fluorescence yield profile. Interestingly, these two factors could be observed individually or simultaneously by adjusting the H₂O fraction. Detailed spectroscopic, electron microscopic and computational studies have been performed to substantiate the photophysics behind the solvent regulated modulation of fluorescence quantum yield.

Probing twisted intramolecular charge transfer of pyrene derivatives as organic emitters in OLEDs

Intramolecular charge transfer (ICT) plays a critical role in determining the photophysical properties of organic molecules, including their luminescence efficiencies. Twisted intramolecular charge transfer (TICT) is a process in which...

Photoinduced and Classical Sol-Gel Synthesis: Spectral and Photophysical Behavior of Silica Matrix Doped by Novel Fluorescent Dye Based on Boron Difluoride Complex

The boron difluoride complex is known as an extraordinary class of fluorescent dyes, which has attracted research interest because of its excellent properties. This article reports the optical properties such as absorption, fluorescence, molar absorptivity, and photo-physical parameters like dipole moment, and oscillator strength of new fluorescent organic dye based on boron difluoride complex 2-(1-(difluoroboraneyl)-1,2-dihydroquinolin-2-yl)-2-(1-methylquinoxalin-2-ylidene) acetonitrile (DBDMA). The spectral characterization of the dye was measured in sol-gel glass, photosol-gel, and organic-inorganic matrices. The absorption and fluorescence properties of DBDMA in sol-gel glass matrices were compared with each other. Compared with the classical sol-gel, it was noticed that the photosol-gel matrix is the best one with immobilized DBDMA. In the latter, a large stokes shift was obtained (97 nm) and a high fluorescence quantum yield of 0.5. Special attention was paid to the addition of gold NPs into the hybrid material. The fluorescence emission intensity of the DBDMA with and without gold nanoparticles in different solid media is described, and that displayed organic-inorganic matrix behavior is the best host.

Long-term live-cell lipid droplet-targeted biosensor development for nanoscopic tracking of lipid droplet-mitochondria contact sites

Background: Lipid droplets (LDs) establish a considerable number of contact sites with mitochondria to enable energy transfer and communication. In this study, we developed a fluorescent biosensor to image LD-mitochondria interactions at the nanoscale and further explored the function of LD-mediated matrix transmission in processes involving multi-organelle interactions. Methods: A fluorescent probe called C-Py (C21H19N3O2, 7-(diethylamino) coumarin-3-vinyl-4-pyridine acetonitrile) was designed and synthesized. Colocalization of C-Py and the commercial LD stain Nile Red was analyzed in HeLa cells. The fluorescence stability and signal to background ratio of C-Py under structured illumination microscopy (SIM) were compared to those of the commercial probe BODIPY493/503. The cytotoxicity of C-Py was assessed using CCK-8 assays. The uptake pattern of C-Py in HeLa cells was then observed under various temperatures, metabolic levels, and endocytosis levels. Contact sites between LDs and various organelles, such as mitochondria, nuclei, and cell membrane, were imaged and quantitated using SIM. Physical changes to the contact sites between LDs and mitochondria were monitored after lipopolysaccharide induction. Results: A LD-targeted fluorescent biosensor, C-Py, with good specificity, low background signal, excellent photostability, low cytotoxicity, and high cellular permeability was developed for tracking LD contact sites with multiple organelles using SIM. Using C-Py, the subcellular distribution and dynamic processes of LDs in living cells were observed under SIM. The formation of contact sites between LDs and multiple organelles was visualized at a resolution below ~200 nm. The number of LD-mitochondria contact sites formed was decreased by lipopolysaccharide treatment inducing an inflammatory environment. Conclusions: C-Py provides strategies for the design of ultra-highly selective biosensors and a new tool for investigating the role and regulation of LDs in living cells at the nanoscale.

Solution and Solid-State Photophysical Properties of Positional Isomeric Acrylonitrile Derivatives with Core Pyridine and Phenyl Moieties: Experimental and DFT Studies

