TD-DFT investigation on the electronic spectra of novel N-methylmaleimides linked with indolizine ring system

The major electronic absorption features in visible region were computationally investigated for a series of novel N-methylmaleimide derivatives. The newly synthesized compounds through the reaction of indolizines with N-methylmaleimides exhibited their maxima ranging 587?634 nm in solution at room temperature. Time dependent density functional theory (TD-DFT) calculations were performed in order to elucidate their structure?color relationship, as well as to assess its performance using a variety of exchange-correlation (XC) functionals and basis sets. 4-(Indolizin-3-yl)-1-methyl-2,5-dioxo-1H-pyrrole-3-carbonitrile (referred to 3a hereafter), a representative of the new compounds, was analyzed in detail on its intramolecular push?pull electronic structure. As a consequence of systematic evaluation of computational strategies for 3a, we found that the theoretical λmax obtained by PCM-TD-DFT/6-31+G(d, p)//DFT/6-311G(2d, 2p) level of theory, which was consistently employed throughout this study, has converged within 2 nm deviation from λmax of the most elaborated level considered. Among some of the molecules with near-planarity structure, unusual discrepancies between the theoretical and the experimental λmax were observed, which should be attributed to the well-known TD-DFT limitation to describe multi-configurational or charge transfer (CT) excitations

Synthesis of a Novel Pyrazine-Pyridone Biheteroaryl-Based Fluorescence Sensor and Detection of Endogenous Labile Zinc Ions in Lung Cancer Cells

A small extent of endogenous labile zinc is involved in many vital physiological roles in living systems. However, its detailed functions have not been fully elucidated. In this study, we developed a novel biheteroaryl-based low molecular weight fluorescent sensor, 3-(phenylsulfonyl)-pyrazine-pyridone (5b), and applied it for the detection of endogenous labile zinc ions from lung cancer cells during apoptosis. The electron-withdrawing property of the sulfonyl group between the phenyl ring as an electron donor and the pyridone ring as a fluorophore inhibited the intramolecular charge transfer state, and the background fluorescence of the sensor was decreased in aqueous media. From the structure-fluorescence relationship analysis of the substituent effects with/without Zn 2+ , compound 5b acting as a sensor possessed favorable properties, including a longer emission wavelength, a large Stokes shift (over 100 nm),a large fluorescence enhancement in response to Zn 2+ under physical conditions, and good cell membrane permeability in living cells. Fluorescence imaging studies of human lung adenocarcinoma cells (A549) undergoing apoptosis revealed that compound 5b could detect endogenous labile zinc ions. These experiments suggested that the low molecular weight compound 5b is a potential fluorescence sensor for Zn 2+ toward understanding its functions in living systems

One-Pot Synthesis of 6-Substituted Amino-2,4-diaminopyrimidine Derivatives Using Ketene Dithioacetals with Amines and Guanidine Carbonate

6-Substituted amino-2,4-diaminopyrimidine derivatives were prepared by one-pot synthesis using ketene dithioacetals, amine compounds, and guanidine carbonate in pyridine. These pyrimidine products displayed blue fluorescence in the solid state

Synthesis, photophysical evaluation, and computational study of 2-methoxy- and 2-morpholino pyridine compounds as highly emissive fluorophores in solution and the solid state

Two 2-pyridone tautomeric analogs, methoxypyridine 4 and N-methylpyridone 5, were synthesized, and their spectroscopic properties were investigated both experimentally and computationally. A detailed photophysical study reveals that 4 shows high fluorescence quantum yields not only in chloroform but also in ethanol, and the strong fluorescence in solution might be attributed to the enol form (pyridine) of the 2-pyridone. Furthermore, we designed and synthesized novel 2-substitued pyridines to achieve more intense emissions in both solution and the solid state. Substituent modification with phenylsulfonyl,morpholino, and 4-diethylamino groups greatly affected the fluorescence properties, and methoxypyridine 7 and morpholinopyridine compound 8 showed fluorescence in various solvents (Ф = 0.59-0.95) and the solid state (Ф = 0.12-0.15). A hypsochromic shift in the emission maximum wavelength and strong fluorescence in the solid state (Ф = 0.39) were observed for dimorpholinopyridine 9. Morpholinopyridine 11 showed intense fluorescence in all nonpolar and polar solvents. Systematic time-dependent density functional theory calculations were performed for the compounds whose electronic and fluorescent maxima were computationally reproduced with good agreement to those from experiment. In detail, the drastic difference in the emission intensity between 4 and 5 in solution was successfully explained using CASSCF calculations, which revealed the presence of conical intersections between the ground and the excited states

Synthesis and Fluorescence of 2-pyrone Derivatives for Electroluminescence Devices(SPECIAL ISSUE CELEBRATING TEN YEARS OF ESTABLISHMENT OF FACULTY OF ENVIRONMENTAL STUDIES)

A convenient method of synthesizing 6-aryl- and 6-styryl-4-methylsulfanyl-2-oxo-2H-pyran derivatives through the reactions of various active methylene compounds with ketene dithioacetals and investigation of the fluorescence of the products in the solid state are described. The structure-activity relationships of various 2-pyrone derivatives and the effects of different aryl and styryl substituents on the aryl group were clarified. Materials which are strongly fluorescent in the primary colors (red, green, and blue) are the most important materials in the field of organic electroluminescence (EL). The 2-pyrone derivatives synthesized in this work emitted light at 447～620 nm in the solid state

High-Affinity Ratiometric Fluorescence Probe Based on 6-Amino-2,2′-Bipyridine Scaffold for Endogenous Zn²⁺ and Its Application to Living Cells

Zinc is an essential trace element involved in many biological activities; however, its functions are not fully understood. To elucidate the role of endogenous labile Zn2+, we developed a novel ratiometric fluorescence probe, 5-(4-methoxyphenyl)-4-(methylsulfanyl)-[2,2′-bipyridin]-6-amine (6 (rBpyZ)) based on the 6-amino-2,2′-bipyridine scaffold, which acts as both the chelating agent for Zn2+ and the fluorescent moiety. The methoxy group acted as an electron donor, enabling the intramolecular charge transfer state of 6 (rBpyZ), and a ratiometric fluorescence response consisting of a decrease at the emission wavelength of 438 nm and a corresponding increase at the emission wavelength of 465 nm was observed. The ratiometric probe 6 (rBpyZ) exhibited a nanomolar-level dissociation constant (Kd = 0.77 nM), a large Stokes shift (139 nm), and an excellent detection limit (0.10 nM) under physiological conditions. Moreover, fluorescence imaging using A549 human lung adenocarcinoma cells revealed that 6 (rBpyZ) had good cell membrane permeability and could clearly visualize endogenous labile Zn2+. These results suggest that the ratiometric fluorescence probe 6 (rBpyZ) has considerable potential as a valuable tool for understanding the role of Zn2+ in living systems