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Free-base meso-propanoyloxylated (–OCOEt) porphyrins and dioxoporphodimethenes (quinoid forms of dihydroxyporphyrins) were efficiently synthesized by the treatment of the corresponding meso-diarylporphyrins with PhI(OAc)2 in propionic acid. Basic hydrolysis of the obtained meso-mono- and -dipropanoyloxyporphyrins provided meso-hydroxyporphyrins (oxophlorins) and dioxoporphodimethenes, respectively. Reduction of the dioxoporphodimethenes generated unstable meso-dihydroxyporphyrins, and one-pot etherification of the meso-dihydroxyporphyrins yielded stable meso-dialkoxyporphyrins.

An inert coordination bond that becomes labile under external stimuli can be termed "molecular lock" because a closed (locked) structure incorporating an inert bond is equilibrated with an open (unlocked) structure via the labilization of the inert bond. A Pt(II)-py bond (py ) pyridyl group) has been previously described as a thermally switchable molecular lock because its inert nature becomes labile at high temperature in the presence of a salt. 1 However, the salt-assisted thermal switching (locking/unlocking) is not a clean and facile process because of salt contamination and tedious procedures in salt removal. Here we report a precise, clean molecular lock that operates by light. We have found that the inert Pt(II)-py bond, whose photochemistry has attracted little attention, is considerably labilized upon UV irradiation (Scheme 1a). We demonstrate the photoswitchable molecular lock by the one-way catenation of coordination rings. 2,3 Namely, Pt(II)-linked ring 1 is rapidly catenated by irradiating 1 in an aqueous solution (Scheme 1b,c).Only a few reports have described the photodissociation of Pt(II)-py coordination bonds, where the dissociation is monitored by subsequent ligand substitution or isomerization. 4,5 We anticipate that, in the absence of any other ligands, the photodissociation is immediately followed by a re-coordination process, which has been often considered as an unfavorable side reaction in previous studies. 6As a result, a pyridyl ligand can be reversibly coordinated to platinum upon irradiation. On the basis of this idea, Pt(II)-ring 1 was irradiated in an aqueous medium in expectation of rapid catenation via the Pt(II)-py bond dissociation. Thus, Pt(II)-clipped coordination ring 1a was prepared from (en)Pt(NO 3 ) 2 and the corresponding ligand according to the procedure described previously. 2 A DMSO-d 6 /D 2 O (1:2) solution of 1a (2 mM) was irradiated at room temperature with an ultra-high-pressure Hg lamp filtered by a band-path glass filter (330 ( 70 nm). 7 Upon irradiation, the signals for 1a disappeared gradually along with the appearance of new signals for catenane 2a. The conversion was very rapid and, only after 15 min, 2a was quantitatively formed (Figure 1b,c). The spectra of both 1a and 2a are qualitatively identical to those of Pd(II) analogues reported previously. 2,8 Cold-spray ionization mass spectrometry (CSI-MS) measurement 9 confirmed the formation of 2a as evident from prominent signals that fully agreed with 2a: for example, m/z 618.3 [2a-(NO 3 -) 4 +(dmso) 7 ] Without irradiation, the once formed catenane 2a is "locked" and not allowed to dissociate into separate rings even in a nonaqueous solvent. In fact, when dissolved in MeCN/MeOH (1:1), catenane 2a remained unchanged and the dissociation was not observed despite the absence of effective hydrophobic interaction between the two rings. Of course, smooth dissociation into the component rings takes place if 2a is "unlocked" in a nonaqueous solvent. Upon irradiation in MeCN/MeOH (1:1), 2a disappeared Figure 1. 1 H N...

meso-Mono- or diazidoporphyrins were readily obtained in high yields by the catalyst-free aromatic nucleophilic reaction of the corresponding bromoporphyrins with azide anions under mild conditions. The molecular structures of the obtained azides were unambiguously determined by X-ray crystallographic analysis.

