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An anionic surfactant (SDS) modulates the photoluminescence of graphene oxide (GO) in both acidic and alkaline medium. In the acidic medium (pH z 2), formation of hemi spherical surface micelles on the GO sheets creates a non-polar environment around the flourophoric moiety of GO and hinders the solvent relaxation. This leads to a significant 36 nm blue shift of the photoluminescence band, whereas in alkaline medium (pH z 10), SDS interacts with GO sheets in a different way due to the presence of negatively charged carboxylate ions at the GO edges. The repulsion between the negatively charged GO sheets and the intercalation of SDS within the basal planes of GO may weaken p-p stacking interaction which produces largely separate layers of GO. The largely separated GO sheets due to very weak stacking interactions among successive layers may behave almost like isolated functionalized GO, resulting in an enhancement of the photoluminescence intensity at 303 nm.

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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.

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.

we calculate the entropy change for irreversible adiabatic expansion for real gas that does not mention in most Physical Chemistry textbook. This often prompts undergrad students, who are customized to study the behavior of real gas and ideal gas in thermodynamic course, to ask about the entropy change in real gases when they are subjected to expand. Change in temperature is also very important in this regard. So how will a student determine the entropy change for irreversible process? This procedure is quite simple according the textbooks. We cannot directly apply the equation ∆S = S2 – S1 = ∫_i^f▒(đQ_rev)⁄T as for irreversible process ∆S may not be necessarily equal to ∫_i^f▒(đQ_irrev)⁄T . Although entropy is a state function, it does not depend on the path how the system changes its course to achieve the final state. First, we have to identify the initial and final states and then find a suitable reversible pathway for the course. The calculations of ideal gases for irreversible pathway are done in textbooks. However, students need to know for the real gases formulas for the entropy change so that one’s expectation matches with the experimental values when done in practical. Here we considered the calculations for irreversible adiabatic expansion (normal and free) and what happens to the temperature of the system when it achieves the final state.