Entropically and enthalpically driven self-assembly of a naphthalimide-based luminescent organic π-amphiphile in water.

Abstract

The self-assembly of π conjugated systems in water has emerged as an efficient method for the development of functional materials for biological applications. But the process is more difficult to understand and to control in water compared to organic solvents due to hydrophobic effects. For π-conjugated molecules, self-assembly in solution generally occurs due to either an enthalpic or entropic gain, but designing π systems that undergo self-assembly via both an entropically and enthalpically favorable process is challenging. Herein, we elucidate in detail the self-assembly of a luminescent naphthalene monoamide-based dipolar π-bolaamphiphile appended with a primary amine and triethylene glycol monomethyl ether (NMI-W) side chain into a vesicular nanostructure. By utilizing a detailed isothermal titration calorimetry (ITC) experiment, we have calculated the thermodynamic parameters associated with the self-assembly of NMI-W in water. Interestingly, the NMI-W shows both entropically and enthalpically favorable robust self-assembly into a vesicular structure, which can encapsulate both hydrophilic and hydrophobic guest molecules. The synergistic effect of dipole-dipole, π-π stacking and hydrophobic interactions of the NMI chromophore is found to be very crucial in driving self-assembly in an aqueous medium as revealed by various experiments and molecular dynamics.