Takuya Hosokai

The design of organic compounds with nearly no gap between the first excited singlet (S₁) and triplet (T₁) states has been demonstrated to result in an efficient spin-flip transition from the T₁ to S₁ state, that is, reverse intersystem crossing (RISC), and facilitate light emission as thermally activated delayed fluorescence (TADF). However, many TADF molecules have shown that a relatively appreciable energy difference between the S₁ and T<

Stable organic luminescent radicals have attracted much attention, but their stability under light irradiation is not yet satisfactory. New luminescent radicals (TTMs) based on terminal benzene ring modified carbazole donors were synthesized and evaluated. Their photostability (half-life under continuous laser irradiation) has improved by 1 order of magnitude compared to simple carbazole donors. This is a new molecular design strategy to improve the photostability of luminescent radicals without

This paper reports that structural imperfection in an organic thin film modulates the electronic structure to result in a serious band bending and change in the energy-level alignment (ELA) at the organic-conductor interface. Ultraviolet photoelectron spectroscopy (UPS) and metastable atom electron spectroscopy (MAES) were adopted to investigate thickness dependences of the electronic structure of polar phthalocyanine (chlorogallium phthalocyanine) thin films grown on graphite with respect to th

The photophysical properties of six types of carbazole benzonitrile (CzBN) derivatives are investigated in different solvents to examine the thermally activated delayed fluorescence (TADF) activation via reducing the energy gap between the singlet charge-transfer and triplet locally excited states, ΔEST(LE). Relative to the ΔEST(LE) values for the CzBN derivatives in the low polarity solvent toluene (ϵ∼2), a reduction of ΔEST(LE) for the CzBN derivatives in the polar solvent acetonitrile (ϵ∼37)

Simultaneous in situ real-time measurements of x-ray reflectivity and differential reflectance spectroscopy were conducted during deposition of perfluorinated copper-phthalocyanine thin films on SiO2/Si. We found a continuous spectral change coinciding with structural changes from submonolayer coverage, to standing βbilayer-phase and to β-phase for thicker films. This combined measurement enables us to study the relationship between structural and optical properties of organic semiconductor thin

Abstract Carbazole‐triazine dendrimers with a bulky terminal substituent were synthesized, and the thermally activated delayed fluorescence (TADF) property was investigated. Compared to unsubstituted carbazole dendrimers, dendrimers with bulky terminal substituents showed comparable to better photoluminescence quantum yields (PLQY) in neat films. Phenylfluorene (PF)‐substituted dendrimers showed the highest PLQY of 81%, a small Δ E st of 0.06 eV, and the fastest reverse intersystem crossing (RIS

Thickness and substrate dependence of film growth, morphology, unit-cell structure, and electronic structures was thoroughly investigated for picene, the zigzag connected 5-ring molecule, by employing complementary techniques of in situ real-time X-ray reflectivity/diffraction, in situ electron spectroscopies, and atomic force microscopy. A different kind of thickness dependent structural transition was observed on SiO2 and graphite, resulting in a distinct electronic structure. On SiO2 picene f

The electronic structure and molecular orientation of dibenzo-18-crown-6 deposited on graphite were studied by ultraviolet photoelectron spectroscopy and metastable atom electron spectroscopy. We observed an alternate orientation of the molecule in the first monolayer and second layer. Moreover, the energy separations of the three top π-bands containing the highest occupied molecular orbital in the first layer were found to be clearly different from those in the multilayers, indicating that the

Excited state dynamics is a central issue in discussing the origin of the high efficiency of thermally activated delayed fluorescence (TADF) molecules. Here we will present experimentally a complexity of the excited state dynamics of the extremely high efficient TADF molecules, 4CzIPN. By means of pump‐probe transient absorption spectroscopy, we will show the sign of intramolecular charge delocalization formed in the excited state. This specific excited state originates from the intramolecular c

A series of halogen-substitute carbazole TTM radicals was synthesized. The effect of halogen substituents on radical luminescence was systematically evaluated. It was found that the well-known heavy atom effect does not work in the emission of radicals and that halogen substitution of the donor carbazole can change the HOMO and alter the absorption and emission wavelengths. In addition, the photostability was found to be improved with respect to TTM but not significantly different from that of c