Cu(I) complexes – Thermally activated delayed fluorescence. Photophysical approach and material design

A series of gold(I) iodide complexes 1-11 have been prepared from di-, tri-, and tetraphosphane ligands. Crystallographic studies reveal that the di- (1-7) and tetrametallic (11) compounds feature linearly coordinated gold(I) ions with short aurophilic contacts. Their luminescence behavior is determined by the combined influence of the phosphane properties, metal-metal interaction, and intermolecular lattice-defined interactions. The proposed variable contribution of (X+M)-centered (X=halogen; M=metal) and XLCT (halogen to ligand charge transfer) electronic transitions into the lowest lying excited state, which is influenced by supramolecular packing, is presumably responsible for the alteration of room-temperature emission color from green (λ=545 nm, for 11) to near-IR (λ=698 nm, for 2). Dinuclear compounds 6 and 7 exhibit distinct luminescence thermochromism with a blueshift up to 5750 cm upon cooling. Such dramatic change of emission energy is assigned to the presence of two coupled triplet excited states of ππ* and (X+M)C/ XLCT nature, the presence of which depends on both molecular structure and the crystal lattice arrangement.

Section: Synthesis and Structural Characterizationsupporting

confidence: 57%

Luminescence Thermochromism of Gold(I) Phosphane–Iodide Complexes: A Rule or an Exception?

Glebko

Dau

Melnikov

et al. 2018

“…The emission intensity remains constant excluding a thermally activated decay pathway, for example, through the ligand‐field 4 T 2 state (Figures c and S1 in the Supporting Information). Hence, no thermally activated delayed fluorescence through back‐intersystem crossing is operative up to 358 K . This is expected from the huge energy difference between the 2 E and 4 T 2 states in [1] 3+ of more than 85 kJ mol −1 (Figure c) .…”

Section: Figurementioning

confidence: 93%

Thermo‐Chromium: A Contactless Optical Molecular Thermometer

Otto

Scholz

Behnke

et al. 2017

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...

“…The temperature dependence of emission decay time for 2 , τ ( T ) (Figure S16 b), was fitted to Equation describing a three‐state kinetic model (assuming fast process of reaching thermal equilibrium between the T 1 and S 1 states and temperature‐independent decay rates),

true τ ((), T) = \frac{3 + e^{(- \frac{Δ E}{k_{B} T})}}{\frac{3}{τ ((), T_{1})} + \frac{1}{τ ((), S_{1})} e^{(- \frac{Δ E}{k_{B} T})}}

…”

Section: Methodsmentioning

confidence: 99%

Excitation‐Wavelength‐Dependent Emission and Delayed Fluorescence in a Proton‐Transfer System

Berezin

Vinogradova

Krivopalov

et al. 2018

Manipulating the relaxation pathways of excited states and understanding mechanisms of photochemical reactions present important challenges in chemistry. Here we report a unique zinc(II) complex exhibiting unprecedented interplay between the excitation-wavelength-dependent emission, thermally activated delayed fluorescence (TADF) and excited state intramolecular proton transfer (ESIPT). The ESIPT process in the complex is favoured by a short intramolecular OH⋅⋅⋅N hydrogen bond. Synergy between the excitation-wavelength-dependent emission and ESIPT arises due to heavy zinc atom favouring intersystem crossing (isc). Reverse intersystem crossing (risc) and TADF are favoured by a narrow singlet-triplet gap, ΔE ≈10 kJ mol . These results provide the first insight into how a proton-transfer system can be modified to show a synergy between the excitation-wavelength-dependent emission, ESIPT and TADF. This strategy offers new perspectives for designing ESIPT and TADF emitters exhibiting tunable excitation-wavelength-dependent luminescence.