The compounds I (Z)-2-(phenyl)-3-(2,4,5-trimethoxyphenyl)acrylonitrile with one side (2,4,5-MeO-), one symmetrical (2Z,2'Z)-2,2'-(1,4-phenylene)bis(3-(2,4,5-trimethoxyphenyl)acrylonitrile), II (both sides with (2,4,5-MeO-), and three positional isomers with pyridine (Z)-2-(pyridin-2- 3, or 4-yl)-3-(2,4,5-trimethoxyphenyl)acrylonitrile, III-V were synthetized and characterized by UV-Vis, fluorescence, IR, H1-NMR, and EI mass spectrometry as well as single crystal X-ray diffraction (SCXRD). The optical properties were strongly influenced by the solvent (hyperchromic and hypochromic shift), which were compared with the solid state. According to the solvatochromism theory, the excited-state (μe) and ground-state (μg) dipole moments were calculated based on the variation of Stokes shift with the solvent's relative permittivity, refractive index, and polarity parameters. SCXRD analyses revealed that the compounds I and II crystallized in the monoclinic system with the space group, P21/n and P21/c, respectively, and with Z = 4 and 2. III, IV, and V crystallized in space groups: orthorhombic, Pbca; triclinic, P-1; and monoclinic, P21 with Z = 1, 2, and 2, respectively. The intermolecular interactions for compounds I-V were investigated using the CCDC Mercury software and their energies were quantified using PIXEL. The density of states (DOS), molecular electrostatic potential surfaces (MEPS), and natural bond orbitals (NBO) of the compounds were determined to evaluate the photophysical properties.

A dendrimer-functionalized turn-on fluorescence probe based on enzyme-activated debonding feature of azobenzene linkage

The hypoxic feature of tumors has led to researchers developing hypoxia-activated prodrugs and probes that leverage oxidoreductases overexpressed in tumor tissues.

Solvation properties of protic ionic liquids and molecular solvents

Ionic liquids (ILs) are highly tailorable solvents with many potential applications. Knowledge about their solvation properties is highly beneficial in the utilization of ILs for specific tasks, though for many ILs this is currently unknown.

Gaining insight into the photophysical properties of a coumarin STP ester with potential for bioconjugation

The photophysical properties of a coumarin 392 4-sulfotetrafluorophenyl ester, C392STP (sodium (E/Z)-4-(4-(2-(6,7-dimethoxycoumarin-3-yl)vinyl)-benzoyl)-2,3,5,6-tetrafluoro-benzenesulfonate), an amine reactive coumarine with potential for bioconjungation, have been studied in different solvents.

Thiocyanate mediated structural diversity in phenol based "end-off" compartmental ligand complexes of group 12 metal ions: Studies on their photophysical properties and phosphatase like activity

The reaction of a pentadentate compartmental ligand LH, namely 4-tert-Butyl-2,6-bis-[(2-pyridin-2-yl-ethylimino)-methyl]-phenol, with group 12 metal ions (Zn^II, Cd^II, Hg^II) followed by addition of NaSCN afforded one discrete dinuclear complex [Zn₂(L)(SCN)₃](1), and two polymeric 1D species [Cd_2.5(L)(SCN)₃(AcO)]_n (2) and [Hg₂(L)(SCN)₃]_n (3). All the complexes have been structurally characterized by single crystal X-ray diffraction. The crystal structure of the complexes reveals different coordination modes of thiocyanate anion that affect the different topology detected in the compounds: the anions are μ¹-NCS and μ^1,1-NCS connected in complex 1, while μ^1,3-NCS bridging mode is observed in 2, and μ¹-SCN and μ^1,3-NCS in 3. The polymeric Hg complex of the bicompartmental ligand system here reported is unprecedented. Detail study of their photophysical properties including the phosphorescence spectra at 77K has been done. Phosphatase like activity of all the three complexes has been performed in DMSO-H₂O medium and their activity follows the order of 1>2>>3.

Aggregation-induced enhanced green light emission from a simple donor–π–acceptor (D–π–A) material: a structure–property relationship study

Organic D–π–A materials, possessing intramolecular charge transfer, have attracted much scientific attention in recent years because of their potential applications in the development of organic light emitting devices (OLEDs). Two new compounds, A1 and A2, having a D–π–A skeleton have been synthesized and single crystals were grown by the solution growth technique. Both compounds were characterized for crystallographic, thermal and photophysical properties. Upon photo-excitation in the solid state, A1 showed very strong green light emission while A2 gave sky-blue emission with much lower intensity. A single crystal X-ray diffraction study revealed that in the crystal lattice of A1, both the donor and acceptor groups are involved in the intermolecular interactions. This results in the restricted intramolecular rotation (RIR) of the D and A moieties, and enables A1 to emit more intensely in the solid state due to aggregation-induced emission (AIE). Intense green light emission, along with a good crystalline nature indicates that A1 might be a potential candidate for opto-electronic devices.

