Long‐Lived Charge Separation in Novel Axial Donor–Porphyrin–Acceptor Triads Based on Tetrathiafulvalene, Aluminum(III) Porphyrin and Naphthalenediimide

Abstract

Two self-assembled supramolecular donor-acceptor triads consisting of Al(III) porphyrin (AlPor) with axially bound naphthalenediimide (NDI) as an acceptor and tetrathiafulvalene (TTF) as a secondary donor are reported. In the triads, the NDI and TTF units are attached to Al(III) on opposite faces of the porphyrin, through covalent and coordination bonds, respectively. Fluorescence studies show that the lowest excited singlet state of the porphyrin is quenched through electron transfer to NDI and hole transfer to TTF. In dichloromethane hole transfer to TTF dominates, whereas in benzonitrile (BN) electron transfer to NDI is the main quenching pathway. In the nematic phase of the liquid crystalline solvent 4-(n-pentyl)-4'-cyanobiphenyl (5CB), a spin-polarized transient EPR spectrum that is readily assigned to the weakly coupled radical pair TTF(.+)NDI(.-) is obtained. The initial polarization pattern indicates that the charge separation occurs through the singlet channel and that singlet-triplet mixing occurs in the primary radical pair. At later time the polarization pattern inverts as a result of depopulation of the states with singlet character by recombination to the ground state. The singlet lifetime of TTF(.+)NDI(.-) is estimated to be 200-300 ns, whereas the triplet lifetime in the approximately 350 mT magnetic field of the X-band EPR spectrometer is about 10 μs. In contrast, in dichloromethane and BN the lifetime of the charge separation is <10 ns.

A Divalent Pentastable Redox‐Switchable Donor–Acceptor Rotaxane

“…], in which e is the elementary charge, ϵ 0 is the electric constant and ϵ r is the relative static permittivity . These values result in a Δ ET G ° value of (−61.5±6.8) kJ mol −1 (−0.64 eV) in dichloromethane, which is in the upper range for similar supramolecular D‐A systems . Therefore, the charge separation between the excited D*‐A complex and D + ‐A − is thermodynamically highly favoured. …”

“…[63] These values result in a D ET G8 value of (À61.5 AE 6.8) kJ mol À1 www.chemeurj.org (À0.64 eV) in dichloromethane, which is in the upper range for similar supramolecular D-A systems. [64][65][66][67] Therefore, the charge separation between the excited D*-A complex and D + -A À is thermodynamically highly favoured.…”

Modulation of Energy Transfer into Sequential Electron Transfer upon Axial Coordination of Tetrathiafulvalene in an Aluminum(III) Porphyrin–Free-Base Porphyrin Dyad

“…These chemical shifts (δ) agree well with those of the axial bonding type porphyrin systems. 42,44,45,70 Hence, the Δδ values (i.e., δ monomer − δ dyad ) are a function of their proximity to the porphyrin ring. Figure 2 shows the 1 H NMR spectrum of the triad (TTFpy→AlPor-Ph-H 2 Por (bottom), that is, a 1:1 mixture of AlPorPh-H 2 Por and TTF-py) along with the individual spectra of AlPor-Ph-H 2 Por (middle) and TTF-py (top).…”

Design and photochemical study of supramolecular donor–acceptor systems assembled via metal–ligand axial coordination

“…assembled such supramolecular donor-acceptor systems consisting of Al(III)Por with axially bounded naphthalenediimide (NDI) and tetrathiafulvalene (TTF) as acceptor and donor, respectively (Fig. 41)[127].The AlPor allowed two different groups to attach at the opposite faces of AlPor. In the triad, the NDI and TTF groups were attached on the opposite faces of the AlPor via covalent bonding and a metal-ligand coordination bond, respectively.…”