Mmm, just a small comment on an old thread: It is "possible" in the sense that TM doesn't complain. COSMO is not implemented for TDDFT, though, so you will misleadingly only do a normal gas-phase TDDFT on top of COSMO orbitals (at least up to the present release V6-2). How much of solvation effects this includes, if any, I don't know. Might be that it only produces crap.