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The present study elucidates the extended nature of the weak interaction between methanol and chloroform in its mixture using steady-state, ultrafast and single molecule spectroscopic methods. UV-vis absorption spectroscopy using a solvatochromic dye indicates a synergistic solvation in the methanol-chloroform binary solvent mixture, which causes the solvatochromic dye to sense increased polarity compared to the bulk counterparts. Such synergism was not observed in the emission study and is explained by the weak nature of the interaction between methanol and chloroform. Fluorescence anisotropy and single molecule fluorescence spectroscopy are employed to understand the nature of such weak interaction on femtosecond to microsecond time scale. Retardation of both the rotational and translational diffusion of the reporter molecule indicates that the observed weak interaction is extended over large dimension in the condensed phase. [ABSTRACT FROM AUTHOR]

In this work, we have addressed the problem of "acidity" of the water-pool of a reverse micelle (RM) through the well-known inversion of sucrose reaction as a tool of investigation. This reaction has been performed inside positively and negatively charged RM and the rates are compared with that in bulk water. We propose that the buffer-like action in a water-pool is much stronger than expected earlier. The rate of sucrose hydrolysis slowed down in the negatively charged AOT reverse micelle while it sped up for the positively charged CTAB reverse micelle. However, temperature-dependent measurements showed that the activation energy remained the same for all the cases. It has been concluded that a proton gradient exists inside the water-pool of the reverse micelle and it determines the buffer-like action of the water-pool that persists until about 2 N of HCl in AOT RM of w0 = 10.5. [ABSTRACT FROM AUTHOR]

Fluorescencequenching studies through steady-state and time-resolvedmeasurements are inadequate to quantify the bimolecular electron transferrate in bulk homogeneous solution due to constraints from diffusion.To nullify the effect of diffusion, direct evaluation of the rateof formation of a transient intermediate produced upon the electrontransfer is essential. Methyl viologen, a well-known electron acceptor,produces a radical cation after accepting an electron, which has acharacteristic strong and broad absorption band centered at 600 nm.Hence it is a good choice to evaluate the rate of photoinduced electrontransfer reaction employing femtosecond broadband transient absorptionspectroscopy. The time constant of the aforementioned process betweenpyrene and methyl viologen in methanol has been estimated to be 2.5± 0.4 ps using the same technique. The time constant for thebackward reaction was found to be 14 ± 1 ps. These values didnot change with variation of concentration of quencher, i.e., methylviologen. Hence, we can infer that diffusion has no contribution inthe estimation of rate constants. However, on changing the solventfrom methanol to ethanol, the time constant of the electron transferreaction has been found to increase and has accounted for the changein solvent reorganization energy. [ABSTRACT FROM AUTHOR]

Cs 3 Cu 2 I 5 perovskite displays a Stokes-shifted photoluminescence (PL) at 445 nm, attributed to the self-trapped excitons (STEs). Unlike that observed in other perovskite materials, the free-exciton emission is not evidenced in this case. Herein, we reveal the existence of a short-lived high-energy emission centered around 375 nm through the reconstruction of time-resolved emission spectra (TRES), which is independent of the shape/size of Cs 3 Cu 2 I 5 perovskite. This high-energy emission is proposed to originate from the free-exciton-derived distorted S1 state of the 0D Cs 3 Cu 2 I 5 moiety. Moreover, STE PL (∼445 nm) was found to have phosphorescence characteristics. Theoretical calculation confirms a facile intersystem crossing at the Franck-Condon geometry, indicating the high lifetime of the STE and its triplet nature. The existence of a high-energy emissive state and the phosphorescent nature of the STE PL band provide valuable insights that could advance our understanding of the photophysics in these materials.