Electrochemical and Spectroelectrochemical Comparative Study of Macrocyclic Thermally Activated Delayed Fluorescent Compounds: Molecular Charge Stability vs OLED EQE Roll-Off

In this work, we present how a small change in molecular structure can affect the electrochemical stability of organic compounds. A new electron donor-acceptor-donor-acceptor (D-A-D-A) macrocyclic π-conjugated compound (tBuMC) comprising of dibenzophenazine as As and N,N’-bis(t-butylphenyl)-p-phenylenediamines as Ds has been synthesized. The photophysical investigation uncovered that tBuMC showed thermally activated delayed fluorescence and that the organic light-emitting diodes (OLEDs) fabricated with tBuMC as the emitter achieved high external quantum efficiency (EQEs) of ca. 10%. However, the OLED with tBuMC showed a slightly lower EQE than that of the OLED with MC (11.6%) and showed greater EQE roll-off. Comparative studies on electrochemical properties of tBuMC, MC, and a linear analogue (Linear) revealed the introduction of t-Bu groups in the D-A-D-A scaffold causes a significant change in redox behavior. Full electrochemical and spectroelectrochemical studies gave clues to understand how the steric hindering group is affecting the charge distribution in the new molecules which results in a significant difference in the OLED roll-off. The electrochemical investigations together with UV-Vis-NIR and EPR analyses supported by quantum chemical theoretical calculations were performed, which provided us insights on the effect of structural modification on the redox properties of the D-A-D-A scaffold.This is the peer reviewed version of the following article: A. Nyga, S. Izumi, H. F. Higginbotham, P. Stachelek, S. Pluczyk, P. de Silva, S. Minakata, Y. Takeda, P. Data, Asian J. Org. Chem. 2020, 9, 2153., which has been published in final form at https://doi.org/10.1002/ajoc.202000475. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving

Using Cyclic Voltammetry, UV-Vis-NIR, and EPR Spectroelectrochemistry to Analyze Organic Compounds

Cyclic voltammetry (CV) is a technique used in the analysis of organic compounds. When this technique is combined with electron paramagnetic resonance (EPR) or ultraviolet-visible and near-infrared (UV-Vis-NIR) spectroscopies, we obtain useful information such as electron affinity, ionization potential, band-gap energies, the type of charge carriers, and degradation information that can be used to synthesize stable organic electronic devices. In this study, we present electrochemical and spectroelectrochemical methods to analyze the processes occurring in active layers of an organic device as well as the generated charge carriers

The impact of replacement of nitrogen with phosphorus atom in the pyromellitic diimides on their photophysical and electrochemical properties

Exploration of optoelectronic properties of novel phosphorus-embedded π-conjugated compounds would provide us with fundamental information about the design of hitherto unknown electroactive organic materials. Herein, detailed photophysical and electrochemical profiles of a series of benzene-cored diketophosphanyl compounds were investigated with steady- and time-resolved spectroscopic and spectroelectrochemical techniques. The comparative studies revealed the impact of phosphorus and nitrogen atoms on their triplet energies and on the behaviour of electrochemical processes to form radical species

Synthesis and mesomorphic properties of laterally substituted 4,4′′′-dialkyl-p-quaterphenyls

Over 20 laterally substituted, mainly by fluorine and other more bulky substituents like chlorine and methyl group, 4,4 '''-dialkyl-p-quaterphenyls have been synthesised and mesomorphic properties, phase transition temperatures and enthalpies were measured. The influence of the number of lateral substituents and their type along with their position in the molecular core have been analysed and compared with similarly substituted terphenyl analogues. The example of the eutectic mixture composed of synthesised quaterphenyl derivatives has been formulated and characterised

Naphthalene Phthalimide Derivatives as Model Compounds for Electrochromic Materials

