Phenothiazinophanes: Synthesis, structure, and intramolecular electronic communication

Article abstract of DOI:10.1021/ol800920d

(Chemical Equation Presented) Ortho-phenylene, ethenylene, and ethylene-bridged phenothiazinophanes are synthesized by Suzuki coupling or McMurry dimerization and catalytic hydrogenation at ambient pressure. Intensive intramolecular electronic communicati

Full text of DOI:10.1021/ol800920d

ORGANIC
LETTERS
2008
Vol. 10, No. 13
2797-2800
Phenothiazinophanes: Synthesis,
Structure, and Intramolecular Electronic
Communication
Karin Memminger,†,‡ Thomas Oeser,‡ and Thomas J. J. Mu¨ller*,†
Institut fu¨r Organische Chemie and Makromolekulare Chemie,
Heinrich-Heine-UniVersita¨t Du¨sseldorf, UniVersita¨tsstr. 1, D-40225 Du¨sseldorf,
Germany, and Organisch-Chemisches Institut der UniVersita¨t Heidelberg, Im
Neuenheimer Feld 270, D-69120 Heidelberg, Germany
thomasjj.mueller@uni-duesseldorf.de
Received April 21, 2008
ABSTRACT
Ortho-phenylene, ethenylene, and ethylene-bridged phenothiazinophanes are synthesized by Suzuki coupling or McMurry dimerization and
catalytic hydrogenation at ambient pressure. Intensive intramolecular electronic communication of the phenothiazinyl subunits is found according
to cyclic voltammetry. In addition, the macrocycles display blue to green fluorescence with large Stokes shifts. In the solid state, the cyclophanes
are arranged in unidimensional stacks. This orientation appears to be favorable for anisotropic charge transport in hole-transport materials
for organic field effect transistors (OFET) applications.
In cyclophanes,1 the π-electron subsystems are placed in
close proximity and in a parallel arrangement. Therefore,
an intense intramolecular electronic communication estab-
lished by through-bond and through-space interactions is
found.2 This overall theme has been exemplied for many
arenes, heteroarenes, nonbenzoid π-systems, and even or-
ganometallic subunits. The incorporation of cyclophanes in
polymers causes a change of the optical and electronical
properties of the polymers.3 However, if the π-system itself
is bent and unsymmetrical, stereochemical and stereoelec-
tronic implications may arise that manifest in the electronic
properties of these cyclophanes. Hence, phenothiazines as a
structural motif in cyclophanes should enhance bending as
a consequence of the butterfly conformation of the benzo
rings. Phenothiazines belong to an important class of tricyclic
nitrogen-sulfur heterocycles.4 They display low oxidation
potentials and radical cations with distinct, deep colored
absorptions5 and have become important spectroscopic
probes in molecular and supramolecular arrangements for
photoinduced electron transfer (PET) studies6 and as motifs
in organic materials.7 The prospect of integrating strongly
coupled redox fragments like phenothiazines into conjugated
(4) Sainsbury, M. In ComprehensiVe Heterocyclic Chemistry; Katritzky,
A. R., Rees, C. W., Eds.; Pergamon: Oxford, 1984; Vol. 3, p 995.
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e.g.: (a) Tinker, L. A.; Bard, A. J. J. Am. Chem. Soc. 1979, 101, 2316–
2319. (b) Padusek, B.; Kalinowski, M. K. Electrochim. Acta 1983, 28, 639.
(c) McIntyre, R.; Gerischer, H. Ber. Bunsen Ges. Phys. Chem. 1984, 88,
963–969.
† Heinrich-Heine-Universita¨t Du¨sseldorf.
‡ Organisch-Chemisches Institut der Universita¨t Heidelberg.
(1) For an excellent recent monography, see, e.g.: Modern Cyclophane
Chemistry; Gleiter, R., Hopf, H., Eds.; Wiley-VCH: Weinheim, 2004.
(2) For a recent review, see, e.g.: Tsuji, T. In Modern Cyclophane
Chemistry; Gleiter, R., Hopf, H., Eds.; Wiley-VCH: Weinheim, 2004; pp
81-104..
