A 4,8,12-triazatriangulene (TATA) cation derivative bearing tetra(ethylene glycol) group was synthesized by direct functionalization of the TATA framework at the 2-, 6-, and 10-positions. Emission properties of the amphiphilic TATA derivative in three different environments-in the monomer state, in aggregates formed in aqueous media, and in the solid state-were carefully analyzed based on the radiative (k(f)) and nonradiative (k(nr)) rate constants. We found that the fluorescence quenching of the TATA cation derivative upon aggregation is dominantly attributed to the decrease in the k(f) value but not to the change in the k(nr) value.