Faculty Profiles - Michihiro Hara

Papers - Michihiro Hara

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Tunable Dye-Sensitized Solar Cells via Co-Sensitization and Energy Transfer from Spiropyran Derivatives to YD2 Reviewed International journal

Keitaro Ono, Ryuhei Ejima, Michihiro Hara

Energies 18 ( 17 ) 4751 2025.9

We fabricated dye-sensitized solar cells (DSSCs) co-sensitized with the organic dye YD2 and a spiropyran derivative (SPNO2), a photochromic molecule capable of reversible isomerization under light irradiation. Upon UV exposure, SPNO2 converts from its closed spiropyran (SP) form to the open photomerocyanine (PMC) form, which absorbs visible light and changes the optical properties of the photoelectrode. Spectroscopic analysis showed an 18% decrease in transmittance at 540 nm after UV irradiation and a 10% increase following visible light exposure. These changes were accompanied by a 0.5% increase in power conversion efficiency (η) after 5 min of UV irradiation, and a 0.83% decrease after 10 min of visible light. Although direct electron injection from PMC into TiO2 appears inefficient, the enhanced performance is attributed to Förster resonance energy transfer (FRET) from PMC to YD2. This photoresponsive behavior highlights a co-sensitization strategy that combines dynamic optical control and efficient energy transfer. Our findings demonstrate a promising approach to designing smart DSSCs with externally tunable photovoltaic properties using photochromic sensitizers.

Fabrication and characterization of co-sensitized dye solar cells incorporating cyclodextrin functional layers with energy transfer from spiropyran derivatives to SQ2 dye Reviewed International journal

Michihiro Hara, Keitaro Ono, Ryuhei Ejima

Journal of Photochemistry and Photobiology A: Chemistry 469 116531 2025.6

We developed dye-sensitized solar cells (DSSCs) using the sensitizing dye 1,5-carboxy-2-[[3-[(2,3-dihydro-1,1-dimethyl-3-ethyl-1H-benzo[e]indol-2-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-3,3-dimethyl-1-octyl-3H-indolium (SQ2) and the photochromic molecule 1,3,3-trimethyl indolino-6′-nitrobenzopyrylospiran (SPNO2). DSSCs incorporating photochromic molecules can regulate photoelectric conversion efficiency (η) through external light irradiation. To enhance η, cyclodextrins (CDs) (α-CD, β-CD, γ-CD) were introduced. Among them, γ-CD improved η from 1.2 % to 1.5 % by suppressing SQ2 aggregation. The color of the SQ2/CDs/SPNO2-containing photoelectrode changed from blue to purple under UV irradiation and from purple to green under visible light. The η of DSSCs increased after UV irradiation and decreased under visible light. However, direct electron injection from the photochromic molecule appeared to be challenging, suggesting that the efficiency enhancement was primarily due to Förster resonance energy transfer (FRET) from SPNO2 to SQ2. FRET efficiency calculations showed that β-CD exhibited the highest efficiency among CDs. These findings indicate that the co-sensitization of DSSCs by SPNO2-SQ2 and SQ2 alone, facilitated by their respective photoabsorption properties, enables externally tunable photoelectric conversion. This study provides insights into high-performance DSSCs with tunable efficiency through CD inclusion effects and photochromic molecular energy transfer, contributing to solar energy advancements.

Fabrication and Characterization of Co-Sensitized Dye Solar Cells Using Energy Transfer from Spiropyran Derivatives to SQ2 Dye Reviewed International journal

