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[32](1,4)Naphthalenophanes, bearing carbon-bridge chains (syn- and anti-NPs) and nitrogen-bridge chains (syn- and anti-ANPs), were synthesized, and their X-ray structures and photoreactions were investigated. The intramolecular separation distance between the naphthalene cores for ANPs was shorter than that for NPs, suggesting that intramolecular interactions between the naphthalene rings were more efficient for ANPs compared to NPs. Upon photoirradiation at 300 nm, anti-NP, syn-ANP and anti-ANP produced the corresponding intramolecular [π4s + π4s] cycloadducts, whereas syn-NP gave an unidentified complex product mixture. Quantum yields for the photo-consumption (ΦPC) of NPs and ANPs were evaluated to quantitatively compare their photoreactivity. The ΦPC values of ANPs were approximately two-fold higher than those of ANPs.Noteworthily, the ΦPC value of syn-ANP was estimated to be unity. Based on these results we discuss the effects of the alignments of the naphthalene cores (antivs. syn) and the bridging elements (C-bridge vs. N-bridge) on the photoreaction efficiencies of [32](1,4)naphthalenophanes. [ABSTRACT FROM AUTHOR]

Radiation detection plays an important role in diverse applications, including medical imaging, security, and display technologies. Scintillators, materials that emit light upon exposure to radiation, have garnered significant attention due to their exceptional sensitivity. Previous research explored polymer dots (P-dots) doped with iridium complexes as nano-sized scintillators for radiation detection, but these were constrained to emitting specific colors like red, green, and blue, limiting their utility. Recently, there has been a breakthrough in the development of white light emitters stimulated by UV–visible light. These emitters exhibit a broad spectral range in the visible wavelength, enhancing contrast and simplifying detection by visible-light sensors. Consequently, the quest for white color scintillators in radiation detection has emerged as a promising avenue for enhancing scintillation efficiency. In this study, we present a novel approach by applying P-dots doped with two iridium complexes to create white light-emitting nano-sized scintillators. These scintillators offer a wider spectral coverage within the visible-light wavelength range. Under UV light (365 nm) excitation, our synthesized P-dots exhibited remarkable white light emission. Moreover, when excited by electron beam irradiation, we observed the clear emission close to white emission which is valuable for improving the detection of radiation. [ABSTRACT FROM AUTHOR]

We prepared amide-heterocycle (HC) compounds having various aromatic π-electron systems (Ar), such as phenyl, naphthyl, furyl, thienyl and phenanthryl moieties, and converted them as ligands to difluoroboronated complexes, Ar@HCs. Blue fluorescence from Ar@HCs was observed in solution and the solid state, and the fluorescence quantum yields (Φf) and lifetimes (τf) were determined. The Φf values in CHCl3 were as small as 0.1 except for the phenanthrene derivatives (0.4–0.6). Observation of the triplet–triplet absorption upon laser flash photolysis of Ar@HCs in solution indicated that the fluorescence process competes with intersystem crossing to the triplet state. Blue fluorescence in the solid state was observed with the Φf values of 0.3–0.7. Based on the crystallographic data, the relationship between the crystal structures and emission features of Ar@HCs in the solid state is discussed. [ABSTRACT FROM AUTHOR]

The absorption and fluorescence spectra of a series of 1,8-naphthalimide derivatives incorporating the amino functionality at the 2-, 3- and 4-positions of the naphthalene ring (2APNI, 3APNI and 4APNI, respectively) were systematically investigated in various solvents and in the solid state. The fluorescence spectra of 2APNI were insensitive to solvent polarity and intermolecular hydrogen-bonding even in a protic medium such as methanol. Thus, 2APNI displayed blue fluorescence with a moderate fluorescence quantum yield (λFmax = 420–445 nm, ΦF 0.2–0.3) in the solvents investigated. In contrast, the fluorescence spectra of 3APNI and 4APNI were strongly solvent dependent showing positive solvatofluorochromism with large Stokes shifts. Upon increasing the solvent polarity, the fluorescence colours changed from blue in hexane (λFmax = 429 nm) to orange-yellow in methanol (λFmax = 564 nm) for 3APNI, and from blue in hexane (λFmax = 460 nm) to yellow in methanol (λFmax = 538 nm) for 4APNI. The fluorescence quantum yields of 3APNI and 4APNI decreased with increasing solvent polarity. In the solid state, APNIs displayed red-shifted fluorescence emission compared to that in solution (λFmax = 541 nm for 2APNI, 575 nm for 3APNI, and 561 nm for 4APNI) and the fluorescence quantum yields in the solid state were lower than those in solution. [ABSTRACT FROM AUTHOR]

