Donor-acceptor substituted phenylethynyltriphenylenes – excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission

• Ritesh Nandy and
• Sethuraman Sankararaman

Beilstein J. Org. Chem. 2010, 6, 992–1001, doi:10.3762/bjoc.6.112

• importance. In this class of molecule, the excited state is generally highly polar compared to the ground state due to intramolecular charge transfer from the donor to the acceptor group. The intramolecular charge transfer results in a large dipole moment in the excited state compared to that of the ground

• transfer quenching of fluorescence. Correlation of Stokes shifts with solvent polarity Solvent induced spectral shifts are often interpreted in terms of the Lippert–Mataga [43][44][45] equation, which describes Stokes shifts in terms of the change in the dipole moment of the fluorophore and the dependence

• and 1g are shown in Figure 5 as representative examples. From the slope of these plots the change in the dipole moment (Δμ) of the fluorophore upon electronic excitation (μES − μGS) was estimated assuming the molecular radius as the cavity radius [11]. The molecules under consideration are non

Chromo- and fluorophoric water-soluble polymers and silica particles by nucleophilic substitution reaction of poly(vinyl amine)

• Katja Hofmann,
• Ingolf Kahle,
• Frank Simon and
• Stefan Spange

Beilstein J. Org. Chem. 2010, 6, No. 79, doi:10.3762/bjoc.6.79

• dipolarity/polarizability. This correlates with a higher dipole moment of the electronically excited state. In contrast to 1-M, 1-P shows no significant influence of the π* term of the solvent on , whereas the influence of the β term is greater compared to that of 1-M. This effect reflects the impact of the

Symmetry breaking and structure of a mixture of nematic liquid crystals and anisotropic nanoparticles

• Marjan Krasna,
• Matej Cvetko and
• Milan Ambrožič

Beilstein J. Org. Chem. 2010, 6, No. 74, doi:10.3762/bjoc.6.74

• magnetic field towards the perpendicular direction. Here we assume that originates from magnetic NPs, where μ0 is the magnetic permittivity constant and represents the magnetization of NPs due to the magnetic dipole moment . The resulting quadrupolar magnetic field free energy density change ΔfB is

The C–F bond as a conformational tool in organic and biological chemistry

• Luke Hunter

Beilstein J. Org. Chem. 2010, 6, No. 38, doi:10.3762/bjoc.6.38

• -fluorocarbonyl compounds, but the effect decreases with the decreasing dipole moment of the carbonyl group (4–6, Figure 1a) [2]. As well as stabilising certain conformations, dipole–dipole interactions can also be responsible for destabilising other conformations. For example, in 1,3-difluoroalkanes (e.g. 7

• liquid crystals. A liquid crystal is a fluid phase in which there is some orientational ordering of the molecules. Liquid crystal display (LCD) technology requires rod-shaped molecules that have a dipole moment perpendicular to the long axis of the molecule, and this is often achieved by incorporating

• molecular conformation as well as the molecular dipole moment. The difluoro compound 60 (Figure 15) can be viewed as a conceptual progression from the axially fluorinated liquid crystal 58. NMR and modelling data show that the fluoroalkyl chain of 60 adopts a zigzag conformation in which the two C–F bonds

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Ring-alkyl connecting group effect on mesogenic properties of p-carborane derivatives and their hydrocarbon analogues

• Aleksandra Jankowiak,
• Piotr Kaszynski,
• William R. Tilford,
• Kiminori Ohta,
• Adam Januszko,
• Takashi Nagamine and
• Yasuyuki Endo

Beilstein J. Org. Chem. 2009, 5, No. 83, doi:10.3762/bjoc.5.83

• angle θ between the ring and substituent increases in the series 25, 28 < 27 < 26 or –OR, –C(O)OR < –OOCR < –CH2R. Further analysis of the computational results demonstrates that molecular dipole moment μ increases in the following order: 26 < 25 < 27 < 28. The quadrupole moment tensor Qxx perpendicular

• molecular dipole moment in phase stabilization. Since p-carboranes are moderately electron withdrawing substituents, the alkoxy derivatives have a larger dipole moment than the alkyl derivatives [16]. Alternatively, the effect can be due to higher rigidity of 1-4, which attenuates the effect as compared to

