No abstract

Local environment dependent photoluminescence (PL) of cerium incorporated GO nanoparticles (GOÀ Ce NPs) is investigated by using fluorescence quenching study in presence of aromatic nitro compounds (ANCs) and fluoride ion. Presence of trivalent and tetravalent cerium ions at the different locations of the GO based nanoparticles interact with ANCs and fluoride ions in a different manner depending upon the accessibility and local polarity of the excited cerium (III) ions. Proposed system is found to be most sensitive towards ortho-nitrophenol (quenching efficiency 70.5 %) with a high constant value of K D and K S , 8.7 × 10 4 and 7.0 × 10 4 respectively. Herein, the fluorescence quenching study of GOÀ Ce NP S reveals the different mode of interactions between the fluorophoric moieties and quenchers.[a] D.

To investigate the interaction among the graphene oxide layers by involving surface functional groups, photoluminescence (PL) from graphene oxide (GO), and hydroxyl enriched graphene oxide (OH-GO) in the UV-visible region are studied. Tuning of PL is observed by varying the concentration of aqueous dispersion of OH-GO, obtained by strong alkaline treatment on graphene oxide (GO). FTIR, Raman, XRD, and the microscopic study suggests the structural orderness of the OH-GO compared to GO. Hydroxyl functional groups at the surface of OH-GO facilitate the formation of aggregates through hydrogen bonds by involving solvent water molecules and the PL band in the visible region may be originated from such aggregates. With the increase in the concentration of OH-GO in the aqueous medium, the contribution of the visible PL band is markedly increased along with the decrease in the PL band in the UV region. The time-resolved study indicates the possibility of energy transfer from the species emitting in the UV region to the species emitting in the visible region. This energy transfer may be responsible for the marked enhancement of the visible band of the PL spectra of OH-GO at high concentrations.

The synthesis is described of a luminescent furophenanthraquinone derivative, 9‐methoxyphenanthro[4,3‐b]furan‐4,5‐dione (MPFD). The biological importance of tetracyclic furophenanthraquinones was considered and the tunable luminescence of MPFD in different solvents was studied to explore the nature of the specific interactions between MPFD and solvents. Observation of dual emission bands and identical nature of the fluorescence excitation spectra of MPFD monitored at the emission wavelength in polar solvents indicated the formation of two different types of species in the excited state, probably due to proton transfer from the solvent to MPFD. Luminescence intensity due to anionic species was found to be increased and the corresponding peak was red shifted with increase in the proton‐donating ability of the solvents, acting as an acid with respect to MPFD. Availability of more acidic protons in the solvent facilitated this phenomenon occurring in the excited state. MPFD also interacted with halogen‐containing solvents by forming electron donor–acceptor charge transfer (CT) complexes. This CT complex formation was dependent on the number of chlorine atoms; the position of the corresponding luminescence band varied with the polarity of the solvent. Extent of the CT increased with increase in the number of chlorine atoms in the dichloro, trichloro and tetrachloro solvents, whereas the luminescence peak due to the CT complex was found to be blue shifted with decrease in solvent polarity. Interaction of the synthesized bioactive MPFD with different solvents deserves biological importance as proton transfer and CT play pivotal roles in biology.

The growing importance of angelicin derivatives in medicine has prompted us to develop an efficient synthesis strategy for a thienoangelicin derivative, ethyl 8-methyl-2-oxo-2H-thieno[2,3h]chromene-3-carboxylate (MTCE), and investigate its potential applications in spatial probing, therapeutics, and optical sensing. This novel fluorophore, MTCE, exhibits large Stokes shift due to the intramolecular charge separation between the thiophene and coumarin nucleus in the excited state. This indicates its potential for probing spatial polarity. Specific solute-solvent interactions play a significant role in experimentally calculated excited state dipole moment, including longrange electrostatic interactions and hydrogen bonding. The multi-spectroscopic and molecular docking approaches reveal that novel MTCE also interacts in subdomain IIA of BSA by forming ground state complexes following a static quenching mechanism, with the binding constant calculated at ~10 4 M À 1 . The complexation is spontaneous (ΔG ~À 24 kJ mol À 1 ), and enthalpy-driven (ΔH ~À 43 kJ mol À 1 and ΔS ~À 61 J mol À 1 ), and is primarily mediated by hydrogen bonding and van der Waal forces. Furthermore, the unique fluorescence selectivity of MTCE towards Fe 3 + ions under neutral pH conditions, through the formation of a 1 : 1 stoichiometric complex, sets it apart from other common metal ions. Therefore, MTCE holds promising potential for effective utilization in optical sensing applications targeting metal ions.