Photophysical properties of 4,4-diaminodiphenyl sulfone in micelles and the role of BF-anion on micellar aggregation

The modulation of already established charge transfer (ICT) emission characteristics of 4,4′-diaminodiphenyl sulfone (Dapsone) in different micelles and also its further alterations due to physicochemical change of micelles in company with added room temperature ionic liquid (IL) have been elucidated in this paper with the help of steady state and time-resolved fluorescence spectroscopy. Dapsone seems to enter inside the cationic micelle beyond interfacial region, as evinced by the emission intensity enhancement and blue shift. In anionic micelle little intensity increase and the blue shift of Dapsone point to the presence of the probe near the interfacial region. From Cu2+ quenching study it has been confirmed that among the ionic micelles the probe makes shallow penetration in anionic micelle compared to that in cationic micelle. In non ionic surfactants the accessibility of the probe to the ionic quencher increases with increasing chain length. The probe's emission intensity is highest in non ionic Tween 20, but it starts decreasing with increasing alkyl chain length up to Tween 60 and it drastically reduces in Tween 80 nearly same as that in water. IL seems to affect the micellization of anionic, cationic and nonionic micelles differently resulting in shrinking and inflating the micellar size. The calculated rotational relaxation time of the micelle–probe complex is very slow compared to the probe rotation inside micelle.

Addition of ionic liquid in probe–surfactant complex increases/decreases the sizes of the micellar complexes differently.Figure optionsDownload as PowerPoint slideHighlights
► Interaction of ionic liquids on probe micellar photophysics.
► Encapsulation of probe in non-ionic micelles is hindered by the increasing chain length of the micelles.
► Decreases probe emission intensity in non-ionic micelle with increasing alkyl chain length which tends to that in water.
► Addition of IL to anionic and cationic micelles effects emission of probe differently downshift and upshift, respectively.
► Addition of IL causes a increase/decrease in diameter of micelles.