(6) (a) Duesing, R.; Tapolsky, G.; Meyer, T. J. J. Am. Chem. Soc. 1990,
112, 5378–5379. (b) Jones, W. E., Jr.; Chen, P.; Meyer, T. J. J. Am. Chem.
Soc. 1992, 114, 387–388. (c) Brun, A. M.; Harriman, A.; Heitz, V.; Sauvage,
J.-P. J. Am. Chem. Soc. 1991, 113, 8657–8663. (d) Burrows, H. D.; Kemp,
T. J.; Welburn, M. J. J. Chem. Soc., Perkin Trans. 2 1973, 969-974. (e)
Collin, J.-P.; Guillerez, S.; Sauvage, J.-P. J. Chem. Soc., Chem. Commun.
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7872–7877.
10.1021/ol800920d CCC: $40.75
Published on Web 06/06/2008
2008 American Chemical Society

Scheme 1
.
Suzuki Approach to ortho-Phenylene-Bridged
Phenothiazinophane 1
Scheme 2. Synthesis of Ethenylene-Bridged
Phenothiazinophanes 4 and 5
chains could constitute a so far unknown class of redox
addressable molecular wires. In this respect, the question
arises as to whether communication of two electrophoric
subunits in phenothiazinophanes is still operative and to what
extent it might occur. As part of our program to synthesize
and investigate phenothiazinyl-based molecular wires8 and
functional molecules,9 phenothiazinyl dyads, and triads,10
we now have focused on the synthesis and studies of
phenothiazines embedded in a cyclophane topology. Here,
we communicate the synthesis and structures of several
phenothiazinophanes as well as the first studies on their
electronic properties and their electronic structures.
NMR spectroscopy, by MALDI-TOF, and additionally by
X-ray structure analysis indicating an anti orientation of the
phenothiazinyl moieties (see Supporting Information).12
Ethenylene-bridged cyclophanes can be readily synthesized
by the McMurry coupling13 of suitable dialdehydes, and this
approach has also been successfully applied to the synthesis
of several heterophanes.14 Therefore, phenothiazinyl dial-
dehydes 2 are the suitable precursors for the synthesis of
ethenylene-bridged phenothiazinophanes.15 Most conve-
niently, TiCl4 and zinc were chosen as reagents as they are
inexpensive and easy to handle.16
Reacting the phenothiazinyl dialdehydes 2 and 3 under
McMurry conditions in boiling dioxane17 under pseudo high
dilution for 2-3 days gave rise to the formation of the
cyclophanes 4 and 5 in good yields (Scheme 2).
The structure of all cyclophanes was unambiguously
supported by extensive NMR spectroscopy, mass spectrom-
etry, combustion analyses, and later by an X-ray structure
analysis of 4a, again revealing an anti orientation of the
phenothiazinyl moieties (Figure 1).12
Upon the basis of our previous experience using borylated
phenothiazines in Suzuki couplings, a cross-coupling strategy
for the formation of phenothiazinophanes was devised
(Scheme 1).
Therefore, upon reacting 1,2-diiodo benzene and 10-n-
hexyl-3,7-bis-(pinacolyl boryl)-10H-phenothiazine under
pseudo high dilution Suzuki conditions,11 the phenothiazi-
nophane 1 was separated and isolated in 13% yield as a
colorless crystalline solid. Besides, column chromatography
allows the isolation of mixtures of higher macrocycles in
minor amounts (identified by mass spectrometry). The
molecular structure of 1 was unambiguously supported by
(12) Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication nos. CCDC 685260 (1), CCDC685261
(4a), and CCDC 685262 (6). Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +
44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk).
(7) (a) Wheland, R. C.; Gillson, J. L. J. Am. Chem. Soc. 1976, 98, 3916–
3925. (b) Berges, P.; Kudnig, J.; Klar, G.; Sanchez-Martinez, E.; Diaz-
Calleja, R. Synth. Met. 1992, 46, 207–219. (c) Knorr, A.; Daub, J. Angew.
Chem., Int. Ed. Engl. 1995, 34, 2664–2666. (d) Spreitzer, H.; Scholz, M.;
Gescheidt, G.; Daub, J. Liebigs Ann. Chem. 1996, 2069-2077. (e) Spreitzer,
H.; Daub, J. Chem.-Eur. J. 1996, 2, 1150–1158.
