Three-component cascade energy transfer with use of oligonaphthalene skeletons

Article abstract of DOI:10.1021/jo800642u

(Chemical Equation Presented) Three oligonaphthalenes with zinc porphyrin and free-base porphyrin moieties were synthesized, in which cascade energy transfer (from naphthalene to free-base porphyrin via zinc porphyrin) was observed when the zinc and free-

Full text of DOI:10.1021/jo800642u

Three-Component Cascade Energy Transfer with
Use of Oligonaphthalene Skeletons
Kazunori Tsubaki,* Kazuto Takaishi, Daisuke Sue,
Kazunari Matsuda, Yoshihiko Kanemitsu, and
Takeo Kawabata
Institute for Chemical Research, Kyoto UniVersity, Gokasho,
Uji, Kyoto, 611-0011, Japan
tsubaki@fos.kuicr.kyoto-u.ac.jp
ReceiVed March 20, 2008
Three oligonaphthalenes with zinc porphyrin and free-base
porphyrin moieties were synthesized, in which cascade
energy transfer (from naphthalene to free-base porphyrin via
zinc porphyrin) was observed when the zinc and free-base
porphyrins were close to each other.
In the field of supramolecular chemistry, considerable research
has focused on developing molecular devices and molecular
machines such as molecular motors, ratchets, and logic gates.1
At the same time, photosensitive functional molecules have been
considered as input/output devices for information and as energy
and/or electron transfer devices related to photosynthesis.2
Several fully conjugated systems containing porphyrins have
been applied and reported for the purpose.3 On the other hand,
FIGURE 1. Oligonaphthalenes 1a-4f and porphyrins 5 and 6.
we have focused our attention on the synthesis and function of
oligonaphthalenes composed of a 2,3-dioxynaphthalene unit
connected at the 1,4-position.4 Herein, we report a three-
component hierarchical energy transfer system5 based on
oligonaphthalenes with zinc porphyrins and/or free-base por-
phyrins 1a-c ≈ 4a-c (Figure 1).
(1) Recent reviews for molecular machines: (a) Kay, E. R.; Leigh, D. A.;
Zerbetto, F. Angew. Chem., Int. Ed. 2007, 46, 72–191. (b) Balzani, V.; Credi,
A.; Silvi, S.; Venturi, M. Chem. Soc. ReV. 2006, 35, 1135–1149. (c) Kinbara,
K.; Aida, T. Chem. ReV. 2005, 105, 1377–1400. (d) Kelly, T. R. Acc. Chem.
Res. 2001, 34, 514–522.
Scheme 1 outlines the synthetic route of oligonaphthalenes.6
Oligonaphthalenes with two hydroxy groups 1e-4e4c were
treated with 4-(10,15,20-triphenyl-21H,23H-porphin-5-yl)ben-
zoic acid (TPP(H2)CO2H) (5) in the presence of 1-ethyl-3-(3-
dimethylaminopropyl)carbodiimide (WSC) ·HCl and 4-dimeth-
(2) (a) Saha, S.; Stoddart, J. F. Chem. Soc. ReV. 2007, 36, 77–92. (b) Satake,
A.; Kobuke, Y. Org. Biomol. Chem. 2007, 5, 1679–1691.
(3) (a) Krebs, F. C.; Hagemann, O.; Spanggaard, H. J. Org. Chem. 2003,
68, 2463–2466. (b) Krebs, F. C.; Spanggaard, H.; Rozlosnik, N.; Larsen, N. B.;
Jørgensen, M. Langmuir 2003, 19, 7873–7880. (c) Hagemann, O.; Jørgensen,
M.; Krebs, F. C. J. Org. Chem. 2006, 71, 5546–5559.
(4) (a) Tsubaki, K. Org. Biomol. Chem. 2007, 5, 2179–2188. (b) Tsubaki,
K.; Takaishi, K.; Sue, D.; Kawabata, T. J. Org. Chem. 2007, 72, 4238–4241.
(c) Tsubaki, K.; Tanaka, H.; Takaishi, K.; Miura, M.; Morikawa, H.; Furuta, T.;
Tanaka, K.; Fuji, K.; Sasamori, T.; Tokitoh, N.; Kawabata, T. J. Org. Chem.
2006, 71, 6579–6587. (d) Tsubaki, K.; Takaishi, K.; Tanaka, H.; Miura, M.;
Kawabata, T. Org. Lett. 2006, 8, 2587–2590. (e) Takaishi, K.; Tsubaki, K.;
Tanaka, H.; Miura, M.; Kawabata, T. YAKUGAKU ZASSHI 2006, 126, 779–
787. (f) Tsubaki, K.; Miura, M.; Nakamura, A.; Kawabata, T. Tetrahedron Lett.
