Polar Solvent Acetonitrile Research Articles

A colorimetric and ratiometric fluorescent sensor for biogenic primary amines based on dicyanovinyl substituted phenanthridine conjugated probe

Two molecules with an aldehyde donor substituted 4'-(7,8,13,14-tetrahydrodibenzo[a,i]phenanthridin-5-yl)-[1,1′-biphenyl]-4-carbaldehyde (5) and a dicyanovinyl acceptor substituted 2-((4'-(7,8,13,14-tetrahydrodibenzo[a,i]phenanthridin-5-yl)-[1,1′-biphenyl]-4-yl)methylene)malanonitrile (7) were synthesized, and both were applied to remarkable solvatochromism studies. Due to their intramolecular charge transfer (ICT) characteristic, both fluorophores, with a positive solvatochromism effect and emission color, changed from blue to green-orange when the polarity was increased from non-polar hexane to polar acetonitrile solvent. Meanwhile, for compound 5 and 7, aggregation induced emission (AIE) and acidochromism studies have been carried out. The obtained results indicated that compound 5 and 7 exhibited tunable aggregation induced emission and quenching of acidochromism for 7. In this study, we have proposed a new method based on dicyanovinyl substituted phenanthridine moiety of 7 for selective and efficient recognition of biogenic primary amines (BPAs), based on the interaction between amine and the dicyanovinyl-linked phenanthridine moiety of 7. It can be cleaved quickly with significant changes in fluorescence (from orange to blue) that produced 7-imine with induced ratiometric fluorescence. UV–visible/fluorescence spectral titration, NMR, mass spectra and DFT spectroscopic studies were proved by the mechanism of amine sensing. Limit of detections 3.67 nM (DA), 28.3 nM (EDA), 65.3 nM (HA) and 15.8 nM (n-BA) are also obtained for this probe 7 with remarkable ratiometric fluorescence enhancement. Additionally, fluorescence test paper with probe (7) was also fabricated and utilized to detect amines.

Preparation and application of teicoplanin functionalized polymeric monolith for enantioseparation of chiral drugs

A novel chiral stationary phase (CSP), based on a monolithic organic polymer chemically modified with teicoplanin, was fabricated within a 100 μm I.D. fused silica capillary. The teicoplanin was firstly derivatized with 2-isocyanatoethyl methacrylate (ICNEML) and then thermally co-polymerized with the crosslinker ethylene dimethacrylate (EDMA) in presence of porogens (methanol and dimethylsulfoxide). The optimal experimental conditions (e.g., concentration and ratio of the reagents), considering enantioresolution and permeability, were systematically investigated. The prepared monolith was evaluated using scanning electron microscopy, and the column exhibited quite good morphology. In order to further evaluate the enantioresolving power of the poly(ICNEML-teicoplanin-co-EDMA) monolith, a series of basic and acidic chiral compounds were analyzed using an isocratic mode of polar organic solvents (methanol and acetonitrile) or the same solvents in combination with water (reversed-phase) by nano-liquid chromatography. Five mandelic acids and six derivatized amino acids were enantioresolved under reversed-phase mode (Rs = 1.22–3.47 and α = 1.43–6.33). This monolithic teicoplanin-CSP was also effective in the enantioseparations of 17 amino alcohol drugs employing polar-organic phase mode (MeOH/ACN/TEA/HOAc (80/20/0.03/0.055, v/v/v/v)). Ten of them were baseline enantioresolved (alprenolol, betaxolol, clenbuterol, isoproterenol, metoprolol, pindolol, propranolol, salbutamol, sotalol, tertatolol) (Rs = 1.55–2.48 and α = 1.21–1.55), while the others were partially enantioseparated (Rs = 1.14–1.48).

Low-level detection of water in polar aprotic solvents using an unusually fluorescent spirocyclic rhodamine

Detection of trace amount of water in polar aprotic solvents (acetonitrile) by novel fluorescent spirocyclic rhodamine (sDRh).

