Topology, Distance, and Orbital Symmetry Effects on Electronic Spin–Spin Couplings in Rigid Molecular Systems: Implications for Long-Distance Spin–Spin Interactions

Abstract

Understanding factors that underpin the signs and magnitudes of electron spin–spin couplings in biradicaloids, especially those that are integrated into highly delocalized electronic structures, promises to inform the design of molecular spintronic systems. Using steady-state and variable temperature electron paramagnetic resonance (EPR) spectroscopy, we examine spin dynamics in symmetric, strongly π-conjugated bis­[(porphinato)­copper] (bis­[PCu]) systems and probe the roles played by atom-specific macrocycle spin density, porphyrin-to-porphyrin linkage topology, and orbital symmetry on the magnitudes of electronic spin–spin couplings over substantial Cu–Cu distances. These studies examine the following: (i) meso-to-meso-linked bis­[PCu] systems having oligoyne spacers, (ii) meso-to-meso-bridged bis­[PCu] arrays in which the PCu centers are separated by a single ethynyl unit or multiple 5,15-diethynyl­(porphinato)­zinc­(II) units, and (iii) the corresponding β-to-β-bridged bis­[PCu] structures. EPR data show that, for β-to-β-bridged systems and meso-to-meso-linked bis­[PCu] structures having oligoyne spacers, a through σ-bond coupling mechanism controls the average exchange interaction (J avg). In contrast, PCu centers separated by a single ethynyl or multiple 5,15-diethynyl­(porphinato)­zinc­(II) units display a phenomenological decay of ln­[J avg] versus Cu–Cu σ-bond separation number of ∼0.115 per bond, half as large as for these other compositions, congruent with the importance of π-mediated spin–spin coupling. These disparities derive from effects that trace their origin to the nature of the macrocycle–macrocycle linkage topology and the relative energy of the Cu d x 2–y 2 singly occupied molecular orbital within the frontier orbital manifold of these electronically delocalized structures. This work provides insight into approaches to tune the extent of spin exchange interactions and distance-dependent electronic spin–spin coupling magnitudes in rigid, highly conjugated biradicaloids.

When Molecular Magnetism Meets Supramolecular Chemistry: Multifunctional and Multiresponsive Dicopper(II) Metallacyclophanes as Proof-of-Concept for Single-Molecule Spintronics and Quantum Computing Technologies?

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Review of porphyrin-based photodynamic therapy materials

“…Porphyrin and its derivatives including chlorins and bacteriochlorins are one of the most typical and useful photosensitizers in PDT [38,39]. The longest absorption of porphyrins is in red light portion, allowing the light penetration to deep tissues which helps in deep tumor treatments.…”

Review of Conjugated Porphyrin Systems

“…CNSs can be produced by a simple and easy method like pyrolysis under controlled conditions. [225][226][227][228][229][230] The synthesis of CNSs from bio-waste materials is an attractive proposition and can be envisioned as a scalable "waste to wealth" approach which will have a strong societal impact. We believe that porphyrin-CNS hybrids will find an array of applications in fields like waste water purification, cleansing technology, etc.…”