(13) For reviews, see, e.g.: (a) McMurry, J. E. Chem. ReV. 1989, 89,
1513–1524. (b) Rieke, R. D.; Kim, S.-H. J. Org. Chem. 1998, 63, 5235–
5239.
(8) (a) Mu¨ller, T. J. J. Tetrahedron Lett. 1999, 40, 6563–6566. (b)
Kra¨mer, C. S.; Zeitler, K.; Mu¨ller, T. J. J. Org. Lett. 2000, 2, 3723–3726.
(c) Kra¨mer, C. S.; Mu¨ller, T. J. J. Eur. J. Org. Chem. 2003, 3534-3548.
(d) Sailer, M.; Franz, A. W.; Mu¨ller, T. J. J. Chem.-Eur. J. 2008, 8, 2602–
2614.
(14) (a) Ephritikhine, M.; Villiers, C. Modern Carbonyl Olefination;
Wiley-VCH Verlag GmbH: Weinheim, New York, Chichester, Brisbane,
Singapore, Toronto; 1. Auflage 2004, 223-285. (b) Kawase, T.; Ueda, N.;
Tanake, K.; Seirai, Y.; Oda, M. Tetrahedron Lett. 2001, 42, 5509–5511.
(c) Vogel, E.; Binsack, B.; Hellwig, Y.; Erben, C.; Heger, A.; Lex, J.; Wu,
Y. D. Angew. Chem., Int. Ed. Engl. 1997, 36, 2612–2615.
(15) For the first phenothiazinophane, see: (a) Petry, C.; Lang, M.; Staab,
H. A.; Bauer, H. Angew. Chem., Int. Ed. Engl. 1993, 32, 1711–1714. (b)
Independently from our studies, a related phenothiazinophane has just
recently been reported. See: Rajakumar, P.; Kanagalatha, R. Tetrahedron
Lett. 2007, 48, 8496–8500.
(9) (a) Sailer, M.; Nonnenmacher, M.; Oeser, T.; Mu¨ller, T. J. J. Eur.
J. Org. Chem. 2006, 423-435. (b) Sailer, M.; Rominger, F.; Mu¨ller, T. J. J.
J. Organomet. Chem. 2006, 691, 299–308. (c) Hauck, M.; Scho¨nhaber, J.;
Zucchero, A. J.; Hardcastle, K. I.; Mu¨ller, T. J. J.; Bunz, U. H. F. J. Org.
Chem. 2007, 72, 6714–6725.
(10) (a) Kra¨mer, C. S.; Zeitler, K.; Mu¨ller, T. J. J. Tetrahedron Lett.
2001, 42, 8619–8624. (b) Kra¨mer, C. S.; Zimmermann, T. J.; Sailer, M.;
Mu¨ller, T. J. J. Synthesis 2002, 1163-1170. (c) Franz, A. W.; Mu¨ller, T. J. J.
Synthesis 2008, 1121-1125.
(16) Lenoir, D. Synthesis 1977, 553-554.
(17) Fu¨rstner, A.; Bogdanovic´, B. Angew. Chem., Int Ed. 1996, 35, 2442–
2469.
(11) Grave, C.; Schlu¨ter, A. D. Eur. J. Org. Chem. 2002, 3075-
3098.
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Org. Lett., Vol. 10, No. 13, 2008

Figure 1. Molecular structure of 4a (most hydrogen atoms were
omitted, and the hexyl substituents were truncated for clarity).
Furthermore, by catalytic hydrogenation of the ethenylene-
bridged cyclophanes 4a and 5, the ethylene-bridged
phenothiazinophanes 6 and 7 were obtained in good yields
as crystalline solids (Scheme 3).
Figure 2. Cyclic voltammogram of 6 in CH2Cl2. T ) 293 K;
electrolyte, 0.1 M NBu4PF6 (CH2Cl2); ν ) 100 mV/s; Pt as a
working and a counter electrode electrode; Ag/AgCl as a reference
electrode (determined vs ferrocene, E00 /+1 ) +450 mV).
between 2 and 7%. Electrochemical data for 1, 4, 5, 6, and
7 were obtained by cyclic voltammetry in the anodic region
(scan area up to 1.5 V) (Figure 2).
