A new hybrid lead iodide material (HP1) having 4-vinylphenylene ammonium as the organic cation has been prepared. The structural formula based on chemical analysis of HP1 corresponds to PbI2.5(4-styrylammonium)0.5. The crystallinity of HP1 was confirmed by powder X-ray diffraction and high resolution transmission electron microscopy. The presence of the styryl ammonium moiety in HP1 allows post-synthetic modification by radical copolymerization with styrene to obtain the HP2 material with higher hydrophobicity. Stability tests reveal that both HP1 and HP2 show hydrogen evolution in the dark, indicating about 0.6% partial decomposition of the hybrid material. This hydrogen evolution increases by a factor of 3 when HP1 and HP2 are exposed to visible light. X-ray photoelectron spectroscopy analysis shows an increase of NH2 groups and a decrease of NH3+ units suggesting that the origin of hydrogen evolution is the deprotonation of ammonium ions.