Performance of 4,5-diphenyl-1H-imidazole derived highly selective 'Turn-Off' fluorescent chemosensor for iron(III) ions detection and biological applications.

Two fluorescent chemosensors, denoted as chemosensor 1 and chemosensor 2, were synthesized and subjected to comprehensive characterization using various techniques. The characterization techniques employed were Fourier-transform infrared (FTIR), proton (1 H)- and carbon-13 (13 C)-nuclear magnetic resonance (NMR) spectroscopy, electrospray ionization (ESI) mass spectrometry, and single crystal X-ray diffraction analysis. Chemosensor 1 is composed of a 1H-imidazole core with specific substituents, including a 4-(2-(4,5-c-2-yl)naphthalene-3-yloxy)butoxy)naphthalene-1-yl moiety. However, chemosensor 2 features a 1H-imidazole core with distinct substituents, such as 4-methyl-2-(4,5-diphenyl-1H-imidazole-2-yl)phenoxy)butoxy)-5-methylphenyl. Chemosensor 1 crystallizes in the monoclinic space group C2/c. Both chemosensors 1 and 2 exhibit a discernible fluorescence quenching response selectively toward iron(III) ion (Fe3+ ) at 435 and 390 nm, respectively, in dimethylformamide (DMF) solutions, distinguishing them from other tested cations. This fluorescence quenching is attributed to the established mechanism of chelation quenched fluorescence (CHQF). The binding constants for the formation of the 1 + Fe3+ and 2 + Fe3+ complexes were determined using the modified Benesi-Hildebrand equation, yielding values of approximately 2.2 × 103 and 1.3 × 104 M-1 , respectively. The calculated average fluorescence lifetimes for 1 and 1 + Fe3+ were 2.51 and 1.17 ns, respectively, while for 2 and 2 + Fe3+ , the lifetimes were 1.13 and 0.63 ns, respectively. Additionally, the applicability of chemosensors 1 and 2 in detecting Fe3+ in live cells was demonstrated, with negligible observed cell toxicity.

Synthesis and Photoluminescence Properties of MoS2/Graphene Heterostructure by Liquid-Phase Exfoliation.

Here, we report the synthesis of MoS2/graphene heterostructure in single-stage, liquid-phase exfoliation using a 7:3 isopropyl alcohol/water mixture. Further, the synthesized heterostructure was characterized using UV-visible and micro-Raman spectroscopies, transmission electron microscopy (TEM), and dynamic light scattering (DLS) analysis. UV-visible and micro-Raman analyses confirmed that the synthesized heterostructure had mostly few-layered (two-to-four sheets) MoS2. The photophysical properties of the heterostructure were analyzed using steady-state and time-resolved luminescence techniques. Enhanced photoluminescence was observed in the case of the heterostructure probably due to an increase in the defect sites or reduction in the rate of nonradiative decay upon formation of the sandwiched heterostructure. Applications of this heterostructure for fluorescence live-cell imaging were carried out, and the heterostructure demonstrated a better luminescence contrast compared to its individual counterpart MoS2 in phosphate-buffered saline (PBS).

Synergistic dynamics of photoionization and photoinduced electron transfer probed by laser flash photolysis and ultrafast fluorescence spectroscopy.

Photoionization (PI) and photoinduced electron transfer (PET) dynamics of coumarin 450 (C450) in micelles were investigated in the time domains of micro to femtoseconds using steady-state and time-resolved absorption and fluorescence spectroscopy. The PI of C450 occurs inside the micelles leads to the formation of C450 cation radical (CR) and hydrated electron, which is characterized by the respective transient absorption. The PI of C450 is monophotonic in nature and the yield is dependent on the charge of the micelles. The observation of amine CR in the transient absorption confirms the PET from amine to the excited state of C450 in micelles, which results in the quenching of both fluorescence intensity and lifetime. The decrease in femtosecond fluorescent decay of C450 and the absence of transient C450 radical anion in the presence of amine implies that the concerted ultrafast PET promoted PI and PET to the C450 CR-electron pair. The decrease in the time constant for the formation of relaxed state in the presence of amines is due to the ultrafast PET to the C450 CR-electron pair, which prevents the formation of a relaxed state through recombination at a longer time scale. In the present investigation, the recombination dynamics of the CR-electron pair is justified as one of the origins of the slow solvation in micelles. The influence of amine concentration on the decay of C450 CR indicates ET reaction between C450 CR and amine, which is further confirmed by the bleach recovery of C450 ground state in the presence of amine.

