Synthesis and raman, electrochemical, fluorescence studies of free-base and transition metal porphyrin-nicacid dyads with different substituent groups

Article abstract of DOI:10.1080/15533174.2012.680145

A series of free-base porphyrin-nicacid dyads with different meso-substituents and some transition metal complexes were synthesized and characterized by means of UV-vis, IR, and ¹H NMR spectroscopies, and elemental analysis. The properties of nicacid linked with porphyrin dyads were studied as a new intramolecular electron transfer system. The effects of different metal ions and different substituent groups on the properties of the porphyrin-nicacid dyads have been investigated. The studies on the electrochemical and fluorescence spectra, and Raman spectra, showed that different substituents and metal ions affect the properties of the compounds in different ways. Copyright Taylor & Francis Group, LLC.

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Synthesis and Reactivity in Inorganic, Metal-Organic,
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Synthesis and Raman, Electrochemical, Fluorescence
Studies of Free-Base and Transition Metal Porphyrin-
Nicacid Dyads With Different Substituent Groups
Er-Jun Sun a b , Bin-Bin Wang a b , Xiang-Yu Yang a , Si-Qi Zhang a , Xiu-Li Cheng b & Tong-
Shun Shi b
a Department of Chemistry , Changchun Normal University , Changchun , P. R. China
b College of Chemistry , Jilin University , Changchun , P. R. China
Published online: 28 Dec 2012.
To cite this article: Er-Jun Sun , Bin-Bin Wang , Xiang-Yu Yang , Si-Qi Zhang , Xiu-Li Cheng & Tong-Shun Shi (2013) Synthesis
and Raman, Electrochemical, Fluorescence Studies of Free-Base and Transition Metal Porphyrin-Nicacid Dyads With Different
Substituent Groups, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:2, 157-164, DOI:
10.1080/15533174.2012.680145
To link to this article: http://dx.doi.org/10.1080/15533174.2012.680145
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:157–164, 2013
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.680145
Synthesis and Raman, Electrochemical, Fluorescence
Studies of Free-Base and Transition Metal Porphyrin-Nicacid
Dyads With Different Substituent Groups
Er-Jun Sun,1,2 Bin-Bin Wang,1,2 Xiang-Yu Yang,1 Si-Qi Zhang,1 Xiu-Li Cheng,2
and Tong-Shun Shi2
1Department of Chemistry, Changchun Normal University, Changchun, P. R. China
2College of Chemistry, Jilin University, Changchun, P. R. China
porphyrin-nicacid dyads offers an opportunity to investigate the
combination of porphyrin and nicacid as DNA structural probes
and mediators of DNA cleavage reactions.
A series of free-base porphyrin-nicacid dyads with different
meso-substituents and some transition metal complexes were syn-
thesized and characterized by means of UV–vis, IR, and 1H NMR
spectroscopies, and elemental analysis. The properties of nicacid
linked with porphyrin dyads were studied as a new intramolecular
electron transfer system. The effects of different metal ions and
different substituent groups on the properties of the porphyrin-
nicacid dyads have been investigated. The studies on the electro-
chemical and fluorescence spectra, and Raman spectra, showed
that different substituents and metal ions affect the properties of
the compounds in different ways.
In addition, porphyrin dyads which have electron acceptor
and donor have been the topic subject of research because they
are very useful to understand the process of photosynthesis.[6]
Many porphyrin dyads, for example porphyrin-quinones,[7]
porphyrin-C60,[8] and porphyrin-cyclodextrin,[9] have been re-
ported to mimic electron transfer and energy transfer processes
observed in nature.
Electrochemistry is an important experimental method
to study porphyrin compounds and a great number of ex-
perimental results have been reported over the past four
decades concerning the electrochemistry of metalloporphyrins.