We studied the photoproducts of 1-(n-phenanthryl)-2-(m-phenanthryl)ethenes (nEm; n, m = 1, 3 and 9) for understanding photocyclization patterns based on NMR spectroscopy. The crystal structures of the photoproducts were analyzed by X-ray crystallography, and the photophysical features of the photocyclized molecules were investigated based on emission and transient absorption measurements. Phenanthrene derivatives substituted at the 1- and 3-positions were prepared for synthesizing nEm by photocyclization of stilbene derivatives. We obtained four types of primary photoproducts (n@m) from the corresponding nEm. Two of them were found to have racemic molecular structures in the single crystal determined by X-ray crystallography. Besides the primary photoproducts, two types of secondary photoproducts (n@mPP) were isolated. Fluorescence quantum yields and lifetimes of the obtained photoproducts were determined in solution whereas the definite fluorescence quantum yields were obtained in the powder. Observation of the triplet–triplet absorption spectra in solution by laser photolysis techniques showed that intersystem crossing to the triplet state competes with the fluorescence process. [ABSTRACT FROM AUTHOR]

We prepared a variety of coumarin derivatives having expanded π-electron systems along the direction crossing the C3–C4 bond of the coumarin skeleton via a photochemical cyclization process and investigated their photophysical features as a function of the number (n) of the added benzene rings based on emission and transient absorption measurements. Upon increasing n, the fluorescence quantum yields of the π-extended coumarins increased. Expanding the π-electron system on the C3–C4 bond of the coumarin skeleton was found to be efficient for increasing the fluorescence ability more than that on the C7–C8 bond. Introducing the methoxy group at the 7-position was also efficient for enhancing the fluorescence quantum yield and rate of the expanded coumarins. The non-radiative process from the fluorescence state was not substantially influenced by the expanded π-electron system. The competitive process with the fluorescence was found to be intersystem crossing to the triplet state based on the observations of the triplet–triplet absorption. The effects of the expanded π-electron systems on the fluorescence ability were investigated with the aid of TD-DFT calculations. [ABSTRACT FROM AUTHOR]

Phenanthrenes substituted with trimethylsilylethynyl and phenylethynyl groups were photochemically prepared, and their photophysical properties were systematically investigated based on measurements of fluorescence quantum yields, lifetimes, and transient absorption. Introducing ethynyl groups into the phenanthrene skeleton caused an increase in the fluorescence quantum yields compared to that of phenanthrene. The quantum yields and rates of fluorescence were dependent on the substituting position(s) and the terminating group for the C–C triple bond. The observation of the triplet–triplet absorption of the substituted phenanthrenes was evident for the nonradiative process being intersystem crossing competitive with the fluorescence process. The mechanism of increasing the fluorescence abilities by substituting with the ethynyl group(s) was discussed with the aid of TD-DFT calculations. [ABSTRACT FROM AUTHOR]

We investigated the photophysical properties of difluoroboronated β-diketones (BF2DK) with chrysene and pyrene skeletons (ChB and PyB, respectively) in solution and in the solid state. Acetylchrysenes, as the key precursors to ChBs, were photochemically prepared from the corresponding (acetylphenyl)naphthylethenes by means of a modified photocyclization method. The absorption and emission spectra of the BF2DKs were obtained in chloroform and acetonitrile, and the quantum yields and lifetimes of the fluorescence were determined. Excimeric fluorescence from PyB was absent even in highly concentrated solution. Based on the Lippert–Mataga analysis of the absorption and fluorescence features, the photophysical properties of the ChBs were discussed in comparison with those of PyB. The fluorescence states of the studied BF2DKs are shown to be of a charge-transfer character. The fluorescence quantum yields decrease with increasing the solvent polarity due to the enhanced internal conversion process. The fluorescence quantum yields in the solid state of the studied BF2DKs were determined, and it was found that PyB is fluorescent, whereas the fluorescence quantum yields of the ChBs depend on the substituted position of the chrysene moiety. [ABSTRACT FROM AUTHOR]

