• Bulletin of the Korean Chemical Society
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• v.6 no.5
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• pp.277-279
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• 1985

Orbital interactions of the types, ${\sigma}-{\pi},\;{\sigma}^*-{\pi},\;{\sigma}-{\pi}^*\;and\;{\sigma}^*-{\pi}^*$ are investigated for the rotamers of ${\alpha}$-X-acetones (X = F and Cl) using STO-3G method of calculation. It was found that the interactions are possible only in gauche forms, and the ${\sigma}^*-{\pi}^*$ interactions are in general greater than the $\sigma-\pi$ interactions due to the greater overlap, in spite of the greater energy gap involved; the greater ${\sigma}^*-{\pi}^*$ interaction causes greater lowering of ${\pi}^*$ level relative to the lowering of ${\sigma}$ in the ${\sigma}-{\pi}$ interaction so that both ${\sigma}-{\pi}^*$ and $n-{\pi}^*$ interactions are enhanced in the gauche forms. The extra stability of the gauche form and the red shift in the $n-{\pi}^*$ transition are thus found to be natural corollaries of the greater ${\sigma}^*-{\pi}^*$ interaction in the gauche forms.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.7
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• pp.500-505
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• 2012

In this study, the influence of the intermolecular distance on the charge mobility in a pentacene thin-film was investigated. In order to increase the mobility which depends on the ${\pi}$-overlap between molecules, the intermolecular distance was shortened by compressive force along the conduction channel. Pentacene thin-film was fabricated on flexible substrates bent outward at different radii to stretch the gate dielectric surface and then the substrates were unbent, producing the compressive force to the film. The result showed that the mobility increased proportionally to the strain applied during the pentacene deposition and the molecular packing inside a grain was not optimal for the charge transport.

• Journal of the Korean Chemical Society
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• v.26 no.2
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• pp.65-72
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• 1982

STO-3G level computations were performed on n-propylamine, n-propylamine radical and cis-and trans-ethylene diamines in order to investigate structural contributions of (n${\pi}$/m) and (n-${\sigma}^*$) structures to the energy variations accompanying the conformational changes. It was found that (5${\pi}$/5) and (4${\pi}$/4) structures had attractive and repulsive nonbonded interactions, respectively, which were approximately additive. anti(n-${\sigma}^*$) structures had more stabilzing hyperconjugative interactions than syn(n-${\sigma}^*$) structures, but due to the large internuclear repulsion the net effect was destabilizing inthe former in contrast with the net stabilizing contribution in the latter. Moreover it was found that the stabilizing ${\pi}$-nonbond structure, (5${\pi}$/5) was always cooperatively reinforced by the more stabilizing anti(n-${\sigma}^*$) interaction, whereas the destabilizing (4${\pi}$/4) structure was accompanied by the less stabilizing syn(n-${\sigma}^*$) interaction. This type of cooperativity was found general through-bond interaction of the terminal lone pair lobes split the energy levels into two, $n_+ = \frac{1}{\sqrt{2}}(n_1 + n_2)$ and $n_- = \frac{1}{\sqrt{2}}(n_1 - n_2)$, the latter being the lower level, which can be shown using simple overlap patterns of the two lobes with a common vicinal ${\sigma}^*$ orbital.

• Journal of the Korean Chemical Society
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• v.30 no.1
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• pp.9-18
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• 1986

MNDO and STO-3G calculations were performed to determine relative stabilities of rotamers for ${\alpha}$-substituted acetones, $CH_2XCOCH_3$, X = F, Cl, OH, SH, and $NH_2$. It was found that rotamers corresponding to gauche forms are preferred for all the ${\alpha}$-substituents except for X = F and NH$_2$, for which the cis forms were the preferred ones. The stability of gauche form was dictated by the stabilizing two-orbital-two-electron interaction ${\sigma}_{cx}$-${\pi}_{co}^*$, operating uniquely in the gauche form due to the substantial vicinal overlap and energy gap narrowing between ${\sigma}_{cx}$ and ${\pi}_{co}^*$ orbitals. The energy gap narrowing was caused by the lowering of ${\pi}_{co}^*$ level due to the hyperconjugative ${\sigma}_{cx}^*$-${\pi}_{co}^*$ interactions; the red shift in the n-${\pi}^*$ transition was another effect of the relatively large ${\sigma}_{cx}^*$-${\pi}_{co}^*$ splitting. Various ${\sigma}-{\pi}$ interactions in the gauche form were found to be stronger in the third-row hetero atom system, X = Cl and SH. Interactions between nonbonding orbital on N, $n_N$ and vicinal C-C ${\sigma}$ bond were shown to be stronger in the trans than in the cis orientation.

• Journal of the Korean Chemical Society
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• v.26 no.3
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• pp.165-171
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• 1982

The thioxanthylium ion ard anthracenium ion have coplanar geometries. The empty $P_z$-orbitals of the positive centers in the cations, therefore, overlap with the ${\pi}$-orbitals of the fused benzen rings. These cations have aromatic characters, obeying Huckel's (4n + 2)${\pi}$ rule. The contribution of the sulfur atom to aromatic stabilization was estimated by comparing the ${^19F}$-nmr chemical shifts of the thioxanthylium ions and anthracenium ions.

