Constructive quantum interference in a bis-copper six-porphyrin nanoring

Abstract

The exchange interaction, J, between two spin centres is a convenient measure of through bond electronic communication. Here, we investigate quantum interference phenomena in a bis-copper six-porphyrin nanoring by electron paramagnetic resonance spectroscopy via measurement of the exchange coupling between the copper centres. Using an analytical expression accounting for both dipolar and exchange coupling to simulate the time traces obtained in a double electron electron resonance experiment, we demonstrate that J can be quantified to high precision even in the presence of significant through-space coupling. We show that the exchange coupling between two spin centres is increased by a factor of 4.5 in the ring structure with two parallel coupling paths as compared to an otherwise identical system with just one coupling path, which is a clear signature of constructive quantum interference.

Quantifying the exchange coupling in linear copper porphyrin oligomers

“…Depending on the conjugation of the electronic p-system, significant exchange couplings have been detected for distances as large as 3.6 nm. 2,3 Understanding the factors influencing the coupling between two spin centers, and therefore electronic communication, is of paramount importance for numerous applications in the fields of spintronics, molecular electronics and photovoltaics. [4][5][6][7] Depending on the magnitude of the interaction, different techniques can be used for its characterization, including the measurement of the magnetic susceptibility and electron paramagnetic resonance (EPR) spectroscopy.…”

“…8 In contrast, EPR can probe exchange interactions of the order of 10 À3 cm À1 and lower. 2,3,9,10 In this study, we investigate electronic communication in linear copper porphyrin oligomers designed as molecular wires [11][12][13] by EPR spectroscopy via measurement of the exchange coupling between the copper centers. The copper oligomers chosen for this case study represent very large spin systems with Hamiltonian dimensions exceeding the capabilities of commonly used simulation approaches.…”

Shadow Mask Templates for Site‐Selective Metal Exchange in Magnesium Porphyrin Nanorings

“…In this reaction, the T4 a template was left in place during the insertion of copper(II) into the two free‐base centers of 1,4‐(H 2 )Mg 4 ‐P6⋅T4 a . We removed T4 a and inserted T6 to obtain 1,4‐Cu 2 Mg 4 ‐P6⋅T6 (see the Supporting Information), which is a valuable compound for investigating quantum interference through long‐range exchange coupling . Many metal cations can be inserted into porphyrins under mild conditions, so the magnesium/free‐base nanorings reported here should be useful intermediates for preparing diverse heterometalated systems.…”

Shadow Mask Templates for Site‐Selective Metal Exchange in Magnesium Porphyrin Nanorings

“…In this reaction, the T4 a template was left in place during the insertion of copper(II) into the two free-base centers of 1,4-(H 2 )Mg 4 -P6·T4 a.W eremoved T4 a and inserted T6 to obtain 1,4-Cu 2 Mg 4 -P6·T6 (see the Supporting Information), which is av aluable compound for investigating quantum interference through long-range exchange coupling. [16] Many metal cations can be inserted into porphyrins under mild conditions, [17] so the magnesium/free-base nanorings reported here should be useful intermediates for preparing diverse heterometalated systems.…”

“…[15] This compound is useful for testing the cooperativity of ligand binding inside nanorings. [16] Many metal cations can be inserted into porphyrins under mild conditions, [17] so the magnesium/free-base nanorings reported here should be useful intermediates for preparing diverse heterometalated systems. In this reaction, the T4 a template was left in place during the insertion of copper(II) into the two free-base centers of 1,4-(H 2 )Mg 4 -P6·T4 a.W eremoved T4 a and inserted T6 to obtain 1,4-Cu 2 Mg 4 -P6·T6 (see the Supporting Information), which is av aluable compound for investigating quantum interference through long-range exchange coupling.…”