The Resonance Raman (RR) spectroscopy is an excellent
technique to study the molecular and electronic structure of
porphyrins and the wavenumbers of RR bands are affected
by the structural changes induced by the electron transfer. In
this study, we synthesized a series of free-base porphyrin-
nicacid dyads: 5-(4-Nicotinicoxylpropyloxy)phenyl-10,15,20-
triphenylporphyrin (NPPTPP), 5-(4-Nicotinicoxylpropyloxy)
phenyl-10,15,20-tri(4-methoxyphenyl)porphyrin (NPPTMPP),
5-(4-Nicotinicoxylpropyloxy)phenyl-10,15,20-tri(4-chlorophe
nyl) porphyrin (NPPTCPP), and transition metal complexes
of the type M(NPPTPP), where M = Mn(III), Fe(III), Co(II),
Ni(II), Cu(II), and Zn(II) (the structures are shown in Figure 1)
and the fluorescence, Raman spectra, and electrochemical
behavior of these compounds were investigated. All of these
studies may provide useful information for the research of their
bioactivities, which can be used for drug screening.
Keywords cyclic voltammetry, fluorescence, porphyrin-nicacid
dyad, resonance Raman spectra, transition metal complex
INTRODUCTION
The syntheses and application of porphyrins and metallopor-
phyrins, especially the binary, ternary, and multiple porphyrins
linked with bioactive substances, have been studied extensively
because of their distinctive structures and predominant phys-
ical, chemical, and optical properties, which are valuable in
potential applications in biological science, biochemistry, and
medical chemistry. Some porphyrins can accumulate selectively,
induce damage in DNA or tumor tissue,[1,2] and have been used
as a tumor-targeting agent in photodynamic therapy (PDT).[3,4]
Nicotinic acid (nicacid) is one of the most extensively studied
pyridine derivatives and it has a wide-ranging ability to reduce
lipid levels.[5] Based on its well-known plasma lipid-lowering
effect, nicacid and its derivative have been used clinically in the
treatment for hyperlipidemia. The synthesis of a series of novel
EXPERIMENTAL
Received 12 September 2011; accepted 6 January 2012.
The authors thank the Foundation of Jilin Educational Committee
(No. 431, [2009]) and the Natural Science Foundation of Changchun
Normal University for financial support of this work.
Address correspondence to Er-Jun Sun, Department of Chemistry,
Changchun Normal University, Changchun 130032, P. R. China+86
431 86168099. E-mail: unerjun1974@hotmail.com
Materials and Physical Measurements
All reagents and solvents were of the commercial reagent
grade and were used without further purification except dimethyl
formamide (DMF), which was predried over activated 4 Å
molecular sieve and vacuum distilled from calcium hydride
157

158
E.-J. SUN ET AL.
according to the literature[12] with sodium nicotinic (40 mg,
0.276 mmol) in DMF (25 mL) solution. The reaction mixture
was heated to 75◦C with stirring and the extent of the reaction
was monitored by TLC. When the reaction was completed, the
mixture was cooled to room temperature. The crude product
was precipitated from the reaction mixture by adding 60 mL
of a saturated NaCl solution. The residue was then washed
using equal volumes of distilled water and methanol and
purified on a neural alumina column with CHCl3 as eluant. The
second red band was collected and condensed. The precipitated
product was crystallized from chloroform and methanol and
was obtained as purple crystal.
Synthesis of NPPTPPZn
The complex NPPTPPZn was prepared according to the stan-
dard method.[13] NPPTPP (80 mg, 0.101 mmol) and ZnCl2
(200 mg, 1.47 mmol) was stirred in 20 mL DMF under the
protection of nitrogen stream. The mixture was refluxed and the
extent of the reaction was monitored by measuring the UV–vis
spectrum of the reaction solution. When the reaction was com-
pleted, the mixture was cooled to room temperature. The crude
product was precipitated from the reaction mixture by adding
60 mL of a saturated NaCl solution. The residue was then
washed using equal volumes of distilled water and methanol
and the product was purified on a neutral alumina column using
CHCl3 as eluant.
FIG. 1. The structures of free-base porphyrin-nicacid dyads and their metal
complexes.
(CaH2) prior to use. The dry CH3CN was obtained by redis-
tillation from CaH2.
