Near-Infrared to Visible Light-Upconversion in Molecules: From Dream to Reality

Abstract

Light-upconversion via stepwise energy transfer from a sensitizer to an activator exploits linear optics for converting low-energy infrared or near-infrared incident photons to higher energy emission. This approach is restricted to activators possessing intermediate long-lived excited states such as those found for trivalent lanthanide cations dispersed in solid-state matrices. When the activator is embedded in a molecular complex, efficient nonradiative relaxation processes usually reduce excited state lifetimes to such an extent that upconversion becomes too inefficient to be detected under practical excitation intensities. Theoretical considerations presented here predict that the combination of at least two millisecond time scale sensitizers with a central lanthanide activator in supramolecular complexes circumvents this bottleneck by creating a novel upconversion pathway, in which successive excitations are stored on the sensitizers prior to inducing stepwise energy transfer processes. Application of this concept to the chromium/erbium pair demonstrates that strong-field trivalent chromium chromophores irradiated with near-infrared photons produce upconverted green erbium-centered emission in discrete dinuclear and trinuclear triple-stranded helicates.

Two Series of Lanthanide Coordination Polymers and Complexes with 4′‐Phenylterpyridine and their Luminescence Properties

“…However, only the latter sensitizes all three mentioned metal ions. For Er 3+ coordination compounds, metal ion based emission in the visible range through the ligand excitation was noticed upon cooling below 200 K or at 3 K,, , and only as exceptions, this phenomenon was observed at room temperature , , . For each compound, enlarged detailed spectra measured at room temperature and 77 K with Designation of observed emission bands with Ln 3+ 4f–4f transitions are reported in the SI.…”

Femtosecond photoswitching dynamics and microsecond thermal conversion driven by laser heating in FeIII spin-crossover solids

“…Indeed, bistable molecules in solution exhibit a wealth of light-induced transformations, which may give rise to inter-or intra-molecular chemical reactions [6], electron transfer [7,8] or changes of the molecular states [9,10,11].In molecule-based solids,light-induced phenomena are important for driving a material between different statesassociated with different macroscopic physical properties [12,13,14,15,16,17].Femtosecond laser pulses are widely regarded as the most likely source for switching molecular solids on ultrafast timescale [18,19,20,21,22,23,24,25].Among the latters, spin-crossover compounds (SCO) are prototypes of systemsshowing molecular bistability in the solid state, which may be converted from low-spin (LS) to high-spin (HS) states under various external perturbations. In these materials, the photoswitching under weak continuous light irradiationat low temperature was extensively studied [26,27],and few reports discussed the relaxation mechanism after nanosecond laserexcitation [28,29].…”

Recent Trends Concerning Upconversion Nanoparticles and Near-IR Emissive Lanthanide Materials in the Context of Forensic Applications

“…Early studies of dimeric complexes that comprised of a single sensitiser coupled to an acceptor ion were generally unsuccessful in generating upconversion, which was justified to be a result of very short lifetimes of the excited state. [69] In silico calculations were then made for trinuclear complexes that comprised of a single acceptor Ln ion sandwiched between two sensitiser species. This arrangement was predicted to improve the upconversion emission intensity by two orders of magnitude.…”

“…Further improvements in emission intensity could be gained when a longer-lived, sensitiser-centric pathway using Cr 3þ was implemented, with an expected increase in intensity of 7-8 times predicted. [69] The desirability of chromium as a sensitiser stems from the six lower excited levels of its [Ar] 3d 3 electronic configuration that can be tuned using ligand-field effects. [70] Efforts to realise these predictions consequently focussed on lanthanide-chromium mixed-metal species to maximise potential improvement of emission.…”