The interactions between polar solvents (methanol, acetonitrile, dimethylsulfoxide) and the ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide

In practical applications, ionic liquids (ILs) are usually used in mixtures with polar solvents to reduce the cost of neat ILs and to manipulate their physicochemical properties. To apply such mixtures in a targeted manner, it is necessary to know the influence of the solvents on the properties of the ILs. In this work, the microscopic structure and hydrogen bonding interactions between 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMIMFSI) and three polar solvents (methanol, acetonitrile, and dimethylsulfoxide) are investigated by employing spectroscopic techniques and quantum chemical calculations. For neat EMIMFSI, hydrogen bonds are a secondary factor to decide the microscopic structure, which is significantly different to most other imidazolium-based ILs. Particular attention is given to the imidazolium ring C2H group in the neat IL and its mixtures with the three solvents. Our results show that CH3CN cannot break the strong electrostatic interactions in the [EMIM]+–[FSI]− ion pair. In contrast, CH3OH and DMSO can break them to form [EMIM]+-solvent complexes. Due to the fact that DMSO can form stronger hydrogen bonds with EMIMFSI, more [EMIM]+-solvent complexes can be found in the EMIMFSI–DMSO mixtures. The results indicate that solvents can influence the microscopic structure of the ILs and thereby change the properties in a targeted fashion.

Rapid Route to Polar Solvent-Directed Growth of Perovskite Nanowires

Despite recent impressive advances in the synthesis of all-inorganic perovskite CsPbX3 (X = Cl, Br, and I) via facile solution-based approaches, it remains challenging to achieve well-defined morphologies of interest, particularly one-dimensional (1D) nanowires. Herein, we report a robust polar-solvent-assisted route to 1D CsPbBr3 nanowires via room temperature supersaturated recrystallization. Notably, compared to CsPbBr3 nanocubes synthesized in the absence of polar solvent acetonitrile (ACN), upon the introduction of a suitable amount of ACN into antisolvent toluene, CsPbBr3 nanowires are rapidly yielded, experiencing a cubic-to-orthorhombic phase transformation and a blue-shifted emission. The formation mechanism of CsPbBr3 nanowires can be qualitatively understood on the basis of the role of ACN as a structure-directing agent. Intriguingly, the addition of ACN renders an accelerated anion-exchange reaction between CsPbBr3 and halide salts (i.e., Br-to-Cl and Br-to-I exchanges) due to improved dissolution of the halide ions in ACN. The polar solvent-directed growth strategy may represent an effective means of expanding the diversity of morphologies accessible to perovskite nanocrystals. As such, it facilitates an investigation into the dimension-dependent optical and optoelectronic properties of perovskite-based nanomaterials and devices. These CsPbBr3 nanowires can be potentially used for nanoscale photonic, electronic, and optoelectronic devices, including photodetectors, light-emitting diodes, lasers, and solar cells.

Immobilization of fullerene C60 at cathodically polarized glassy carbon for the generation of thin nucleophilic layers and their carboxylation and alkylation

Fullerene-C60 deposited onto solid substrates (glassy carbon, gold) was polarized between 0 V and −2 V vs. Ag/AgCl/KClsat (aq) in polar aprotic solvents (dimethylformamide or acetonitrile) containing tetramethylammonium salts in the presence of electrophilic reagents, namely primary haloalkanes (Hal = Br, I) and carbon dioxide. The electrogenerated reduced forms of C60 (C60− to C604−, fullerene polyanions), show high reactivity towards various electrophiles which permits preparing C60 dicarboxylates whose formation was established through coulometric integration. Importantly, anodic oxidation (Ep ≈ +1 V) of thus produced C60 dicarboxylates led to the complete regeneration of C60 via a Kolbe bis-decarboxylation.

Copper-Mediated Selective Mono- and Sequential Organochalcogenation of C-H Bonds: Synthesis of Hybrid Unsymmetrical Aryl Ferrocene Chalcogenides.

An 8-aminoquinoline-directed, copper/1,10-phenanthroline-mediated selective mono-organothiolation of the C-H bond in ferroceneamide has been developed using aryl/alkyl disulfide substrates. The sequential ferrocene C-H organochalcogenation (chalcogen = S, Se, and Te) has also been established for the synthesis of novel hybrid unsymmetrical aryl chalcogenides with the aid of a catalytic amount of Cu(OAc)2 under ambient reaction conditions. The developed protocol results in a broad functional group tolerance to allow alkyl-, aryl-, heteroaryl-, bromo-, chloro-, and nitro-containing diorgano dichalcogenides as coupling partners. Furthermore, the 8-aminoquinoline directing group is easily removed to afford the aldehyde functionality after C-H organochalcogenation. A mechanistic understanding of the copper-mediated selective mono-organothiolation reaction suggests that the rigid bicoordinated 1,10-phenanthroline ligand and freshly generated copper(II) from Cu(I) in the less polar solvent acetonitrile are crucial to the selective mono-C-H functionalization of ferroceneamide.