Michihiro Hara, Ryuhei Ejima

Molecules 29 ( 20 ) 4896 2024.10

We developed dye-sensitized solar cells (DSSCs) using 1,5-carboxy-2-[[3-[(2,3-dihydro-1,1-dimethyl-3-ethyl-1H-benzo[e]indol-2-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-3,3-dimethyl-1-octyl-3H-indolium and 1,3,3-trimethyl indolino-6′-nitrobenzopyrylospiran. The DSSCs incorporate photochromic molecules to regulate photoelectric conversion properties. We irradiated photoelectrodes adsorbed with SQ2/SPNO2 using both UV and visible light and observed the color changes in these photoelectrodes. Following UV irradiation, the transmittance at 540 nm decreased by 20%, while it increased by 15% after visible light irradiation. This indicates that SPNO2 on the DSSCs is photoisomerized from the spiropyran form (SP) to the photomerocyanine (PMC) form under UV light. The photoelectric conversion efficiency (η) of the DSSCs increased by 0.15% following 5 min of UV irradiation and decreased by 0.07% after 5 min of visible light irradiation. However, direct electron injection from PMC seems challenging, suggesting that the mechanism for improved photoelectric conversion in these DSSCs is likely due to Förster resonance energy transfer (FRET) from PMC to the SQ2 dye. The findings suggest that the co-sensitization of DSSCs by PMC-SQ2 and SQ2 alone, facilitated by their respective photoabsorption, results in externally responsive and co-sensitized solar cells. This study provides valuable insights into the development of advanced DSSCs with externally controllable photoelectric conversion properties via the strategic use of photochromic molecules and energy transfer mechanisms, advancing future solar energy applications.

Diarylethene derivative photoionization control via two-color two-laser optical manipulation in the presence of cyclodextrins Reviewed International journal

Michihiro Hara

Optical Materials 154 115698 2024.6

In this study, the photodynamics of 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene (DE) was investigated in the presence of α-, β- and γ-cyclodextrin (CD) inclusion complexes and under the influence of one- and two-laser excitations. Thus, this study aimed to elucidate the ionization quantum yield of DE and how it is affected by the type of CD and laser configuration. Specifically, DE/CD was flash photolyzed using a single laser (355 nm) or a double laser (355 nm and 532 nm) and observed at a wavelength of 720 nm to examine the transient absorption of hydrated electrons. The ionization efficiency with the two lasers was found to exceed that with the single laser. This suggests the existence of a two-step process involving S0→S1 and S1→Sn singlet transitions in the two-photon ionization (TPI) of DE. Furthermore, when the ring-closing isomer of DE was initiated via laser irradiation at 532 nm, the photoionization efficiency increased, especially in the presence of γ-CD. This implies that the 532-nm irradiation, which is not directly involved in TPI, contributed to promoting the TPI of DE, thus increasing its photo-steady state (saturation). Thus, the possibility of using CD-containing lasers to control photochemical reactions with photo-steady state processes was demonstrated. This investigation contributes to a broader understanding of the potential applications and underlying mechanisms of photochromic materials influenced by multi-laser interactions.

Fabrication and characterization ofsensitized dye solar cells - SQ2/CDs • SQ2/SPNO2 system Reviewed

( 54 ) 85 - 96 2024.10

In this study, we report an investigation of the fabrication and characterization of SQ2-based film-type DSSCs (SQ2 devices), SQ2/CDs (α-CD, β-CD, γ-CD: CDs) devices and SQ2/SPNO2 devices. The fabricated SQ2 devices were irradiated at 655 nm and the photoelectric conversion property (IPCE655) was observed. The IPCE655 for SQ2 devices was 2.4%, and this value was also observed for SQ2/CDs film-type devices. The IPCE655 of the SQ2/γ-CD device was 3.2% and 30% larger than that of the SQ2 device. This suggests that γ-CD　suppressed the aggregation of SQ2 and increased IPCE655. The fabricated film-type SQ2/SPN02 devices was the IPCE655 were observed. The IPCE655 of the SQ2/SPN02 device was less than half that of the SQ2 device, but the IPCE655 increased by 40% with UV irradiation and decreased by about 40% with visible light irradiation. The increase of IPCE655 by UV irradiation suggests that PMC is involved in the photoelectric conversion ofSQ2.

Fabrication and Characterization of Firm type OLED Devices Containing Cyclodextrin Polymer Layers as Ecology devises -TPD/Alq3 System- Reviewed

( 54 ) 97 - 104 2024.10

In this study, we present findings on the production and evaluation of organic light-emitting diode (OLED) devices featuring cyclodextrin polymer layers. These devices were composed of N, N-Bis(3-methylphenyl)-N, N-bis(phenyl) benzidine (TPD), cyclodextrin polymers (a-, -, y-CDP), Tris-(8-hydroxyquinoline) aluminum (A)q3), LiF, and Al, deposited onto ITO PEN films substrates. With CDP present, the OLEDs emitted green light due to the fluorescence of TPD and Alq3, achieving a peak brightness of3444 cd m-2. Our investigation suggests that the enlargement of the cavity size, weakening the encapsulation effect, facilitates the extraction of fluorescence. Moreover, we verified that the existence of CDP induces structural alterations at the interface, impacting the pathways of energy transfer during the excited state process of OLEDs. These discoveries offer significant insights into the design and potential applications of OLEDs, spanning various sectors including space technology and the evolving landscape of organic electronics.

