Dibenzothiophene Sulfone-Based Phosphine Oxide Electron Transporters with Unique Asymmetry for High-Efficiency Blue Thermally Activated Delayed Fluorescence Diodes

Dimerization effects on the electronic properties of candidate OLED materials for optimized performance: a quantum DFT study

In recent years, there has been growing interest in organic light-emitting diode (OLED) materials, highlighting the importance of a thorough understanding of the key factors that influence their electronic and non-linear optical (NLO) properties. To achieve this objective, we considered five candidate OLED compounds: dibenzothio-phen-sulfone-3-yl-9-phenyl-9H-carbazole (DBTS-CzP), 9H-thioxanthene-9-one-dibenzothiophene-sulfone (TXO-CzP), spiro[fluorene-9,9-thioxanthene]-10,10-dioxide (SpDBTS-CzP), 9-[4-(diphenylphosphoryl)-2,2-dimethyl-4-biphenylyl]-9H-carbazole (mCBPPO), and N,N-bis[2-(pyridin-2-yl)phenyl]-N,N-di(n-butyl)phenylamine (DPA-2Py). We employed density functional theory (DFT) and time-dependent DFT (TD-DFT) methods to investigate how dimerization can affect their electronic and NLO characteristics. The results of electronic structure analysis, including HOMO-LUMO gaps and NLO characteristics, reveal that dimerization enhances dipole moments and polarizabilities, facilitating improved charge transfer and electronic transitions. Among the studied compounds, TXO-CzP demonstrates stable electronic properties and exhibits enhanced NLO characteristics post-dimerization-such as efficient charge mobility and superior color purity-positioning it as a promising candidate for advanced OLED applications. These findings underscore dimerized structures' potential to enhance optoelectronic device performance.

An effective method in modulating thermally activated delayed fluorescence (TADF) emitters from green to blue emission: the role of the phenyl ring

Developing efficient blue emitters with high performance and low cost is crucial for the further development of organic light-emitting diodes (OLEDs). Based on the two experimentally reported green thermally activated delayed fluorescence (TADF) emitters, which are thioxanthone derivatives consisting of carbazole as an electron donor and 9H-thioxanthen-9-one-S,S-dioxide (SOXO) as an electron acceptor with donor-acceptor (D-A) or donor-acceptor-donor (D-A-D) structures, two new blue TADF emitters are designed by simply inserting a phenyl ring between D and A units. The TADF processes of the four thioxanthone derivatives are studied systematically through first-principles calculations. The role of the introduced phenyl ring in the excited state properties of the designed molecules is explored by analyzing the changes in molecular geometries, frontier molecular orbital distributions, the lowest singlet-triplet energy splitting (ΔEST), the spin orbit coupling (SOC) constants, the radiative decay rates (kr) and the nonradiative decay rates (knr), as well as the intersystem crossing rates (kISC) and reverse intersystem crossing rates (kRISC). The results show that when incorporating phenyl units into the D-A and D-A-D structures, both high kr and enhanced kRISC are achieved in Cz-Ph-SOXO and DCz-DPh-SOXO, demonstrating that incorporating the phenyl unit in D-A and D-A-D structures is an efficient way for developing new SOXO-based TADF molecules. It is worth noting that the kRISC values for Cz-Ph-SOXO and DCz-DPh-SOXO are significantly increased with respect to those of the experimental molecules. The present results would provide helpful guidelines for developing new SOXO-based TADF molecules experimentally.

Charge transporting and thermally activated delayed fluorescence materials for OLED applications

The design and synthesis of effective charge transporting (CT) and thermally activated delayed fluorescence (TADF) materials are in high demand to obtain high-performing OLED devices. Recently, the significant development in the field of OLEDs has led to the creation of numerous charge transporting and TADF materials with diverse structures. To further improve the device performance, a better understanding of the structural characteristics and structure-property relationships of these materials is essential. Moreover, to enhance the efficiency of OLEDs, all the electrogenerated excitons should be constrained in EMLs. The TADF mechanism can theoretically register 100% IQE through a potent up-conversion method from non-radiative triplet excitons to radiative singlet excitons. In this review, the structural importance, classification, physical properties, and electroluminescence data of some recent charge transporting and TADF materials are summarized and discussed. Moreover, their molecular structural dependence on functional groups and linkers is classified, which can enhance their charge transporting or emitting ability. To offer a potential roadmap for the further development of charge transporting and TADF materials, it is hoped that this study will encourage researchers to acknowledge their important role in OLEDs.

