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We report the absorption spectra and photophysical properties of homo and hetero‐aggregate assemblies of a strongly emissive N‐annulated perylene dye (P) and of a dyad made of P and a methyl viologen derivative (P‐MV), in ethanol‐water solutions. In homo‐aggregate assemblies of P, the π‐π* fluorescence of the isolated chromophore is replaced by excimer emission at lower energy, with a lifetime of 900 ps, due to excimer formation from the initially prepared excitons. In homo‐aggregate assemblies of P‐MV, photoinduced charge separation, with formation of P+‐MV− species, occurs in 3 ps with a charge recombination of 20 ps. In hetero‐aggregate P/P‐MV systems, the light energy absorbed by the P components delocalizes over various P subunits, and when a P‐MV unit is reached, charge separation occurs; however, excimer emission is present for P/P‐MV ratio larger than 3 : 1, indicating that delocalized excitons within the hetero‐aggregate systems extend over a limited number of P chromophores. [ABSTRACT FROM AUTHOR]