2006, 47, 1241–1244. (g) Tsubaki, K.; Miura, M.; Morikawa, H.; Tanaka, H.;
Kawabata, T.; Furuta, T.; Tanaka, K.; Fuji, K. J. Am. Chem. Soc. 2003, 125,
16200–16201.
(5) For multicomponent energy transfer system: (a) Faiz, J. A.; Williams,
R. M.; Pereira Silva, M. J. J.; De Cola, L.; Pikramenou, Z. J. Am. Chem. Soc.
2006, 128, 4520–4521. (b) Cotlet, M.; Vosch, T.; Habuchi, S.; Weil, T.; Mu¨llen,
K.; Hofkens, J.; De Schryver, F. J. Am. Chem. Soc. 2005, 127, 9760–9768. (c)
Pan, Y.; Lu, M.; Peng, Z.; Melinger, J. S. J. Org. Chem. 2003, 68, 6952–6958.
(d) Weil, T.; Reuther, E.; Mu¨llen, K. Angew. Chem., Int. Ed. 2002, 41, 1900–
1904. (e) Serin, J. M.; Brousmiche, D. W.; Fre´chet, J. M. J. Chem. Commun.
2002, 2605–2607. (f) Hahn, U.; Gorka, M.; Vo¨gtle, F.; Vicinelli, V.; Ceroni, P.;
Maestri, M.; Balzani, V. Angew. Chem., Int. Ed. 2002, 41, 3595–3598.
(6) Full experimental details: see the Supporting Information.
10.1021/jo800642u CCC: $40.75
Published on Web 05/08/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 4279–4282 4279

SCHEME 1. Synthetic Route of Oligonaphthalenes 1a-4f
ylaminopyridine (DMAP) to afford bis-TPP(H2) 1a-4a in
53-76% yields. On the other hand, diols 1e-4e were treated
with (TPP(Zn)CO2H) (6) under the WSC/DMAP condition to
give corresponding mono-TPP(Zn) 1f-4f and bis-TPP(Zn)
derivatives 1c-4c in low to moderate yields, respectively.
Oligonaphthalenes with both TPP(Zn) and TPP(H2) 1b-4b were
prepared by the condensation of mono-TPP(Zn) 1f-4f with the
TPP(H2)CO2H (5) in 54-90% yields.
First, with 4b as an example, the interaction among the
oligonaphthalene skeleton, free-base porphyrin part, and zinc
porphyrin part in the grand state was investigated. Figure 2
shows the UV-vis spectra of 4b with all components, oligo-
naphthalene 4d, free-base porphyrin 5, and zinc porphyrin 6,
as well as their fluorescence spectra. Because the absorption
spectrum of 4b is the sum of the spectra of the constituent, 4d,
5, and 6, each fragment in the grand state does not interact. A
wide overlap with the emission of the donor naphthalene unit
4d (around 380 nm) and absorption of the Soret band of acceptor
porphyrin 5 and/or 6 (around 420 nm) was observed. Because
porphyrins 5 and 6 have a negligible absorption near 320 nm,
the naphthalene units can be excited with a high selectivity at
this wavelength. Furthermore, because the fluorescence spec-
trum of zinc porphyrin 6 exhibits peaks at 596 and 647 nm
FIGURE 3. Fluorescence spectra of 1a-4a. Conditions: CH2Cl2
containing 1.0 × 10-8 M triethylamine to remove HCl. [1a-4a] ) 1.0
× 10-6 M, 20 °C, light path length ) 10 mm. (a) λext ) 320 nm; (b)
λext ) 420 nm.
and that of free-base porphyrin 5 displays a peak at 651 nm,
the source of the fluorescence can be easily discriminated.
When the naphthalene units of 1a-4a were selectively
irradiated at 320 nm, the fluorescence was not due to the
naphthalene units, but rather the corresponding porphyrin units
(Figure 3a). These results demonstrate that an effective intramo-
lecular energy transfer occurs from the naphthalene units to the
porphyrin units. Furthermore, the intensity of the fluorescence
increased as the number of naphthalene rings increased. Because
the fluorescent spectra of 1a and 3a, which were composed of
four naphthalene units, excited at 320 nm are similar, it is
concluded that the position of TPP on the oligonaphthalene
skeleton is not related to the fluorescent intensity. It should be
noted that the fluorescence spectra derived from the porphyrin
units had nearly the same intensities and shapes when the
porphyrin units of 1a-4a were directly excited at 420 nm
(Figure 3b).