Raman spectra were recorded with a Renishaw RM1000
Raman spectrophotometer (Gloucestershire, United Kingdom)
equipped with an integral microscopy. Radiation of 514.5 nm
was obtained from an Ar+ laser. Redox potentials of the com-
pounds (10–3 mol/dm–3) in dried DMF containing 0.1 mol/dm–3
TBAP as supporting electrolyte were determined at room tem-
perature by cyclic voltammetry with a CHI 660A electrochem-
ical work station (Shanghai CH Instruments Co., China) using
a three-electrode system under deaerated conditions. Platinum
button and platinum wire were used as working and counter
electrodes. The reversibility of the electrochemical processes
was evaluated by standard procedures, and all potentials were
recorded against an Ag/Ag+ reference electrode (0.01 mol/dm–3
AgNO3 in acetonitrile (CH3CN) solution). Fluorescence spectra
were recorded with a SPEX Fluorolog–2T2 spectrofluorometer
(Spex Industries Inc., Edison, NJ, USA, 450–W xenon lamp as
the excitation source). The quantum yields of porphyrins were
estimated from the emission and absorption spectra by a com-
parative method[10] using the following equation:
The preparation methods and results of NPPTMPP,
NPPTCPP, and the other metal complexes of NPPTPP are sim-
ilar to those mentioned above.
RESULTS AND DISCUSSION
Characterization
NPPTPP
Yield: 90.5%. 1H NMR (CDCl3, 500Hz δ / ppm):
–2.76(s, 2H, NH), 2.46–2.50(2H, m, CH2), 4.42–4.45(2H,
t, OCOCH2), 4.74–4.76(2H, t, OCH2), 7.27–7.29(2H, d,
ArO-3,5-H), 7.42–7.44(1H, m, Py-5-H), 7.73–7.78(9H, m,
Ar-3,4,5-H), 8.11–8.22(8H, d, Ar-2,6-H), 8.38–8.60(2H,
d, Py-4,6-H), 8.81–8.87(8H, d, β-H), 9.33(1H, s, Py-2-
H); UV–vis (CHCl3) (λmax / nm (ε × 10–4 L mol–1
cm–1)) 420.0(44.80), 515.0(3.16) 550.0(1.78), 590.0(1.32)
650.0(1.19); IR (KBr, cm–1): 3323(υN–H), 2918, 2848(υCH2),
1720(υC O), 1244(υC–O–C), 966(δN–H); Elemental analysis:
Anal. Calcd. for C53H39N5O3: C 80.18, H 4.95, N 8.82; Found:
C 80.09, H 4.98, N 8.80. FAB-MS m/z 794.5 (M + 1).
ꢀsample = ꢀTPPZn(Fsample/FTPPZn)(ATPPZn/Asample
)
[1]
Where Fsample and FTPPZn are measured fluorescence integral
areas (under the fluorescence spectra) of the sample and the
reference TPPZn, respectively. Asample and ATPPZn are the ab-
sorbance of the sample and the reference. ꢀsample and ꢀTPPZn
(ꢀTPPZn = 0.033)[11] are the quantum yields of the sample and
the reference TPPZn at same excitation wavelength.
NPPTMPP
Yield: 84.0%. 1H NMR (CDCl3, 500Hz δ / ppm): -
2.76(2H, s, NH), 2.47–2.53(2H, m, CH2), 4.10(6H, s, CH3),
4.16(3H, s, CH3), 4.43–4.46(2H, t, CO2CH2), 4.74–4.77(2H, t,
OCH2), 7.28–7.30(8H, d, Ar-3,5-H), 7.44–7.46(1H, m, Py-5-
Preparation of Free-Base and Transition Metal
Porphyrin-Nicacid Dyads
Synthesis of NPPTPP
NPPTPP was prepared by the reaction of the 5-(4-(3- H), 8.12–8.13(8H, d, Ar-2,6-H), 8.39–8.52(2H, d, Py-4,6-H),
brmopropyloxy)phenyl)-10,15,20-tri-(4-phenyl)porphyrin
8.82–8.86(8H, d, β-H), 9.34(1H, s, Py-2-H); UV–vis (CHCl3)
(100 mg, 0.133 mmol) which was synthesized in our laboratory (λmax / nm (ε × 10–4 L mol–1 cm–1)) 425.0(42.80), 520.0(2.53)

PORPHYRIN-NICACID DYADS
159
555.0(1. 86), 595.0(1.12) 650.0(1.32); IR (KBr, cm–1):
NPPTPPNi
Yield: 83.8%. UV–vis (CHCl3) (λmax / nm (ε × 10–4
L
mol–1 cm–1)) 415.0(34.90), 530.0(2.96); IR (KBr, cm–1): 2922,
2852(υCH2), 1724(υC O), 1242(υC–O–C), 1005(πP); Elemental
analysis: Anal. Calcd. for C53H37N5O3Ni: C 74.84, H 4.38, N
8.23; Found: C 74.68, H 4.40, N 8.22.
