Molecular-size uncapped CdSe clusters are synthesized via the electroporation of synthetic dioleoylphosphatidylcholine vesicles of diameter 178 nm. Cd²⁺ ions, originally entrapped in the vesicles, are ejected through the transient pores of the vesicle membrane into the bulk where they can react with SeSO₃²⁻ ions in basic condition to form CdSe clusters at room temperature. Growth and self-aggregation of CdSe clusters is slowed down to timescales of days by their adsorption at the exterior surface of the vesicle, which permits spectral monitoring of the continuous growth process over a long period of time. Growth in the molecular size regime is found to entail novel blue-shifts of the characteristic absorption band. The blue-shift of the transition energy is in agreement with an analogous oscillation of the HOMO–LUMO gap calculated by the use of density functional theory for (CdSe)_n clusters. The reason for the blue-shift absorption spectra of molecular-size CdSe clusters is interpreted as the higher stability and bigger gaps of magic number. On the basis of the similarity between the experimental and theoretical trends, the characteristic absorption peaks of 256 nm, 215 nm can be assigned to the monomer or dimer, trimer clusters of CdSe, respectively. Any further growth beyond trimers is associated with the customary monotonic red-shift of the absorption band, due to quantum size effects.