92nd CEMS Colloquium


Dr. Yong-Jin Pu (Emergent Supramolecular Materials Research Team, RIKEN CEMS)


17:30 - 18:30, July 28, 2021 (Wednesday)


Welfare Conference Bldg. 2F, RIKEN


Excited States Control of Organic Semiconductors and Colloidal Quantum Dots


Control of excited states of organic semiconductors and colloidal quantum dots has been fundamentally important in their light-related applications such as LEDs, solar cells, sensors, photocatalysts, etc. When neutral and closed-shell organic molecules are optically or electrically excited, spin multiplicity of the excited state will be either singlet or triplet. In general, without any heavy atoms, the singlet excited state is bright and the triplet excited state is dark because of a spin selection rule. Therefore, reverse intersystem crossing from triplet excited states to singlet excited states makes light emission efficient. Energetically low and long-lived triplet excited states are involved in unique photophysical characteristics: singlet exciton fission, triplet–triplet annihilation, delayed fluorescence, etc. We designed and synthesized the organic semiconductor molecules showing unique triplet excited states–related phenomena. We have also studied controlled self-assembly of colloidal quantum dots (QDs), which are semiconductor nanocrystals with the size smaller than or close to their exciton Bohr radius, showing quantum size effects. They also have attracted extensive attention because of their light-emitting properties and low-energy fabrication process. We demonstrated self-assembled one-dimensional structure of CdS and PbS colloidal QDs and simple cubic packing of PbS QDs in their supercrystal. CsPbBr3 perovskite QDs were controlled to align three-dimensionally by layer-by-layer method, and their 3D assembly showed interparticle electronic coupling through selectively modified ligands on the QDs.