Angewandte
Chemie
DOI: 10.1002/anie.200702854
Expanded Porphyrins
A Core-Modified Rubyrin with meso-Aryl Substituents and
Phenanthrene-Fused Pyrrole Rings: A Highly Conjugated Near-
Infrared Dye and Hg2+ Probe**
Di Wu, Ana B. Descalzo, Fritz Weik, Franziska Emmerling, Zhen Shen,* Xiao-Zeng You,* and
Knut Rurack*
Expanded porphyrins[1] with five or more heterocyclic rings,
such as sapphyrins, rubyrins, and more extended structures,
are large conjugated macrocycles that basically preserve key
characteristics of porphyrins (e.g. Soret and Q-type absorp-
tion bands, photoactivity) yet often show various novel
features that have led to applications in medical and
pharmaceutical areas, nonlinear optics, and supramolecular
photochemistry.[2] Expanded-porphyrin structures have been
elaborated by macrocycle expansion, the introduction of
heterocycles other than pyrrole (core modification), meso
substitution, and heterocycle inversion (“confused” porphyr-
ins).[1] Because such porphyrins are macrocycles, their inter-
esting cation and anion coordination properties render them
promising hosts in molecular recognition and chemical
sensing.[3,4]
signaling.[5] Core-modified expanded porphyrins have been
employed even less frequently, for example, thiophene-
modified sapphyrins and rubyrins in anion-binding studies.[6]
Although the cation-coordination chemistry of expanded
porphyrins has been investigated,[7,8] reports on the use of
such compounds in metal-ion sensing are even scarcer.[9]
Based on our interest in the optical determination of
heavy-metal ions, in particular of Hg2+,[10] and the develop-
ment of new red/near-infrared (NIR) dyes,[11] we became
intrigued by the possibility of equipping expanded porphyrins
such as rubyrin, that is, [26]hexaphyrin(1.1.0.1.1.0), with
various “soft” donor sites,[12–14] to shift metal-ion preferences
from, for example, Zn2+, Cu2+, and Co2+ in all-pyrrole
derivatives[7] to more thiophilic target ions. Moreover, since
the strategy of core annelation has been successfully
employed to shift the optical spectra of porphyrins into the
NIR,[15,16] we synthesized rubyrin 1 and investigated its
spectroscopic properties and Hg2+-sensing features.
Of the large number of expanded porphyrins published in
the past 20 years, only few have been employed in recognition
and sensing studies, mainly all-pyrrole derivatives for anion
The synthesis of 1 started from the oxidative coupling of
monolithiated thiophene[17] and commenced with the con-
densation of 5,5’-dilithiated 2 with 4-fluorobenzaldehyde to
yield the novel bithiophene diol 3 (Scheme 1).[18] Condensa-
tion of 3 and phenanthrene-anellated pyrrole under modified
Lindsey conditions and subsequent oxidation with DDQ
yielded rubyrin 1 in 10% yield. In agreement with observa-
tions on 7,[13] 1H NMR measurements at À408C in CDCl3
showed two multiplets at d = 9.47 and 9.16 ppm, correspond-
ing to two types of magnetically nonequivalent bithiophene
protons that presumably reflect a different degree of dis-
tortion from planarity for the two bithiophene units. Since the
ortho and meta protons of the phenyl rings are directed
toward the rubyrin macrocycle and are thus deshielded by the
rubyrin and phenanthrene ring currents, multiplets are found
at d = 8.55 (8H) and 7.95 ppm (8H). The remaining two
multiplets at d = 7.39 (8H) and 7.09 ppm (8H) are assigned to
the protons of the phenanthrene rings.
[*] Dr. D. Wu, Prof. Z. Shen, Prof. X.-Z. You
State Key Laboratory of Coordination Chemistry
Nanjing University–Jinchuan Group Ltd.
Joint Laboratory of Metal Chemistry
Nanjing University, Nanjing, 210093 (China)
Fax: (+86)25-8331-4502
E-mail: zshen@nju.edu.cn
Dr. A. B. Descalzo, Dr. F. Emmerling, Dr. K. Rurack
Federal Institute for Materials Research and Testing (BAM)
Richard-Willstätter-Strasse 11, 12489 Berlin (Germany)
Fax: (+49)30-8104-5005
E-mail: knut.rurack@bam.de
Dr. F. Weik
Max-Born-Institute for Nonlinear Optics and
Short Pulse Spectroscopy
Max-Born-Strasse 2A, 12489 Berlin (Germany)
[**] We thank the National Basic Research Program of China (Nos.
2006CB806104, 2007CB925103), the National Natural Science
Foundation of China (No. 20401009), the Fok Ying Tung Education
Foundation (No. 104013), the Alexander-von-Humboldt Founda-
tion, and the European Commission’s Human Resources &
Mobility Programme (Marie Curie Intra-European Fellowship) for
financial support; as well as Dr. T. Okujima and Prof. N. Ono (Ehime
University) for MALDI-TOF MS, Dr. A. Jakob (Bruker GmbH) for
HRMS, Dr. J. P. Lei (Nanjing University) for CV, and Dr. K. Hoffmann
(BAM) for CLSM measurements; Dr. J. W. Tomm (MBI) for use of
the FTIR spectrometer and Dr. N. Dantan (BAM) for provision of
D4.
Figure 1 shows the X-ray crystal structure of 1.[19] Average
À
À
bond lengths of 1.354 and 1.395 for the N Ca and Cmeso Ca
bonds indicate p-electron delocalization in the macrocyclic
À
core. Double-bond character is also found for the average Ca
À
Cb (1.397 ) and Cb Cb (1.389 ) bonds of the thiophene
À
À
rings. In contrast, Ca Cb and Cb Cb bond lengths of 1.504 and
1.374 indicate localized single and double bonds in the
pyrrole rings. As a result of steric crowding, the phenanthrene
units are largely bent away from the least-squares plane of the
macrocyclic core (Figure 1) and the fluorophenyl rings are
only tilted by q = 8.5–34.48 out of that plane; the average
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