5,15-Bis(di-p-anisylamino)-10,20-diphenylporphyrin: Distant and intense electronic communication between two amine sites

Article abstract of DOI:10.1039/b907413a

Distant and intense electronic communication between two amine sites through a porphyrin π-spacer was quantified with inter-valence charge transfer (IVCT) band analyses. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b907413a

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5,15-Bis(di-p-anisylamino)-10,20-diphenylporphyrin: distant and intense
electronic communication between two amine sitesw
Ryota Sakamoto,* Taishiro Sasaki, Norikazu Honda and Takeshi Yamamura
Received (in Cambridge, UK) 14th April 2009, Accepted 25th June 2009
First published as an Advance Article on the web 16th July 2009
DOI: 10.1039/b907413a
Distant and intense electronic communication between two
amine sites through a porphyrin p-spacer was quantified with
inter-valence charge transfer (IVCT) band analyses.
however, none of them induces intense electronic communication
between the amine sites.10
Here H2-1 and Zn-1 (Fig. 1) in the MV state were subjected
to IVCT band analyses, to find intense electronic communication
between two distant di-p-anisylamine sites that reaches
Robin and Day class III classification.
The exploration of electronic communication through organic
p-bridges in mixed-valence (MV) compounds remains of great
interest and importance because it affords valuable knowledge
on electron-transfer and -transport issues.1 Above all, the
acquisition of intense communication through long distances
has been one of the most important and recent topics in MV
chemistry: the distance decay of electronic communication is
known to be severe,2 but distant and intense interaction is
highly desirable for the creation of molecule-based devices for
electronic circuits,3 such as molecular quantum dot cellular
automata (QCA) for quantum computing.4 Porphyrins with
highly developed p-orbitals5 have great potential to induce
intense and distant electronic communication when used as
p-bridges. Furthermore, recent innovation of various kinds of
porphyrin arrays6 has made this class of compounds more
promising as materials for molecular electronics, however,
thus far, there have only been a few porphyrin-bridged MV
systems, and they have suffered from some drawbacks. For
example, those with ferrocene as redox sites ended in weak
communication,7 or they precluded quantitative analyses of
inter-valence charge transfer (IVCT) bands due to severe
overlap with other electronic transitions in which porphyrin
macrocycles participate.7,8
H2-1 and Zn-1 were synthesized via Buchwald–Hartwig
amination to the meso-position as reported by Chen and
Zhang,10a followed by a general method for the insertion of
the Zn(II) ion.w Fig. 2a and b show an optimized structure of
H2-1 from a DFT calculation at the B3LYP/Lanl2DZ level.
The N atoms of the di-p-anisylamine moieties adopt an sp2
coordination just as other triarylamines, though, the porphyrin
ring is highly tilted due to steric hindrance with the aryl
moieties; dihedral angles between the plane defined by the
three sp2 C–N bonds, and the planes of the porphyrin macro-
cycle or the two p-anisyl groups, are 731, 331, and 341,
respectively. The HOMO and HOMOꢀ1 are chiefly located
on the two di-p-anisylamine nitrogens, forming out-of-phase
and in-phase combinations through the porphyrin p-orbital,
respectively (Fig. 2c and d). In contrast, the HOMOꢀ2 and
HOMOꢀ3 are porphyrin-based p-orbitals (Fig. S1w). These
facts indicate that oxidation of the two di-p-anisylamine
moieties precede those of the porphyrin macrocycle in H2-1.
We note that an identical discussion is applicable to Zn-1
(Fig. S2 and S3w).