Scheme 3
.
Synthesis of Ethylene-Bridged Phenothiazinophanes
6 and 7 by Hydrogenation
According to spectroscopic and X-ray analyses, phenothi-
azinophanes are highly symmetric, and their phenothiazinyl
moieties are identical due to symmetry. Interestingly, all
cyclophanes show cooperative behavior of their first two one-
electron oxidations which are fully reversible in most cases
in accordance with Nernstian behavior. Upon reduction of
the bridging double bonds of 4a and 5 to give the biseth-
ylenyl-bridged cyclophanes 6 and 7, the first oxidations are
expectedly shifted cathodically as a consequence of 3,7-
dialkyl substitution. Most remarkably, the cyclophanes
display clearly separated first and second one-electron
oxidations which can be attributed to an intramolecular
electronic communication. The separations of half-wave
potentials lie between 113 and 206 mV and reveal a
considerable stabilization of the initially formed radical cation
by σ-π through-bond and through-space interactions. Fur-
thermore, DFT computations19 reveal that the electron
In addition to NMR spectroscopy supporting the C2h
symmetry of the cyclophane structure by appearance of a
single set of signals for the benzo and ethenylene proton
and carbon nuclei, and combustion analytical characterization
of 6 and 7, the structure of cyclophane 6 was corroborated
by an X-ray structure analysis that displays an anti orientation
of the phenothiazinyl moieties (see Supporting Informa-
tion).12
The electronic properties of the phenothiazinophanes 1,
4, 5, 6, and 7 have been investigated by absorption and
emission spectra and cyclic voltammetry (Table 1). Optical
spectroscopy (UV/vis and fluorescence spectra) reveals
fluorescence with emission of blue to green light and large
Stokes shifts (∆ν˜ ) 7900-9700 cm-1), however, with
relatively low fluorescence quantum yields Φf18 ranging
Figure 3. HOMOs of 1 (top left), 4a (top center), 6 (top right), 5
(bottom left), and 7 (bottom right) as calculated on the level of
DFT (B3LYP/6-31+G (d,p)).
(18) Fluorescence quantum yields were determined with perylene (Φf
) 0.32) or with coumarine 6 (Φf ) 0.78) as standards. For a reference,
see: Du, H.; Fuh, R. A.; Li, J.; Corkan, A.; Lindsey, J. S. Photochem.
Photobiol. 1998, 68, 141–142.
Org. Lett., Vol. 10, No. 13, 2008
2799

Table 1. Selected UV/vis, Fluorescence, and Electrochemical Data of the Cyclophanes 1, 4, 5, 6, and 7 (Recorded in Dichloromethane
at 20 °C, Cyclic Voltammetry in a 0.1 M Solution of NBu4PF6 in CH2Cl2 as an Electrolyte, Pt as a Working and Counter Electrode, vs
Ag/AgCl, at ν ) 100 mV)
Stokes shifta
[cm-1] (Φf)
E
E
1/2
0/+1
+1/+2
absorption λmax
emission λmax
1/2
compd
[nm]
[nm]
[mV]
[mV]
1
240,268,304,330
268,316, 346
266,314, 346
268,316, 346
266,312, 346
248,302,352,388
256, 310
466
522
521
521
519
572
440
484
8800(7%)b
9700
9700
782
733
767
735
796
445d
611
600
913
911
960
912
4a
4b
4c
4d
5
9700
9600
1002
680e,f,g
753
8300(4%)c
9500
6
7
242,291, 350
7900(3%)c
713h
a ∆ν˜ ) λmax,abs [cm-1] - λmax,em [cm-1]. b Fluorescence quantum yield was determined with perylene as a standard. c Fluorescence quantum yield was
determined with coumarine 6 as a standard. d Quasireversible oxidations. e Irreversible oxidation wave. f Sharp signal at E+2/+4 ) 925 mV indicating chemically
1/2
reversible electrode adsorption. g Irreversible oxidation wave at 1240 mV and cathodic peak potentials at 1110 and 1050 mV. h An additional reversible two
+2/+4
electron oxidation is found at E
) 1150 mV.
