Thermo‐Chromium: A Contactless Optical Molecular Thermometer

Abstract

The unparallelede xcited-state potential-energy landscape of the chromium(III)-based dye [1] 3 + + ([Cr(ddpd) 2 ] 3 + ;d dpd = N,N'-dimethyl-N,N'-dipyridin-2-ylpyridin-2,6-diamine) enables as trong dual emission in the near infrared region. The temperature dependence of this dual emission allows the use of [1] 3 + + as an unprecedented molecular ratiometric thermometer in the 210-373 Kt emperature range in organic and in aqueous media. Incorporation of [1] 3 + + in biocompatiblen anocarriers, such as 100 nm-sized polystyrene nanoparticles and solutol micelles, providesn anodimensional thermometers operating under physiological conditions. Optical sensing of physicochemical quantities, such as temperature (T), pressure, oxygen concentration, or pH, is of tremendous importance in many fields.[1] Applications requiring T sensing range from biology( e.g.,i ntracellular thermometry) [2] and medicald iagnostics (e.g.,p oint-of-care diagnostics [3] using amplifyinge nzymatic reactions) [4] to chemical synthesis (e.g., microfluidics [5] ), and materials sciences (e.g., T-sensitive paints [6] for spatial sensing in wind tunnels). Optical T measurements utilizing T-dependentf luorometric parameters, such as luminescence intensity (or intensity ratios) and lifetime, have been achieved with different classes of molecular and nanoscale emitters. [1c, d] Examples are polymerbased nanoparticles, [7] lanthanide-based nanocrystals, [8] and DNA-based systems, such as molecular beacons (MBs). [9] Fluorometric T sensing can be done nonratiometrically,e xploiting the T sensitivity of the fluorescencei ntensity of as ingle-emissionb and (e.g.,r hodamine B), [10] which is prone to artefacts due to fluctuationsi n, for example, excitation light intensity,o rr atiometrically requiring two emission bands, one being T sensitive and one not responding to changes in T for signal referencing.R atiometric T sensing can be achieved with three design concepts:a )a combination of two emissive dyes (T-responsive probe and T-inert reference);b )acombination of two dyes whichi nteract by ad istance-dependent process, such as fluorescencer esonance energy transfer (EnT) in systems, in which dye distance is modified by T;a nd c) as ingle dye displaying dual emission (Figure 1).[1] Scenario a) is commonly achievedb ycombining two organic fluorophores in af ixed ratio, fore xample, within nanoparticles ( Figure 1a). Both dyesm ust be excitable at the same wavelength and shows pectrally distinguishable emission bands to allow separating andi ntegrating the luminescence signals for the calculation of the excitation light intensity-independent Tsensitivequotient I probe /I ref .Fluorescent T sensors, which exploit T-dependent structural features communicated as changes in fluorescencei ntensity of the reporter dyes are fluorophore-labeled MBs ( Figure 1b). [9] These flexible single-stranded oligonucleotides are either dually labeled att heir 5'-a nd 3'-ends with af luorophore and an onemissive quencher( nonratiometric M...

Deuterated Molecular Ruby with Record Luminescence Quantum Yield

“…[5] Wengersd 6 metal(0) isocyanide chelate complexes display MLCT luminescence in solution (Scheme 1). [8] Emerging novel applications of these extraordinary emitters such as triplet-triplet annihilation upconversion, [6a] demanding photoredox reactions, [6] optical temperature sensing with as ingle dye [10] and selective energy transfer/singlet oxygen formation [11] have already been realized in this short time and ap lethora of others are expected in the future. [9] The" molecular ruby" 1 3+ Scheme 1.…”

“…[9] The" molecular ruby" 1 3+ Scheme 1. [8,10,11,[14][15][16] In many of the above-mentioned complexes (Scheme 1), detrimental ligand-field excited states, [17,18] which lead to nonradiative deactivation, are either absent (d 0 and d 10 electron configuration) or have been successfully shifted to highenough energy,sothat these states do not provide an efficient deactivation pathway.A st hese typically dissociative ligandfield states are not populated for as ufficiently long time, photosubstitution is virtually impossible.This photostability is especially pronounced for 1 3+ with ah igh-energy 4 T 2 ligandfield state preventing substitution reactions (k chem ;F igure 1, center) as back-intersystem crossing (BISC) from the doublet states to the 4 T 2 state is thermodynamically impeded (k BISC ; Figure 1, center). [4][5][6][7][8] [*] C. Wang displays asharp,unprecedentedly intense spin-flip emission in the NIR with aphotoluminescence quantum yield of F = 0.11 and al uminescence lifetime of t = 898 msi nH 2 Oa tr oom temperature.…”

Molecular Ruby under Pressure

“…[12,13] These molecular rubies have emerging applications in photocatalysis [14] and sensing. [15,16] Thet wo sharp spin-flip transitions 2 E! 4 A 2 and 2 T 1 !…”

“…4 A 2 (O symmetry group labels) of [Cr-(ddpd) 2 ] 3+ are close in energy and enable optical ratiometric temperature sensing in solution, in micelles,a nd in nanoparticles containing the molecular ruby [Cr(ddpd) 2 ] 3+ as asingle dye. [15] Optical pressure sensing using molecular luminescent complexes typically relies on the quenching of the luminescence by O 2 . [17] In combination with an oxygen-independent fluorophore,ratiometric optical pressure sensing with molecular systems has been achieved capitalizing on intensity differences of the emission bands.…”

A Strongly Luminescent Chromium(III) Complex Acid

“…First applications of the strongly luminescent “molecular ruby” comprise optical temperature sensing in solution, in micelles, or in nanoparticles with a single dye based on its two NIR emission bands, optical pressure sensing in the solid state and in solution, and selective energy transfer to triplet oxygen, yielding singlet oxygen for organic photoinduced transformations . Further applications of 1 3+ and its derivatives are envisioned for the near future …”