Near‐Infrared Luminescence Switching in a Spin‐Crossover Polymer Nanocomposite

Abstract

A near-infrared-emitting luminescent nanocomposite material was obtained by the association of polyethylenimine, a cyanine dye, and nanoparticles of the [Fe(Htrz) 2 -(trz)](BF 4 ) spin-crossover complex. The nanocomposite was characterized by electron microscopy, as well as by temperature-dependent magnetic and fluorescence measurements. An IntroductionCertain coordination compounds of 3d 4 -3d 7 transition metals can exist in two spin states. The reversible switching between the low-spin (LS) and high-spin (HS) states under external stimuli (temperature, pressure, electromagnetic irradiation, magnetic field, and others) is known as the spin-crossover (SCO) phenomenon. [1,2] Since this phenomenon involves drastic physical property changes (color, stiffness, magnetic susceptibility, and others), SCO compounds have a great potential for the creation of sensors, actuators, memory, and display devices. [3] While SCO behavior has been observed in numerous coordination compounds of different metal ions, the majority of them are octahedral ferrous complexes. In particular, the family of triazole-based 1D coordination networks, which has the general formula [Fe II (4-R-trz) 3 ](A) n (where trz is 1,2,4-triazolato, R is a substituent at the fourth position of the triazole ring, and A is a counterion), is one of the most studied in terms of nanoparticle synthesis, surface deposition, and device fabrication. [4,5] Among them, the robust [Fe(Htrz) 2 (trz)](BF 4 ) (where Htrz is 4H-1,2,4-triazole) SCO complex, with a large (ca. 40 K), reproducible, and above-room-temperature thermal hysteresis, is considered a good candidate for the development of new hybrid materials and devices. [6][7][8] Recently, bifunctional luminescent SCO materials have been the subject of numerous reports. [9] The rising interest in these hybrid materials can be explained by the possibility they offer for tuning the luminescence intensity with external stimuli, and vice versa, for probing the spin-state of the system through variation in the luminescence intensity. Indeed, compared with conventional methods, such as magnetic measurements, this [a]

Construction of Magneto‐Fluorescent Bifunctional Spin‐Crossover Fe(II) Complex from Pyrene‐Decorated Pybox Ligand

“…[14][15][16][17][18][19][20] Impressively, some cases in these bifunctional complexes display strong synergy between SCO and fluorescence emission. [21][22][23][24][25][26][27][28][29][30][31][32][33] The research on these bifunctional complexes will create numerous molecule-based functional materials that display potential applications in biosensors, thermometry, optical memory devices, and biological imaging, etc. However, metal ions such as Co II and Fe II can easily quench fluorescence, and it is still a great challenge to maintain fluorescence in an SCO molecule.…”

Bilayer Thin Films That Combine Luminescent and Spin Crossover Properties for an Efficient and Reversible Fluorescence Switching

“…This will lead to a modulation of the luminescence intensity and, in certain cases, to spectral shifts, but the excited state lifetime of the luminophore will remain obviously unaffected. For example, this 'emission-reabsorption' mechanism has been proposed to be dominant in refs [20,21]. (ii) Alternatively, the excited state energy of the luminescent molecule can be transferred to the metal complex via Förster-type dipole-dipole interactions [19] without photon emission.…”

A flexible polymer–nanoparticle hybrid material containing triazole-based Fe(ii) with spin crossover properties for magneto-optical applications

“…[38][39][40] The engineering of composite materials is a promising way to address this ultimate goal. In this frame, SCO compounds have been encapsulated within polymer matrices of synthetic [41][42][43][44][45][46][47][48][49] and biological 38,[50][51][52][53] origin, providing nanoscale confinement suitable for maintaining cooperativity between SCO complexes. Sol-gel techniques were also used for encapsulation.…”