Since the mechanical properties of individual polymers have become accessible with single molecule force spectroscopy, detailed insight was gained into the molecular origin of their elasticity. Active, optically switchable polymers were introduced as photonic muscles and used in single molecule motors. Here, we present experimental data and calculations to describe the mechanical properties of poly(azobenzene-peptides) in the complete force regime accessible by AFM. The high force regime is very well described by ab initio quantum mechanical calculations, while for the low force regime we combine ab initio calculations with a description of the entropic forces based on the freely rotating chain model. Finally, a one-parameter fit for the different configurations of the poly(azobenzene-peptide) and a quantitative description of the optically induced actuation are given.