Naoya Aizawa

Hund's multiplicity rule states that a higher spin state has a lower energy for a given electronic configuration¹. Rephrasing this rule for molecular excited states predicts a positive energy gap between spin-singlet and spin-triplet excited states, as has been consistent with numerous experimental observations over almost a century. Here we report a fluorescent molecule that disobeys Hund's rule and has a negative singlet-triplet energy gap of -11 ± 2 meV. The energy inversion of the

Reverse intersystem crossing (RISC), the uphill spin-flip process from a triplet to a singlet excited state, plays a key role in a wide range of photochemical applications. Understanding and predicting the kinetics of such processes in vastly different molecular structures would facilitate the rational material design. Here, we demonstrate a theoretical expression that successfully reproduces experimental RISC rate constants ranging over five orders of magnitude in twenty different molecules. We

Poly(N-vinylcarbazole) undergoes cross-linking to highly solvent-resistant films through an oxidative coupling reaction, for which an annealing process takes only 3 min at 110 °C. This reaction allows the construction of a solution-processed multilayer OLED without a time-consuming annealing process. The maximum external quantum efficiency reaches 18%, and remains at 17%, even at a high brightness of 10 000 cd m(-2) for all-solution-processed blue OLEDs.

Thermally activated delayed fluorescence (TADF) materials generate energetically equivalent spin-singlet and spin-triplet excited states. In the presence of an energy acceptor, each excited state undergoes energy transfer on different length scales. However, the lack of quantitative understanding of the length dependence of the excited energy-transfer processes hampers the rational design of molecular systems that control exciton transport in organic light-emitting diodes (OLEDs) using TADF. We

Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) is shown to be simultaneously cross-linked and p-doped when immersed into a phosphomolybdic acid solution, yielding conductive films with low solubility that can withstand the solution processing of subsequent photoactive layers. Such a modified PCDTBT film serves to improve hole collection and limit carrier recombination in organic solar cells.

The OFCDM (orthogonal frequency and code division multiplexing) system is receiving attention to achieve a high data rate transmission for multimedia communication. A problem with the system is that PAPR (peak to average power ratio) of the OFCDM signal increases as the number of carriers increases. In this paper, we investigate peak reducing methods for OFCDM system with a predistorter power amplifier. We show that the peak reduction scheme and adaptive predistortion gives a high power efficien

Reverse intersystem crossing (RISC), the uphill spin-flip process from a triplet to a singlet excited state, plays a key role in a wide range of photochemical applications. Understanding and predicting the kinetics of such processes in vastly different molecular structures would facilitate the rational design of new materials. Here, we demonstrate a theoretical expression that successfully reproduces experimental RISC rate constants ranging over five orders of magnitude in twenty different molec

Poly(N-vinylcarbazole) undergoes crosslinking to form highly solvent-resistant films through an oxidative coupling reaction induced by phosphomolybdic acid, which occurs rapidly upon spin-coating their precursor solutions and annealing them for 3 min at 110 °C, removing acetonitrile, which acts as an inhibitor of the oxidative coupling. This reaction allows highly efficient solution-processed multilayer organic light-emitting devices to be constructed without a time-consuming annealing process,

We report instant low-temperature cross-linking of PVK. The preparation and characterization of cross-linked PVK films will be presented as well as their application in solution-processed OLEDs with each organic layer processed from the solution.

Hund's multiplicity rule states that for a given electronic configuration, a higher spin state has a lower energy. This energetic ordering demands thermal activation of ‘dark’ triplet excited states to ‘bright’ singlet excited states to emit delayed fluorescence. Here we report an organic molecule that exhibit delayed fluorescence from energetically inverted singlet and triplet excited states.