Identification ofmalodorous substances emitted by bacteria isolated from the kendo protective gear warehouse and their effects on fungal growth

Kimiko YABE, Michihiro HARA, Marni YAMAGUCHI, Takeyoshi SUNAGAWA, Tatsuya TAKESHITA , Shigehiro NISHIJIMA

( 54 ) 72 - 80 2024.10

Elucidation ofthe bacteria related to malodors in the kendo protective gear warehouse and sterilization ofthe bacteria by X-rayirradiation as well as deodorization

Kimiko YABE, Michihiro HARA, Marni YAMAGUCHI, Takeyoshi SUNAGAWA, Tatsuya TAKESHITA , Shigehiro NISHIJIMA

( 54 ) 61 - 71 2024.10

Decomposition of Unpolarized Fluorescence Spectrum of Uniaxially Oriented 1,3,5-Triphenylbenzene Microcrystals Into Polarized Fluorescence Spectra Reviewed International journal

Michihiro Hara, Tatsuya Takeshita, Hiroyuki Kurata, Tsunehisa Kimura

Journal of Fluorescence 33 1559 - 1563 2023.2

Luminescence from solids such as crystals and aggregates is of growing academic and industrial interest. In this study, we report decomposition of the unpolarized fluorescence spectrum of uniaxially oriented 1,3,5-triphenylbenzene (TPB) microcrystals into four polarized spectra measured with polarizer (V: vertical and H: horizontal) and analyser (V: vertical and H: horizontal), where V and H indicate perpendicular and parallel to the layer of TPB molecules in the crystal, respectively. Resolved spectra were interpreted in terms of the molecular and excimer like (J- and H-dimer) emissions. The origin of the excimer like emissions was discussed in relation to the molecular packing in the crystal. It was shown that polarized crystal fluorescence can provide insight into the excitation/emission process in the crystal. Although preliminary, this study demonstrates the potential of polarized fluorescence to elucidate the luminescent mechanism.

Fabrication and Characterization of OLED Devices Containing Cyclodextrin Polymer Layers as Ecology devies-ｍ-MTDATA/PBD Sysytem- Reviewed

( 53 ) 79 - 87 2023.10

In this study, we report an investigation of the fabrication and characterization of OLEDs containing cyclodextrin polymer layers. The OLEDs was fabrication by deposition of 4,4',4"-Tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA), cyclodextrin polymer(CDP), 2-(4-tert-Biphenylyl)-5-(4-tert-butylphenyl)-l,3,4-oxadiazole (PBD), LiF, and Al on the ITO-glass. The OLEDs indicates the green emission, which is due to the fluorescence of m-MTDATA and PBD (exciplex) in the presence of CDP, and the highest luminance reached 1947 cd m-2 (Non). Our study revealed that the weakening of the inclusion effect, caused by an increase in cavity size, facilitates the extraction of exciplex emission. Moreover, we observed that the presence of CDP induces structural modifications at the interface, thereby affecting the energy transfer pathway during the excited state process in the OLEO. These findings provide important insights into the design of exciplex-based OLEDs and their potential applications in the field of organic electronics.

Two-photon ionization of cis-1,2-dicyano-1,2-bis-(2,4,5-trimethyl-3-thenyl)ethene in the presence of cyclodextrin by using 266-nm laser pulse irradiation

Michihiro Hara, Naohiro Kawashima

Memoirs of Fukui University of Technology ( 52 ) 55 - 62 2022.10

Fabrication and Characterisation of Organic EL Devices in the Presence of Cyclodextrin as an Interlayer Reviewed

Michihiro Hara, Takao Umeda, Hiroyuki Kurata

Sensors 21 ( 11 ) 3666 - 3674 2021.5

Effect of cyclodextrin cavity size on the photovoltaic performance of unanchored ruthenium(II) polypyridine complex-containing dye-sensitized solar cells(査読有) Reviewed

Michihiro Hara, Tatsuya Takeshita, Takao Umeda

Journal of Photonics for Energy 10 ( 4 ) 045503 2020.11

Photoionization and trans-to-cis isomerization of β-cyclodextrin-encapsulated azobenzene induced by two-color two-laser-pulse excitation Reviewed

