The emission spectra of [2.2](2,7)pyrenophane and the zero field splitting parameters D and E of its excited triplet state were measured in glasses and in small single crystals at 1.3 K. The results are being compared with monomer pyrene and 2,7 dimethylpyrene in liquid and solid solutions as well as in single crystals

Hausser, Karl H.

Kirrstetter, Reiner G. H.

Schweitzer, Dieter

Staab, Heinz A.

The emission spectra of [2.2] (2,7) pyrenophane and the zero field splitting parameters D und E of its excited triplet state were measured in glasses and in small single crystals at 1.3 K. The results are being compared with monomer pyrene and 2,7-dimethylpyrene in liquid and solid solutions as well as in single crystals

Schweitzer, D.

Hausser, K.

Kirrstetter , R.

Staab, H.

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Transanular interaction in [2.2]Phanes: [2.2](2,7)Pyrenophane

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Transanular Interaction in [2.2]Phanes: [2.2](2,7)Pyrenophane 
-D. Schweitzer, K. H. Hausser, R. G. H. Kirrstetter, and H. A. Staab 
Mu·Planc:k·Iru.titutc, Department of Molecular Pbyaics, Department of Organic Chemistry, 
Heidelbers 
(Z. Naturforam. 31~ 1189-1192 [1916}; received AUgus126. 1976) 
The eDlission spectra of [2.21 (2,7)pyrenophane and the zero field splitting parameters D und E 
of its excited triplet elate were measured in glasses and in amaU siogle cry .. ~.Ls at 1.3 .K. The .results 
are beiDg compand with monomer pyrene and 2.7·dimelbylpyrene in liqUid and solid solultons as 
weD as in lingle C1')'I1815. 
Introduction 
The investigation of [2.2]phanes provides infor-
mation on the transanular intramolecular ;r-eIectron 
interaction through space. In two preceding pa-
pers I,! we have studied a number of isomers of 
naphthalenophanes as well 85 hiphenylophane and 
pbenanthrenophane. Methods U5ed were emission 
spectroscopy at low temperatures (1 .3 -4.2 K) and 
the measurement of the triplet zero field splitting 
parameters D and E by optical detection of magnetic 
resonance (ODMR) both i.n glass matrices and in 
some cases in single crystals. The results are rele-
vant for the understanding of similar intennolecular 
interactions in excimers and exciplexes. 
The phenomenon of excimer fonnation was first 
discovered with the example of pyrene in solution 
by Forster and Kasper'. Later on an excimer fluo-
rescence was also observed in a pyrene single crys· 
tal·,5. Hence it seemed to be of particular interest 
to extend tbe investigations of the [2.2]phanes to 
[2.2) (2,7)pyrenophane (1) whim has recenlly been 
synthesized IS and to compare the results with pyrene 
(2) and 2,7·dimelhylpyrene (3) and wilh Ihe ex· 
cimers in solution and in single crystals. 
Results 
We report here on the Buorescence and phospho-
rescence spectra as well as on the D and E parame· 
ter of pyrene 2, dimethylpyrene 3 and pyrenophane 1 
measured in small single crystals and in glasses 
and solulions of 2.melhyltelrahydrofuran (MTHF). 
The experimental set-up used to record the lumi· 
ne!cence and the ODMR spectra was similar to the 
one described by Zuclich et al. 1 equipped with the 
photomultiplier RCA 310 34A02 for recording the 
long wavelength spectra. The measurements were 
perfonned al 1.3 K. 
The fluorescence and phosphorescence spectra are 
shown in the Figure: The emission spectra of py-
rene 2 (a) and dimethylpyrene 3 (c), concentration 
5 ' 10-3 mol, in a rigid glass of MTHF at 1.3 K are 
typical monomer spectra; they exhibit the well· 
known excimer fluorescence 3 after melting at room 
temperature (b and d) . The fluorescence spectra of 
single crystals of pyrene 2 and dimethylpyrene 3 
differ considerably. The broad fluorescence band 
(f) of pyrene single crystals 5 which consists of 
pairs of pyrene molecules occurs at almost the same 
wave number as the excimer in solution (h). in 
contrast to the fluorescence of small single crystals 
of dimelhylpyrene 3 (e) the red shift of whim with 
respects to the monomer is much smaller. The fluo· 
rescence spectra of [2.2] (2,7)pyrenophane (1) in 