Electrochromism of organic compounds is a well-known phenomenon; however, nowadays, most research is focused on anodic coloring materials. Development of efficient, cathodic electrochromic materials is challenging due to the worse stability of electron accepting materials compared with electron donating ones. Nevertheless, designing stable cathodic coloring organic materials is highly desired—among other reasons—to increase the coloration performance. Hence, four phthalimide derivatives named 1,5-PhDI, 1,4-PhDI, 2,6-PhDI and 3,3′-PhDI were synthesized and analyzed in depth. In all cases, two imide groups were connected via naphthalene (1,5-PhDI, 1,4-PhDI, 2,6-PhDI) or 3,3′-dimethylnaphtidin (3,3′-PhDI) bridge. To observe the effect of chemical structure on physicochemical properties, various positions of imide bond were considered, namely, 1,5- 1,4- and 2,6-. Additionally, a compound with the pyromellitic diimide unit capped with two 1-naphtalene substituents was obtained. All compounds were studied in terms of their thermal behavior, using differential calorimetry (DSC) and thermogravimetric analysis (TGA). Moreover, electrochemical (CV, DPV) and spectroelectrochemical (UV–Vis and EPR) analyses were performed to evaluate the obtained materials in terms of their application as cathodic electrochromic materials. All obtained materials undergo reversible electrochemical reduction which leads to changes in their optical properties. In the case of imide derivatives, absorption bands related to both reduced and neutral forms are located in the UV region. However, importantly, the introduction of the 3,3′-dimethylnaphtidine bridge leads to a noticeable bathochromic shift of the reduced form absorption band of 3,3′-PhDI. This indicates that optimization of the phthalimide structure allows us to obtain stable, cathodic electrochromic materials

Electrochemically deposited poly(selenophene)-fullerene photoactive layer: Tuning of the spectroscopic properties towards visible light-driven generation of singlet oxygen

A selenophene-containing fullerene dyad (C60Se) was electrochemically co-deposited with bis-selenophene (BisSe) to form a visible light absorbing poly(selenophene) layer with incorporated fullerene photosensitizers on platinum (Pt) or indium-tin oxide (ITO) substrates. The resulting photoactive films (P(C60Se_BisSe)) were characterized by cyclic voltammetry, UV–Vis, IR, Raman and X-ray photoelectron spectroscopies. The efficiency of P(C60Se_BisSe) towards singlet oxygen photogeneration was investigated by applying reactions with chemical traps, i.e. α-terpinene and 1,3–diphenylisobenzofuran (DPBF), monitored by UV–Vis spectroscopy. The composition of the electropolymerized layer was controlled by varying the monomers ratio in the feed solution and it had a strong influence on the spectroscopic and photosensitizing properties of the deposited film. It has been shown that the efficiency of the visible light-driven singlet oxygen generation can be increased by optimizing the ratio between C60 photosensitizers and organic units in the layer

Electrochemical and Spectroelectrochemical Comparative Study of Macrocyclic Thermally Activated Delayed Fluorescent Compounds: Molecular Charge Stability vs OLED EQE Roll‐Off

In this work, we present how a small change in molecular structure can affect the electrochemical stability of organic compounds. A new electron donor–acceptor–donor–acceptor (D–A–D–A) macrocyclic π‐conjugated compound ( t BuMC ) comprising of dibenzophenazine as As and N,N‐ bis( t ‐butylphenyl) ‐p ‐phenylenediamines as Ds has been synthesized. The photophysical investigation uncovered that t BuMC showed thermally activated delayed fluorescence and that the organic light‐emitting diodes (OLEDs) fabricated with t BuMC as the emitter achieved high external quantum efficiency (EQEs) of ca. 10%. However, the OLED with t BuMC showed a slightly lower EQE than that of the OLED with MC (11.6%) and showed greater EQE roll‐off. Comparative studies on electrochemical properties of t BuMC , MC , and a linear analogue ( Linear ) revealed the introduction of t ‐Bu groups in the D–A–D–A scaffold causes a significant change in redox behaviour. Full electrochemical and spectroelectrochemical studies gave clues to understand how the steric hindering group is affecting the charge distribution in the new molecules which results in a significant difference in the OLED roll‐off. The electrochemical investigations together with UV‐Vis‐NIR and EPR analyses supported by quantum chemical theoretical calculations were performed, which provided us insights on the effect of structural modification on the redox properties of the D–A–D–A scaffold