Tatsuya Takeshita, Michihiro Hara

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 193 ( 15 ) 475 - 479 2018.3

Light-Driven Proton Release of Spirobenzopyran-Derived Protonated Photomerocyanine in Cyclodextrin Aqueous Solution Reviewed

Tatsuya Takeshita, Atsushi Yano, Michihiro Hara

ChemistrySELECT 2 ( 34 ) 11288 - 11292 2017.12

Protonated photomerocyanine (PMCH), which is a ring-opening isomer of spirobenzopyran, functions as a metastable-state photoacid (PAH) driven by blue or visible light. Enhancement of the proton photodissociation efficiency and thermal stability of the deprotonated isomer facilitates pH adjustments and control by light irradiation. In this article, we report the proton photodissociation of PMCH based on 1,3,3-trimethylindolino-8’-methoxybenzopyrylospiran (1) in an aqueous cyclodextrin (CD) solution. In the aqueous solution, the spirobenzopyran form of 1 underwent a spontaneous ring-opening reaction and formed the thermodynamically stable PMCH form of 1 (PMCH-1). After a laser flash at 355 nm, the photomerocyanine form of 1 (PMC-1) was generated by proton photodissociation from the singlet excited state of PMCH-1. The quantum yield of the proton photodissociation was changed by the stoichiometry or binding constant of the inclusion complex between PMCH-1 and CD. Additionally, the encapsulation effects of CD inhibited the re-protonation of PMC-1. We conclude that these findings are useful for pH adjustment and control using PAHs based on PMCH.

Improvement of photoionization efficiency of diarylethene-cyclodextrin complexes by using multi-laser pulse excitation(査読あり) Reviewed

Tatsuya Takeshita, Hiroyuki Kurata, Michihiro Hara

Journal of Photochemistry and Photobiology A: Chemistry 344 28 - 35 2017.4

Fabrication of a dye-sensitized solar cell containing a noncarboxylated spiropyran-derived photomerocyanine with cyclodextrin Reviewed

Tatsuya Takeshita, Takao Umeda, Michihiro Hara

Journal of Photochemistry and Photobiology A: Chemistry 333 87 - 91 2017.1

The fabrication, photovoltaic conversion, and photo-response of dye-sensitized solar cell (DSSC) containing a noncarboxylated spiropyran 1,3,3-trimethylindolino-β-naphthopyrylospiran (1) and carboxymethyl-β-cyclodextrin sodium salt (CM-β-CD) were investigated for the first time. In fact, we found the adsorption of photomerocyanine form (PMC) of 1 and inclusion complexes between the PMC and CM-β-CD (PMC/CM-β-CD) to the TiO2 surface. The formation of PMC/CM-β-CD was confirmed by fluorescence spectroscopy. The incident photon-to-current conversion efficiency (IPCE) of the PMC-containing DSSC obtained 4.1% under 570-nm light irradiation, and the highest IPCE reached 11.1% by inclusion effect of CM-β-CD. Similar, the fillfactor and the open-circuit voltage were improved by CM-β-CD layer. The IPCE value of PMC/CM-β-CD-containing DSSC was decreased by visible light treatment, and it was considered that decrease of IPCE values are attributed to the formation of PMC isomer. Therefore, we demonstrated the photovoltaic conversion and photoresponsivity of the DSSC by incorporating a noncarboxylated PMC with inclusion effect of CM-β-CD layer.

Resonant two-photon ionization of aromatic hydrocarbons included in cyclodextrins(査読有) Reviewed

Tatsuya Takeshita, Yuuta Kasaba, Michihiro Hara

Journal of Photochemistry and Photobiology A: Chemistry 321 128 - 136 2016.5

Application of a Noncarboxylated Dye Compound in a Dye-Sensitized Solar Cell Containing a Cyclodextrin Layer(査読有) Reviewed

Tatsuya Takeshita, Takao Umeda, Noriaki Oonishi, Michihiro Hara

International Journal of Photoenergy Article ID 786246 2015.5

Resonance photoionization of a diarylethene derivative in the presence of cyclodextrins using multi-color multi-laser irradiation(査読有） Reviewed

Tatsuya Takeshita, Michihiro Hara

Journal of Photochemistry and Photobiology A: Chemistry ( 310 ) 180 - 188 2015.5

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