It is also clarified that 1c-4c with oligonaphthalene skeletons
and two zinc porphyrins show similar behaviors against irradia-
tion at 320 and 420 nm (Figure 4). These results indicate that
(1) regardless of which naphthalene unit in the oligonaphthalene
skeleton is excited, an effective and fast energy transfer should
occur from the excited naphthalene unit to an adjacent naph-
thalene unit,7 and (2) a through-space energy transfer, which
determines the efficiency of the total energy transfer should
occur from the naphthalene possessing TPP to the TPP unit.
Figure 5 shows the normalized fluorescence spectra of 1b-4b
with both free-base and zinc porphyrins as well as that of an
equimolar mixture of 5 and 6. The fluorescence spectrum of
4b, in which the zinc porphyrin part and free-base porphyrin
part are far from each other, overlapped with that of the
equimolar mixture of 5 and 6. As the two porphyrins became
closer, the fluorescence derived from the zinc porphyrin clearly
FIGURE 2. (a) Fluorescence spectra of 4b, 4d, 5, and 6. Conditions:
CH2Cl2, 20 °C, λext ) 320 nm for 4d, λext ) 420 nm for 4b, 5, and 6.
(b) UV-vis spectra of 4b, 4d, 5. and 6. Conditions: CH2Cl2 containing
1.0 × 10-8 M triethylamine to remove HCl. [4b] ) [4d] ) 1.0 × 10-5
M, [5] ) [6] ) 2.0 × 10-5 M, 20 °C, light path length ) 1 mm. Inset:
Expansion of the Soret absorption region.
(7) For another interpretation of the energy transfer, the oligonaphthalene
skeleton itself acts as a single chromophore. However, the AM1 calculation of
the most stable conformation all-(S)-octamer, which was determined through
CONFLEX-MM2 implemented in CAChe ver. 6.1.12 for Windows, indicates
obitals from HOMO-5 to LUMO+5 are localized on only one or two naphthalene
rings. Therefore, we adopted the interpretation in context.
4280 J. Org. Chem. Vol. 73, No. 11, 2008

FIGURE 6. Fluorescence spectra of 3a-c and a mixture of 5 and 6.
Conditions: CH2Cl2 containing 1.0 × 10-8 M triethylamine to remove
HCl. [3a-c] ) [5] ) [6] ) 1.0 × 10-6 M (λext ) 420 nm), 20 °C,
light path length ) 10 mm.
TABLE 1. Quantum Yields of Compounds 1a-4d
entry
compd
Φ320 (%)a
Φ420 (%)b
Φ320/Φ420
1
2
3
4
5
6
7
8
5
6
0.19
0.36
0.19
0.18
0.33
0.19
0.21
0.33
1a
1b
1c
2a
2b
2c
2d
3a
3b
3c
3d
4a
4b
4c
4d
0.11
0.10
0.17
0.11
0.11
0.16
19.0
0.12
0.13
0.17
55.0
0.12
0.14
0.17
60.8
0.58
0.54
0.53
0.58
0.55
0.50
FIGURE 4. Fluorescence spectra of 1c-4c. Conditions: CH2Cl2
containing 1.0 × 10-8 M triethylamine to remove HCl. [1c-4c] ) 1.0
× 10-6 M, 20 °C, light path length ) 10 mm. (a) λext ) 320 nm; (b)
λext ) 420 nm.
9
10
11
12
13
14
15
16
17
0.20
0.23
0.32
0.59
0.58
0.53
0.21
0.28
0.33
0.58
0.50
0.51
a λext ) 320 nm. λext ) 420 nm. Conditions: CH2Cl2 containing 1.0
× 10-8 M triethylamine to remove HCl. The fluorescence quantum
yields were determined by using a solution of quinine sulfate in 1 N
H2SO4 as a reference standard (Φ ) 0.546) for λext ) 320 nm and
fluorescein in 0.1 N NaOH as a reference standard (Φ ) 0.95) for λext
) 420 nm.
b
FIGURE 5. Normalized fluorescence spectra of 1b-4b and a mixture
of 5 and 6. Conditions: CH2Cl2 containing 1.0 × 10-8 M triethylamine
to remove HCl. [1b-4b] ) 1.0 × 10-6 M (λext ) 320 nm), [5] ) [6]
) 1.0 × 10-6 M (λext ) 420 nm), 20 °C, light path length ) 10 mm.
and 0.32%, respectively. As a result, the values of Φ320/Φ420
were relatively constant at 0.57 for 1a-4a, and at about 0.51
for 1c-4c. The values of Φ320/Φ420 were considered to reflect
the efficiency of through-space energy transfer from the
naphthalene possessing the porphyrin moiety to the porphyrin.
