(44−51) The spherical nature of the carboranes, with slightly polarized hydrogen atoms and the presence of the hydride-like hydrogens at the B–H vertexes, make the carboranes very hydrophobic.
(37−43) Carborane-based MOFs were first synthesized at Northwestern University, and they showed an increase in their thermal stabilities among other interesting properties. Herein, we hypothesized that such limitations can be overcome with the introduction of carborane clusters such as icosahedral carboranes 1, n-C 2B 10H 12 ( n = 2, 7 or 12), a class of commercially available and exceptionally stable three-dimensional (3D) aromatic boron-rich clusters that possess material-favorable properties such as thermal/chemical stability and high hydrophobicity. However, regardless of the great potential of these materials, to date they have proved unsuitable for practical applications due to their limited chemical (28−35) and/or optical (27,36) stability under environmental conditions (e.g., humidity, temperature, etc.). (16−22) Of particular interest would be the exploitation of emissive Ln-MOFs as optical markers for high-security anticounterfeiting technologies aimed to prevent illegal copies of sensitive identity documents, banknotes, diplomas, and certificates, (23−27) which require an ever-increasing tunability (e.g., emission colors) and authentication complexity. (14,15) Their luminescence is associated with an energy transfer (ET) from the ligand, acting as an antenna, owing to its larger extinction coefficient, to the accepting electronic levels of the emitting lanthanides and it is potentially interesting in a variety of applications, such as e.g., sensors, optoelectronic and in solid-state lighting (SSL) devices, or bioimaging among others. (2,5−13) Especially interesting is the combination of MOFs with lanthanide (Ln) ions resulting in inherent optical properties, including high luminescence quantum yields, narrow and strong emission bands, large Stokes shifts, long luminescence lifetimes, and an emission wavelength undisturbed by the surrounding chemical environment. (1−4) Their large surface areas, framework flexibility, and tunable pore surface properties, as well as “tailor-made” framework functionalities, empower them to be promising candidates for a diverse range of applications. Porous coordination polymers (CPs), also known as metal–organic frameworks (MOFs), are a class of highly crystalline materials formed by metal ions or metal clusters connected by multitopic organic linkers, which have attracted extensive attention over the past few decades. We report a convenient method to prepare mixed-metal Eu/Tb coordination polymers (CPs) that are printable from water inks for potential applications, among which anticounterfeiting and bar-coding have been selected as a proof-of-concept.
The observed time-dependent emission (and color), in addition to the high QY, provides a simple method for designing high-security anticounterfeiting materials. An outstanding increase in the quantum yield (QY) of 239% of mCB-Eu (20.5%) in the mixed mCB-Eu 0.1Tb 0.9 (69.2%) is achieved, along with an increased and tunable lifetime luminescence (from about 0.5 to 10 000 μs), all of these promoted by a highly effective ET process.
DLIGHT S30 INSTRUCTIONS SERIES
Tunable emission from green to red, energy transfer (ET) from Tb 3+ to Eu 3+, and time-dependent emission of the series of mixed-metal m CB-Eu y Tb 1– y MOFs are reported. The new materials are stable in water and at high temperature. Herein, we design and synthesize a series of m CB-Eu y Tb 1– y ( y = 0–1) MOFs using a highly hydrophobic ligand mCBL1: 1,7-di(4-carboxyphenyl)-1,7-dicarba- closo-dodecaborane. To be suitable for practical applications, Ln-MOFs must be not only water stable but also printable, easy to prepare, and produced in high yields. Luminescent lanthanide metal–organic frameworks (Ln-MOFs) have been shown to exhibit relevant optical properties of interest for practical applications, though their implementation still remains a challenge.