Light‐Induced Spin Transitions in Copper‐Nitroxide‐Based Switchable Molecular Magnets: Insights from Periodic DFT+U Calculations

Abstract

The electronic structure and magnetic interactions of three members of the breathing crystal Cu(hfac) L family (hfac=hexafluoroacetylacetonato, L =pyrazole-substituted nitronyl nitroxides with R=Me, Et, Pr, iPr, Bu ), mainly Cu(hfac) L (1), Cu(hfac) L ⋅0.5 C H (2) and Cu(hfac) L ⋅0.5 C H (3), have been analyzed by means of periodic plane-wave based DFT+U calculations. These Cu -nitroxide based molecular magnets display thermally and optically induced switchable behavior and light-induced excited spin state trapping phenomena. The calculations confirm the presence of temperature-dependent exchange interaction within the spin triads formed by the nitroxide-copper(II)-nitroxide units, in line with the changes observed in the effective magnetic moment. Moreover, they quantify the interchain interaction mediated by the terminal nitroxide group of two spin triads in neighboring polymer chains. This interaction competes with the exchange interaction within the spin triads at high temperature, and introduces 1D exchange channels that do not coincide with the polymeric chains. The density of states reveal that the low-lying conduction states potentially involved in the UV/Vis transitions are located on the nitroxide radicals, the hfac groups and the Cu atoms. Then, the density of states is almost independent of the solvent and the R group. This suggests the possibility of light-induced spin switching for other members of this family. The 500 nm band of the low-temperature phase can be ascribed to a ligand-to-metal charge transfer transition between the nitroxide and Cu bands.

Elucidating the Electronic Structure and Magnetic and Conducting Properties of μ-Oxo Mn-phthalocyanine [MnPc(CN)]2O Complex

“…The amplitude of this interaction is 1 order larger than that resulting from the CASSCF calculations. This overestimation of the antiferromagnetic coupling is a well-known feature of the DFT-based estimations of the magnetic coupling constants, observed for both isolated molecules and crystals. − …”

Optical Phenomena in Molecule-Based Magnetic Materials

“…The light-induced changes and kinetics of this transition were also studied for thin film samples using optical absorption spectroscopy and time-resolved EPR technique (Figure e,f). , Light-induced SS to WS transition is also observed for the [Cu II (hfac) 2 L i‑Pr ] (L i‑Pr = isopropyl-substituted nitronyl nitroxide ligand) analog, where the thermal spin transition does not appear. Additionally, the temperature-variable FTIR experiment under photoirradiation revealed different orientations of propyl groups between WS states obtained thermally and by light irradiation, which may influence the relaxation of the photoexcited state. , The latest results of the density of states calculations attribute the irradiation band to the LMCT states, and suggest the possibility of light-induced spin switching for all members of the family of Cu­(II)-based breathing crystals …”

“…490,491 The latest results of the density of states calculations attribute the irradiation band to the LMCT states, and suggest the possibility of light-induced spin switching for all members of the family of Cu(II)-based breathing crystals. 492…”

Diacetyliminoxyl as a selective radical reagent for organic synthesis: dehydrogenation and dehydrogenative C–O coupling reactions

“…Stable organic radicals play an important role in modern organic chemistry. Among them stable N-oxyl radicals 1,2 are of great current interest because of their applications in various fields, including the development of magnetic materials, [2][3][4][5][6][7][8][9][10][11][12][13] radical polymerization (nitroxide-mediated polymerization, NMP), [14][15][16][17][18][19][20][21][22][23][24] organic batteries, [25][26][27][28][29] spin-labeling, 2,[30][31][32][33][34][35][36] oxidation processes 2,37,38 and scavenging of free radicals. 2,16 The majority of stable N-oxyl radicals are amine-N-oxyl radicals.…”