The merocyanine isomer of 1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-indoline] spontaneously forms colored nano-objects on the substrate when cast from an aliphatic solvent solution at room temperature. During solvent evaporation and simultaneous exposition to UV irradiation, the blue substance abundantly precipitates from a photochromic solution within several seconds. Depending on the substrate pretreatment, the photochromic material either appears as a dark blue powder composed of globules similar to200 nm in diameter or forms a blue film consisting of small plates of similar to100 nm in size and larger flakes. Absorption spectra of globules are hypsochromically shifted as compared to monomer, while platelike structures exhibit a red shift indicating the presence of J-aggregates. Molecular association is strongly influenced by the presence of a nitro group in the 6-position in the pyran part and a bulky group at the nitrogen atom in an indolyl moiety. Solid samples of pure merocyanine stuff are thermally stable at room temperature for months after preparation, as was confirmed by Fourier transform infrared spectroscopy and C-13 NMR with cross-polarization and magic angle spinning. The method allows selective control of the formation of molecular assemblies by changing the solvent, the substituent position, or preparation conditions (i.e., temperature, concentration). Furthermore, it provides new opportunities in fundamental research on UV-mediated aggregate formation and for practical application of the photochromic spiropyrans. The material has been characterized by spectroscopic methods in order to derive structural information on the aggregates. A mechanism for a photomerocyanine association is proposed.