M. Durmus¸ et al. / Spectrochimica Acta Part A 70 (2008) 42–49
43
nines but also establishing a typical photochemical model of
energy transfer in chemical conjugates.
(Japan)usingPerseptiveBiosystemMALDI-TOFMassVoyager
DE-SI2 spectrometer with dithranol as matrix. The MALDI-
TOF mass spectra of the rest of the complexes was determined
usingPerseptiveBiosystemsVoyager DE-PROBiospectrometry
Workstation and Processing Delayed Extraction Technology at
the University of Cape Town in South Africa.
From the physics point of view, the concept of fluores-
cence resonance energy transfer (FRET) may help to solve the
energy transfer problem in porphyrin–phthalocyanine conju-
gates. FRET is a photophysical process based on a non-radiative
energy transfer between a fluorescent donor and a suitable
¨
energy acceptor [14]. According to the Forester theory, FRET
2.3. Synthesis
is related to the distance separating the donor–acceptor pair,
and it generally happens when such distance is approximately
equal to or smaller than 5 nm [15]. Moreover, the efficiency of
energy transfer depends upon the amount of overlap between
the wave functions describing the donor–acceptor dipoles, e.g.
the amount of spectral overlap between the emission spectrum
of the donor and the absorption spectrum of the acceptor [16]. In
porphyrin–phthalocyanine compounds, porphyrin may be con-
jugated to phthalocyanine with a distance which can easily be
controlled to be smaller than 5 nm, thus these compounds are
suitable for FRET studies.
In this work, FRET was used as the modality to investigate
the energy transfer from porphyrin moiety to phthalocyanine
part in zinc porphyrin–phthalocyanine heterotrimer and het-
erononamer, synthesized in our laboratory. The efficiency of
energy transfer in these compounds is evaluated in this work.
Here the acceptor was either Zn-phthalocyanine (ZnPc) or H2-
phthalocyanine (H2Pc), and the donor was two or eight zinc
triphenyl porphyrins that conjugated to form ZnPc–(ZnTPP)2,
Zn-(ZnTPP)8, H2Pc–(ZnTPP)2 and H2Pc–(ZnTPP)8, respec-
tively.
2.3.1. 2,3-Di-[5-(4-phenoxy)-10,15,20-triphenyl porphyrin
zinc (II)] phthalocyanine (H2Pc–(ZnTPP)2) (Scheme 1)
Chloro[7,12,14,19-diimino-21,5-nitrilo-5H-
tribenzo[c,h,m]-[1,16,1]triazacyclopentadecinato-(2-)-
N22,N23,N24] boron (SubPc) was synthesized according
to literature methods [20]. SubPc (86 mg, 0.2 mmol) in DMSO
(10 ml) was heated at 60 ◦C for 2 h with stirring under nitrogen.
P(ZnCNOTPP)2 (151 mg, 0.1 mmol) and DBU (two drops)
were added to the solution. The mixture was heated to 120 ◦C
for 24 h with stirring under nitrogen. After cooling to room
temperature, the green reaction mixture was poured into 100 ml
dichloromethane and washed three times with 100 ml water
to remove DMSO. The dichloromethane layer was collected,
evaporated and the solid applied to a silica gel column. A series
of purple bands were eluted by dichloromethane. The desired
compound (green bands) was eluted using dichloromethane
containing 5% methanol. The by-product ZnPc remained on
the top of column. Removal of dichloromethane and methanol
by evaporation afforded 12.7 mg (6%) of a green solid.
The green product H2Pc–(ZnTPP)2 was recrystallized from
dichloromethane with methanol.
2. Experimental
UV–vis [DMSO, λmax/nm (log ε)]: 349 (4.47), 429 (5.82),
560 (4.23), 602 (4.33), 673 (5.01); 1H NMR (400 MHz, CDCl3),
δ 9.38 (s, 2H, phthalocyanine H), δ 8.92 (m, 6H, phthalocyanine
H), 8.16–8.21 (m, 16H, pyrrole H), 7.69–7.76 (m, 16H, phenyl
H), 7.49–7.52 (m, 22H, phenyl H), 6.98 (s, 6H, phthalocyanine
H).
2.1. Materials
phenyl porphyrin [18], 4,5-di-[5-(4-phenoxy)-10,15,20-
triphenyl porphyrin]-1,2-dicarbonitrile [P(CNOTPP)2] [19],
4,5-di[5-(4-phenoxy)-10,15,20-triphenyl
porphyrin]-1,2-
2.3.2. 2,3-Di-[5-(4-phenoxy)-10,15,20-triphenyl porphyrin
zinc (II)] phthalocyanine zinc (II) (ZnPc–(ZnTPP)2)
(Scheme 1)
dicarbonitrile zinc (II) [P(ZnCNOTPP)2] [19] were synthesized
as in literature. 4-Hydroxybenzaldehyde, benzaldehyde,
pyrrole, 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU), sodium
methoxide, potassium carbonate, zinc acetate, lithium and
propan-1-ol, were purchased from Sigma–Aldrich and used
without further purification. Dimethylsulfoxide (DMSO) was
dried over alumina before use. All other solvents were dried by
standard methods prior to use. Silica gel 60 (0.04–0.063 mm)
for chromatography was purchased from Merck.
A mixture of H2Pc–(ZnTPP)2 (190 mg, 0.1 mmol) and anhy-
drous zinc acetate (92 mg, 0.5 mmol) in dimethylformamide
(DMF) (30 ml) was heated at 70 ◦C for 1 h with stirring under
nitrogen. After cooling to room temperature, the green reaction
mixture was poured into 100 ml dichloromethane and washed
three times with 100 ml water to remove excess zinc acetate,
acetic acid and DMF. Column chromatography on silica gel
with dichloromethane containing 5% methanol as eluent gave
one band. Removal of dichloromethane and methanol by
evaporation afforded 178 mg (91%) of a blue-green solid.
The crude product was recrystallized from dichloromethane
with absolute methanol. UV–vis [DMSO, λmax/nm (log ε)]:
2.2. Equipment
UV–vis absorption spectra were recorded on a Varian 500
UV–vis/NIR spectrophotometer. IR spectra (KBr pellets) were
recorded on a Perkin-Elmer Spectrum 200 FTIR spectrometer.
1H NMR spectra were recorded using a Bruker EMX 400 NMR
spectrometer. Fluorescence spectra were recorded with a Varian
Eclipse Spectrofluoremeter. MALDI-TOF mass spectra of the
nonamer ZnPc–(ZnTPP)8 was obtained at Tohoku University
1
350 (4.72), 428 (5.73), 561 (4.32), 607 (4.45), 675 (5.13); H
NMR (400 MHz, DMSO-d6), δ 9.42 (s, 2H, phthalocyanine
H), δ 9.05 (d, 6H, phthalocyanine H), 8.77–8.90 (m, 16H,
pyrrole H), 8.07–8.25 (m, 16H, phenyl H), 7.49–7.75 (m, 22H,
phenyl H), 6.74 (d, 6H, phthalocyanine H). IR(KBr) C–O–C