Fig. 3 shows the electronic spectra of H2-1 and Zn-1 in
dichloromethane. It is worthy of mention that both
compounds exhibit intense and broad absorptions around
600–800 nm; these bands are in sharp contrast to the Q bands
of porphyrin, which are weaker, narrower, and located at
shorter wavelengths.5 According to time-dependent DFT
(TD-DFT) calculations, these absorptions are assigned as
charge transfer (CT) transitions from the di-p-anisylamine
based HOMO, to the LUMO or LUMO+1, the p*-orbitals
of the porphyrin moiety (Fig. S1 and S3w). This kind of lowest-
lying CT transition implies that the HOMO is chiefly based on
the two di-p-anisylamine moieties, and that there is electronic
communication in the MV state.9d,11 We note that the
Given the aforementioned background, diarylamine as a
redox site is considered to be the best partner for porphyrins.
This series of functional groups forms a covalent C–N bond
between its N atom, the redox centre, and the C atom of a
p-spacer, resulting in intense electronic communication.2b,9 In
addition, MV compounds based on diarylamine show intense
IVCT bands that are well separated from other electronic
transitions,2b,9 which is in marked contrast to those with
inorganic and organometallic redox sites that exhibit weak
and complex IVCT bands. We note that there are several
reports on the porphyrin–arylamine conjugated systems;
Department of Chemistry, Faculty of Science, Tokyo University of
Science, 1-3, Kagurazaka, Shinjuku-ku, Tokyo, 162-8601, Japan.
E-mail: ryota_s@rs.kagu.tus.ac.jp; Fax: (+81) 3-5228-8251
w Electronic supplementary information (ESI) available: Experimental
details, TD-DFT calculations for H2-1 and Zn-1 (Fig. S1 and S3),
optimized structure of Zn-1 by a DFT calculation (Fig. S2), cyclic
voltammograms of H2-1 and Zn-1 with further sweeps (Fig. S4), and
addition of pyridine (Fig. S5), UV/Vis/NIR spectra of H2-1 and Zn-1
upon titration of the oxidant (Fig. S6 and S7), UV/Vis spectra of H2-1
and Zn-1 before the titration and after re-reduction from the dicationic
forms (Fig. S8), and IVCT bands of H2-1+ and Zn-1+ in a mixture of
acetonitrile and dichloromethane (Fig. S9). See DOI: 10.1039/b907413a
Fig. 1 5,15-Bis(di-p-anisylamino)-10,20-diphenylporphyrin.
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(Fig. S4w). We attribute the redox behaviour shown in Fig. 4
to oxidations of the two di-p-anisylamine moieties, rather than
to those of the porphyrin macrocycle, considering the facts
enumerated below. (1) Porphyrin-based oxidations tend to
show low reversibility in free-base compounds.12 In H2-1,
the first two oxidations are reversible (Fig. 4), whereas the
next one is irreversible (Fig. S4w). (2) The addition of pyridine
brings about the loss of reversibility for porphyrin-based
oxidation processes, giving rise to the corresponding isopor-
phyrins.13 In our system the redox waves shown in Fig. 4 are
not affected by the presence of pyridine, whereas it signifi-
cantly reduces the reversibility of the third oxidation in Zn-1
(Fig. S5w). (3) The DFT calculations and electronic spectra
suggest that the HOMO and HOMOꢀ1 are mainly associated
with the di-p-anisylamine moieties (Fig. 1c–d, S1, and S3w).
Fig. 5 shows the NIR bands with the lowest transition
energies of H2-1+ and Zn-1+ in dichloromethane, which are
generated by chemical oxidation with 1,10-dichloroferroce-
nium hexafluorophosphate (E1/2 = 399 mV vs. ferrocenium/
ferrocene).w Disappearing upon further oxidations to the
corresponding dications (Fig. S6 and S7w), these absorptions
are assignable to IVCT bands. We note that the original
spectra of H2-1 and Zn-1 recover well on chemical reduction
of the dicationic species with decamethylferrocene
(E1/2 = ꢀ550 mV vs. ferrocenium/ferrocene) (Fig. S8w). As
expected, the IVCT bands are intense and distinct enough from
other electronic transitions to be quantitatively analyzed.
