Spin Crossover Nanoparticles

Abstract

Spin crossover (SCO) materials that switch between two different spin states, that is, the high spin (HS) and the low spin (LS) state, with very different optical, magnetic, and structural properties offer a unique platform to understand the consequences induced by the different electronic configurations of transition metal complexes. Due to the significant changes associated with the spin transition, it can be followed by different techniques such as UV−vis and IR optical spectroscopy, magnetism, crystallography, calorimetric analysis, nuclear magnetic resonance, etc. Hence, a practical experiment for laboratory classes dedicated to the topic of SCO focused on the thermal transition, that is, the transition triggered by temperature, results in a simple yet attractive way to understand not only fundamental concepts of inorganic and physical chemistry but also to get acquainted with the synthesis of nanoparticles and the characterization of inorganic solid samples.

Dynamics of Spin Crossover Molecular Complexes

“…With 830 nm irradiation, the [Fe(ptz) 6 ](BF 4 ) 2 HS state is excited to the 5 E state, a metal center weighted state, which permits an optically allowed spin state transition to occur. Immediately after irradiation, the 5 E state relaxes to the ligand field state 3 T 1 via an intersystem crossing, with a time constant of 1.7 ps [ 92 , 93 ]. Next, the system reaches the LS state by undergoing another intersystem state crossing with a measured time constant of 39 ps [ 92 ].…”

Dynamic Aggregation Triggering Reversible Spin-State Switching

“…22−24 We then made reverse thinking on the ACQ-type luminophores: although the aggregation has led to self-quenching, the resulting charge transfer (CT) can show great potential to tune the ligand field strength, as the CT can tune the π-acceptor and π-donor of the ligand, and the latter is correlated closely with the ligand field strength, according to the ligand field theory. 25,26 Motivated by this, our attention moves to the D−A−D (D = donor; A = acceptor)-type second near-infrared window (NIR-II) fluorophores, which was featured with water-induced J-aggregation and significant ICT, as well as NIR-triggered ligand-to-ligand charge transfer (LLCT) owing to the narrow band gaps. 27−29 Here, in this work, by employing D−A−D-type NIR-II fluorophore L-C 2 H 5 , we prepared a ferrous complex Fe-(NCS) 2 (L-C 2 H 5 ) 2 (Scheme 1a), which has displayed the significant aggregation state-dependent SSS under ambient conditions (Scheme 1b).…”

“…The introduction of luminescence represents a promising strategy to study the SSS phenomena at a single molecular level in a high spatial and temporal resolution manner, − which usually requires a high overlap between the emission band of luminophores and UV–vis absorption band of the SSS center. − However, one huge obstacle to this aspect lies in the self-quenching problem of luminophores in the solid state, owing to the strong intermolecular interaction-induced aggregation-caused quenching (ACQ) effects and the nonradiative decay in the dark twisted intramolecular charge transfer (TICT) state. − We then made reverse thinking on the ACQ-type luminophores: although the aggregation has led to self-quenching, the resulting charge transfer (CT) can show great potential to tune the ligand field strength, as the CT can tune the π-acceptor and π-donor of the ligand, and the latter is correlated closely with the ligand field strength, according to the ligand field theory. , Motivated by this, our attention moves to the D–A–D (D = donor; A = acceptor)-type second near-infrared window (NIR-II) fluorophores, which was featured with water-induced J-aggregation and significant ICT, as well as NIR-triggered ligand-to-ligand charge transfer (LLCT) owing to the narrow band gaps. − …”

Estimating Quantum Dot Size with Pulsed Field Gradient NMR

“…Quantum-mechanical considerations can perturb material properties at such short length scales, allowing these properties to be “tuned” by controlling the QD size. This Journal has published syntheses and studies of a wide range of QDs, often with an emphasis on producing a range of colored QDs in a single synthesis or across a range of similar syntheses, − exploiting the effects of quantum confinement, − or serving as an introduction to nanotechnology. , A recent report focuses on the synthesis and extensive characterization of PbS QDs as the theme of an undergraduate senior research project designed to teach nanoparticle synthesis and provide insights with advanced instrumental techniques …”