3323(υN–H), 2922, 2852(υCH2), 1720(υC O), 1242(υC–O–C),
966(δN–H); Elemental analysis: Anal. Calcd. for C56H45N5O6: C
76.09, H 5.13, N 7.92; Found: C 75.78, H 5.16, N 7.89. FAB-MS
m/z 884.5 (M + 1).
NPPTCPP
Yield: 87.0%. 1H NMR (CDCl3, 500Hz δ / ppm):
–2.84(2H, s, NH), 2.47–2.55(2H, m, CH2), 4.44–4.46(2H,
t, CO2CH2), 4.74–4.77(2H, t, OCH2), 7.30–7.31(2H, d,
ArO-3,5-H), 7.44–7.46(1H, d, Py-5-H), 7.74–7.76(6H, d,
Ar-3, 5-H), 8.10–8.14(8H, d, Ar-2,6-H), 8.39–8.55(2H,
d, Py-4,6-H), 8.81–8.90(8H, d, β-H), 9.34(1H, s, Py-2-
H); UV–vis (CHCl3) (λmax / nm (ε × 10–4 L mol–1
cm–1)) 420.0(54.20), 515.0(2.90) 550.0(1.64), 590.0(1.22)
645.0(1.04); IR (KBr, cm–1): 3319(υN–H), 2922, 2852(υCH2),
1724(υC O), 1242(υC–O–C), 966(δN–H); Elemental analysis:
Anal. Calcd. for C53H36Cl3N5O3: C 70.95, H 4.04, N 7.81;
Found: C 70.66, H 4.07, N 7.77. FAB-MS m/z 897.6 (M + 1).
NPPTPPCu
Yield: 87.4%. UV–vis (CHCl3) (λmax / nm (ε × 10–4
L
mol–1 cm–1)) 420.0(47.40), 539.9(3.41); IR (KBr, cm–1): 2924,
2852(υCH2), 1722(υC O), 1242(υC–O–C), 999(πP); Elemental
analysis: Anal. Calcd. for C53H37N5O3Cu: C 74.41, H 4.36, N
8.19; Found: C 74.26, H 4.37, N 8.17.
RR Spectra
Effect of the central metal ion
Figure 2 displays the RR spectra of NPPTPP and its transi-
tion metal complexes excited at 514.5 nm. The observed Raman
frequencies and their assignments are listed in Table 1. The RR
spectra of tetraphenylporphyrin ligands and their metal deriva-
tives have been studied extensively.[14–16] Using these spectra
and the published data of similar compounds, we have made
detailed vibrational assignments. Besides, we have paid more
attention on those bands that are the most obvious and persistent
from compound to compound. The wavenumber positions of vi-
bration bands in the high-frequency region (1300−1600 cm–1)
are sensitive to the core size, axial ligation, and electron den-
sity of the central metal ion. In this region, the bands near 1550,
1460, and 1360 cm–1 of NPPTPP and its complexes are assigned
to ν(Cβ−Cβ) stretch ν2, ν(Cα−Cm) stretch ν3, and ν(Cα−N/
Cα−Cβ) stretch ν4, respectively, by analogy to the previous
works on M(TPP) complexes.[17] These three bands are metal
sensitive. According to the crystal field theory of coordination
NPPTPPZn
Yield: 87.5%. 1H NMR (CDCl3, 500Hz δ / ppm):
2.14–2.16(2H, m, CH2), 4.12–4.14(2H, t, OCOCH2),
4.31–4.34(2H, t, OCH2), 7.12–7.14(1H, d, Py-5-H), 7.28(2H,
s, ArO-3,5-H), 7.71–7.74(9H, m, Ar-3,4,5-H), 8.21–8.22(8H, d,
Ar-2,6-H), 8.89–8.99(8H, m, β-H); UV–vis (CHCl3) (λmax / nm
(ε × 10–4 L mol–1 cm–1)) 425.1(43.85), 555.0(2.04) 595.0(0.72);
IR (KBr, cm–1): 2925, 2858(υCH2), 1730(υC O), 1242(υC–O–C),
997(πP); Elemental analysis: Anal. Calcd. for C53H37N5O3Zn:
C 74.25, H 4.35, N 8.17; Found: C 74.10, H 4.36, N 8.15.
