pH triggered self-assembly induced enhanced emission of water soluble phosphonic acid–NDI amphiphiles 1 is described. At pH 4.5, the amphiphile self-assembled into interwoven fibres, whilst a ladder-type network was observed at pH 7. At pH 9.5, NDI amphiphile assembled into more complex fractal nanostructures. Interestingly, enhancement of emission was observed under both acidic and basic conditions.