Intramolecular charge transfer emission of a new ketocyanine dye: Effects of hydrogen bonding and electrolyte

Simple dihydropyridine-based colorimetric chemosensors for heavy metal ion detection, biological evaluation, molecular docking, and ADMET profiling

In this study, two novel chemosensors containing dihydropyridine fragment namely; (2E, 2E')-1,1'-(2,6-dimethyl-1,4-dihydropyridine-3,5-diyl)bis(3-(4-(dimethylamino)phenyl)prop-2-en-1-one) (1), (2E,2E',4E,4E')-1,1' -(2,6-dimethyl-1,4-dihydropyridine-3,5-diyl)bis(5-(4-(dimethylamino)phenyl)penta-2,4-dien-1-one) (2) have been synthesized and characterized. The solvatochromic behavior was explored in different solvents of various polarities. The visual detection, as well as UV-Vis and fluorescence measurements were carried out to explore the colorimetric and optical sensing properties of the investigated chemosensors towards various metal ions such as Al3+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Mg2+, Hg2+ and Zn2+. The chemosensors 1 and 2 have strong detecting abilities, with excellent sensitivity and selectivity for Cu2+ and Fe3+, respectively, over the other metal ions. The chemosensors were totally reversible upon addition of EDTA to the formed complexes and displayed a turn on-off-on fluorescence response based on an effect of chelation-quenching fluorescence. The antioxidant activities of the investigated chemosensors were assessed. They were examined in-silico for their capacity to block the Akt signaling pathway, which is involved in cancer proliferation with interpreting their pharmacokinetics aspects. Furthermore, in-vitro antitumor evaluation against a panel of cancer cell lines for the investigated chemosensors has been examined. Conclusively, chemosensor 1 was more effective at scavenging free radicals and as an anticancer agent and could be exploited as a therapeutic candidate for cancer therapy than chemosensor 2 due to its potential inhibition of Akt protein.

Distinctive tunable photophysical properties of versatile environmentally-sensitive tribranched cyanopyridine fluorophores

In the present work, twenty-four environmentally-sensitive cyanopyridine fluorophores bearing pyrene and/ or fluorene with different para-substituted-phenyl moieties that have been previously designed and synthesized by us are studied in depth for their photophysical properties. Initially, the optical performances of the compounds were investigated by employing UV-visible and fluorescence spectroscopic tools in various aprotic and protic solvents. All the compounds exhibited absorption bands between 310 and 452 nm, and emission bands between 454 and 633 nm. High sensitivity emission spectra with solvents of different polarities were recorded and studied. The fluorescence quantum yield (ϕ_f) increased in solvents of low polarity and decreased on increasing the polarity of solvents. On the other hand, in case of strong electron donating (-NMe₂) and strong electron attracting (-CN) substitution, a pronounced increase in Stokes shifts (up to 252 nm, 14250 cm^-1) were recorded. Lippert-Mataga and Reichardts correlations, applied for estimating the variation in dipole moments (Δμ), suggested that the emissive state of designed fluorescence 3-cyanopyridine derivatives is of strong ICT character. The aprotic and protic solvents gave a linear plot for the Stokes shifts in a Lippert-Mataga plot, which appeared as two distinct domains in E_T(30) scales indicating the presence of hydrogen bondings. It was observed that for compounds 5b - 8b, with (-NMe₂) group on the skeleton of phenyl ring, the Lippert-Mataga and Reichardt-Dimroth's plots deviated from linearity signifying that 5b - 8b molecules were involved in specific interaction with protic solvents.

Synthesis, Structure, Properties, and Bioimaging of a Fluorescent Nitrogen-Linked Bisbenzothiadiazole

This paper describes the synthesis, structure, photophysical properties, and bioimaging application of a novel 2,1,3-benzothiadiazole (BTD)-based rationally designed fluorophore. The capability of undergoing efficient stabilizing processes from the excited state allowed the novel BTD derivative to be used as a stable probe for bioimaging applications. No notable photobleaching effect or degradation could be observed during the experimental time period. Before the synthesis, the molecular architecture of the novel BTD derivative was evaluated by means of DFT calculations to validate the chosen design. Single-crystal X-ray analysis revealed the nearly flat characteristics of the structure in a syn conformation. The fluorophore was successfully tested as a live-cell-imaging probe and efficiently stained MCF-7 breast cancer cell lineages.

Synthesis, spectral behaviour and photophysics of donor-acceptor kind of chalcones: Excited state intramolecular charge transfer and fluorescence quenching studies

The spectral and photophysical properties of two chalcones containing electron donating and accepting groups with intramolecular charge transfer characteristics were synthesized and characterized by (1)H NMR, (13)C NMR and X-ray crystallography. Both compounds show very strong solvent polarity dependent changes in their photophysical characteristics, namely, remarkable red shift in the emission spectra with increasing solvent polarity, large change in Stokes shift, significant reduction in the fluorescence quantum yield; indicating that the fluorescence states of these compounds are of intramolecular charge transfer (ICT) character. The solvent effect on the photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of both compounds have been investigated comprehensively. For both dyes, Lippert-Mataga and Reichardt's correlations were used to estimate the difference between the excited and ground state dipole moments (Δμ). The interactions of dyes with colloidal silver nanoparticles (Ag NPs) were also studied in ethanol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of dyes by Ag NPs.

Ultrafast dynamics and computational studies on diaminodicyanoquinodimethanes (DADQs)

Three diaminodicyanoquinodimethanes, 4-(R(1)R(2)C)-1-[(NC)2C]-C6H4 (R(1),R(2) = H2N, 1; R(1) = 3,5-Me2-4-OCH4H6N-, R(2) = H2N, 2; R(1) = 3,5-Me2-4-OCH4H6N-, R(2) = 4-Me-C5H9N, 3), were investigated using carbon-13 NMR, steady-state, and ultrafast transient absorption and ultrafast fluorescence spectroscopies to unravel the unusual characteristics of this class of chromophores. Computed (GIAO)B3LYP/6-31G* data for the zwitterions 1-3 using necessary solvation (PCM) models were shown to be in excellent agreement with observed structural and carbon-13 NMR data. The ground-state geometries of 1-3 contain a cationic methine group R(1)R(2)C- twisted from the C6H4 ring and an anionic methine group (NC)2C- in plane with the C6H4 ring in solution and solid state. The (13)C chemical shifts of the peak corresponding to the methine carbon at the (NC)2C- group of 1-3 are observed at 32.5-34.7 ppm, which are some 55 ppm upfield compared with the (13)C chemical shift for the methine carbons in TCNQ, 1,4-[(NC)2C]2-C6H4. The decay of the excited state in diaminodicyanoquinodimethanes is fast and dominated by nonradiative processes on the picosecond time scale, which depends on the viscosity of the medium. The dynamics of the excited-state decay is therefore limited by conformational changes through an intramolecular twisting motion. This twisting motion is hindered by friction, which, in turn, also depends on the functional group size of the system. The dominant nonradiative pathways after excitation are due to twisted excited-state conformers according to TD-DFT computations.