• : ethoxybenzene (25), propylbenzene (26), phenyl acetate (27), and methyl benzoate (28) and pertinent molecular parameters: dihedral angle θ, dipole moment μ, and quadrupole moment tensor QXX perpendicular to the ring plane. Preparation of diesters 16[n]. Preparation of esters 18–20. Preparation of phenol 24

Influence of spacer chain lengths and polar terminal groups on the mesomorphic properties of tethered 5-phenylpyrimidines

• Gundula F. Starkulla,
• Elisabeth Kapatsina,
• Angelika Baro,
• Frank Giesselmann,
• Stefan Tussetschläger,
• Martin Kaller and
• Sabine Laschat

Beilstein J. Org. Chem. 2009, 5, No. 63, doi:10.3762/bjoc.5.63

• twisted conformation with a dihedral angle of 43.1° [3]. The different conformations together with differences of the polarisation and dipole moment between 2- and 5-phenylpyrimidines also lead to different mesomorphic properties as was shown by Lemieux for phenylpyrimidines tethered to terminal

• nucleophilic substitution. Depending on the terminal group and the tether lengths the formation of smectic A mesophases was observed for the chloro-, bromo- and azido derivatives. Surprisingly, the strong latent dipole moment of hydroxy and cyano derivatives and the ability of hydroxy derivatives to form

Functional properties of metallomesogens modulated by molecular and supramolecular exotic arrangements

• Alessandra Crispini,
• Mauro Ghedini and
• Daniela Pucci

Beilstein J. Org. Chem. 2009, 5, No. 54, doi:10.3762/bjoc.5.54

• -mesogenic 4,4′-disubstituted 2,2′-bipyridine ligands with Pt(II) salts confirmed the role of coordination chemistry in the metal-mediated formation of liquid crystals. Indeed the induction of a dipole moment upon coordination with an MX2 moiety, allowed most of the half-disc shaped complexes [LnPtX2

• depend on the size of the X group and on the dipole moment associated with the Pt-X bond, with the sequence, for the clearing points Cl

Acid- mediated reactions under microfluidic conditions: A new strategy for practical synthesis of biofunctional natural products

• Katsunori Tanaka and
• Koichi Fukase

Beilstein J. Org. Chem. 2009, 5, No. 40, doi:10.3762/bjoc.5.40

• reactive sialyl donors having C-5 cyclic imides (Table 1), especially N-phthalimide 1a, by virtue of the “fixed-dipole moment effects” (α-only, 92% on 50 mg scale) [41]. The scale-up in a batch process, however, significantly decreased the yield and selectivity. Thus, a 100 mg scale reaction of 1a gave

• alternative to the N-phthalyl function, we also employed the C-5 azide group in sialyl donor 1b because this azide group should direct similar “fixed-dipole moment effects”, but should be easier to convert to naturally occurring N-substituents of neuraminic acids, i.e., N-acetyl or N-glycolyl groups (see

Convenient method for preparing benzyl ethers and esters using 2-benzyloxypyridine

• Susana S. Lopez and
• Gregory B. Dudley

Beilstein J. Org. Chem. 2008, 4, No. 44, doi:10.3762/bjoc.4.44

• trifluorotoluene, but toluene has a lower dipole moment and also is subject to Friedel–Crafts benzylation under the reaction conditions [6][22]. Trifluorotoluene (also known as benzotrifluoride or BTF) is recommended as a “green” solvent alternative to dichloromethane [23]. Benzylation reactions of N-Boc-serine 3d

The vicinal difluoro motif: The synthesis and conformation of erythro- and threo- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives

• David O'Hagan,
• Henry S. Rzepa,
• Martin Schüler and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2006, 2, No. 19, doi:10.1186/1860-5397-2-19

• free energy differences arising from vibrational terms) does not alter the relative energies of a and b, despite a having a zero dipole moment and b having a relatively large value (3.5D) [26]. Although the more polar b should perhaps gain more from electrostatic solvation, it has a smaller solvent

• and appears to be dominated by solvation of the trans relationship of the aryl rings and the zero dipole moment, although the smaller 3JHH coupling of 2.6 Hz and the slightly larger 3JHF coupling of 15 Hz in the NMR, measurement does suggest some contribution of conformer b in solution. The threo-13

• significantly smaller than the NMR estimate and may reflect a limitation of the solvation model. Taking all of the data together (theory, X-ray and NMR) conformer d appears to be the most favoured conformer for threo-13 with both the fluorine and the phenyl rings gauche, despite its larger dipole moment. 2,3