Axially chiral biaryls based on pyrene, 1,1¤-bipyrene-2,2¤-diol derivatives 2, were designed and synthesized from 2-hydroxypyrene. Simple optical resolution was carried out and the absolute configuration was determined by diffraction study. Title compounds 2 and corresponding menthylcarbonate 4 showed clear circularly polarized luminescence (CPL) spectra. The degree of dimensionless Kuhn's anisotropy in the photoexcited state («g em «) of 2 and 4 were ca. 3.6 © 10 ¹4 and ca. 1.2 © 10 ¹3, respectively. Noteworthy properties were as follows: 1) high fluorescent quantum yields of 2 and 4, 0.57 and 0.80, respectively, in marked contrast to that of BINOL, 0.04 and 2) bathochromic shifts of CPL .Circularly polarized luminescence (CPL) is luminescence emitted by a chiral molecule. Because of the high sensitivity of steady-state luminescence, CPL spectroscopy has attracted much attention, particularly in the analysis and evaluation of naturally occurring chiral chromophores, such as chlorophyll (vide infra).1 Although CPL spectroscopy is a relatively new technique, a pioneering review was published as early as in 1977.2 Currently, CPL is regarded as an important chiroptical technique. The applications of CPL have shifted from the analytical chemistry of biological chiral molecules 2 to advanced science using polarized light, such as three-dimensional displays and quantum computing. 3CPL spectroscopy has flourished under the watch of physical chemists. However, the lack of a standard molecule having a large quantum yield (Φ fl ) and a large dimensionless Kuhn's anisotropy in the photoexcited state («g em «) (vide infra), 2 has hindered the development of new materials for CPL. Although 1,1¤-binaphthalen-2,2¤-diol (BINOL) 1 (Chart 1) and its corresponding derivatives are well used in this research field, Φ fl and g em are small (vide infra). In this study, our aim was to design a standard molecule for CPL spectroscopy. The expansion of the π-electronic system seemed to be the most promising strategy, i.e., replacement of the naphthalene moiety of BINOL with other π-expanded polycyclic aromatic hydrocarbons (PAHs). Generally, the expansion of the π-electronic system induces 1) a small HOMOLUMO gap and a resultant low excitation energy, 2) an increase in the fluorescence lifetime, 3) a low redox potential, and so on. 4 These properties are preferred for advanced materials. We focused on pyrene as PAH because it showed strong emission, long lifetime, and high quantum yield, making it one of the standard molecules for photochemistry. 5,6 We designed 1,1¤-bipyrene-2,2¤-diol 2, a pyrene-based axially chiral molecule, with a eye to improving the chiroptical properties of BINOLs.Optically pure title compounds 2 and reference 5 were prepared according to Scheme 1. 7 The issues to be addressed were 1) the solubility improvement of 2 and 2) optical resolution. PAHs are notorious for their poor solubilities and our targets 2, dimers of pyrene, ought to be sparingly soluble materials. To solve this problem, a tertbutyl group was intro...

We conducted the first systematic study on the synthesis, structure, and properties of various divalent metal complexes (Ni

Detection and use of physical noise fluctuations in a signal provides significant advantages in the development of bio- and neuro-sensing and functional mimicking devices. Low-dimensional carbon nanomaterials are a good candidate for use in noise generation due to the high surface sensitivity of these materials, which may themselves serve as the main building blocks of these devices. Here, we demonstrate that the addition of a molecule with high redox activity to a carbon nanotube (CNT) field-effect transistor provides tunable current fluctuation noise. A unique charge-trap state in the vicinity of the CNT surface due to the presence of the single molecule is the origin of the noise, which generates a prominent and unique slow discrete random telegraph signal in the device current. The power spectral density reveals the peculiar frequency limit of the fluctuation for different types of molecules depending on their redox activity and adsorption configuration. These results indicate that the detected noise will provide new opportunities to obtain electronic information for a single molecule combined with a nanotube surface, and that controllability of the noise may contribute to the expansion of noise utilization in future bio-inspired devices.

Photo-induced self-assembly of Pt(II)-linked rings and cages via the photolabilization of a Pt(II)-py bond