Furthermore, for compounds 1b-4b with zinc and free-base
decreased. In particular, the fluorescence from the zinc porphyrin
in 1b was nearly quenched.8
Figure 6 shows the fluorescence spectrum of 3b, in which
partial quenching was observed, as well as those of 3a, 3c, and
an equimolar mixture of 5 and 6. Comparing 3b to 5 + 6, it is
clear that the emission intensity from the zinc porphyrin part
of 3b near 600 nm is decreased, whereas that from the free-
base porphyrin part near 650 nm is increased. The data indicate
that the additional energy transfer from the zinc porphyrin part
to the free-base porphyrin part8 should occur after the energy
transfer from the naphthalene rings to each porphyrin.
The quantum yields of the compounds are listed in Table 1.
Compared to the quantum yields with irradiation at 320 nm
(Φ320), oligonaphthalenes with two free-base porphyrins 1a-4a
are about 0.11% (entries 3, 6, 10, and 14), and those with two
zinc porphyrins 1c-4c are 0.16% (entries 5, 8, 12, and 16).
When porphyrins were directly excited at 420 nm (Φ420), the
corresponding quantum yields of 1a-4a and 1c-4c were 0.20%
porphyrins, the quantum yields of 1b-4b (Φ320 and Φ420
)
gradually decrease as the distance between the zinc porphyrin
and free-base porphyrin decreases, due to the additional energy
transfer from the zinc porphyrin to the free-base porphyrin
(entries 4, 7, 11, and 15).
The fluorescence lifetimes of some typical compounds were
determined by time-resolved fluorometry (Table 2). The lifetime
at 650 nm of the free-base porphyrin (5) irradiated at 420 nm
was 8.8 ns, and the lifetimes at both 600 and 650 nm of zinc
porphyrin (6) were ca. 1.9 ns. Oligonaphthalenes with either
free-base or zinc porphyrin had lifetimes that reflected the
corresponding fragmental porphyrins (entries 3, 5, 6, and 8).
For 1b and 4b which have both porphyrins, 4b, in which the
two kinds of porphyrins are sufficiently separated from each
other, indicated two lifetimes based on the zinc porphyrin (τ )
1.9 ns, λem ) 600 nm) and free-base porphyrins (τ ) 8.2 ns,
λem ) 650 nm) (entry 7). On the other hand, 1b, in which the
two porphyrins are near each other, showed one lifetime derived
from the free-base porphyrin (τ ) 8.2 ns, λem ) 650 nm) and
(8) (a) Maes, W.; Vanderhaeghen, J.; Smeets, S.; Asokan, C. V.; Van
Renterghem, L. M.; Du Prez, F. E.; Smet, M.; Dehaen, W. J. Org. Chem. 2006,
71, 2987–2994. (b) Holten, D.; Bocian, D. F.; Lindsey, J. S. Acc. Chem. Res.
2002, 35, 57–69. (c) Hori, T.; Aratani, N.; Takagi, A.; Matsumoto, T.; Kawai,
T.; Yoon, M.-C.; Yoon, Z. S.; Cho, S.; Kim, D.; Osuka, A. Chem. Eur. J. 2006,
12, 1319–1327.
J. Org. Chem. Vol. 73, No. 11, 2008 4281

TABLE 2. Fluorescence Lifetimes of Some Typical Compoundsa
energy transfer (naphthalene f zinc porphyrin f free-base
porphyrin) occurred. We are currently developing a more
complicated energy transfer system as well as an electron
transfer system using a combination of oligonaphthalene,
porphyrin and fullerene C60.
τ (ns)
entry
compd
(λem ) 600 nm)b
(λem ) 650 nm)b
1
2
3
4
5
6
7
8
5
6
8.8
2.0
9.3
8.2
1.9
8.9
8.2
1.7
1.9
1a
1b
1c
4a
4b
4c
ndc
1.9
Experimental Section
General Procedure for the Synthesis of Compounds 1f-4f
and 1c-4c. The preparation of 2f and 2c is typical. To a solution
of (S)-2e (20 mg, 0.047 mmol) in CH2Cl2 (1.0 mL) were added
TPP(Zn)CO2H (6) (34 mg, 0.047 mmol), WSC ·HCl (27 mg, 0.14
mmol), and DMAP (34 mg, 0.28 mmol) under argon atmosphere
and the solution was stirred at room temperature for 24 h. The
reaction mixture was quenched with water, extracted with CHCl3,
washed successively with water and brine, dried over Na2SO4, and
evaporated to give a residue that was purified by recycling
preparative HPLC (Japan Analytical Industry Co., Ltd. LC-908)
with connected JAIGEL-1H (20 × 600 mm) and JAIGEL-2H (20
× 600 mm) under the conditions of 3.5 mL/min of flow rate with
CHCl3 detected by UV (254 nm) and RI (refractive index) to afford
(S)-2f (24 mg, 0.021 mmol, 46%) and bis-adduct (S)-2c (17 mg,
0.0093 mmol, 20%).