Novel charge transfer-hydrogen bonded complex between 2-amino-4,6-dimethoxy-pyrimidine (ADMP) with chloranilic acid (H2CA): temperature, solvation and DFT computational studies

ABSTRACTNew charge transfer complex associated with hydrogen bonding between 2-amino-4,6-dimethoxypyrimidine (ADMP) with chloranilic acid (H2CA) was studied in solution and solid state. The solution studies were carried out in three polar solvents ethanol (EtOH), methanol (MeOH) and acetonitrile (ACN). The formed complex exhibited new absorption maxima above 500 nm. The molecular composition was done by job and photometric titration methods where the complex proceeded through 1:1 ratio. Moreover, the stability constant was calculated by Bensie-Hildebrand equation, the highest value was in methanol and least one in ethanol. The solid complex was synthesised and characterised by elemental analysis and infrared spectra, and they confirmed the formation of 2:1 (donor: acceptor) complex and its structure included charge transfer besides hydrogen bonding. DFT computations using the hybrid method B3LYP-DFT at the basis set 6-31G(d,p) were running out in gas phase to support the mechanism of complex formation in solid state.

Composite Al∙Ti powders prepared by high-energy milling with different process controls agents

Aluminum-rich Al-Ti composite powders with controllable particle size distributions were prepared by staged mechanical milling using polar and nonpolar organic process control agents. Staged milling allowed the separation of formation of composites in the first stage from control of particle size and ignition behavior in the second stage. Using the polar solvent acetonitrile in the second stage resulted in more finely dispersed particles with lower onset temperatures for intermetallic formation reactions, and lower ignition temperatures, compared with using the non-polar hexane. All composites showed lower ignition temperatures than reference aluminum. Combustion rates for all composites were greater than for reference aluminum, while net energy release remained comparable. The results suggest that staged milling with process control agents of different polarity is a viable method to control particle size distributions and ignition behavior in mechanically milled, metal-based energetic composite powders while maintaining the energy content. Particle size control is critical for adopting such materials in practical systems.

Dynamic Excited-State Intramolecular Proton Transfer Mechanisms of Two Novel 3-Hydroxyflavone-Based Chromophores in Two Different Surroundings.

The dynamic excited-state intramolecular proton transfer (ESIPT) mechanisms of two novel 3-hydroxyflavone-based chromophores (1 and 2) in different surroundings (nonpolar cyclohexane and polar acetonitrile solvents), which are reported in the recent work (Chou et al. J. Phys. Chem. A. 2010, 114, 10412), are explored in terms of the density functional theory (DFT) and time-dependent DFT theoretical methods. The computational absorption and emission spectra for the work rendered here were in reasonable agreement with the relevant experiment. In order to present the molecular-level exposition of the ESIPT reactions for these compounds in two different solvents, we calculated the hydrogen bond (HB) parameters, corresponding infrared vibrational frequencies, frontier molecular orbitals, and maps of electron density difference between the S0 and S1 states, and the HB strengthening tendency in S1 states was verified, giving the probability of ESIPT reactions. In addition, to definitely expose the ESIPT mechanisms of compounds 1 and 2, we built the potential energy curves and potential energy surfaces in the S0 and S1 states. Calculated results exhibited that the ESIPT reaction of compound 1 in nonpolar cyclohexane solvent was more susceptible than that in polar acetonitrile solvent. For the asymmetric compound 2, only single-ESIPT processes could occur in both the solvents, and double-ESIPT processes were prohibitive due to high potential energy barriers. Moreover, the single-ESIPT processes [I (6.26 kcal/mol) and II (6.62 kcal/mol)] in cyclohexane were more susceptible than that [I' (6.91 kcal/mol) and II' (6.90 kcal/mol)] in acetonitrile. Furthermore, the single-ESIPT process I had a little advantage over the process II in cyclohexane, while the probabilities of processes I' and II' were roughly the same in acetonitrile.