Influence of para substituents in controlling photophysical behavior and different non-covalent weak interactions in zinc complexes of a phenol based "end-off" compartmental ligand

Three dinuclear zinc(II) complexes with "end-off" compartmental ligands, namely 2,6-bis(N-ethylmorpholine-iminomethyl)-4-R-phenol (R = -CH3, Cl, (t)Bu) have been synthesized with the aim of exploring the role of the para substituent present in the ligand backbone in controlling the structural diversity, photophysical properties and different weak interactions of the complexes. All three species, with the general formula {2[Zn2L(CH3COO)2][Zn(NCS)4]}, show the complex anion Zn(NCS)4(2-) as a common structural feature decisive for crystallization. Interestingly, all of them possess several non-covalent weak interactions where the nature of the "R" group plays an essential role as exposed by DFT study. Besides exhibiting fluorescence behavior, the complexes also show para substitution controlled phosphorescence both at room and low temperature. Anisotropy studies suggest the existence of complexes 2 and 3 as dimers in solution. The origins of the unusual room temperature phosphorescence and fluorescence behavior of the complexes have been rationalized in the light of theoretical calculations.

An investigation on single crystal growth, structural, thermal and optical properties of a series of organic D–π–A push–pull materials

We present the large single crystal growth of a series of donor–π–acceptor (D–π–A) push–pull chromophores (1–4). The thermal, structural and optical properties of the synthesized chromophores were explored. These studies indicate the potential opto-electronic application of these push–pull chromophores.

Syntheses of 3-[(Alkylamino)methylene]-6-methylpyridine-2,4(1H,3H)-diones, 3-Substituted 7-Methyl-2H-pyrano[3,2-c]pyridine-2,5(6H)-dione Fluorescence Probes, and Tetrahydro-1H,9H-2,10-dioxa-9-azaanthracen-1-ones

Various condensation and ring-closing reactions were used for the syntheses of 3-[(alkylamino)methylene]-6-methylpyri-dine-2,4(1H,3H)-diones, bicyclic pyridinones, and tricyclic morpholinopyrones. For instance, 3-[(dialkylamino)methylene]-6-methylpyridine-2,4(1H,3H)-diones were synthesized from the condensation of dialkylamines and 3-formyl-4-hydroxy-6-methylpyridin-2(1H)-one. 3-Formyl-4-hydroxy-6-methylpyridin-2(1H)-one, derived from 3-formyl-4-hydroxy-6-methylpyridin-2(1H)-one, was used to construct a number of bicyclic pyridinones via a one-pot Knoevenagal and intramolecular lactonization reaction. Tricyclic morpholinopyrones were assembled from a dialkylation reaction involving a dinucleophile, 3-amino-4-hydroxy-6-methyl-2H-pyran-2-one, and a dielectrophile, trans-3,6-dibromocyclohexene. Depending on the reaction conditions, isomers of the tricyclic molecules can be selectively produced, and their chemical structures were unequivocally determined using single-crystal X-ray analyses and 2D COSY spectroscopy. The fluorescently active bicyclic pyridinone compounds show longer absorption (368-430 nm; maximum) and emission wavelengths (450-467 nm) than those of 7-amino-4-methylcoumarin (AMC; λabs,max = 350 nm; λem = 430 nm) suggesting these molecules, such as 3-(2-aminoacetyl)-7-methyl-2H-pyrano[3,2-c]pyridine-2,5(6H)-dione, can be employed as fluorescence activity based probes for tracing biological pathways.

3-(7-Dimethylamino)coumarin N-phenylsemicarbazones in solution and polymer matrices: Tuning their fluorescence via para-phenyl substitution

The photo-physical properties of five new para-phenyl substituted derivatives of 3-(7-dimethylamino)coumarin N-phenylsemicarbazone with various electron-withdrawing substituents R (RF, Br, CF3, CN or NO2) in the para-position on the phenyl ring were investigated in solvents and in polymer matrices. Tuning their fluorescent properties via para-substitution is discussed in terms of Twisted Intra-molecular Charge-Transfer (TICT) state formation, specific solute-solvent interactions (hydrogen bonding), fluorescent H-aggregates formation, and the solvent polarity and polymer matrix effects.

A Recent Review on Chemiluminescence Reaction, Principle and Application on Pharmaceutical Analysis

This paper provides a general review on principle of chemiluminescent reactions and their recent applications in drug analysis. The structural requirements for chemiluminescent reactions and the different factors that affect the efficiency of analysis are included in the review. Chemiluminescence application in immunoassay is the new version for this review. Practical considerations are not included in the review since the main interest is to state, through the aforementioned applications, that chemiluminescence has been, is, and will be a versatile tool for pharmaceutical analysis in future years.

