Lighting up green nanodomains: how 4-aminophthalimide reveals the secrets of biocompatible reverse micelles

The photophysical properties of 4-aminophthalimide (4-AP) were investigated in reverse micelles formed by sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (AOT) using two biocompatible solvents, isopropyl myristate (IPM) and methyl laurate (ML), as the continuous phase. Absorption and fluorescence spectroscopy were employed to analyze the influence of surfactant concentration and water content (W 0 = [water]/[AOT]) on the microenvironment sensed by the probe. A bathochromic shift in both absorption and emission bands were observed with increasing AOT concentration, indicating that 4-AP resides in increasingly polar environments. Red-edge excitation experiments revealed restricted interfacial dynamics, and in the IPM/AOT/water system, the emergence of an additional emission band suggests the formation of an intramolecular charge-transfer (ICT) excited-state species. Partition constants (K p ) between the micellar interface and external solvent were determined, showing that water enhances probe incorporation and polarity at the interface. The comparison with benzene and n-heptane systems underscores the potential of biocompatible solvents as sustainable media to mimic organized microenvironments for photophysical and biochemical studies.