Understanding dynamic relaxation Mechanisms in self-diffusion and constraint release processes of rod-coil block copolymers is important for many technological applications, that employ neat melts or concentrated solutions. Using,a model system composed of poly(alkoxyphenylenevinylene) rods, and,polyisoprene coils reptation theories of entangled rod-coil block copolymers are investigated in the isotropic melt state. Self-diffusion was Measured by forced Rayleigh scattering using a red laser line and a new blue photoswitchable dye that allow operation above the bandgap of most semiconducting polymers In contrast to previous tracer studies where the diffusion of rod-coils through a coil homopolymer matrix is slowed relative to coil homopolymers because of a Mismatch in the curvature of the rod and coil entanglement tubes, slowed diffusion is only present in self-diffusion measurements above a critical molecular weight. An activated reptation mechanism with constraint release is proposed as a modification to the description of entangled rod-coil block copolymer dynamics, where the slowing occurs when-the time scale of rod block reptation is faster than the reorganization of the surrounding entanglement,tube. This mechanism is supported by additional tracer diffusion experiments on polyalanine-b-poly(ethylene oxide) diblocks in aqueous entangled poly(ethylene oxide) matrix solutions and Kremer-Grest simulations where the matrix molecular weight is varied. The slowing of tracer diffusion in rod-coil block copolymers relative to coil homopolymers is significantly weaker for smaller matrix polymers, confirming the proposed constraint release effects.