Electronic and optical properties of phosphorene quantum dots functionalized with an organic molecule, porphyrin, are investigated using density functional theory with two different van der Waals functionals. The electronic structure of this complex is obtained and with this information, the real and imaginary parts of the dielectric function are calculated, from which, the interband optical response can be determined. Depending on the size of the quantum dot and the relative orientation between the dot and the organic molecule, it is found that the porphyrin physisorption leads to important modifications of the energy spectrum of the functionalized blue phosphorene quantum dots. These changes reflect in the optical response of the complex which shows features that come from both the blue phosphorene structure and the organic molecule. It is also found that the rotations of the molecule with respect to the phosphorene quantum dot do not practically alter the value of the binding energy. © 2019 Elsevier B.V.