1/2
density is delocalized over the complete molecular frame-
work in the oxidation relevant HOMOs (Figure 3).
As a consequence of an average intramolecular distance
of the central thiazinyl cores of 6.0 Å (as extracted from
X-ray structure analyses) and the mutual orthogonalization
of the bridges and the phenothiazinyl moieties, π-π through-
bond interactions are very unlikely for 1, 4, 6, and 7;
however, cyclophane 5 opens this pathway by efficient
π-conjugation. With this respect, these phenothiazinophanes
can be classified a Robin-Day class II electron transfer
system.20
Finally, as a consequence of high molecular symmetry,
of ellipsoidal shape, and anti-orientation of the phenothiazinyl
cores, intermolecular stacking and its influence on crystal
packing can be expected. Indeed, the molecules are organiz-
ing along the crystallographic z-axis with intermolecular
benzo ring distances of 8.0-11.8 Å (Figure 4).12 Hence,
demonstrated for triphenylamine-based cyclophanes,23 phe-
nothiazinophanes should be good candidates as novel organic
field effect transistors (OFET).
In conclusion, we have developed a general synthesis to
ethenylene and ethylene-bridged phenothiazinophanes ap-
plying McMurry dimerization to phenothiazinyl aldehydes.
All representatives reveal intensive intramolecular electronic
communication of the phenothiazinyl subunits according to
cyclic voltammetry. DFT calculations show that the HOMOs
of the cyclophanes possess a fully delocalized structure, and
communication over the bridges rather likely occurs by σ-π
interaction. In the solid state, the cyclophanes are arranged
in unidimensional stacks, a favorable orientation for aniso-
tropic hole-transport in OFET applications.
Acknowledgment. Dedicated to Prof. Dr. Manfred Braun
on the occasion of his 60th birthday. The support of this work
by the Deutsche Forschungsgemeinschaft (Graduate College
850) and by the Fonds der Chemischen Industrie is gratefully
acknowledged. The authors also cordially thank cand.-chem.
Erik Johnsen, Martin Ga¨rtner, and Annabelle Fu¨lo¨p (all
University of Heidelberg) for experimental assistance and the
BASF AG for the generous donation of chemicals.
Supporting Information Available: Experimental pro-
cedures, spectroscopic and analytical data of compounds 1,
1
4, 5, 6, and 7, H and 13C NMR spectra, crystallographic
data of compounds 1, 4a, and 6, and molecular modeling
coordinates of structures 1, 4a, 6, 5, and 7. This material is
available free of charge via the Internet at http://pubs.acs.org.
Figure 4. Crystal packing of phenothiazinophanes 1 (left) and 4a
(right) (views along the crystallographic z-axes, hydrogen atoms
were omitted for clarity).
OL800920D
structural anisotropy, a prerequisite for solid state phenomena
such as electrical charge transport in semiconductors in the
direction of the intermolecular stacks,21 can be expected. In
particular, phenothiazines are able to form π-mers upon
interaction of radical cation and neutral species.22 As recently
(20) (a) Robin, M. B.; Day, P. AdV. Inorg. Chem. Radiochem. 1967,
247-422. (b) Bott, A. W. Curr. Sep. 1997, 61-66. (c) Stoll, M. E.;
Lovelace, S. R.; Geiger, W. E.; Schimanke, H.; Hyla-Kryspin, I.; Gleiter,
R. J. Am. Chem. Soc. 1999, 121, 9343–9351.
(21) Facchetti, A.; Mushrush, M.; Yoon, M.-H.; Hutchison, G. R.;
Ratner, M. A.; Marks, T. J. J. Am. Chem. Soc. 2004, 126, 13859–13874.
(22) Sun, D.; Rosokha, S. V.; Kochi, J. K. J. Am. Chem. Soc. 2004,
126, 1388–1401.
(19) As implemented in: PC Spartan 02; Wavefunction Inc.: Irvine, CA,
2002.
(23) Song, Y.; Di, C.; Yang, X.; Li, S.; Xu, W.; Liu, Y.; Yang, L.;
Shuai, Z.; Zhang, D.; Zhu, D. J. Am. Chem. Soc. 2006, 128, 15940–15941.
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