A series of amino-2,3-naphthalimide derivatives having the amino functionality at 1-, 5- and 6-positions (1ANI, 5ANI and 6ANI, respectively) were prepared, and their photophysical properties were systematically investigated based on the measurements of steady-state absorption and fluorescence spectra, fluorescence lifetimes as well as transient absorption spectra. The ANIs efficiently fluoresced in solution, and the emission spectra appreciably shifted depending on the solvent polarity. 1ANI displayed only a slight fluorescence red-shift upon increasing the solvent polarity. In contrast, 5ANI and 6ANI showed marked positive solvatofluorochromism with large Stokes shifts displaying multicolour fluorescence; the fluorescence colours of 5ANI and 6ANI varied from violet–blue in hexane to orange–red in methanol. 5ANI and 6ANI, thus, serve as micro-environment responding fluorophores. In methanol, the intensity of the fluorescence emission band of 5ANI and 6ANI significantly reduced. Based on the fluorescence quantum yields and lifetimes, and transient absorption measurements, it has been revealed that internal conversion from the S1 state of ANIs to the ground state was accelerated by the protic medium, resulting in a reduction in their fluorescence efficiency, while intersystem crossing from the S1 state to a triplet state was not responsible for the decrease of fluorescence intensity. [ABSTRACT FROM AUTHOR]

Six difluoroboronated β-diketones having the phenanthrene skeleton (Phe@Ar) are prepared. Based on the measurements of the fluorescence quantum yields, lifetimes and transient absorption, the photophysical features of Phe@Ar are studied in comparison with those of difluoroboronated diketones having phenyl, naphthyl and anthryl moieties. β-Diketones having 1-, 2-, 3- and 9-phenanthryl moieties (PheDKAr) were prepared as the precursor to Phe@Ar. 1-Acetylphenanthrene was synthesized by the photocyclization method as the key building block of PheDKAr having the 1-phenanthryl moiety. The counter aromatic moieties (Ar) of the prepared PheDKAr are varied with phenyl, furyl and thienyl rings (Ar = Ph, F and T, respectively) to investigate the effects of π-conjugation on the fluorescence properties. The prepared Phe@Ars are fluorescent with appreciable fluorescence quantum yields which depend on the substitution position of the phenanthrene moiety. 3-Phe@Ph having the 3-phenanthryl moiety provides the largest fluorescence quantum yield (0.81) in acetonitrile among the Phe@Ars whereas 2-Phe@Ph having the 2-phenanthryl moiety shows the smallest fluorescence quantum yield (0.07) in acetonitrile. All the Phe@Ars show fluorescence also in the solid state, and the fluorescence spectra and quantum yields were determined. Transient absorption measurement using laser flash photolysis of the Phe@Ars revealed the triplet formation. DFT and TD-DFT calculations of Phe@Ars rationalize the dependency of the fluorescence quantum yields on the substitution position of the phenanthrene skeleton in terms of difference in the oscillator strength for the HOMO–LUMO transition. [ABSTRACT FROM AUTHOR]

Photochemical processes of 4-tert-butyl-4′-methoxydibenzoylmethane (Avobenzone, AB), 4-phenylbenzoylbenzoyl-, 4-phenylbenzoyl-2′-furanyl- and 4-phenylbenzoyl-2′-thenoylmethanes (PB@Ph, PB@F and PB@T, respectively) substituted with Br and Cl at the C2 position were studied by stationary and laser flash photolyses in solution. The absorption spectral features showed that the molecular structures of the halogenated diketones are in the keto forms while those of halogen-free diketones are in the enol forms. The excited singlet and triplet state energies were determined from the absorption and emission spectra. From the absorption spectral changes upon steady state photolysis of brominated diketones in ethanol, the corresponding halogen-free diketones were formed due to Br elimination being the major photochemical process. The determined quantum yields for the formation of the halogen-free diketones were independent of the amount of dissolved oxygen, indicating that the elimination process is an event in the excited singlet (S1) states. In contrast, from the observed absorption spectra obtained upon photolysis of chlorinated AB and PB@Ph, it was inferred that Norrish type I is the major photochemical reaction in the S1 states in acetonitrile. Chlorinated PB@F and PB@T were found to undergo Cl elimination in the S1 states in cyclohexane to form the corresponding halogen-free diketones. Laser photolysis studies of brominated AB in acetonitrile and ethanol provided a transient absorption spectrum ascribable to the Avobenzone radical (ABR) produced by debromination as the initial intermediate, followed by the AB formation in ethanol. The quenching rate constant of ABR by ethanol and the quantum yield of the AB formation via ABR were determined. These observations provided evidence that H-atom abstraction of ABR from ethanol is responsible for the AB formation. Conversely, laser flash photolysis of brominated and chlorinated PB@Ph, PB@F and PB@T demonstrated the formation of the triplet–triplet absorption spectra. No chemical reactions were found to occur in the triplet (T1) states. Two-color two-laser photolysis studies were carried out on the T1 state of chlorinated PB@Ph, PB@F and PB@T, resulting in the formation of the corresponding halogen-free diketones. These observations confirmed the occurrence of Cl elimination in the highly excited triplet (Tn, n≥ 2) states. Based on the computed bond dissociation energies for the C–halogen and C–C bonds, switching mechanisms of dehalogenation and α-cleavage were discussed. [ABSTRACT FROM AUTHOR]

