Double proton transfer in a polar nano-droplet: Phototautomerization of alloxazine in AOT/alkane reverse micelles containing water or glycerol

[Display omitted] •No Alloxazine tautomerization in AOT/alkane dispersions in absence of polar liquids.•Added water forms a nano-droplet at the core of the AOT reverse micelle particle.•Alloxazine molecules inside water nano-droplets undergo phototautomerization.•Steric factors hinder similar Alloxazine tautomerization in Glycerol nano-droplets. Alloxazine phototautomerization is believed to occur through an excited state double proton transfer (ESDPT) mechanism involving cyclic intermolecular H-bonded complexes between Alloxazine and hydroxylic solvents like water and alcohols. In AOT/alkane dispersions in the absence of any polar liquid, Alloxazine molecules reside inside the polar core of the AOT reverse micelle nanoparticles, where they involve in H-bonding with the anionic sulfonate head-groups of the AOT molecules, but are unable to generate the appropriate cyclic intermolecular H-bonded complexes conducive to ESDPT. However, tautomerization is switched on with addition of water and formation ofwater nano-droplet at the core of reverse micelle. Evidently, the Alloxazine⋅⋅⋅⋅AOT H-bonds are now replaced by Alloxazine⋅⋅⋅⋅Water H-bonds, promotingESDPT. On the other hand, Alloxazine phototautomerization is hindered in Glycerol, irrespective of whether the latter is in the bulk liquid state or in the form of a polar nano-droplet. This may be explained by steric considerations.