Session Chair: Hiroko Yamada, Nara Institute of Science and Technology
1:30pm - 2:00pm Invited
Molecule-Based Flexible and Stretchable Sensors
Joon Hak OH
Pohang University of Science and Technology, South Korea
With the advent of the Internet of Things (IoT), sensors are becoming increasingly important. Particularly, sensors based on molecules covering small organic molecules and polymers have recently attracted great interest due to their high potential for use in flexible, low-cost, solution-processable, large-area electronics. Functional properties of organic active layers can be tailored by rational molecular design or surface functionalization to enhance their selectivity and sensitivity. Compared with conventional sensing devices composed of two terminals, field-effect transistor (FET)-type sensors enable easy amplification of the detected signals and facile electrical tuning of the sensitivity by controlling the applied voltage on the third electrode, i.e., the gate terminal. Furthermore, nanoscopically engineered organic semiconducting materials have emerged as promising building blocks for high-performance flexible sensors. This talk will introduce recent technologies on molecule-based flexible and stretchable sensors. In addition, this talk will cover our recent works on molecule-based soft electronics. Unconventional organic semiconducting nanomaterials including single-crystalline nanowires, nanoporous organic semiconducting films, and core-shell structured 1-D nanomaterials have been fabricated and applied to high-performance flexible and wearable sensors such as photodetectors, chemical and biological sensors. In addition, the fundamental charge transport and photophysical phenomena of molecule-based active layers have been investigated.
2:00pm - 2:30pm Invited
Novel Materials Design of High-Efficiency Light-Emitting Organic Semiconductors for Optoelectronic Devices
Kyushu University, Japan
High-efficiency organic light-emitting diodes (OLEDs) are being developed intensively for next-generation flat-panel displays and general lighting sources owing to their advantages of wide view angles, light weight, flexibility, as well as improved brightness. In the past decade, nearly 100% internal electroluminescence (EL) quantum efficiency has been achieved by employing transition metal-centered phosphorescent emitters such as Ir and Pt organometallic complexes that can harvest both singlet and triplet excitons by fast intersystem crossing (ISC) for phosphorescence.
In contrast, OLEDs incorporating fluorescent emitters provide remarkably high reliability and stability, whilst their hint should be theoretically limited to 25% because of the spin statistical limit of 1:3 for the singlet-to-triplet exciton ratio under electrical excitation. Hence, it still remains a challenge to develop new luminescent materials rendering high singlet exciton generation efficiency in fluorescence OLEDs. To maximize the actual efficiency in fluorescence OLEDs, we have recently demonstrated a brand new viable mechanism for EL, that is, thermally-activated delayed fluorescence (TADF). In TADF processes, triplet excitons can be thermally converted into emissive singlet excitons, leading to an increase in the fluorescence intensity. Therefore, it is anticipated that emitters with a small energy gap between the lowest excited singlet and triplet states will allow an efficient reverse ISC.
In this presentation, we focus on advanced molecular design for TADF luminophores for realizing highly efficient OLEDs. By utilizing TADF mechanism, we have successfully achieved high-performance TADF-based OLEDs, exhibiting significantly high external EL quantum efficiencies, comparable to those obtained with phosphorescence OLEDs. Using a variety of electron-accepting building blocks tethered by appropriate electron-donating aromatic segments would be a versatile and promising strategy to construct high-performance TADF materials and OLEDs.
2:30pm - 3:00pm Invited
Artificial Synapses using Organic Nanowires and Organic-Inorganic Hybrid Perovskites
1Seoul National University, South Korea; 2Pohang University of Science and Technology (POSTECH), South Korea
We present our recent research on the fabrication of artificial synapses using organic nanowires and organic-inorganic hybrid perovskite materials. Both two-terminal and three-terminal structures are discussed. Important synaptic working principles have been emulated, including short-term plasticity (STP), long-term plasticity (LTP) and spike-timing dependent plasticity (STDP). Using our home-built electrohydrodynamic nanowire (e-NW) printer, digitally aligned semiconducting nanowires were printed for synaptic transistor arrays, which will allow nano feature size. High-quality organic-inorganic hybrid perovskite thin film facilitated the fabrication of two-terminal artificial synapses, which is essential for high-density cross-bar electrode architectures. These properties are essential for brain-inspired computation, nano-circuit integration and represent an important step towards the future building up neuromorphic electronics.
3:00pm - 3:15pm Oral
Cyclo-penta Fused Bisanthene and its Redox Species: Singlet Diradicaloids and Annulene within an Annulene Structure
Qing WANG, Chunyan CHI
National University of Singapore, Singapore
Cyclo-penta fused bisanthene, a molecule that incorporates two five-membered rings at the bay positions of bisanthene, has been easily synthesized as a rather stable compound. Its two charged species are also successfully obtained and characterized by H-NMR after attempting different reaction reagents. The neutral compound has a singlet diradical character in the ground state and a small singlet-triplet energy gap of -3.17 kcal/mol. H-NMR and AICD suggest there's a paramagnetic ring current in the rim, which is because of its antiaromatic 4n pi (20) electrons in the out layer. The dication is then attained by oxidizing the neutral with 4 equiv. of NOSbF6. It exhibits totally different electronic absorption spectra, NMR spectra, NICS values, and diatropic ring current from the neutral one, that results from its aromatic state of 4n+2 pi (18) electrons outside. What’s more, AICD plot implies the dication can be regarded as an annulene within an annulene (AWA) molecule, with both rim and hub obey Hückel's 4n+2 rule. In addition, its ground state is singlet diradical. For the dianion, it can be formed by reacting the neutral with 2 equiv. of sodium anthracenide as the reducing agent. Different from the dication, it's closed shell in the ground state and has super aromaticity in the outer layer only. The dianion is relatively more stable than the dication, which attributes to the formation of 5-carbon-six-electron system. In a word, the neutral, dication and dianion of hydrocarbon polycyclic compound are easily synthesized at the same time and they possess quite different physical properties from each other. This work also gives some insight into the design and synthesis of molecules with AWA structure in the future.