7-(Dimethylamino)coumarin-3-carbaldehyde and its phenylsemicarbazone: TICT excited state modulation, fluorescent H-aggregates, and preferential solvation

The photophysical properties of 7-(dimethylamino)coumarin-3-carbaldehyde 3 and its phenylsemicarbazone 4 were investigated in solvents of various polarity and in differing solvent mixtures. The different fluorescent quantum yield (ΦF) behavior of 3 and 4 in highly polar solvents is discussed in terms of Twisted Intramolecular Charge-Tranfer (TICT) state formation and the specific solute-solvent interactions. Because of the weak intermolecular hydrogen bonding ability of both the radiative ICT and nonradiative TICT excited state of 3 and the linear steep decrease in ΦF from a medium to high polarity region, coumarin 3 could be a useful polarity probe for microenvironments containing hydrogen bonding groups. Compared to 3, coumarin 4 exhibits the highest ΦF values in highly polar solvents with strong hydrogen bond acceptor ability. The high quantum yield of fluorescence in DMSO, DMF, and alcohols qualifies coumarin 4 as a laser dye in the given medium, with kF higher than k(nr). Contrary to previous reports that many H-aggregates are nonfluorescent in nature, coumarin 3 forms highly fluorescent H-aggregates in MeOH and EtOH. On the basis of the restrictions of the Kasha-exciton theory model, we assume that the formation of fluorescent H-dimer aggregates of 3 is driven by π(+)-π(-) interactions. To the best of our knowledge, this is the first report on aggregation of coumarin dye in alcoholic solutions. In addition, restrictions in the fitting procedure relating to determination of the solvation number, n, using the Covington-Newman model of preferential solvation and also the solvent nonideality parameter, h', are discussed in this article.

Spectral tuning of the phosphorescence from metalloporphyrins attached to gold nanorods

The spectral shape of the phosphorescence emission of organometallic porphyrin molecules is shown to be altered when these chromophores are incorporated into hybrid nanostructures with gold nanorods. This result shows that triplet-singlet transitions, which are (at least partially) dipolar forbidden, can be modified by the dipolar resonances of gold nanoparticles. By choosing nanorods of increasing aspect ratios, it is possible to match the long axis plasmon resonance of the nanorods to a specific phosphorescence transition. Consequently, the emission colour of the hybrids can be tuned.

Spectral properties of binaphthalene-coumarins interconnected through hydrazone linkage

Photophysical properties of new coumarin-3-carbaldehyde (dihydrodinaphtho[2,1-c:1',2'-e]azepin-N-yl)imines bearing dimethylamino and methoxy groups at position 7 of coumarin were investigated. Dimethylamino derivative exhibits different solvent polarity dependence of fluorescent characteristics for nonpolar, medium polar and highly polar solvents. This effect can be rationalized by diverse charge distribution in the singlet excited state due to its different stabilization by solvation in the solvents of particular group. While 2-fold higher values of Stokes shift were observed for methoxy derivative, its quantum yield of fluorescence is much lower due to high nonradiative decay rate constant of the excited state.

Spectral properties of substituted coumarins in solution and polymer matrices

The absorption and fluorescence spectra of substituted coumarins (2-oxo-2H-chromenes) were investigated in solvents and in polymer matrices. The substitutions involved were: (1) by groups with varying electron donating ability such as CH₃, OCH₃ and N(CH₃)₂, mainly, but not exclusively, in positions 7 and (2), by either CHO or 4-PhNHCONHN=CH- in position 3. While the spectra of non-substituted coumarin-3-carbaldehyde has absorptions at approximately 305 and 350 nm, substitution at position 7 leads to remarkable changes in the shape of the absorption spectrum and shifts the absorption to a longer wavelength. Similarly, the replacement of the formyl group with a semicarbazide group substantially influences the shape of the absorption spectrum, and coumarins which have only N(CH₃)₂ in position 7 experience small changes. These changes are associated with the increasing intramolecular charge transfer (ICT) character and increasing conjugation length of the chromophoric system, respectively, in the studied molecules. The fluorescence is almost negligible for derivatives which have H in this position. With increasing electron donating ability, and the possibility of a positive mesomeric (+M) effect of the substituent in position 7 of the coumarin moiety, the fluorescence increases, and this increase is most intense when N(CH₃)₂ substitutes in this position, for both 3-substituted derivatives. Spectral measurements of the studied coumarins in polymer matrices revealed that the absorption and fluorescence maxima lay within the maxima for solvents, and that coumarins yield more intense fluorescence in polymer matrices than when they are in solution. The quantum yield of derivatives which have a dimethylamino group in position 7 in polymer matrices approaches 1, and the fluorescence lifetime is within the range of 0.5–4 ns. The high quantum yield of 7-dimethylamino derivatives qualifies them as laser dyes which have k_F higher than k_nr in the given medium. This is caused by stiffening of the coumarin structure in polar polymer matrices, such as PMMA and PVC, due to higher micro-viscosity than in solution and intermolecular dipole-dipole interaction between chromophore (dopant) and matrix.