To remotely control ionization of polymer assemblies, we tailored amphiphilic diblock polyacrylates with varying hydrophilic and hydrophobic block lengths and containing pendant 2-hydroxyazobenzene photoswitchable groups in the hydrophilic block. Formation in water of rodlike polymer micelles was obtained upon hydrophobic assembly of the pendant cholesterol groups present in the hydrophobic block. Phototriggered variation of both pH and UV-vis spectral properties confirmed that hydroxylazobenzene moieties, gathered in the hydrophilic corona, underwent both isomerization and ionization upon exposure to UV light. Dispersions of rods can accordingly be ionized on demand.