Elucidation of an Aggregate Excited State in the Electrochemiluminescence and Chemiluminescence of a Thermally Activated Delayed Fluorescence (TADF) Emitter

Critical Aspects and Challenges in the Design of Small Molecules for Electrochemiluminescence (ECL) Application

Electrochemiluminescence (ECL) has gained renewed interest due to the strong parallel development of luminophores in the field of organic light emitting diodes (OLEDs) with which this technique shares several aspects. In this perspective review we discuss the most relevant advances of the past 15 years in the study of organic and organometallic compounds as ECL emitters, by dividing them in three different classes: i) fluorescent emitters, ii) phosphorescent emitters and iii) Thermally Activated Delayed Fluorescence (TADF) emitters; then, water-soluble organic luminophores will be also discussed. We focus on how their design, their photo- and electrochemical properties and, in particular, the nature of the emitter, affect their efficiency in ECL. Regardless of the type of luminophore or the photoluminescence quantum yield (PLQY), the literature converges on the fact that the most determining aspect is the stability of the oxidized/reduced form of the emitter. Even if phosphorescent emitters can show outstanding efficiency, this often requires the absence of oxygen. In the case of TADFs, there is also a strong dependence of photoluminescence both in terms of PLQY and emission energy on the polarity of the media, so compounds, that appear promising in organic solvents, may be very inefficient in aqueous media.

Tailoring thermally activated delayed fluorescence emitters for efficient electrochemiluminescence with tripropylamine as coreactant

Using a unified metal-free procedure, a selection of Thermally Activated Delayed Fluorescence (TADF) emitters has been synthesized and characterized. Different acceptor and donor moieties have been explored in order to develop red emitting dyes with reduction potentials suitable for the application in ECL using tri-propylamine as coreactant. The most promising compound shows terephthalonitrile as the acceptor and diphenylamines as donors, and it displayed an ECL efficiency that is double the one of the standard [Ru(bpy)3](PF6)2. Based on such findings, a novel water-soluble TADF emitter (Na4[4DPASO3TPN]) has been synthesized and characterized to enable electrochemiluminescence in an aqueous medium.

Highly Efficient Electrochemiluminescence from Imidazole-Based Thermally Activated Delayed Fluorescence Emitters

A family of novel thermally activated delayed fluorescence (TADF) emitters has been synthesized by a straightforward and metal-free synthesis, and structurally characterized. In this work we kept the acceptor moiety, 4-(1H-imidazol-1-yl)benzonitrile, fixed and systemically tested different donors to correlate their photophysical and electrochemical properties with their performance in electrochemiluminescence using both benzoyl peroxide as co-reactant and co-reactant free (annihilation) conditions. Some compounds exceeded the efficiency of the standard [Ru(bpy)3 ]Cl2 by up to 28 times with benzoyl peroxide and 38 times in annihilation. Interestingly, we found that the efficiency is mainly dictated by the electrochemical reversibility of the redox processes rather than by the photophysical properties in terms of photoluminescence quantum yields or excited-state lifetime. In addition, the annihilation electrochemiluminescence efficiency strongly depends on the pulse sequence. The imidazole moiety can be conveniently alkylated, thus allowing the insertion of functional groups, such a carboxylic acid, and enabling practical applications.

Materials for Electrochemiluminescence: TADF, Hydrogen-Bonding, and Aggregation- and Crystallization-Induced Emission Luminophores

Electrochemiluminescence (ECL) is a rapidly growing discipline with many analytical applications from immunoassays to single-molecule detection. At the forefront of ECL research is materials chemistry, which looks at engineering new materials and compounds exhibiting enhanced ECL efficiencies compared to conventional fluorescent materials. In this review, we summarize recent molecular design strategies that lead to high efficiency ECL. In particular, we feature recent advances in the use of thermally activated delayed fluorescence (TADF) emitters to produce enhanced electrochemiluminescence. We also document how hydrogen bonding, aggregation, and crystallization can each be recruited in the design of materials showing enhanced electrochemiluminescence.

Kinetic Intricacies of the Light Emission and Antiradical Influence of Exogenous Bioantioxidants Transformation Products in the Chemiluminescence Bioantioxidant Assay

The subject matter of the reported work refers to studying the interactions followed by the excited-state generation, which are chemical models of oxidative processes leading to a weak light emission emerging from living cells, and to explore the possibilities of using them as tools for evaluating the activity of oxygen-metabolism modulators, most prominently, natural bioantioxidants of biomedical value in particular. Methodologically, major attention is paid to analyzing the shapes of the time profiles of the light emission derived from a model sensory system in the presence of lipid samples of vegetable and animal (fish) origin rich in bioantioxidants. As a result, a modified reaction mechanism involving 12 elementary steps is proposed to rationalize the light-emission kinetics in the presence of natural bioantioxidants. We conclude that free radicals formed from bioantioxidants and their dimerization products contribute significantly to the general antiradical activity of lipid samples, which should be taken into account in developing efficient bioantioxidant assays for biomedical applications and while establishing the mechanisms of bioantioxidant effects on metabolic processes in vivo.