PYRENE DIMERIZATION INTO 1,1'-DIPYRENYL
1165
was recovered practically unchanged from the reaction
mixtures. The pyrene proper readily entered into these
reactions.
the spontaneous recovery of the contact after some time,
and the film then shows the initial electroluminescent
characteristics. In the other words, the film “remembers”
the primary electric impact.
Dipyrenyl possesses intensive blue fluorescence in
solution and in solid state, it is insoluble in concn. H2SO4,
the characteristic feature of benzoid polycycles. The
reduced reactivity of an aromatic compound is commonly
regarded as indication of a decreased electron density
on the molecule; the latter feature in its turn results in
some enhancement of the vibration frequency of C–H
in aromatic ring as seen in the IR spectra and in the
The known [6] pyrene dimerization under the treat-
ment of periodic acid in the aqueous acetic acid is
accompanied with side products formation. Surely this
reaction is not based “on a specific ability of the oxidant
to form associates with pyrene molecules” but merely
on the single-electron oxidation of pyrene. The applica-
tion to the dimerization of typical single-electron oxidants
like Cu(BF4)2 is far more efficient. In the synthesis of
1,1'-dipyrenyl from 1-bromopyrene by Ullman reaction
the yield was 20% [7].
1
downfield shift of signals in the H NMR spectra,
whereby the frequencies of the out-of-plane C–H
vibrations in the IR spectrum of dipyrenyl are increased:
846 (pyrene), 853 and 860 cm–1 (1,1'-dipyrenyl). The
higher frequencies were observed also for two other
bands in the region 700–770 cm–1.
EXPERIMENTAL
In the 1H NMR spectrum of 1,1'-dipyrenyl as compar-
ed with the spectrum of pyrene the proton signals are
shifted both downfield [doublets at 8.37 and 8.26, for
pyrene 8.20 ppm (d, H1,3,5,8)] and upfield [doublets at
7.89 and 7.67, for pyrene 8.03 ppm (t, H2,7)]. All these
data suggest that in the dipyrenyl appear more benzoid
aromatic sextets than in two molecules of the initial
pyrene (see the scheme), and just this increase is the
driving force of pyrene dimerization. However the
possibility of the polycycle existence in two forms
distinguished by the number and position of the aromatic
sextets seems doubtful. The calculations (Hyper Chem)
suggest that both pyrene fragments are located in one
plane, and the intensive fluorescence and the high
melting point also evidence the planar structure of the
dipyrenyl. However the anthracene dimer (9,9'-dianthryl)
did not possess analogous planar structure, the number
of aromatic sextets did not increase, and consequently
the dimer did not form. The same is also valid for peryl-
ene. In our investigation on electroluminophors synthesis
the 1,1'-dipyrenyl was the first among the polycyclic
hydrocarbons endowed with the electroluminescence
qualities. An interesting feature of the substance is its
ability to recrystallize even in a thin film (0.5 μ) under
the effect of heat generated by electric current passage.
A visual model of the process is the formation of
transparent crystals vertically standing on a heated
surface. Under conditions of electroluminescence
observation the recrystallization in a thin layer obtained
by vacuum deposition between two electrodes (I2O3 and
Al) gradually violates the electric contact, and the film
stops to luminesce. The most striking fact consists in
1
Mass, H NMR, and IR spectra were obtained on
instruments Kratos MS-890, Bruker WD-200 SY (200
MHz), and UR-20 respectively.
1,1'-Dipyrenyl. To a solution of 20.2 g (0.1 mol) of
pyrene (content of the main substance 99%) in 200 ml of
boiling acetonitrile was added gradually at vigorous
.
stirring a solution of 35 g of Cu(BF4)2 6H2O in 50 ml of
acetonitrile. After adding each portion of the solution
the reaction mixture for a short time turned dark and then
decolorized, and fine crystals of dipyrenyl precipitated.
To the mixture was added by portions 6 g of copper
subcarbonate till the end of frothing caused by CO2
liberation. Then for 10 min the mixture was cooled to
30–40°C, the precipitate was filtered off and washed with
acetonitrile (2×10 ml). The colored acetonitrile filtrate
contained the inorganic salts and 1,6-pyrenequinone. The
dipyrenyl precipitate was washed from the initial pyrene
by stirring with 30 ml of acetone followed by filtration
and washing of the precipitate with acetone. To remove
the copper salt impurity the precipitate was stirred with
a solution of 5 ml of acetic acid in 50 ml of hot water,
then filtered, washed with water, with acetic acid till the
washings were colorless, then with acetone, and dried.
Yield 14 g (70%), mp 333°C (327–328°C [6]). Before
melting (320–325°C) the powder of the substance turns
into transparent plates vertically standing on the hot
surface.
UV spectrum (benzene) λmax, nm: 285, 315, 330,
346(identical to the spectrum published in [7]). IR
spectrum (mull in mineral oil), cm–1: 3060, 3040 (νC–H),
1600, 1466, 1386, 1233, 1174, 1150–1080, 966, 860–
853 (γC–H), 833, 773, 766, 723, 713, 687, 647, 637, 550.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 8 2007