Indoline based donor–acceptor system (InBT) exhibits a colour transition from pink to orange to yellow in chloroform facilitated by the photo-oxidation of the N,N-dimethyl indoline of InBT and neutralized by chloride counter ions upon light irradiation at short and long range excitation wavelengths of 320 and 500 nm, which leads to spherical aggregates when subjected to methanol vapour diffusion (MVD).