Following previous reports,2b,9a,b we tabulate parameters for
the IVCT bands of H2-1+ and Zn-1+ in Table 1, together with
those previously reported for di-p-anisylamine-based class III (2+)
and class II (3+) MV compounds2b,9i that are bridged with the
same number of unsaturated bonds as H2-1+ and Zn-1+.
Worthy of mention is the asymmetric nature of the IVCT
bands, which is one of the convincing proofs for class III or
class II/III borderline systems.9h nꢀ1/2(High)/nꢀ1/2(Low) values
for H2-1+ and Zn-1+ are comparable to 2+ and larger than
for 3+. In addition, the solvent dependence of the IVCT bands
of H2-1+ and Zn-1+ is quite small (Fig. S9w), which supports
our assignment that both H2-1+ and Zn-1+ belong to class
III. Narrower bandwidths than those theoretically predicted
for class II compounds, quantified as nꢀ1/2(High)/nꢀ1/2(Hush)
here, are also typical of class III compounds (Table 1).2b,9b
Zn-1+ has a larger value of electronic coupling Hab than that
of H2-1+; this is consistent with the fact that Zn(II) porphyrins
Fig. 2 (a), (b) Optimized structure of H2-1 by a DFT calculation at
the B3LYP/Lanl2DZ level: (a) top view, (b) side view. (c), (d) Contour
plot of molecular orbitals: (c) HOMO, (d) HOMOꢀ1.
Fig. 3 Electronic spectra of H2-1 and Zn-1 in dichloromethane.
TD-DFT calculations reproduce well the other features of the
electronic spcetra (Fig. S1 and S3w).
Fig. 4 shows cyclic voltammograms of H2-1 and Zn-1 in
0.1 mol dmꢀ3 tetrabutylammonium hexafluorophosphate
(TBAH) in dichloromethane. Zn-1 exhibits two reversible
one-electron processes, whereas H2-1 apparently shows one
two-electron process. However, the DEp for H2-1 (56 mV)
indicates that there are, in fact, two one-electron processes
with similar E1/2, rather than one two-electron process with a
theoretical DEp of 29 mV. Further sweeps result in irreversible
(H2-1) and reversible (Zn-1) processes at fairly high potentials
Fig. 4 Cyclic voltammograms of H2-1 and Zn-1 (0.9 mM) in 0.1 M
TBAH in dichloromethane at a sweep rate of 100 mV sꢀ1. Halfwave
potentials E1/2 are 107 mV (2eꢀ) for H2-1, ꢀ26 mV (1eꢀ) and 191 mV
(1eꢀ) for Zn-1.
Fig. 5 NIR spectra of H2-1+ and Zn-1+ with PF6 as a counter
ꢀ
anion in dichloromethane.
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Table 1 Parameters for the IVCT bands of H2-1+, Zn-1+, and reference compounds in dichloromethane
nꢀmax/cmꢀ1
e
max/Mꢀ1cmꢀ1
nꢀ1/2(obs)/cmꢀ1
nꢀ1/2(Hush)/cmꢀ1a
nꢀ1/2(High)/nꢀ1/2(Low)b
nꢀ1/2(High)/nꢀ1/2(Hush)c
Hab/cmꢀ1d
H2-1+
Zn-1+
2+e
5300
6140
6080g
5760g
12 700
13 600
39 300g
21 800g
2400
2280
2760g
3460g
3500
3760
3750g
3650g
1.35
0.75
2650
3070
3040
1080h
1.39
0.74
1.40g
1.23g
0.86g
1.04g
3+f
a
1/2
b
c
Ratio of halfwidth on the high energy side to that on the low energy side. Ratio of twice the
Calculated with nꢀ1/2(Hush) = (2310emax
)
.
d
e
halfwidth on the high energy side to nꢀ1/2(Hush). Calculated with Hab = nꢀmax/2. 2 = (E)-4,40-bis[4-bis(4-methoxyphenyl)amino]stilbene, with
f
ꢀ
g
h
Data taken from ref. 2b. Data taken from ref. 9i,
SbCl6ꢀ as a counter anion. 3 = 4,40-bis[4-bis(4-methoxyphenyl)amino]tolane, with SbCl6
calculated with the Hush equation.
