Aliphatic poly(carbonate)s (APCs) with rapid and controlled degradation upon specific stimulation have great advantages for a variety of biomedical and pharmaceutical applications. In the present work, we reported a new poly(trimethylene carbonate) (PTMC)-based copolymer containing multiple 4,5-dimethoxy-2-nitrobenzyl photo cleavable groups as pendent chains. The six-membered light-responsive cyclic carbonate monomer (LrM) was first prepared from 2(hydroxymethyl)-2-methylpropane-1,3-diol and 4,5-dimethoxy-2-nitrobenzyl alcohol and then copolymerized with trimethylene carbonate (TMC) by 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) catalyzed ring-opening polymerization (ROP) to afford the light-responsive polycarbonate (LrPC). The light-triggered decomposition of LrM and LrPC was studied by NMR, UV/vis spectroscopy, and size exclusion chromatography (SEC), as well as ESI-ToF mass spectrometry. Stable monodisperse nanoparticles with hydrodynamic diameter of 100 nm could be formulated from 25% LrPC and 75% poly(lactide-co-glycolide) (PLGA) and applied for the encapsulation of temoporfin. Upon irradiation with UV light these particles displayed a significant decrease of the particle countrate and increased the release rate of temoporfin in comparison to standard PLGA nanoparticles. This work demonstrated that a combination of encapsulation of photosensitizer and light degradation using light-responsive polymers is suitable to enhance photodynamic therapy (PDT).