For the first time, fully characterized and stable trinuclear "double sandwich" molecules are reported with Hg(II) ion using a highly flexible porphyrin dimer. The molecules display interesting and intense luminescence properties at room temperature. The present investigation clearly demonstrates that attractive mercurophilic interactions do play an essential role in bringing two porphyrin macrocycles exactly on top of each other with an unfavorable fully eclipsed geometry to produce short Hg center dot center dot center dot Hg distances. Interactions between Hg(II) dz(2) orbitals provide the directionality with a linear Hg-3 core having short Hg center dot center dot center dot Hg distances despite the fact that ligand framework is highly flexible.