Based on spectroscopic measurements and DFT calculations, fluorescence properties of thiazolo[4,5-b]pyrazine (TPy) derivatives with the phenyl group at the C2 position were studied. TPys were readily prepared from the corresponding amidopyrazines, which have a similar fluorescent core to a bioluminescence light emitter, Cypridina oxyluciferin. It was found that the introduction of electron-donating (methoxy and dimethylamino) groups onto the 2-phenyl moiety of the TPy derivatives, as well as the phenyl and 4-(dimethylamino)phenyl groups at C2 and C6, respectively, increases the fluorescence yield and appearance of solvatochromic character. The mechanism of increasing the fluorescence yield depending on the substituents is discussed. These findings provide useful information on designing new TPy fluorophores. [ABSTRACT FROM AUTHOR]

Photophysical and photochemical properties of naphthalenes substituted with trimethylsilylethynyl, tert-butylethynyl, and trimethylsilylbutadiynyl groups were investigated by measurement of fluorescence yields, lifetimes, and triplet absorption. Introducing trimethylsilylethynyl and tert-butylethynyl groups to the 1-position of the naphthalene skeleton substantially enhanced fluorescence and intersystem crossing (ISC). The rates of fluorescence of 2-substituted naphthalenes were low. The effect of ethynyl groups on the 1-substituted naphthalenes was rationalized in terms of an increase of the transition moment along the short axis of the naphthalene skeleton. Substitution of the trimethylsilylbutadiynyl group at the 1 or 2-position of the naphthalene skeleton caused a considerable decrease in the fluorescence yield (approximately 0.01) and an increase in the ISC yield (0.99). [ABSTRACT FROM AUTHOR]

Facile synthesis of fulminene ([6]phenacene) was achieved through the Mallory reaction of 1-(1-naphthyl)-2-(1-phenanthryl)ethene or the 9-fluorenone-sensitized photo-ring-closure of 1-(1-naphthyl)-2-(1-phenanthryl)ethane. The electronic spectral properties of fulminene were investigated for the first time using photoluminescence as well as transient absorption spectroscopy. The spectral features were compared with those of a series of lower phenacene homologs such as phenanthrene ([3]phenacene), chrysene ([4]phenacene), and picene ([5]phenacene). For the [ n]phenacene series, both the fluorescence and phosphorescence bands linearly red-shifted with an increase in the number of the benzene rings ( n). Trends in the energy levels of the excited singlet ( E) and the triplet ( E) states were expressed as E = −2.6 n + 89.1 (kcal mol) and E = −1.8 n + 66.2 (kcal mol), respectively. In the case of fulminene, laser flash photolysis displayed a transient spectrum with an absorption maximum ( λ) at 675 nm, which was assigned as the triplet fulminene excited state. The λ values for the [ n]phenacene series showed a linear correlation as a function of the ring number n, given by an equation, λ = 60 n + 318 (nm). [ABSTRACT FROM AUTHOR]

