A styrene based water soluble polymer (polymer-A) has been explored as a host for solubilizing otherwise insoluble aromatic hydrocarbons in water. The increased local concentration of encapsulated aromatic hydrocarbons within the hydrophobic pockets of polymer-A was utilized for performing efficient photodimerization of acenaphthylene (1) and six 9-substituted anthracenes [AnCOOH, AnCHO, AnCH2OH, AnCH3, AnBr and AnCN] in water. Photodimerization of these aromatic hydrocarbons were more efficient than in water and yielded dimers even at low concentrations (∼10−4 M). At the same concentration of anthracenes in organic solvents such as benzene and methanol, no dimers were formed even after 48 h of irradiation. Although the polymer-A was able to increase the local concentration of the reactant aromatics it was unable to orient them towards a single dimer.