Critical assessment of solvent effects on absorption and fluorescence of 3HF in acetonitrile in the QM/PCM framework: A synergic computational and experimental study

Absorption and fluorescence properties of 3-hydroxyflavone (3HF) dissolved in the polar aprotic solvent acetonitrile have been investigated by electronic spectroscopies, associated to mixed quantum mechanical (QM)/classical calculations, where the effect of the solvent is included at the classical level by means of the polarizable continuum model (QM/PCM).Whereas absorption and fluorescence (λexc = 342 nm) spectra confirmed previous results, a detailed spectrofluorimetric investigation of the anion, deriving from solvent-induced deprotonation of the OH group of 3-hydroxyflavone, showed for the first time that a single anionic form is present in solution, differently from what observed in another polar aprotic solvent, DMSO.A detailed computational study based on Density Functional Theory (DFT), using five different functionals, has been carried out in order to reproduce and better understand absorption and emission bands on the different existing forms for 3HF in solution: Normal (N), Tautomer (T), Anion (A).The results are discussed in terms of solvent effects on 3HF spectroscopic properties. It was found that simulations are in good agreement with the spectroscopic data for the N and T forms, whereas for the A form larger discrepancies are observed, especially for absorption properties. The effect of specific solute solvent hydrogen bond interactions involving the CO and OH moieties of 3HF was also explored, aiming to better simulate anionic spectroscopic properties. Results suggest that a more complete description of the whole solvation shell is necessary.

Behavior of fullerene C70 in binary organic solvent mixtures as studied using UV-Vis spectra and dynamic light scattering

In this paper, the formation of colloidal species of fullerene C70 in organic solvents was studied. The examining of the UV-visible spectra was accompanied by particle size analysis using dynamic light scattering, DLS. Stock solutions of C70 in non-polar toluene and n-hexane were diluted with polar solvents acetonitrile and methanol. The appearance of colloidal species with a size within the range of ≈50–500 nm is accompanied by alterations of the absorption spectra. In the toluene–acetonitrile and toluene–methanol binary mixed solvents at 25 oC, the absorption spectra of C70 (5×10–6 M) tend to retain the features of the spectrum in neat aromatic solvent even if the C70 molecules are gathered into colloidal aggregates. Earlier such phenomenon was observed for C60 in benzene–acetonitrile and toluene–methanol solvent systems. This gives support to the idea of rather stable primary solvate shells formed by aromatic molecules around the fullerene molecules. The behavior of C70 in toluene mixtures with methanol was compared with the earlier reported results from this laboratory for the C60 fullerene in the same solvent system. The study of n-hexane–methanol mixtures was performed at elevated temperature because of limited miscibility of these solvents at 25 oC. Accordingly, the C70–toluene–methanol system was also examined at 40 oC. A small but distinctly noticeable difference was revealed. Whereas in the case of the last-named system, the absorption spectrum typical for molecular form of C70 is still observable when colloidal species are already present in the solution, the turning-point between molecules and colloids as determined by both UV-visible spectra and DLS coincides for the n-hexane–methanol binary mixed solvent. Hence, the solvation shells formed by the aliphatic solvent around C70 are less stable as compared with those formed by toluene. Finally, the absorption spectra of C70 in the mixed solvents toluene–n-hexane were analyzed. These data give some support to the assumption of preferable solvation of the C70 molecules by the aromatic co-solvent.

Ab Initio Prediction of Fluorescence Lifetimes Involving Solvent Environments by Means of COSMO and Vibrational Broadening.

The fluorescence lifetime is a key property of fluorophores that can be utilized for microenvironment probing, analyte sensing, and multiplexing as well as barcoding applications. For the rational design of lifetime probes and barcodes, theoretical methods have been developed to enable the ab initio prediction of this parameter, which depends strongly on interactions with solvent molecules and other chemical species in the emitteŕs immediate environment. In this work, we investigate how a conductor-like screening model (COSMO) can account for variations in fluorescence lifetimes that are caused by such fluorophore-solvent interactions. Therefore, we calculate vibrationally broadened fluorescence spectra using the nuclear ensemble method to obtain distorted molecular geometries to sample the electronic transitions with time-dependent density functional theory (TDDFT). The influence of the solvent on fluorescence lifetimes is accounted for with COSMO. For example, for 4-hydroxythiazole fluorophore containing different heteroatoms and acidic and basic moieties in aprotic and protic solvents of varying polarity, this approach was compared to experimentally determined lifetimes in the same solvents. Our results demonstrate a good correlation between theoretically predicted and experimentally measured fluorescence lifetimes except for the polar solvents ethanol and acetonitrile that can specifically interact with the heteroatoms and the carboxylic acid of the thiazole derivative.

