We present ab initio time-dependent density-functional calculations for the optical properties of molecules, atomic clusters, functionalized carbon nanotubes, and metal-nanotube heterostructures. Our calculations are carried out in the framework of a real-space higher-order finite difference method combined with the pseudopotential approximation. In this method, the Kohn–Sham equations for electronic states are solved self-consistently on a real-space three-dimensional Cartesian grid without the use of explicit basis functions. The time-dependent density-functional linear response formalism is applied to calculate the excited-state properties of the water molecule, analyze the optical spectra of potassium atoms and clusters adsorbed on graphene and carbon nanotubes, study the assembly of organic molecules to carbon nanotubes and compute the Stokes shifts in hydrogenated silicon clusters. The results of our calculations show that the time-dependent density-functional computational approach is flexible and can be successfully applied to a variety of different physical problems.