1.9
1.7
a Conditions: CH2Cl2 containing 1.0 × 10-8 M triethylamine to
remove HCl. b Lifetime was determined by curve-fitting of the decay
profile assuming a single exponential function. c Lifetime could not be
determined since it was shorter than the measurement limit (about 0.2
ns).
(S)-2f: 46% yield; purple solid; mp 175 °C; [R]20 -3382 (c
D
0.054, CHCl3); IR (KBr) 3503, 2955, 1739, 1598, 1339, 1243 cm-1
;
1H NMR (400 MHz, CDCl3) δ 0.51 (t, J ) 7.3 Hz, 3H), 0.67 (t, J
) 7.3 Hz, 3H), 0.8-1.5 (m, 8H), 3.5-3.7 (m, 3H), 3.89 (dt, J )
6.4 Hz, 9.2 Hz, 1H), 6.16 (s, 1H), 7.1-7.5 (m, 6H), 7.7-7.8 (m,
11H), 7.96 (d, J ) 7.8 Hz, 1H), 8.01 (s, 1H), 8.1-8.3 (m, 6H),
8.39 (d, J ) 7.8 Hz, 2H), 8.65 (d, J ) 8.2 Hz, 2H), 8.91 (d, J )
4.6 Hz, 2H), 8.95-9.05 (m, 6H); HRMS (FAB+) calcd for
C73H56N4O5Zn 1132.3542, found 1132.3524.
FIGURE 7. Energy transfer in oligonaphthalenes with zinc and free-
base porphyrins.
(S)-2c: 20% yield; purple solid; mp 281 °C; [R]20 -3990 (c
D
1
0.048, CHCl3); IR (KBr) 2955, 1740, 1598, 1339, 1244 cm-1; H
no fluorescence from the zinc porphyrin (entry 4). These results
indicate that rapid energy transfer (exceeding the detection limit
<0.2 ns) occurs from zinc porphyrin to free-base porphyrin.
The energy transfer in oligonaphthalenes with zinc and free-
base porphyrins is summarized in Figure 7. Thus, when a
discrete naphthalene unit was selectively excited by irradiation
at 320 nm, (i) an effective and fast energy transfer occurs from
an excited naphthalene unit to an adjacent naphthalene unit.
Next, (ii) a through-space energy transfer occurs from the
naphthalene with a zinc and/or free-base porphyrin side chain
to the porphyrin unit. (iii) If the zinc and free-base porphyrins
are close to each other, additional energy transfer occurs from
the zinc porphyrin unit to the free-base porphyrin unit. Finally,
(iv) emission occurs from the corresponding porphyrin unit.
In the present study, we described the energy transfer from
naphthalene rings to the porphyrin part using oligonaphthalene
derivatives. In particular, in oligonaphthalenes 1b-3b which
have zinc porphyrin and free-base porphyrin moieties, cascade
NMR (300 MHz, CDCl3) δ 0.64 (t, J ) 7.3 Hz, 6H), 0.8-1.5 (m,
8H), 3.7-3.9 (m, 2H), 3.9-4.1 (m, 2H), 7.3-7.5 (m, 6H), 7.6-7.8
(m, 18H), 7.98 (d, J ) 8.1 Hz, 2H), 8.05 (s, 2H), 8.1-8.3 (m,
12H), 8.41 (d, J ) 8.1 Hz, 4H), 8.69 (d, J ) 7.8 Hz, 4H), 8.8-9.0
(m, 16H); MS (FAB+) m/z 1835 (M + H)+. Anal. Calcd for
C
118H82N8O6Zn2 ·3CH2Cl2: C, 69.42; H, 4.24; N, 5.35. Found: C,
69.72; H, 4.35; N, 5.24.
Acknowledgment. This study was partly supported by a
Grant-in-Aid for Scientific Research (17659004) from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan.
Supporting Information Available: Full experimental details
and characterization data of all new compounds, and fluores-
cence decay profiles of 1a-c and 4a-c. This material is
available free of charge via the Internet at http://pubs.acs.org.
JO800642U
4282 J. Org. Chem. Vol. 73, No. 11, 2008