Ting Chen

Bio: Ting Chen is an academic researcher from Nanjing University of Posts and Telecommunications. The author has contributed to research in topics: Singlet fission & Excited state. The author has an hindex of 8, co-authored 10 publications receiving 2204 citations. Previous affiliations of Ting Chen include Center for Advanced Materials.

Thermally Activated Delayed Fluorescence Materials Towards the Breakthrough of Organoelectronics

Abstract: The design and characterization of thermally activated delayed fluorescence (TADF) materials for optoelectronic applications represents an active area of recent research in organoelectronics. Noble metal-free TADF molecules offer unique optical and electronic properties arising from the efficient transition and interconversion between the lowest singlet (S1) and triplet (T1) excited states. Their ability to harvest triplet excitons for fluorescence through facilitated reverse intersystem crossing (T1→S1) could directly impact their properties and performances, which is attractive for a wide variety of low-cost optoelectronic devices. TADF-based organic light-emitting diodes, oxygen, and temperature sensors show significantly upgraded device performances that are comparable to the ones of traditional rare-metal complexes. Here we present an overview of the quick development in TADF mechanisms, materials, and applications. Fundamental principles on design strategies of TADF materials and the common relationship between the molecular structures and optoelectronic properties for diverse research topics and a survey of recent progress in the development of TADF materials, with a particular emphasis on their different types of metal-organic complexes, D-A molecules, and fullerenes, are highlighted. The success in the breakthrough of the theoretical and technical challenges that arise in developing high-performance TADF materials may pave the way to shape the future of organoelectronics.

Stabilizing triplet excited states for ultralong organic phosphorescence

Abstract: The control of the emission properties of synthetic organic molecules through molecular design has led to the development of high-performance optoelectronic devices with tunable emission colours, high quantum efficiencies and efficient energy/charge transfer processes. However, the task of generating excited states with long lifetimes has been met with limited success, owing to the ultrafast deactivation of the highly active excited states. Here, we present a design rule that can be used to tune the emission lifetime of a wide range of luminescent organic molecules, based on effective stabilization of triplet excited states through strong coupling in H-aggregated molecules. Our experimental data revealed that luminescence lifetimes up to 1.35 s, which are several orders of magnitude longer than those of conventional organic fluorophores, can be realized under ambient conditions. These results outline a fundamental principle to design organic molecules with extended lifetimes of excited states, providing a major step forward in expanding the scope of organic phosphorescence applications.

Understanding the Control of Singlet-Triplet Splitting for Organic Exciton Manipulating: A Combined Theoretical and Experimental Approach

Abstract: Developing organic optoelectronic materials with desired photophysical properties has always been at the forefront of organic electronics. The variation of singlet-triplet splitting (ΔEST) can provide useful means in modulating organic excitons for diversified photophysical phenomena, but controlling ΔEST in a desired manner within a large tuning scope remains a daunting challenge. Here, we demonstrate a convenient and quantitative approach to relate ΔEST to the frontier orbital overlap and separation distance via a set of newly developed parameters using natural transition orbital analysis to consider whole pictures of electron transitions for both the lowest singlet (S1) and triplet (T1) excited states. These critical parameters revealed that both separated S1 and T1 states leads to ultralow ΔEST; separated S1 and overlapped T1 states results in small ΔEST; and both overlapped S1 and T1 states induces large ΔEST. Importantly, we realized a widely-tuned ΔEST in a range from ultralow (0.0003 eV) to extra-large (1.47 eV) via a subtle symmetric control of triazine molecules, based on time-dependent density functional theory calculations combined with experimental explorations. These findings provide keen insights into ΔEST control for feasible excited state tuning, offering valuable guidelines for the construction of molecules with desired optoelectronic properties.

Promoting Singlet/triplet Exciton Transformation in Organic Optoelectronic Molecules: Role of Excited State Transition Configuration.

Abstract: Exciton transformation, a non-radiative process in changing the spin multiplicity of an exciton usually between singlet and triplet forms, has received much attention recently due to its crucial effects in manipulating optoelectronic properties for various applications. However, current understanding of exciton transformation mechanism does not extend far beyond a thermal equilibrium of two states with different multiplicity and it is a significant challenge to probe what exactly control the transformation between the highly active excited states. Here, based on the recent developments of three types of purely organic molecules capable of efficient spin-flipping, we perform ab initio structure/energy optimization and similarity/overlap extent analysis to theoretically explore the critical factors in controlling the transformation process of the excited states. The results suggest that the states having close energy levels and similar exciton characteristics with same transition configurations and high heteroatom participation are prone to facilitating exciton transformation. A basic guideline towards the molecular design of purely organic materials with facile exciton transformation ability is also proposed. Our discovery highlights systematically the critical importance of vertical transition configuration of excited states in promoting the singlet/triplet exciton transformation, making a key step forward in excited state tuning of purely organic optoelectronic materials.

Heteroatom-Bridged Benzothiazolyls for Organic Solar Cells: A Theoretical Study

Abstract: On the basis of a typical organic photovoltaic (OPV) building block of 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT), a series of novel DTBT derivatives were designed following a heteroatom-bridging strategy to take advantage of the diversified interactions between heteroatoms and π-conjugated systems. These heteroatom-bridged DTBTs, whose outer electron-rich thiophene moieties are covalently fastened to the central electron-deficient benzothiadiazole with additional heteroatom bridges, exhibit promising features for OPV applications with rigid molecular structures, properly lain frontier molecular orbitals (FMOs), broad and intense absorption spectra, and adequate charge transport properties, as revealed by systematic theoretical calculations on molecular geometries, FMOs, absorption spectra, and relaxation and reorganization energies. The structure–property relationship investigations show that the mono-/di-heteroatom bridging is effective not only in tuning the rigidity of the molecular geomet...

Recent advances in organic thermally activated delayed fluorescence materials.

Abstract: Organic materials that exhibit thermally activated delayed fluorescence (TADF) are an attractive class of functional materials that have witnessed a booming development in recent years. Since Adachi et al. reported high-performance TADF-OLED devices in 2012, there have been many reports regarding the design and synthesis of new TADF luminogens, which have various molecular structures and are used for different applications. In this review, we summarize and discuss the latest progress concerning this rapidly developing research field, in which the majority of the reported TADF systems are discussed, along with their derived structure–property relationships, TADF mechanisms and applications. We hope that such a review provides a clear outlook of these novel functional materials for a broad range of scientists within different disciplinary areas and attracts more researchers to devote themselves to this interesting research field.

Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes.

Abstract: We thank the University of St Andrews for support. EZ-C thanks the Leverhulme Trust for financial support (RPG-2016-047). and the EPSRC (EP/P010482/1) for financial support.

Organic Optoelectronic Materials: Mechanisms and Applications

Abstract: Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjug...

Sky-Blue Organic Light Emitting Diode with 37% External Quantum Efficiency Using Thermally Activated Delayed Fluorescence from Spiroacridine-Triazine Hybrid.

Abstract: Extremely efficient sky-blue organic electroluminescence with external quantum efficiency of ≈37% is achieved in a conventional planar device structure, using a highly efficient thermally activated delayed fluorescence emitter based on the spiroacridine-triazine hybrid and simultaneously possessing nearly unitary (100%) photoluminescence quantum yield, excellent thermal stability, and strongly horizontally oriented emitting dipoles (with a horizontal dipole ratio of 83%).

Design of efficient molecular organic light-emitting diodes by a high-throughput virtual screening and experimental approach

Abstract: A high-throughput virtual screening approach is used to select molecules with efficient, thermally activated delayed fluorescence. The good performance of several selected emitters in organic LED applications has also been confirmed experimentally.