A diacetylenic molecular hinge bearing two ethynyltriphenylene units (1) has been synthesized. Evidence from 1H NMR and variable temperature NMR (VT-NMR) of 1 in comparison to model compounds bearing only one triphenylene unit suggests that there is an equilibrium between the open conformer and the intramolecularly π-π interacting closed conformer in solution (equilibrium constant K = 6.5 at 298 K in CDCl3) arising from the rotation of the diacetylenic hinge. Unusual fluorescence emission observed from 1 has been assigned to excimer formation arising from intramolecularly π-π interacting triphenylene units in the excited state. Steady state and picosecond time resolved fluorescence spectra of 1 were nearly identical and corresponded to intramolecular excimer emission. © 2010 The Royal Society of Chemistry.

Sethuraman Sankararaman

Department Of Chemistry

Ritesh Nandy

BEARING-ONLY

EXCIMER FORMATION

Excimers

Fluorescence emission

INTRAMOLECULAR EXCIMER EMISSION

MODEL COMPOUND

PICOSECOND TIME

steady state

TRIPHENYLENES

VARIABLE-TEMPERATURE NMR

Bearings (structural)

Equilibrium constants

Fluorescence

nuclear magnetic resonance

Acetylene

alkyne

fluorescent dye

phenanthrene derivative

article

chemical structure

chemistry

Nuclear magnetic resonance spectroscopy

synthesis

Temperature

Alkynes

Fluorescent Dyes

Magnetic Resonance Spectroscopy

Molecular Structure

Phenanthrenes

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IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Organic and Biomolecular Chemistry

Several 2-(phenylethynyl)triphenylene derivatives bearing electron donor and acceptor substituents on the phenyl rings have been synthesized. The absorption and fluorescence emission properties of these molecules have been studied in solvents of different polarity. For a given derivative, solvent polarity had minimal effect on the absorption maxima. However, for a given solvent the absorption maxima red shifted with increasing conjugation of the substituent. The fluorescence emission of these derivatives was very sensitive to solvent polarity. In the presence of strongly electron withdrawing (-CN) and strongly electron donating (-NMe2) substituents large Stokes shifts (up to 130 nm, 7828 cm-1) were observed in DMSO. In the presence of carbonyl substituents (-COMe and-COPh), the largest Stokes shift (140 nm, 8163 cm-1) was observed in ethanol. Linear correlation was observed for the Stokes shifts in a Lippert-Mataga plot. Linear correlation of Stokes shift was also observed with ET(30) scale for protic and aprotic solvents but with different slopes. These results indicate that the fluorescence emission arises from excited state intramolecular charge transfer in these molecules where the triphenylene chromophore acts either as a donor or as an acceptor depending upon the nature of the substituent on the phenyl ring. HOMO-LUMO energy gaps have been estimated from the electrochemical and spectral data for these derivatives. The HOMO and LUMO surfaces were obtained from DFT calculations. © 2010.

Fulltext

Beilstein Journal of Organic Chemistry

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

(Chemical Equation Presented) The first example of isolation and X-ray crystallographic structural characterization of two conformers arising from rotation along a diacetylenic bond is reported. In both the conformers extensive π-π interactions are observed in the solid state. VT-NMR and fluorescence spectroscopic studies in solution suggest that the closed and open conformers are in equilibrium and that the closed conformer is the predominant species at room temperature. © 2008 American Chemical Society.

Journal of Organic Chemistry

Conformational isomers from rotation of diacetylenic bond in an ethynylpyrene-substituted molecular hinge

(Chemical Equation Presented) Synthesis of a tetrakis(1-pyrenylethynyl)- substituted rigid hinge-like molecule (1) is described. The intramolecular π-stacking interaction of the pyrene units is studied by 1H NMR and fluorescence spectroscopy. Due to intramolecular π-stacking interactions, chemical shifts of the pyrene protons in 1 are highly shielded in the NMR spectrum. Fluorescence from the static excimer state is observed due to π-stacking interactions among the pyrene units in the ground state of 1. Based on the spectroscopic evidence, conformations and dynamics of 1, arising from the hindered rotation of the major axis, are proposed. © 2007 American Chemical Society.

Intramolecular π-stacking interaction in a rigid molecular hinge substituted with 1-(pyrenylethynyl) units

The Cadiot-Chodkiewicz coupling of cis-1,4-diethynyl-1,4- dimethoxycyclohexa-2,5-diene and the corresponding ethynyl bromide gave a mixture of acetyenic macrocycles ranging from dimer to octamer in good isolable yields. The trimeric and tetrameric macrocycles have been structurally characterized by single-crystal X-ray crystallography. In the crystal structure of the trimeric macrocycle a molecule of benzene is sandwiched between a pair of macrocyles. The tetrameric macrocycle exhibited a tub-shaped conformation and encapsulated a molecule of ethyl acetate inside the tub. © 2006 American Chemical Society.

Synthesis of 1,4-cyclohexadiene-based acetylenic macrocycles with Cadiot-Chodkiewicz coupling. Structure of a tub-shaped tetrameric container

Synthesis of a pyrene octaaldehyde derivative and its aggregation through π-π and C-H⋯O interactions in solution and in the solid state probed by fluorescence emission and other spectroscopic methods are reported. The effect of solvent, concentration, and temperature on the aggregation is investigated. © 2006 American Chemical Society.

Organic Letters

Synthesis and spectroscopic investigation of aggregation through cooperative π-π and C-H⋯O interactions in a novel pyrene octaaldehyde derivative

The synthesis of several 1,3,6,8-tetraethynylpyrene derivatives is reported. The effect of extended acetylenic conjugation on their absorption and fluorescence-emission properties is studied. Significant bathochromic shifts of both the absorption and fluorescence emission bands are observed. These derivatives emit fluorescence in the visible (400-550 nm) region. © Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

European Journal of Organic Chemistry

Synthesis, absorption, and fluorescence-emission properties of 1,3,6,8-tetraethynylpyrene and its derivatives

Unusual fluorescene emission from ethynyltriphenylene-substituted diacetylenic molecular hinge. Formation of intramolecular excimer

Journal	Organic and Biomolecular Chemistry
ISSN	14770520
Open Access	No