Fully Conjugated Porphyrin Tapes with Electronic Absorption Bands That Reach into Infrared

Abstract

Scandium(III)-catalyzed oxidation of meso-meso-linked zinc(II)-porphyrin arrays (up to dodecamers) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) led to efficient formation of triply meso-meso-, beta-beta-, and beta-beta-linked zinc(II)-oligoiporphyrins with 62 to 91% yields. These fused tape-shaped porphyrin arrays display extremely red-shifted absorption bands that reflect extensively pi-conjugated electronic systems and a low excitation gap. The lowest electronic absorption bands become increasingly intensified and red-shifted upon the increase in the number of porphyrins and eventually reach a peak electronic excitation for the dodecamer at approximately 3500 wavenumber. The one-electron oxidation potentials also decreased progressively upon the increase in the number of porphyrins. These properties in long and rigid molecular shapes suggest their potential use as molecular wires.

Near-infrared absorption of π-stacking columns composed of trioxotriangulene neutral radicals

“…1,2 One of the methodologies to design a molecule showing low-energy absorption involves the extension of π-conjugated systems that narrow the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap. In two extreme examples, the absorption band of zinc(II) porphyrin (400 nm) exhibits a red-shift in the fused tape-shaped array (3500 nm, dodecamer), 3,4 and the giant hydrocarbon sheet, C 222 H 42 , shows a broad absorption band around 250-1400 nm. 5 π-Stacking also increases the absorption wavelength, since the intermolecular overlap of π-orbitals causes exciton delocalization.…”

Nonlinear Absorption by Porphyrin Supramolecules

“…connecting porphyrins at meso-positions (Osuka & Shimidzu, 1997;Aratani et al, 2005;Tsuda & Osuka, 2001;Anderson, 1994;Anderson, 1999;Lin et al, 1994).…”

Molecular orbital analysis of frontier orbitals for molecular electronics: a case study of unimolecular rectifier and photovoltaic cell

“…In this strategy to realize a rectifying function, HOMO and LUMO have to localize on a donor and an acceptor, respectively. Porphyrin possesses good electron-donating properties due to its large easily ionized p-electron system and a long molecular wire of fully conjugated porphyrin polymer has been reported by Tsuda and Osuka [32]. In this study, we propose that a rectifier diode can be created by combining two metal porphyrin molecules with different transition metal atoms.…”