Effect of Stabilizers on Nanoparticles

In the present study, photophysical properties of Chlorin e6 (Ce6) in 12 different protic, aprotic and non-polar solvents were determined using UV-visible and fluorescence spectroscopy. Solvatochromic effects were determined by the changes in quantum yield, Stokes shift, fluorescence half-life and excited state dipole moment of Ce6 in the different solvents. The absorption shifts observed in different solvents were further analysed using the Kamlet-Abboud-Taft model and the nature of solute-solvent interaction between Ce6 and different protic and aprotic solvents elucidated. The quantum yield was found to be the highest in protic solvents (except water), followed by aprotic and non-polar solvents. Solvent polarity parameters showed a linear increasing trend with Stokes shift and fluorescence half-life, which indicated the presence of Ce6-solvent interaction. Using the Kamlet-Abboud-Taft model, a direct correlation between the solvent polarity parameters and absorption shift was observed, which substantiated the existence of Ce6-solvent interaction hydrogen bond formation. Finally, the excited state dipole moment in alcohols was found to be relatively high, suggesting a highly π-π* excited state transition and greater fluorescence activity of Ce6 in alcohols. The solute-solvent interaction study is an important consideration for organic dyes as it provides changes in the electronic distribution upon excitation. Such interaction thus generates new solvent properties such as preferential solvation, which makes the nature of solute-solvent interaction more specific and complex. One of the simplest ways to study such interactions is with the use of UV-visible absorption spectra. Interaction of a solute with various solvents usually correlated with a shift in absorption wavelength. This shift is commonly termed as solvatochromism and depends on the electronic structure of the probe and the solvent molecule. Solvatochromism is an important factor for determination of intermolecular solute-solvent interactions in the ground state and the first excited state. Solvatochromism mainly caused by the differential solvation of the ground and the first excited state of the molecule of interest. The positive or negative shift in the λmax depends on the relative stabilization of the ground and excited state. The observation of solvent induced shift in electronic spectra has been widely used to study the changes in electronic distribution in excited state of solute molecules. Fluorescent probes have been extensively used for determination of solvent polarity for studies of heterogeneous media, biochemical and biological systems.

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