Linear and Nonlinear Optical Properties of Expanded Porphyrins: A DMRG Study

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 117; no. 33; pp. 7804 - 7809
• Main Authors: Thomas, Simil, Pati, Y. A, Ramasesha, S
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 22.08.2013
• Subjects: Bonding; Carbon; Carbon-carbon composites; Charge density; EPS; Exact sciences and technology; Excitation; Fundamental areas of phenomenology (including applications); Molecular Structure; Nonlinear optics; Optical Phenomena; Optical susceptibility, hyperpolarizability; Optics; Physics; Porphyrins; Porphyrins - chemistry; Pyrroles; Quantum Theory; Inorganic compounds; Nitrogen heterocycle; Pyrroles; Theoretical study; Density matrix; Nitrogen; Excited states; Carbon; Electron-electron interactions; Bond lengths; Pyrrole derivatives; Macrocycle; Hamiltonians; Optical properties; Excitation; Absorption spectra; Two photon absorption; Nonlinear optics; Cross sections; Porphyrin derivatives; Organic compounds; Porphyrins
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp4052352

We study absorption spectra and two photon absorption coefficient of expanded porphyrins (EPs) by the density matrix renormalization group (DMRG) technique. We employ the Pariser–Parr–Pople (PPP) Hamiltonian which includes long-range electron–electron interactions. We find that, in the 4n+2 EPs, there are two prominent low-lying one-photon excitations, while in 4n EPs, there is only one such excitation. We also find that 4n+2 EPs have large two-photon absorption cross sections compared to 4n EPs. The charge density rearrangement in the one-photon excited state is mostly at the pyrrole nitrogen site and at the meso carbon sites. In the two-photon states, the charge density rearrangement occurs mostly at the aza-ring sites. In the one-photon state, the C–C bond length in aza rings shows a tendency to become uniform. In the two-photon state, the bond distortions are on C–N bonds of the pyrrole ring and the adjoining C–C bonds which connect the pyrrole ring to the aza or meso carbon sites.