NPPTPPMnCl
Yield: 82.3%. UV–Vis (CHCl3) (λmax / nm (ε × 10–4 L mol–1
cm–1)) 380.1(7.59), 405.3(6.70), 479.9(14.07),585.0(2.86),
620.1(3.16); IR (KBr, cm–1): 2923, 2854(υCH2), 1724(υC O),
1244(υC–O–C), 1010(πP); Elemental analysis: Anal. Calcd. for
C53H37N5O3MnCl: C 72.15, H 4.23, N 7.94; Found: C 72.01,
H 4.24, N 7.92.
NPPTPPFeCl
Yield: 77.5%. UV–vis (CHCl3) (λmax / nm (ε × 10–4 L mol–1
cm–1)) 379.9(7.76), 420.0(14.00), 510.1(2.29), 575.0(1.04),
655.0(0.91); IR (KBr, cm–1): 2922, 2852(υCH2), 1724(υC O),
1242(υC–O–C), 999(πP); Elemental analysis: Anal. Calcd. for
C53H37N5O3FeCl: C 72.08, H 4.22, N 7.93; Found: C 71.93, H
4.24, N 7.91.
NPPTPPCo
Yield: 84.5%. UV–vis (CHCl3) (λmax / nm (ε × 10–4
L
mol–1 cm–1)) 409.9(26.00), 530.0(2.23); IR (KBr, cm–1): 2922,
2852(υCH2), 1724(υC O), 1244(υC–O–C), 1001(πP); Elemental
analysis: Anal. Calcd. for C53H37N5O3Co: C 74.82, H 4.38, N
8.23; Found: C 74.66, H 4.40, N 8.21.
FIG. 2. The Raman spectra of NPPTPP and its metal complexes in
200–1800 cm–1 region with excitation wavelength at 514.5 nm.

160
E.-J. SUN ET AL.
TABLE 1
Raman spectra data and assignment of NPPTMPP, NPPTCPP, NPPTPP, and its six metal complexes
Assigned∗
Mn
Zn
Cu
Ni
Co
Fe
NPPTPP NPPTCPP NPPTMPP
Phenyl/Py
ν2, ν(CβCβ)
1579vs 1598w 1594w 1593w 1595w 1589w 1590w
1566s 1547m 1556vs 1566vs 1562vs 1551vs 1551vs
1496s 1492w 1500s 1508m 1500vs 1496m 1496m
1458w 1443m 1456w 1472m 1462m 1454m 1456m
1372m 1350vs 1361vs 1373vs 1363vs 1360m 1363w
1267m 1269w 1304 1342m 1338m 1335m 1329w
1232m 1230w 1232m 1228m 1228w 1232w 1240m
1136w
1599w
1550vs
1494m
1457m
1360w
1327w
1240m
1132w
1572w
1548vs
1493m
1454m
1361w
1329m
1240m
1134w
ν11, ν(CβCβ) /ν(CαCm)
ν3, ν(CαCm)
ν4, ν(Cα-N) /ν(CαCβ)
ν20, ν(pyrrole quarter-ring)
ν1, ν(Cm-Ph)
N-H bend + ν(Cα-N)asym
ν34, νasym(Cα-H) +νasym (Cα-Cβ) 1188w 1176m 1182w 1188m 1188w 1184w
ν17, δ(Cβ-H)
ꢀ7, Phenyl
1084w 1066m 1078w 1082w 1079w 1080w 1082w
1025w 1021w 1025w 1031w 1022w 1016w 1038w
1007m 998m 1003m 1003s 1003m 1003w 1001w
962w
1078w
1039w
999w
962w
885w
328w
1080w
1040w
1001w
962w
886w
324w
ν15, ν(pyrrole breath) + Phenyl
ν6, ν(pyrrole breath)
Phenyl/Py
ν8, ν(pyrrole translation)
ν(M-N)
872w
875w
887w
887w
887w
887w
885w
337w
393w
328w
422w
390m
391s
387m
390m
368w
ν(M-Cl)
avs = very strong; s = strong; m = medium; w = weak.
