The photophysics and photochemistry of alpha-terthiophene (alpha T), compartmentalized in mixed nonionic/anionic micelles, hove been investigated with focus on the influence of the micellar surface charge density on the formation of the radical coupling product alpha-hexathiophene (alpha H). By varying the ratio of nonionic-to-anionic surfactants, and assuming ideal mixing, the charge density of the mixed micelles was varied. From Poisson-Boltzmann calculations, performed using the cell model, the electrostatic potential and the counterion activity were estimated as a function of the distance from the micellar surface. Upon excitation, the triplet state of alpha T is formed, from which the alpha T radical cation con be formed by absorption of a second photon. The radical cation con form alpha H if it encounters another alpha T radical cation. Under the experimental conditions used, this implies that the alpha H formation only occurs if the compartmentalized radical cation is able to migrate from its host micelle to another micelle, either via the surrounding bulk or by fusion of two micelles followed by mixing of their contents before micellar fission. The formation yield of the radical cation depends on the charge density of the mixed micelle; a lower charge density that is, at amount of nonionic surfactant, lowers the yield. The yield of the coupling product alpha H, however, does not follow the some trend. A maximum yield of alpha H is found at intermediate nonionic surfactant molar ratios. This behavior is understood in terms of the Poisson-Boltzmann simulation results and by comparing charge-density changes as a function of molar fraction with the changes in counterion activity. The alpha H yield is a result of the balance between an increased possibility of radical cation bulk migration and a lowered electrostatic stabilization of the radical.