• Korean Educational Research Journal
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• v.37 no.1
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• pp.33-45
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• 2016

We propose a research for detection of the fluoride ion using borane compounds. Based on the Lewis acid-base reaction, we discussed the fundamental of sensing for fluoride ion. One of the important aspects in the chemistry of organoboranes is their behaviors as Lewis acids, which is a result of the vacant $2p_{\pi}$ orbital on the tricoordinate boron center. The electronic interaction between boron atoms and ${\pi}$-orbitals of donor molecules, constructed from the carbon 2p orbitals, is generally strong. Boron atoms can reach the desired octet configuration either through ${\pi}$-overlap with a suitable X or through formation of Lewis acid-Lewis base complexes.

• Journal of The Korean Astronomical Society
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• v.52 no.4
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• pp.121-131
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• 2019

I investigate the origin of arc degeneracies in satellite microlens parallax ${\pi}_E$ measurements with only late time data, e.g., t > $t_0+t_E$ as seen from the satellite. I show that these are due to partial overlap of a series of osculating, exactly circular, degeneracies in the ${\pi}_E$ plane, each from a single measurement. In events with somewhat earlier data, these long arcs break up into two arclets, or (with even earlier data) two points, because these earlier measurements give rise to intersecting rather than osculating circles. The two arclets (or points) then constitute one pair of degeneracies in the well-known four-fold degeneracy of space-based microlens parallax. Using this framework of intersecting circles, I show that next-generation microlens satellite experiments could yield good ${\pi}_E$ determinations with only about five measurements per event, i.e., about 30 observations per day to monitor 1500 events per year. This could plausibly be done with a small (hence cheap, in the spirit of Gould & Yee 2012) satellite telescope, e.g., 20 cm.

• Bulletin of the Korean Chemical Society
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• v.2 no.1
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• pp.12-16
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• 1981

Alkyl and alkenyl substituent effects on nonbonded interactions of hexatriene were examined using CNDO/2 method. The results showed that: (1) rapid rate of thermal electrocyclization of 3-vinyl hexa-1, 3, 5-triene is due to increased overlap population between atom pair reacting resulting from strong electron repelling interaction of vinly group on the triene moiety; (2) stability of a conformer is determined by additive effect of composite ${\pi}$ structures; (3) a substituent on positions 2 and 3 increases the HOMO AO coefficient of sites 1 and 4 considerably and activates interactions with these sites.

• Journal of the Korean Chemical Society
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• v.68 no.3
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• pp.146-150
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• 2024

Precise molecular configuration elucidation of poly(3-hexylthiophene) (P3HT) through advanced spectroscopic techniques is pivotal for enhancing P3HT-based photovoltaic device efficiencies since its high charge-carrier mobility is directly correlated to its well-ordered structure. In this study, we examine Raman depolarization ratios of annealed and non-annealed P3HT films to elucidate their intermolecular π-π configurations. Our findings suggest that the backbone of the annealed film possesses stronger π-π conjugation overlaps than that of the non-annealed film owing to the greater depolarization ratio of the annealed film. In addition, the depolarization ratios are also supported by theoretical calculations, where parallel-stacked thiophene structures display a higher depolarization ratio compared with that of twisted-stacked structures, as calculated by the Møller-Plesset perturbation theory. This study highlights the utility of polarized Raman spectroscopy as a versatile tool for assessing the degree of molecular order in highly conjugated polymer films.

• Macromolecular Research
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• v.17 no.9
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• pp.672-681
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• 2009

A series of inert and photo-stable Er(III)-encapsulated complexes based on ${\pi}$-extended dendritic anthracene ligands bearing G3-aryl-ether dendron ([G3-AnX]-$CO_2H$), which retain different ${\pi}$-bridging systems, such as single (X= S), double (X= D) and triple (X= T) bonds was designed and synthesized to establish the structure-property relationship. The near infrared emission intensities of Er(III)-encapsulated complexes were enhanced dramatically by increasing the ${\pi}$-conjugated extension of anthracene ligands. The time-resolved luminescence spectra show monoexponential decays with a lifetime of $2.0{\sim}2.4ms$ for $Er^{3+}$ ions in thin films, and calculated intrinsic quantum yields of $Er^{3+}$ ions are in the range of $0.025{\sim}0.03%$. As a result, all Er(III)-encapsulated dendrimer complexes exhibit the near IR emission with the following order: $Er^{3+}-[G3-AnD]_3$(terpy) > $Er^{3+}-[G3-AnS]_3$(terpy) ${\approx}$ $Er^{3+}-[G3-AnT]_3$(terpy), because $Er^{3+}-[G3-AnD]_3$(terpy) has a higher relatively spectral overlap J value and energy transfer efficiency. In addition, the lack of detectable phosphorescence and no significant spectral dependence of the ${\pi}$-extended anthracene moieties on the solvent polarity support energy transfer from their singlet state to the central $Er^{3+}$ ion taking place in $Er^{3+}-[G3-AnX]_3$(terpy).