.
tend to show a less positive oxidation potential than the
corresponding free-base,12,14 which affords better hole super-
exchange than the former.
5 The Porphyrin Handbook, ed. K. M. Kadish, K. M. Smith and
R. Guilard, Academic Press, San Diego, 2000.
6 (a) Y. Nakamura, N. Aratani and A. Osuka, Chem. Soc. Rev.,
2007, 36, 831; (b) A. Tsuda and A. Osuka, Adv. Mater., 2002, 14,
75; (c) N. Aratani and A. Osuka, Bull. Chem. Soc. Jpn., 2001, 74,
1361.
7 (a) V. N. Nemykin, C. D. Barrett, R. G. Hadt, R. I. Subbotin,
A. Y. Maximov, E. V. Polshin and A. Y. Koposov, Dalton Trans.,
2007, 3378; (b) A. Auger, A. J. Muller and J. C. Swarts, Dalton
Trans., 2007, 3623; (c) A. Auger and J. C. Swarts, Organometallics,
2007, 26, 102.
8 P. D. W. Boyd, A. K. Burrell, W. M. Campbell, P. A. Cocks,
K. C. Gordon, G. B. Jameson, D. L. Officer and Z. Zhao, Chem.
Commun., 1999, 637.
In conclusion, we have elucidated that H2-1 and Zn-1 have
intense electronic communication between two di-p-anisylamine
sites, reaching Robin and Day class III. This interaction is
communicated through as many as 11 unsaturated bonds of
the porphyrin spacer. Taking advantage of the beneficial
characteristics of diarylamine as redox sites, we have quantified
the IVCT bands of porphyrin-bridged MV compounds for the
first time. This series of results lead to areas of further
exploration, such as ‘‘shortcutting’’ communication through
central metals that afford metal-centered oxidations, or
explicitly have contributions from the porphyrin p-orbitals,
and ultra-distant communication through various kinds of
porphyrin arrays.
9 (a) C. Lambert and G. No
(b) S. A. Odom, K. Lancaster, L. Beverina, K. M. Lefler,
N. J. Thompson, V. Coropceanu, J.-L. Bredas, S. R. Marder and
¨
ll, J. Am. Chem. Soc., 1999, 121, 8434;
´
S. Barlow, Chem.–Eur. J., 2007, 13, 963; (c) C. Lambert, G. Noll
¨
and J. Schelter, Nat. Mater., 2002, 1, 69; (d) R. Sakamoto, S. Kume
and H. Nishihara, Chem.–Eur. J., 2008, 14, 6978; (e) G. Zhou,
M. Baumgarten and K. Muellen, J. Am. Chem. Soc., 2007, 129,
12211; (f) A. V. Szeghalmi, M. Erdmann, V. Engel, M. Schmitt,
This work was partly supported by the Sasakawa Scientific
Research Grant from The Japan Science Society.
S. Amthor, V. Kriegisch, G. Noll, R. Stahl, C. Lambert,
¨
D. Leusser, D. Stalke, M. Zabel and J. Popp, J. Am. Chem. Soc.,
2004, 126, 7834; (g) P. J. Low, M. A. J. Paterson, H. Puschmann,
A. E. Goeta, J. A. K. Howard, C. Lambert, J. C. Cherryman,
D. R. Tackley, S. Leeming and B. Brown, Chem.–Eur. J., 2004, 10,
Notes and references
1 (a) Electron Transfer in Chemistry, ed. V. Balzani, Wiley-VCH,
Weinheim, 2001, vol. 1–5; (b) K. D. Demadis, C. M. Hartshorn
and T. J. Meyer, Chem. Rev., 2001, 101, 2655; (c) B. S. Brunschwig,
C. Creutz and N. Sutin, Chem. Soc. Rev., 2002, 31, 168;
(d) D. Astruc, Acc. Chem. Res., 1997, 30, 383.
