We use density-functional theory calculations to study the stability, electronic, and optical properties of free-base and Zn porphyrins and phthalocyanines (H${}_{2}$P, H${}_{2}$Pc, ZnP, and ZnPc) noncovalently attached onto a semiconducting carbon nanotube (CNT). The macrocycle physisorption is described by van der Waals density functional while optical response is obtained through the imaginary part of the dielectric function. Our results show a rather strong macrocycle binding energy, ranging from 1.0 to 1.5 eV, whereas the CNT geometry and electronic properties are weakly affected by the adsorbates. The optical spectrum shows that CNT-porphyrins and CNT-phthalocyanines assemblies would absorb at different energies of the visible solar radiation spectrum, which would increase the conversion energy efficiency in a photovoltaic device including both macrocycles.