Martin Gouterman first proposed the four-orbital model in the 1960s to explain the absorption spectra of porphyrins [17, . According to this theory, the absorption bands in porphyrin systems arise from transitions between two HOMOs and two LUMOs, and it is the identities of the metal center and the substituents on the ring that affect the relative energies of these transitions. The HOMOs were c...

Studies show that solid copper(I) cyanide has interesting photoluminescent properties. Recent work has shown that the UV spectrum of CuCN may be attributed to Laporte-allowed excitations from occupied to unoccupied π-type molecular orbitals (MOs). The emission spectrum is attributed to the relaxation from an excited state triplet with a bent structure due to distortions that remove degeneracies...