Synthesis, Characterization, and Properties of Iron(II) Spin-Crossover Molecular Photoswitches Functioning at Room Temperature

Abstract

Spin-crossover molecular switches [Fe(HB(pz))L] (L = novel phenanthroline-based ligands featuring photochromic diarylethene units; pz = 1-pyrazolyl) were synthesized and thoroughly characterized by variable-temperature X-ray crystallography, Mössbauer spectroscopy, and magnetic measurements. The effect of substituents introduced into the phenanthroline backbone (L2) and into the photochromic diarylethene unit (L3) on photophysical properties of metal-free ligands and spin-crossover iron(II) complexes 2 and 3, respectively, were investigated in detail. Both ligands and complexes could be switched with light in solution at room temperature. The photocyclization of 2 was accompanied by a high-spin to low-spin photoconversion determined at 19%. The closed-ring isomers of L3 and 3 reveal the lifetimes in the range of minutes, whereas those of L2 and 2 are thermally stable for days in solutions at room temperature. The reversibility of the photoswitching can be improved by avoiding the photostationary states. Prospective introduction of anchoring groups to the phenanthroline backbone might allow the construction of chemisorbed self-assembled monolayers of spin-crossover species switchable with light at room temperature.

Stille Expands the Family: Access to 5,6‐Bis‐2‐thienyl‐Substituted Phenanthroline Under Mild Conditions for Luminescent Ruthenium Complexes

“…These results are in line with previously reported absorption properties of 5,6‐bis‐thiophene‐phenanthrolines, accessible via Suzuki‐coupling reactions (L1–4) which have been performed in benzene and acetonitrile, respectively (Table and Scheme ), , ,…”

“…This is in contrast with literature value for related compounds favoring the parallel orientation with 75 % Taking the less steric demand of thiophene moieties within 2 into account, the measured torsion angles of the two thiophenes with 65.31° and 67.60° with respect to the phenanthroline plane seem reasonable, which is very similar to previously reported thiophene‐substituted phenanthrolines. Interestingly, in case of even more sterically demanding dimethyl‐substituted thiophenes torsion angles lie in the same region , …”

“…Regarding the photophysical properties of phenanthroline complexes, it is well known that substitution of phenanthroline in 3,8‐ and 4,7‐positions significantly influences the photochemistry of coordination complexes as π‐orbital energies are strongly influenced , . In this context, the effects of substituents introduced at 5‐ or 5,6‐position of phenanthroline are far less explored , . This is mainly due to the demanding synthetic procedures in order to access these positions efficiently.…”

“…Towards this aim, several different coupling patterns have already been realized with various oligothiophene substrates. Very successfully, synthetic concepts utilizing Sonogashira, Suzuki, and Stille coupling have been developed and applied mainly to bipyridine cores.…”

Rational Design of Electronically Labile Dinuclear Fe and Co complexes with 1,10‐Phenanthroline‐5,6‐Diimine: A DFT study

“…Due to lability of their electronic shells transition metal coordination compounds with switchable magnetic properties represent key substructures of molecular electronics and spintronics devices . They have a good application prospect as single‐ion and single‐molecule magnets, molecular switches, sensors, and logical elements of quantum computers . Among the magnetically active systems, a special place is belonged to the transition metal complexes with redox‐active (noninnocent ) ligands, in which proximity of energy levels of the metal valence d ‐electrons and frontier molecular orbitals of the ligand creates opportunities for low‐energy barrier intramolecular electronic transfers (IETs).…”