Crystallization induced room-temperature phosphorescence and chiral photoluminescence properties of phosphoramides

We report the design and synthesis of a series of room temperature phosphorescent phosphoramides TPTZPO, TPTZPS, and TPTZPSe with a donor (phenothiazine)-acceptor (P = X, X = O, S, and Se) architecture. All the compounds show structureless fluorescence with a nanosecond lifetime in dilute solutions. However, these compounds show dual fluorescence and room temperature phosphorescence (RTP) in the solid state. Both the intensity and energy of luminescence depend on the heteroatom attached to the phosphorus center. For example, compound TPTZPO with the P[double bond, length as m-dash]O unit exhibits fluorescence at a higher energy region than TPTZPS and TPTZPSe with the P[double bond, length as m-dash]S and P[double bond, length as m-dash]Se groups, respectively. Crystalline samples of TPTZPO, TPTZPS, and TPTZPSe show stronger RTP than the amorphous powder of respective compounds. Detailed steady-state, time-resolved photoluminescence and computational studies established that the 3n-π* state dominated by the phenothiazine moiety is the emissive state of these compounds. Although TPTZPS and TPTZPSe crystallized in the chiral space group, only TPTZPSe showed chiroptical properties in the solid state. The luminescence dissymmetry factor (g lum) value of TPTZPS is small and below the detection limit, and a CPL spectrum could not be observed for this compound.

Molecular-engineered highly photosensitive triarylphosphine oxide compounds for apoptosis imaging and selectively inducing apoptosis of tumor cells by photodynamic therapy

Although photodynamic therapy (PDT) has wide applications, tumor-targeting probes with high photosensitivity or apoptosis-monitoring capability are still scarce, which possess low phototoxicity and can be used for evaluating the therapeutic...

Oligofluorene with multiple spiro-connections: its and their use in blue and white OLEDs

This work reports the synthesis and characterization of super rigid oligofluorenes. We also demonstrate their applications in blue and white OLEDs.

Versatile functionalization of trifluoromethyl based deep blue thermally activated delayed fluorescence materials for organic light emitting diodes

Four deep blue TADF compounds with trifluoromethyl-substituted phenyl/N-heterocyclic rings were investigated both as hosts and guests in OLEDs with excellent performance.

A Phosphanthrene Oxide Host with Close Sphere Packing for Ultralow-Voltage-Driven Efficient Blue Thermally Activated Delayed Fluorescence Diodes

A phosphanthrene oxide host, 5,10-diphenyl-phosphanthrene 5,10-dioxide (DPDPO₂ A), with intra- and intermolecular hydrogen bonds achieves spheroidal cis-configuration and close sphere packing. DPDPO₂ A realizes effective exciton suppression and excellent and balanced carrier transporting ability, both at the same time, demonstrating favorable photoluminescence quantum yield of 84% from its blue thermally activated delayed fluorescence (TADF) dye, namely bis[4-(9,9-dimethyl-9,10-dihydroacridine) phenyl]sulfone, doped films and high electron and hole mobility at the level of 10^-4 and 10^-5 cm² V^-1 s^-1 , respectively. DPDPO₂ A endows its blue TADF devices with record-low driving voltages, e.g., turn-on voltage of 2.5 V, and the state-of-the-art efficiencies with maxima of 22.5% for external quantum efficiency and 52.9 lm W^-1 for power efficiency, which is the best comprehensive performance to date of ultralow-voltage-driven blue TADF diodes.

Recent advances in organic thermally activated delayed fluorescence materials

Thermally activated delayed fluorescence: harvesting dark triplet excitons to generate bright emissive singlet excitons.