Meso-β doubly linked and meso-meso, β-β, β-β triply linked oligoporphyrin molecular tapes as potential non linear optical (NLO) materials: Quantum chemical calculations

Abstract

The quantum chemical calculations of the non linear optical properties of meso-β doubly linked and meso-meso, β-β, β-β triply linked porphyrin tapes are reported. The π electron movement across the porphyrin tape was enhanced by introducing a donor group and an acceptor group in either side of the tape. Geometries of porphyrin oligomers starting from two units to four units were optimized using the PM5 Hamiltonian employing MOPAC 2002 within the BioMedCAChe 6.1 software package. The calculations of linear and non linear optical properties were performed using the same level of the theory. In addition to the calculation of first static hyperpolarizability, polarizabilities of these molecules are also reported. The frontier orbital energy calculations were done using the same software package. The overall increase of first static hyperpolarizability of porphyrin tapes was observed as the number of porphyrin units increases in the array. The triply linked porphyrin tapes show much better enhancement of NLO properties than the doubly linked tapes. In all cases metallo porphyrin tapes show high hyperpolarizability than the free base porphyrin tapes. The triply linked oligoporphyrins are rigid and not susceptible for twists and turns which makes these compounds promising for a variety of applications. The study suggested that the prophyrin tapes show very large optical non linearities and hence may have potential applications in the development of non linear optical materials. © 2005 Elsevier B.V. All rights reserved.