the rigid glass of MTHF (g) and in 5mall singh~ 
crystals (h) are broad and structureless as well, but 
they are shifted considerably farther to the red than 
in the case of the pyrene crystal. Inspite of the Jarge 
shift of the fluorescence the phosphorescence is only 
very little shifted to the red. The phosphorescence 
of the pyrenophane 1 exhihi15 essentially the same 
although somewhat broadened structure ~ t~e phos. 
phorescence of the monomers. For quanhtattve com· 
parison, the wave numbers of the fluorescence and 
of the phosphorescence are compiled in the Table 
together with the zero field splitting parameters D 
and E. 
1190 D. sm"'eitzer d al • . Transanular Interaction in [2.2] Phanes 
}5ooo , 000 15JCO , .... }5fXX) 
a ~ " 'UHF 15·,.-'m. N I.JK 
,", i> """" UK e 
Fig. 1. 
Lell: 
Emission IIpectra of pyrene (2) 
and 2,7-dimethylpyrene (3) 
in 2.methyltetrahydrofuran (MTHF) 
at 1.3 K (a and c) and at 
,", 
k ~ 
room temperalure (b and d). 
Right: 
Emission spectra of 2 and 3 
in single crystala (e and f) 
~nd of [2.2] (2,7)PJieJIophane (1) 
In MTHF (g) and in single 
crystals (b) at 1.3 K. 
~ I, HTHF (5 ·"-'m' b 
roo", '.mp. ~ ~ .. ",.", l,lK 
f P indicate! phosphorescence, and 
"'as taken with higher amplification 
than the total emission epectr •. 
'H, C @ g o I, HTHF " . ,,-3,.) I, MTHF (_ lO" m , I,JK ",K CH, 
- ~ • " ~ ,.U"«J < , , ~ 
• • 
" ~ ~ d h -e III MTHF (So/O'1m, @ """" ~ l,lK ." room , .mp. < ~ < 
,", 
-
1 ,. "010' \. 
' 00 '!:I sao SSO 600 650 70 """ ~OO 'so 500 550 600 650 700 NrI 
Discussion 
In previous papers J, 2 we have compared the 
phanes with the dimethyl substituted monomers. An 
analogous comparison of the pyrenophane 1 with 
the dimethyIpyrene 3 is appropriate when dealing 
with liquid and solid solutions in MTHF, but single 
crystals of dimethylpyrene 3 are not appropriate for 
comparison. While the red shih of the fluorescence 
of pyrene 2 in solution at room temperature (b) is 
almost identical with the one observed in single 
crystals, i.e. about5000cm-t, the mum smaller red 
shift in crystalline dimethylpyrene 3 of 1450 cm- I 
indicates a considerably weaker :r·electron inter-
action. Since the crystal structure of dimethylpyrene 
3 is not known, it remains open whether it does not 
crystallize in a type B JaUice with two molecules 
forming a pair like pyrene. 2 or whether the crystal 
structure is similar to pyrene 2, but the planes are 
kept farther apart because of the steric hinderance 
of the methyl groups, 
The fluorescence hand of the pyrenophane I, on 
the otber hand, is shifted still considerably farther 
D. Schweitzer et al • • Transanular Interaction in [2.2] Phanes 1191 
Table 1. Wave numbers of the O-O·transitions vo_o and of the centers of the broad eIcimer bands VIIlU of the Ouores· 
cence and of the phosphorescence as ~el1 a., the zero fiel~ splitting parameters I D I and I E I of the [2.2] (2,7)pyreno-
pbane (I), pyrene (2) and 2,7~eth,.lpyrene (3) m 2·metbyltetrahydro€uran (MTHFj and in single crystals. 
Temp. Fluorescence [cm-I] Phosphorescense [cm-II IDI lEI [K] "0-0 .~ "'max,mOD -"'miX 1'0_0 VO_0.1I10D- VO_0 [cm-I] [em-I] 
Pyrcne 2 in 1.3 26900 26150 
MTHF 
Dimethylpyrene 3 1.3 26400 25850 
in l\lTHF 
Pyrenc2 in r.t. 21100 5050 
MTHF 
Dimeth}'lpyrene 3 r.t. 20400 5450 
inMTHF 
Pyrene2 1.3 21200 4950 
Single ,Cryatal 
Dimethylpyrene 3 1.3 25200 24400 1450 
Single Crystals 
Pyrenophane 1 1.3 18000 7850 
inMTHF 
Pyrenophane 1 1.3 17600 8250 
Crystalline 
to the red (7850 em-I) indicating an even stronger 
interaction between the two :f·electron systems. This 
result is at least qualitatively plausible if one takes 
into account that the distance between two pyrene 
molecules forming a pair in a crystal is 3.53 A 
which is reduced in the excimer following calcula· 
tions of Birks and Kazzaz 5 by about two tens of an 
A, while the distance in the pyrenophane I is cer-
tainly not more than 3 A in the average·. 
The pyrene crystal is known to emit only excimer 
fluorescence and phosphorescence typical for mono· 