2 (a) A.-C. Ribou, J.-P. Launay, M. L. Sachetleben, H. Li and
C. W. Spangler, Inorg. Chem., 1996, 35, 3735; (b) S. Barlow,
C. Risko, S.-J. Chung, N. M. Tucker, V. Coropceanu,
S. C. Jones, Z. Levi, J.-L. Bredas and S. R. Marder, J. Am. Chem.
Soc., 2005, 127, 16900.
3 (a) J.-P. Launay, Chem. Soc. Rev., 2001, 30, 386; (b) C. Joachim,
J. K. Gimzewski and A. Aviram, Nature, 2000, 408, 541;
(c) T. M. Swager, Acc. Chem. Res., 1998, 31, 201;
(d) R. L. Carroll and C. B. Gorman, Angew. Chem., Int. Ed.,
2002, 41, 4378; (e) J. Park, A. N. Pasupathy, J. I. Goldsmith,
C. Chang, Y. Yaish, J. R. Petta, M. Rinkoski, J. P. Sethna,
H. D. Abruna, P. L. McEuen and D. C. Ralph, Nature, 2002,
417, 722.
4 (a) C. S. Lent, Science, 2000, 288, 1597; (b) C. S. Lent, B. Isaksen
and M. Lieberman, J. Am. Chem. Soc., 2003, 125, 1056; (c) J. Jiao,
G. J. Long, L. Rebbouh, F. Grandjean, A. M. Beatty and
T. P. Fehlner, J. Am. Chem. Soc., 2005, 127, 17819.
83; (h) V. Coropceanu, M. Malagoli, J. M. Andre and J. L. Bredas,
´ ´
J. Am. Chem. Soc., 2002, 124, 10519; (i) S. Barlow, C. Risko,
V. Coropceanu, N. M. Tucker, S. C. Jones, Z. Levi,
V. N. Khrustalev, M. Yu. Antipin, T. L. Kinnibrugh,
´
T. Timofeeva, S. R. Marder and J.-L. Bredas, Chem. Commun.,
2005, 764.
10 (a) Y. Chen and X. P. Zhang, J. Org. Chem., 2003, 68, 4432;
(b) C.-W. Huang, K. Y. Chiu and S.-H. Cheng, Dalton Trans.,
2005, 2417; (c) W.-N. Yen, S.-S. Lo, M.-C. Kuo, C.-L. Mai,
G.-H. Lee, S.-M. Peng and C.-Y. Yeh, Org. Lett., 2006, 8, 4239;
(d) J.-C. Chang, C.-J. Ma, G.-H. Lee, S.-M. Pengb and C.-Y. Yeh,
Dalton Trans., 2005, 1504; (e) C.-W. Lee, H.-P. Lu, C.-M. Lan,
Y.-L. Huang, Y.-R. Liang, W.-N. Yen, Y.-C. Liu, Y.-S. Lin, E.
W.-G. Diau and C.-Y. Yeh, Chem.–Eur. J., 2009, 15, 1403.
11 R. Sakamoto, M. Murata and H. Nishihara, Angew. Chem., Int.
Ed., 2006, 45, 4793.
12 A. Wolberg and J. Manassen, J. Am. Chem. Soc., 1970, 92, 2982.
13 (a) K. M. Kadish and R. K. Rhodes, Inorg. Chem., 1981, 20, 2961;
(b) L. E. Kahef, M. Gross and A. Giraudeau, J. Chem. Soc., Chem.
Commun., 1989, 963.
14 A. Giraudeau, H. J. Callot and M. Gross, Inorg. Chem., 1979, 18,
201.
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5158 | Chem. Commun., 2009, 5156–5158