Engineering multifunctionality in hybrid polyoxometalates (hybrid POMs) is an interesting but scarcely explored topic. Herein, we set about engineering two important materials properties, viz., photochromism and self-separating catalysis, in a hybrid POM by modulating the counterion motif. A series of six aromatic sulfonium counterions have been developed on the basis of an aromatic sulfonium counterion motif that allows structural and electronic fine-tuning by changing substituents at multiple locations. Using the aromatic sulfonium counterions and sodium molybdate, six new aromatic sulfonium octamolybdate hybrids (1-6) having formulas (HPDS)(4)[Mo8O26] (1), (HMPDS)(4)[Mo8O26] (2), (MPDS)(4)[Mo8O26] (3), (APDS)(4)[Mo8O26] (4), (AMPDS)(4)[Mo8O26] (5), and (MAPDS)(4)[Mo8O26] (6) (where HPDS = (4-hydroxyphenyl)dimethylsulfonium, HMPDS = (4-hydroxy-2-methylphenyl)dimethylsulfonium, MPDS = (4-methoxyphenyl)dimethylsulfonium, APDS = (4-(allyloxy)phenyl)-dimethylsulfonium, AMPDS = (4-(allyloxy)-2-methylphenyl)dimethylsulfonium and MAPDS = (4(methacryloyloxy)phenyl)-dirnethylsulfonium) have been synthesized, and their structures were confirmed by single crystal X-ray diffraction and ESI-MS analyses. Hybrids 1-6 acted as good solid-state photochromic materials exhibiting color change from white to purple under UV illumination (350 nm), and we show here that the photochromic properties of hybrids 1-6 could be modulated by changing the substitutions on the counterion motif. A coloration kinetic half-life (t(1/2)) of 0.33 min was achieved with this class of hybrid POMs. Hybrids 1-6 exhibited excellent self-separating catalytic properties toward the epoxidation of olefins, yielding up to 99% epoxide product with good selectivity in short time. The substituents on the aromatic sulfonium counterions helps to fine-tune the electronic, lipophilic, and solubility properties of the hybrids and thereby their catalytic properties. Moreover, we used ESI-MS analyses to understand the mechanism of catalysis exhibited by octamolybdates 1-6 in the presence of H2O2, and we succeeded in identifying a hitherto undetected intermediate, tetraperoxo-octamolybdates, shedding more light on the epoxidation mechanism.