Structure Of S0 Research Articles

Interplay of Steric Effects and Aromaticity Reversals to Expand the Structural/Electronic Responses of Dihydrophenazines.

To gain insights into the coupling of conformational and electronic variables, we exploited steric hindrance to modulate a polycyclic skeleton with a bent conformation in the S0 state and a twisted conformation in the S1 state under the guidance of photoexcited aromaticity reversals. Polycyclic 5,10-dihydrophenazine (DHP) adopted a bent structure in S0 but involved a bent-to-planar transformation in S1 due to the excited-state aromaticity of the 8π-electron central ring. The N,N'-locations and 1,4,6,9-sites of the DHP skeleton provided a versatile chemical handle for fine-tuning intramolecular steric hindrance. Specifically, N,N'-diphenyl-5,10-dihydrophenazine (DPP-00) and its derivatives DPP-10-DPP-22 were synthesized with different numbers of methyl groups on the 1,4,6,9-sites. X-ray crystal analyses suggested that the DHP skeletons of DPP-00-DPP-22 had more bending configurations along the N···N axis with an increase in the number of methyl groups. Following the bending-promoted interruption of π-conjugation, the absorption spectra of DPP-00-DPP-22 significantly blue-shifted from 416 to 324 nm. By contrast, the emission bands exhibited a reverse shift to longer wavelengths from 459 to 584 nm as the number of methyl substituents increased. Theoretical calculations revealed that introducing methyl groups caused the planar DHP skeleton in S1 to further twist along the N···N axis, resulting in a twisted high-strain conformation. The greater Stokes shift of the more steric-hindered structure can be attributed to the release of larger strain and aromatic stabilization energy. This research highlighted the potential promise associated with the interplay of steric effects and aromaticity reversals in a single fluorophore.

Dissecting the red sequence: the bulge and disc colours of early-type galaxies in the Coma cluster

We explore the internal structure of red sequence galaxies in the Coma cluster across a wide range of luminosities ($-17>M_g>-22$) and cluster-centric radii ($0<r_{\rm{cluster}}<1.3 r_{200}$). We present the 2D bulge-disc decomposition of galaxies in deep Canada-France-Hawaii Telescope $u,g,i$ imaging using GALFIT. Rigorous filtering is applied to identify an analysis sample of 200 galaxies which are well described by an `archetypal' S0 structure (central bulge + outer disc). We consider internal bulge and/or disc colour gradients by allowing component sizes to vary between bands. Gradients are required for $30\%$ of analysis sample galaxies. Bulge half-light radii are found to be uncorrelated with galaxy luminosity ($R_e \sim 1$ kpc, $n\sim2$) for all but the brightest galaxies ($M_g<-20.5$). The S0 discs are brighter (at fixed size, or smaller at fixed luminosity) than those of star-forming spirals. A similar colour-magnitude relation is found for both bulges and discs. The global red sequence for S0s in Coma hence results from a combination of both component trends. We measure an average bulge $-$ disc colour difference of $0.09\pm0.01$ mag in $g-i$, and $0.16\pm0.01$ mag in $u-g$. Using simple stellar population models, bulges are either $\sim2$-$3\times$ older, or $\sim2\times$ more metal-rich than discs. The trend towards bluer global S0 colours observed further from Coma's core is driven by a significant correlation in disc colour with cluster-centric radius. An equivalent trend is detected in bulge colours at a marginal significance level. Our results therefore favour environment-mediated mechanisms of disc fading as the dominant factor in S0 formation.

Determination of Elemental Sulfur in Naphtha and Gasoline by Gas Chromatography/Mass Spectrometry

Trace elemental sulfur, S0, in naphtha and gasoline seriously affects the quality of naphtha and gasoline. It is difficult to analyze the contents of trace elemental sulfur because of their low concentrations. Presently, the S0 contents are usually determined by polarography, but the practical use of this method is limited because of some interference factors. In this work, S0 structure in naphtha and gasoline was studied through many experiments by gas chromatography/mass spectrometry (GC/MS) and S0 is mainly present as S8. A new analytical method for S0 determination in naphtha and gasoline using GC/MS was developed. The S0 was analyzed through selected ion monitoring (SIM) and quantitative determination was achieved through an external standard method. One microliter of sample oil was directly injected and analyzed by GC/MS within 16 min. In comparison with the existing method for S0 determination, this technique was found to be much simpler, faster, more sensitive and interference-free. Good correlation coefficients (> 0.9995) for the S0 calibration curves were obtained in the concentration range of 0.01 mg/L–100 mg/L by using appropriate GC/MS parameters. The absolute limit of detection of this method was 9.55 pg and the precision relative standard deviation (RSD) was usually better than 5% and the recoveries were 93.01–106.21%. The method was used successfully in the determination of S0 in naphtha and gasoline samples collected in Jiujiang Refinery and it had great application prospects. In addition, this technique required only a very small sample size to perform a good analysis, which was an important advantage for studies where sample size was restricted.

1,6-Methano[10]annulene has a Delocalized Structure in S0 and S1 : High-Resolution Spectroscopy in a Supersonic Jet.

For the ground state of the Hückel aromatic ring 1,6-methano[10]annulene (MA) both a localized and a delocalized structure have been proposed in the past, depending on the theoretical methods used. A high-resolution electronic spectrum in a supersonic jet unambiguously shows that isolated, ultracold MA has a delocalized structure in its S0 ground state as well as in its S1 excited state.

Transient Resonance Raman and ab Initio MO Calculation Studies of the Structures and Vibrational Assignments of the T1 State and the Anion Radical of Coumarin and Its Isotopically Substituted Analogues

Transient resonance Raman and absorption spectra of the anion radical CM•- and lowest excited triplet state 3CM* of coumarin were measured. Vibrational assignments of the ground state S0, CM•-, and 3CM* were performed based on both the frequency shifts on isotopic (18O, 13C, and deuterium) substitutions and normal-coordinate calculations using the force constants obtained by ab initio molecular orbital computations. The vibrational assignments and ab initio MO calculations provided much information on the structures of S0, CM•-, and 3CM*. It is concluded that the C(3)C(4) bond of the pyrone ring is lengthened markedly in CM•- and drastically in 3CM*. This suggests that the C(3)C(4) bond is one of the reactive sites of coumarin and furocoumarins in their photochemical reactions, which is in good accord with the formation of cyclobutane-type adducts with pyrimidine bases, particularly with thymine, through the C(3)C(4) bond of furocoumarins and the C(5)C(6) bond of pyrimidine bases. The CO bond was found to be moderately lengthened both in CM•- and 3CM*. The moderate lengthening of the CO bond of 3CM* is consistent with the π−π* character of 3CM*.