Viscosities of 1-Hexyl-3-methylimidazolium Tetrafluoroborate and Its Binary Mixtures with Dimethyl Sulfoxide and Acetonitrile

New dynamic viscosity data are reported for binary mixtures of ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate, [C6mim][BF4], with polar aprotic solvents dimethyl sulfoxide (DMSO) and acetonitrile (ACN) over the whole composition range at experimental pressure p = 0.1 MPa. The temperature dependence of viscosity was studied in the T = (293.15 to 353.15) K temperature range. The viscosity data for binaries have been correlated with models based on Eyring’s absolute rate theory with one, two, and three parameters and also with the classical equations of Grunberg–Nissan and McAllister. We also analyzed the capacity of the group contribution methods recently proposed by Zhao and Jacquemin for predicting the viscosity of binary mixtures with ILs. The results we obtained were promising, especially at lower temperatures, where the relative deviations, AAD%, were about 5 to 6%. The deviations in viscosity were calculated and correlated by a fourth-order Redlich–Kister type equation. The results were discussed in terms of interactions and interstitial accommodation between components in the binary mixtures.

Zeolitic Imidazolate Framework Membranes for Organic Solvent Nanofiltration: A Molecular Simulation Exploration

Organic solvents are intensively used in chemical and pharmaceutical industries. Their separation and recovery account for a significant portion of energy consumption and capital cost in many industrial processes. In this study, three microporous crystalline zeolitic imidazolate frameworks (ZIF-25, ZIF-71, and ZIF-96) are investigated as organic solvent nanofiltration (OSN) membranes by molecular simulations. The fluxes of five solvents (methanol, ethanol, acetone, acetonitrile, and n-hexane) are predicted. Despite the smallest aperture size among the three ZIFs, ZIF-25 exhibits the highest flux for polar solvents (methanol, ethanol, acetone, and acetonitrile) because of its hydrophobic nature, whereas hydrophilic ZIF-96 shows the highest flux for nonpolar n-hexane. The analysis of structural information and interaction energy reveals that the solvent-framework interaction is crucial to determine solvent permeation. Good correlations between solvent permeances and a combination of solvent properties are found. In the presence of a model solute (paracetamol), solvent permeances are marginally affected; moreover, the rejection of paracetamol is 100% for the three ZIF membranes in all five solvents. This study highlights that the pore chemistry, in addition to pore size, plays an important role in solvent permeation, and it suggests that ZIFs are potential OSN membranes for the recovery of organic solvents.

Solvent and Autocatalytic Effects on the Stabilisation of the σ-Complex during Electrophilic Aromatic Chlorination.

The solvent and autocatalytic effects of the electrophilic aromatic chlorination of benzene are studied using a combined approach of static calculations and ab initio metadynamics simulations. Different possible reaction pathways are investigated and the influence of the solvents (CCl4 , acetonitrile and acetic acid) is thoroughly assessed. Our results show that the stability and lifetime of a charged σ-complex is increased by electrostatic stabilisation effects of the environment, which can originate from catalytic HCl, solvating effects of polar solvents (acetonitrile), or specific hydrogen bonding interactions with the solvent (acetic acid). Metadynamics simulations reveal a new chlorine addition mechanism explaining the autocatalytic effects of the reaction. The strength of combining static calculations and metadynamics simulations is highlighted, which provide complementary insight into chemical reactions in solvent.

Ligand-Free Nanocrystals of Highly Emissive Cs4PbBr6 Perovskite

Although ligands of long carbon chains are very crucial to form stable colloidal perovskite nanocrystals (NCs), they create a severe barrier for efficient charge injection or extraction in quantum-dot-based optoelectronics, such as light emitting diode or solar cell. Here, we report a new approach to preparing ligand-free perovskite NCs of Cs4PbBr6, which retained high photoluminescence quantum yield (44%). Such an approach involves a polar solvent (acetonitrile) and two small molecules (ammonium acetate and cesium chloride), which replace the organic ligand and still protect the nanocrystals from dissolution. The successful removal of hydrophobic long ligands was evidenced by Fourier transform infrared spectroscopy, ζ potential analysis, and thermogravimetric analysis. Unlike conventional perovskite NCs that are extremely susceptible to polar solvents, the ligand-free Cs4PbBr6 NCs show robust resistance to polar solvents. Our ligand-free procedure opens many possibilities not only from a material hybridi...

