Phototunable supersoft elastomers were prepared by photo-cross-linking molecular bottlebrushes with poly(n-butyl acrylate) (PBA) side chains. Bottlebrushes were synthesized by atom transfer radical polymerization (ATRP) and Br-chain end functionalities were replaced by photo-cross-linkable coumarin units. Photo-cross-linking and photoscission of molecular bottlebrushes resulted in tunable elastomeric behavior quantified by dynamic mechanical analysis. The cellsubstrate interactions, tuned by UV-light, depended on surface morphology and softness that could be as low as several kilopascals.