mers 10. It was concluded that in the triplet state it 
does not fonn excimers 10 but has about the same 
distance like the ground state 11_ However, although 
the phosphorescence shows sharp vibrational struc-
1ure, its red shift is not zero but 330 cm-1 for 
pyrene 2 and 100 cm-1 for dimethyJpyrene 3 with 
respect to the monomers. The ratio of the shifts of 
the fluorescence to the phosphorescence are very 
similar, i. e_ about 15 both for2 and 3. 
The most striking observation of the phospho-
rescence of the pyrenophane I in MTHF is tbat in-
spite of the mum closer distance it shows a similar 
although somewhat broadened structure and a red 
• The X·ray structure analysis of pyrenophane 1 is not 
yet completed, but as known in the case of the [2.2]· 
paracyclophane I the aromatic nuclei are deformed into 
a boat conformation resulting in a distance of about 
2.8 A. close to the - CHt-CHI·bridges and of about 
3.1 A. in the middle. 
17020 0.0859 0.0168 
16935 0.0855 0.0169 
16690 330 0.0835 0.0157 
16835 100 0.0818 0.0\62 
16785 ISO 0.0834 0.0166 
16690 330 0.0790 0.0160 
shift of 150 cm-1 with respect to 3 whim is only 
about one half of the shift in the pyrene crystal. 
The zero field splitting parameter D is found to 
be identical for crystalline pyrene and for pyreno-
phane 1 in MTHF and only 3% smaller than for 
the monomers 2 and 3 the D values of whim are 
very similar. For small single crystals of the pyreno-
phane 1, on the other hand. the D value is reduced 
by about 8% with respect to the monomers. 
A somewhat weaker coupling between the two 
sub-units of a phane in a triplet state as compared 
to the singlet state was interpreted previously 1 in 
terms of a smaller spatial extension of the triplet 
orbital than the one of the singlet orbital in analogy 
to the results obtained with smaller systems. 
The importance of the exciton resonance and the 
marge resonance for the energy of the excimer 
state was also emphasized 11 and it was pointed out 
that these interactions might reduce the energy of 
the triplet excimer state less than the one of the 
singlet excimer state 11. However. it remains sur-
prising that both the red shift of the phosphores. 
cence and the D value are almost identical for crys· 
talline pyrene 2 and for pyrenophane 1 and differ 
very little from monomere pyrene inspite of the 
rather large difference in the distance between the 
relevant .n-electron systems. The theoretical aspects 
of these experimental findings will be discussed in a 
subsequent paper together with additional experi-
mental results_ 
1192 D. Schweitzer d al .. Tranaanular Interaction in [2.2]Phanes 
I D. 5mweilter. J. P. Colpa. J. Behnke. K. H. Hauser. 
M. Haenel. and H. A. Staab, Chern. Phys. 11, 373 
[1975J. 
! D. Schweitzer, J. P. Colpa, K. H. HaUMef, M. Haenel. 
and H. A. Staab, J. Luminescence 12/13, 363 [1976]. 
, Th. Forster and K. Kasper. Z. Physik. Chem. (Frank-
lurt) NF I, 275 [1954J; Z. EI,k"omem. 59, 976 [1955J. 
f, B. Stevens, Spectrodtim. Acta 18, 439 [1962]. 
S J. B. Birb Ind A. A. Ka.z:zu. Proc, Roy. Soc. London 
A 3M, 291 [1968J. 
• R. G. H. KirntcUer and H. A. Staab. to be publi5bcd. 
- See also: T. Umemoto, S. Satani. Y. Sakata. and S. 
Misumi, Tetrahedron Lett. 1975, 31S9;R. H. Mitchell, R. 
J. Carruthers. and J. C. M. Zwinkels, Tetrahedron Lett. 
1976,2585. 
T J. Zuctich. D. Schweitzer, and A. H. Maki, Pbotodtem. 
Pho'ob;ol.l8, 161 [1973J, 
• A. Camerman and J. Trotter, Acta Cryst. lB, 636 [1965]. 
• D. K. Lonsdale. H. J. Milledge, and K. V. Krishna Rao, 
Proc. Roy. Soc. London A 255. 82 [1960]; n. Hope, J. 
Bernstein. and K. N. Trueblood, Acta Cryll. 828, 1733 
[1972J. 
10 1.. Peter and G. VaubeJ. Chem. Pbrs. Leu. 21. 158 
[1973J • 
II J. B. Birks. In IOThe Exciplex" eM. Cordon and W. R. 
Ware. eds.}, p. 39, Academic Press Inc., New York. 1975, 
and literature quoted there. 


Transanular interaction in [2.2]phanes: [2.2](2,7)pyrenophane

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Transanular interaction in [2.2]phanes: [2.2](2,7)pyrenophane

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