In this study, a millimeter-thick photoresponsive polymer capable of dynamic viscoelastic modulation under blue light irradiation is reported. This star-shaped polymer has a polydimethylsiloxane (PDMS) backbone networked via photoresponsive hexaarylbiimidazole (HABI) and is referred to as PDMS–HABI. By controlling the molecular weight of the PDMS precursor, the density of HABI was tuned, thereby enabling light penetration and photoresponse in samples with thicknesses up to 2 mm. Compression test