Re(bpy)(CO)3 Cl Immobilized on Bipyridine-Periodic Mesoporous Organosilica for Photocatalytic CO2 Reduction.

This paper describes the physicochemical properties of a rhenium (Re) complex [Re(bpy)(CO)3 Cl] immobilized on a bipyridine-periodic mesoporous organosilica (BPy-PMO) acting as a solid support. The immobilized Re complex generated a metal-to-ligand charge transfer absorption band at 400 nm. This wavelength is longer than that exhibited by Re(bpy)(CO)3 Cl in the polar solvent acetonitrile (371 nm) and is almost equal to that in nonpolar toluene (403 nm). The photocatalytic activity of this heterogeneous Re complex was lower than that of a homogeneous Re complex due to the reduced phosphorescence lifetime resulting from immobilization. However, the catalytic activity was enhanced by the co-immobilization of the ruthenium (Ru) photosensitizer [Ru(bpy)3 ]2+ on the PMO pore surfaces. Quantum chemical calculations suggest that electron transfer between the Ru and Re complexes occurs through interactions between the molecular orbitals in the pore walls. These results should have applications to the design of efficient heterogeneous CO2 reduction photocatalysis systems.

Spectroscopic investigations of interaction between TiO2 and newly synthesized phenothiazine derivative-PTA dye and its role as photo-sensitizer

Interaction of TiO2 nanoparticles (NPs) on newly synthesized phenothiazine derivative-(E)-2-cyano-3-(10-decyl-10H-phenothiazin-7-yl) acrylic acid (PTA dye) has been studied using absorption, fluorescence and electrochemical techniques. From the results of absorption spectra of PTA dye in the presence of TiO2 NPs and the magnitude of association constant (ka) determined from Benesi-Hildebrand theory, strong association between the PTA dye and TiO2 NPs was confirmed. Fluorescence study, under both steady and transient states, reveals the energy transfer between PTA dye and TiO2 NPs as dynamic phenomenon in ethyl acetate. A study of Rehm-Weller theory indicates the predominant electron transfer process between PTA dye and TiO2 NPs in polar solvent (Acetonitrile) than in less polar solvent (Ethyl acetate). Electron transfer process has been exploited in solar energy harvesting applications by fabricating PTA dye sensitized solar cell. Photovoltaic energy conversion efficiency (η) and fill factor (FF) of PTA dye were found to be 1.24% and 0.54 respectively under AM 1.5 irradiation (1000 W/m2).

Solvent-dependent investigation of carbazole benzonitrile derivatives: does the LE3−CT1 energy gap facilitate thermally activated delayed fluorescence?

The photophysical properties of six types of carbazole benzonitrile (CzBN) derivatives are investigated in different solvents to examine the thermally activated delayed fluorescence (TADF) activation via reducing the energy gap between the singlet charge-transfer and triplet locally excited states, ΔE ST(LE) . Relative to the ΔE ST(LE) values for the CzBN derivatives in the low polarity solvent toluene ( ϵ ∼ 2 ), a reduction of ΔE ST(LE) for the CzBN derivatives in the polar solvent acetonitrile ( ϵ ∼ 37 ) was confirmed while maintaining fairly constant Δ E ST values. Notably, TADF activation was observed in acetonitrile for some CzBN derivatives that are TADF inactive in toluene. A numerical analysis of various rate constants revealed the cause of TADF activation as an increase in the reverse intersystem crossing rate and a suppression of the non-radiative decay rate of the triplet states. The positive effect of ΔE ST(LE) was limited, however, as an excessive decrease in ΔE ST(LE) facilitates the nonradiative deactivation of the triplet states, leading to a loss of the TADF efficiency. This paper shows that ΔE ST(LE) provides a measure of TADF activation and that appropriate regulation of ΔE ST(LE) is required to achieve high TADF efficiency.