Water-Soluble Pyrene-Adorned Imidazolium Salts with Multicolor Solid-State Fluorescence: Synthesis, Structure, Photophysical Properties, and Application on the Detection of Latent Fingerprints.

New water-soluble acetylpyrene-bound imidazolium salts (1-N-methyl-3-(2-oxo-2-(pyren-1-yl)ethyl)-imidazolium bromide (1), 1-N-isopropyl-3-(2-oxo-2-(pyren-1-yl)ethyl)-imidazolium bromide (2), 1-N-allyl-3-(2-oxo-2-(pyren-1-yl)ethyl)-imidazolium bromide (3), and 1-N-isopropyl-3-(2-oxo-2-(pyren-1-yl)ethyl)-imidazolium hexafluorophosphate (4)) were synthesized from the reaction between 1-bromoacetylpyrene and N-substituted imidazoles in excellent yield. The new molecules were fully characterized by elemental analysis, FT-IR, multinuclear (1H, 13C, and 19F) NMR techniques, and single-crystal X-ray diffraction analysis. Investigations on the crystal packing of 1, 3, and 4 show the presence of inter/intramolecular weak interactions, including the π···π stacking interaction between the pairs of pyrene molecules. The photophysical properties were investigated in detail for the four imidazolium salts. Experiments show that the emissions observed for all the four compounds are due to the excited monomer and static excimer. Very interestingly, all the four compounds exhibit solid-state multicolor fluorescence depending on the excitation wavelength. The solid-state emissions were monitored using a fluorescence microscope. Finally, a fingerprint powder was formulated based on compound 4 and demonstrated as an efficient fluorescent fingerprint powder for forensic applications. The formulated powder revealed all the 3 level information along with peculiar individual characteristics of the fingerprints under investigation. The fingerprints were further viewed through a fluorescence microscope, and the results were discussed in detail.

Thermal-Induced Twisting and Photoinduced Planarization of Salicylideneaniline in Alcohols.

Thermofluorochromism and photochromism of salicylideneaniline (SA) in alcohol were investigated using steady-state and time-resolved fluorescence and absorption spectroscopy. The planar trans-enol form of SA in alcohols is converted into the twisted trans-enol form on heating. This conversion results change in the emission maximum from the 530 to the 440 nm region with an increase in fluorescence intensity, which confirms the absence of intramolecular hydrogen bonding between imine nitrogen and phenolic hydrogen in the twisted trans-enol form. The activation barrier for thermal-induced formation of the twisted trans-enol form in methanol was determined experimentally and was found to be 20.15 ± 2.22 kcal/mol. The rotation of the phenolic C7-C8 and C7-N1 bond followed by breaking of the intramolecular hydrogen bond and formation of an intermolecular hydrogen bond with alcohol solvent molecules results in the thermally stable twisted trans-enol form in alcohol solvents. The biexponential nature of the fluorescence decay of the twisted trans-enol form of SA confirms that the emission originates from multiple (π-π* and n-π*) excited states. On photolysis under UV light, the twisted trans-enol form is converted back into the planar trans-enol form. The time-resolved absorption and excitation-resolved fluorescence spectrum of SA in methanol confirm the existence of the twisted cis-keto form as a transient photochromic intermediate in the light-induced planarization of SA in alcohols. In alcohols, an interplay between the intra- and intermolecular hydrogen-bonding controls excited-state reaction dynamics and conformational relaxation of SA, which are responsible for the photochromism of salicylideneaniline.

Excitation-resolved area-normalized emission spectroscopy: a rapid and simple steady-state technique for the analysis of heterogeneous fluorescence.

Excitation-resolved area-normalized emission spectroscopy (ERANES) is proposed as a new steady-state fluorescence technique for the investigation of heterogeneous fluorescence (HGF) from a mixture of fluorophores and fluorophores present in various environments and proteins. The presence of a single isoemissive point was used to confirm the presence of two absorbing and emitting species in the system. The isoemissive point was found to occur at the wavelength where the ratio of wavelength dependent fluorescence quantum yield of the emissive species equals to the ratio of their total fluorescence quantum yield. The application of the ERANES method for resolving HGF from a mixture of fluorophores having similar or different fluorescence lifetimes with a relatively high degree of fluorescence spectral overlap was demonstrated. When compared to excitation fluorescence (EF) matrix and time-resolved methods, ERANES was found to be a simple analytical method for analyzing HGF from a mixture of fluorophores, and from fluorophores present in heterogeneous media, such as cells, membranes, etc., and for analyzing protein fluorescence, without the requirement for sophisticated instrumentation and data analysis.