To clarify the acyl substitution effect on the fluorescent property of Cypridina oxyluciferin analogs, which have the 4-(dimethylamino)phenyl group at C5, we compared the spectroscopic properties of benzamide 1b and its 2,6-dimethylphenyl derivative 1c in various solvents with those of acetamide 1a. Similarity of the fluorescence wavelengths of 1a- c indicates that the π-electronic conjugation in the excited singlet (S) state is terminated at the acyl group and that the benzamide moiety in 1b has little effect on modulating the florescence color. The similar fluorescence solvatochromism of 1a- c reveals that their S states have a similar intramolecular charge transfer character. The fact that 1a- c have various fluorescence quantum yields and lifetimes depending on solvent polarity and hydrogen bonding interactions in solutions provides information about the decay processes competing with the fluorescence process in the S states. Among 1a- c, benzamide 1b exhibits the most sensitive variation of the fluorescence intensity depending on the solvent used. Similarity of the fluorescence spectra of 1a- c adsorbed in NaY zeolites was also observed, which indicates that the S states of 1a- c give mobile conformers in the NaY supercages. The relationship between the molecular structures of 1a- c and their spectroscopic properties will provide a guide for designing a new fluorophore based on Cypridina oxyluciferin. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Efforts to identify and develop new superconducting materials continue apace, motivated by both fundamental science and the prospects for application. For example, several new superconducting material systems have been developed in the recent past, including calcium-intercalated graphite compounds, boron-doped diamond and—most prominently—iron arsenides such as LaO1–xFxFeAs (ref. 3). In the case of organic superconductors, however, no new material system with a high superconducting transition temperature (Tc) has been discovered in the past decade. Here we report that intercalating an alkali metal into picene, a wide-bandgap semiconducting solid hydrocarbon, produces metallic behaviour and superconductivity. Solid potassium-intercalated picene (Kxpicene) shows Tc values of 7 K and 18 K, depending on the metal content. The drop of magnetization in Kxpicene solids at the transition temperature is sharp (<2 K), similar to the behaviour of Ca-intercalated graphite. The Tc of 18 K is comparable to that of K-intercalated C60 (ref. 4). This discovery of superconductivity in Kxpicene shows that organic hydrocarbons are promising candidates for improved Tc values. [ABSTRACT FROM AUTHOR]

Photo-induced β-bond dissociation of phenacyl phenyl sulfide (PPS) has been investigated in acetonitrile by laser photolysis techniques. Direct excitation of PPS at 295 K provided the acetylmethyl and phenylthiyl radicals with a quantum yield (Φrad) of 0.18, whereas triplet sensitization using xanthone revealed an efficiency for β-cleavage of triplet PPS (αrad) of ≥0.64. From disagreement between the Φrad and αrad values, it was concluded that both the lowest excited single and triplet states are reactive for β-bond dissociation in PPS. The photochemical processes of excited PPS, including β-cleavage, are discussed in detail. [ABSTRACT FROM AUTHOR]

Investigations using CIDEP techniques showed that an H-atom abstraction from phenol and the electron transfer from 1,2,4,5-tetramethoxybenzene to photoexcited 2,3-dibromo-1,4-naphthoquinone (DBNQ) and 2,3-dichloro-1,4-naphthoquinone (DCNQ) in the polar media originated from their triplet states. Nanosecond laser photolysis at 355 nm was carried out to determine the absorption spectra and coefficients of the corresponding triplet states, semiquinone, and anion radicals for a quantitative investigation of the mechanisms involved in the H-atom abstraction and the electron transfer. The steric hindrance of the substituted groups was indifferent to H-atom abstraction. The electronic structures of triplet DBNQ and DCNQ at 295 K were both revealed to be the mixed states of 3(n,π*) with a 3(π,π*) character. [ABSTRACT FROM AUTHOR]

It has been shown by means of laser flash photolysis at 355 nm that (1) hydrogen atom transfer (HT) from triplet naphthalene derivatives (produced by the triplet sensitization of benzophenone (BP)) to BP occurs via a triplet exciplex having a weak charge-transfer structure; (2) in the presence of protons, HT is enhanced in the naphthol-BP system via a protonated triplet exciplex whereas in the naphthylammonium ion-BP system, markedly reduced; (3) in the methoxynaphthalene-BP system, proton-induced electron transfer (ET) takes place via a protonated triplet exciplex, and (4) these triplet exciplexes have sandwich-like structures on the basis of experiments for intramolecular HT and ET of the methylene bridged compounds. [ABSTRACT FROM AUTHOR]