Pathway Diversity Leads to 2D-Nanostructure in Photo-triggered Supramolecular Assembly.

This Communication reports photo-triggered supramolecular assembly of a naphthalene-diimide (NDI) derivative, appended with a photo-labile ortho-nitrobenzyl (ONB)-ester protected carboxylic acid. Photo-irradiation produces the free COOH group which facilitates H-bonding-driven face-to-face stacking of the NDI chromophores producing an ultra-thin (height <2.0 nm) two-dimensional (2D) nanosheet. In contrast, spontaneous supramolecular assembly of the same active monomer exhibits entirely different features such as uncontrolled growth, J-aggregation and fibrillar morphology. A completely different pathway for photo-triggered assembly is attributed to the dual function of the photo-caged pro-monomer in i) producing the carboxylic acid in controlled manner and ii) simultaneously inhibiting the spontaneous J-aggregation of the photo-generated monomers by ester-carboxylic acid H-bonding and in turn directing a distinct growth mechanism.