Photocatalytic H 2 evolution under a wide visible spectral range is a challenging issue. In this work, we report the synthesis of a novel organic dyad consisting of an indoline−rhodanine π-conjugation with a strong absorption in the green region and a chlorophyll derivative with intense absorbance in the purple and red regions. This synthetic dyad (Dyad) was employed as a photosensitizer in the TiO 2 -based system for photocatalytic H 2 evolution with Pt as the assisting catalyst and ascorbic acid (AA) as the sacrificial reagent. The Dyad-sensitized Pt/TiO 2 photocatalyst exhibited a maximum turnover number (TON) of 1044 after 6 h of continuous light irradiation (λ > 400 nm). In comparison, under the same conditions, the TONs of photocatalytic systems based on sole counterpart chlorophyll (Chl) or indoline dye (Ind) were merely 267 or 301, respectively. Moreover, the apparent quantum yield of Dyad/Pt/TiO 2 (1.27%) is much higher than those of Chl/Pt/TiO 2 (0.37%) and Ind/Pt/TiO 2 (0.20%) under 420 nm monochromatic light irradiation. The interfacial charge transfer and recombination processes between TiO 2 and Dyad, Chl, or Ind were evaluated with photocurrent responses and electrochemical impedance spectroscopy. The DFT calculations were in accordance with the observed charge recombination processes. The high photocatalytic activity of Dyad was attributed to not only an excellent light absorption ability over the whole visible range, but also an efficient electron transfer and balanced charge recombination processes between TiO 2 and Dyad. In addition, the sustained activities of the H 2 evolution systems were 78%, 84%, and 38% for Dyad, Chl, and Ind, respectively, after three 6 h illumination periods, indicating a similarly high reusability of both Dyad and Chl dyes as compared to Ind dye. This study simultaneously solves the problems of insufficient visible spectral response, poor stability, and high cost in photocatalytic water-splitting H 2 evolution.
Melatonin receptors (MTNRs) belonging to the G protein-coupled receptor family are considered to consist of three subtypes in vertebrates: MTNR1a, MTNR1b and MTNR1c. Additionally, MTNR1a-like genes have been identified in teleostean species as a fish-specific subtype of MTNR1a. However, similar molecules to this MTNR1a-like gene can be found in some reptiles upon searching the DNA database. We hypothesized that a vertebrate can essentially have four functional subtypes of MTNR as ohnologs. Thus, in the present study we examined the molecular phylogeny, expression patterns and pharmacological profile(s) using the teleost medaka ( Oryzias latipes ). The four conserved subtypes of MTNR (MTNR1a, MTNR1b, MTNR1c and MTNR1a-like) in vertebrates were classified based on synteny and phylogenetic analysis. The fourth MTNR, termed MTNR1a-like, could be classified as MTNR1d. It was observed by using RT-qPCR that expression patterns differed amongst these subtypes. Moreover, mtnr1a , mtnr1c and mtnr1a-like / mtnr1d expression was elevated during short days compared to long days in diencephalons. All the subtypes were activated by melatonin and transduced signals into the Gi pathway, to perform a cAMP-responsive reporter gene assay. It was shown that MTNR originally consisted of four subtypes: MTNR1a, MTNR1b, MTNR1c and MTNR1d. These subtypes were functional, at least in fish, although some organisms, including mammals, have lost one or two subtypes.
The power conversion efficiency (PCE) of chlorophyll (Chl)-based organic solar cells (OSCs) is generally about 2%. Herein, a Chl-a derivative (CHL) and [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) are successfully used to fabricate Chl-based OSCs with PCE over 5%. Two different preparation methods are used to prepare the active layer: 1) two-step spin-coating the self-aggregated CHL and PC 71 BM solutions sequentially and 2) one-step spin-coating the solution of CHL:PC 71 BM blends, forming the "bilayer" (BL) and traditional bulk heterojunction (BHJ) configurations, respectively. Based on the aforementioned two kinds of active-layer preparation methods, both inverted and regular types of OSCs are successfully investigated. All four types of devices work normally, which is likely due to the ambipolar characteristics of the CHL aggregate. Unexpectedly, the BL-based devices yield PCEs of 5.17% for the regular type and 5.19% for the inverted type, which are higher than those of the BHJ-based devices (3.96% for the regular type and 3.50% for the inverted type). The main improvement in PCEs of BL-based devices comes from the enhanced short-circuit currents, which is due to the decreased charge transfer resistance and enlarged photocurrent contribution of PC 71 BM as well as slightly enhanced electron and hole mobilities.
Organic hole-transporting materials (HTMs) are essential components of high-performance perovskite solar cells (PSCs). Three zinc-coordinated chlorophyll derivatives with bacteriochlorin, chlorin, and porphyrin macrocycles, namely, ZnBChl, ZnChl, and ZnPor, respectively, were newly synthesized and employed as HTMs in PSCs. The difference in the π backbones of these HTMs causes differences in their photophysical properties, and thus different hole-extraction abilities, as revealed by steady-state photoluminescence spectra. The power conversion efficiencies (PCEs) of PSCs with a typical mesoporous structure, fluorine-doped tin oxide/compact TiO 2 /mesoporous TiO 2 / CH 3 NH 3 PbI 3 /HTM/Ag, are 8.26%, 11.88%, and 0.68% for ZnBChl, ZnChl, and ZnPor, respectively. The small PCE of the ZnPor-based PSC is partially attributed to the small energy gap of the highest occupied molecular orbital (HOMO) levels between ZnPor and CH 3 NH 3 PbI 3 perovskite. Therefore, we increased this energy gap slightly by shifting the HOMO level of CH 3 NH 3 PbI 3 perovskite downward by incorporating formamidinium and bromide ions into the crystal lattice of CH 3 NH 3 PbI 3 . As a result, the PCE of the ZnPor-based PSC improved to 4.04%, and it exhibited a clearly normal current−voltage curve, indicating better energy alignment between ZnPor and the modified perovskite. In addition, the barriers both in the perovskite/ ZnPor interface and in the ZnPor layer originated from the delocalization of π-electrons on the symmetric aggregates determine the low PCE of ZnPor-based PSCs; this was deduced from measurements of atomic force microscope, ultraviolet photoelectron spectroscopy, and the electric impedance spectroscopy.
Solid-state chlorophyll solar cells (CSCs) employing a carboxylated chlorophyll derivative, methyl trans-3 -carboxypyropheophorbide a, as a light-harvesting dye sensitizer chlorophyll (DSC) deposited on mesoporous TiO , on which four zinc hydroxylated chlorophyll derivatives were spin-coated for hole transporter chlorophylls (HTCs), are described. Key parameters, including the effective carrier mobility of the HTC films, as determined by the space charge-limited current method, and the frontier molecular orbitals of these DSCs and HTCs, as estimated from cyclic voltammetry and electronic absorption spectra, suggest that both charge separation and carrier transport are favorable. The power conversion efficiencies (PCEs) of the present CSCs with fluorine-doped tin oxide (FTO)/TiO /DSC/HTCs/Ag were determined to follow the order of HTC-1>HTC-2>HTC-3>HTC-4, which coincided perfectly with the order of their hole mobilities. The maximum PCE achieved was 0.86 % with HTC-1. The photovoltaic devices studied herein with two types of chlorophyll derivatives as dye sensitizers and hole transporters provide a unique solution for the utilization of solar energy with a view to truly realizing "green energy".
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