A Closely-Coupled Pyrene Dimer Having Unusually Intense Fluorescence
FULL PAPER
through the sample, was directed to a high-radiance monochroma-
tor and then to a fast-response PMT. Transient differential absorp-
tion spectra were recorded point-by-point and were corrected for
small changes in laser intensity. Kinetic measurements were re-
corded at a fixed wavelength, using signal averaging techniques. A
fresh aliquot of solution was used for each laser shot.
Experimental Section
General Remarks: High purity solvents for spectroscopic measure-
ments were purchased from Aldrich Chemical Co. and, unless
stated otherwise, were used as received. Butyronitrile was dried over
CaH2 and distilled under N2 before use. The title compound 1 was
prepared by modification of the literature procedure[16] as out-
lined below.
Semi-empirical calculations were made at the PM3 level using the
Gaussian-03 package. The ground-state structure was optimized
both in vacuo and in a bath of acetonitrile as an inert solvent. The
energy was minimized and single-point calculations performed for
this geometry using the PM3 model Hamiltonians. The LUMO and
HOMO were visualized for the fully optimized structure. The di-
hedral angle was varied manually, with the structure for the rest of
the molecule being optimized. The energy was computed at the
PM3 level for each angle.
1,4-Di(1-pyrenyl)butadiynylene (1): Cupric acetate monohydrate
(4.56 g, 2.07 mmol) was added to a stirred solution of 1-ethynylpyr-
ene (460 mg, 23 mmol) in pyridine (20 mL). The mixture was
stirred for 3 hours at 55 °C. The insoluble material which was de-
posited on cooling the reaction mixture was collected by filtration,
and washed successively with methanol (100 mL) and water
(100 mL) to give a deep yellow solid. The crude material was puri-
fied by at least two column chromatography separations (silica gel,
petroleum ether {boiling range 40Ϫ60 °C} / ethyl acetate 19:1) to
yield 325 mg (36%) of the desired product as a yellow solid.
Samples for fluorescence measurements were purified by prepara-
tive TLC on silica using the same solvent mixture. M.p. Ͼ 250 °C.
1H NMR (300 MHz, CDCl3): δ ϭ 8.19 (m, 16 H), 8.73 (d, J ϭ 9.1
Hz, 2 H). 13C NMR (75.5 MHz, CDCl3): δ ϭ 80.2 (2C), 83.1 (2C),
116.6 (2C), 124.4 (2C), 124.6 (2C), 124.8 (2C), 124.9 (2C), 125.8
(2C), 126.3 (2C), 126.3 (2C), 126.8 (2C), 127.6 (2C), 129.2 (2C),
129.3 (2C), 130.9 (2C), 131.4 (2C), 132.1 (2C), 133.7 (2C). HR-
MS calculated for C36H18: 450.1409. Found: 450.1423. Elemental
analysis calcd. (found) C, 95.97 (95.60), H 4.03 (4.43). Although
the analysis for carbon and hydrogen is within 0.4%, the absolute
purity of 1 was established by fluorescence spectroscopy which is
significantly more sensitive to impurities (see text).
Acknowledgments
We thank the EPSRC (GR/S00088) and the University of Newc-
astle for their financial support of this work.
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2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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