chemistry, the electron structure of the metal ions are: Co2+
,
fects of the meso-substituents. But the substituent groups have
some effects on the vibration of phenyl group. For example,
the 1590 cm–1 band of NPPTPP is assigned to vibration of
phenyl/Py, which upshifts to 1599 cm–1 of NPPTCPP and down-
shifts to 1572 cm–1 of NPPTMPP.
Ni2+—-dx02−y2 , Cu2+—-dx12−y2 , Zn2+—-dx22−y2 . When the dx −y
2
2
orbit is filled with electrons, the distance of metal−nitrogen
is increased and the porphyrin core expanded. As we know,
the diameter of Co2+ is bigger than Ni2+, so the core expan-
sion of NPPTPPCo is larger than NPPTPPNi. With increasing
metal–nitrogen distance or core size on going through Ni, Co,
Cu, Zn complexes results in significantly downshifted frequen-
cies as shown in Figure 3. The result is same with tetraarylmet-
alloporphyrins[18] and octaethylporphyrins.[19]
Electrochemistry
Effect of the central metal ion
The cyclic voltammograms of the metal complexes of
NPPTPP in DMF containing 0.1 mol/dm–3 TBAP as support-
ing electrolyte are shown in Figure 4 and a summary of the
half-wave potentials is listed in Table 2.
Effects of the substituent groups
All cycle voltammograms of NPPTPPNi, NPPTPPCu, and
NPPTPPZn are similar in shape. Each compound undergoes one
From Table 1 we can see that the ν2, ν3, and ν4 frequencies of
NPPTPP, NPPTCPP, and NPPTMPP are almost identical, and
they appeared to be relatively insensitive to the electronic ef-
TABLE 2
Half-wave electrochemical redox data (vs. Ag/Ag+) of metal
complexes in DMF
Compound
O1
(III)/(II) (II)/(I)
R1
R2
NPPTPPMnCl 0.631 –0.636
NPPTPPFeCl 0.832 –0.567
–1.722 –2.297
–1.380
NPPTPPCo
NPPTPPNi
NPPTPPCu
NPPTPPZn
0.711 –0.325 –1.223
0.586
0.590
0.430
–1.577 –2.152
–1.583 –2.096
–1.738 –2.138
Scan rate = 0.1 V/s. O1 is the half-wave potential of the first
oxidation; R1, R2 are the half wave potentials of the first and second
reduction, respectively.
FIG. 3. Positions of bands sensitive to metal complexes.

PORPHYRIN-NICACID DYADS
161
FIG. 4. The cyclic voltammograms of the metal complexes of NPPTPP in DMF containing 0.1 mol/dm–3 TBAP as supporting electrolyte. Scan rate 100 mV/s.
one-electron oxidation and two one-electron reductions with the respectively, are not completely reversible and gives rise to a
potential range of the solvent. The first reduction potentials of new reoxidation peak at Epa = –0.714, –0.726, –0.848 V. These
NPPTPPNi, NPPTPPCu and NPPTPPZn are at –1.582, –1.583, irreversible processes are probably due to the formation of iso-
and –1.738 V, respectively, and they are quasireversible. But for porphyrin. Only one oxidation is seen from Figure 4, at E1/2
the second reduction, at E1/2 = –2.149, –2.081, and –2.133 V, = 0.587, 0.590, and 0.433 V for NPPTPPNi, NPPTPPCu, and

162
E.-J. SUN ET AL.
NPPTPPZn, respectively, andtheyarenot completelyreversible.
From Table 2, we can see that the first reduction of NPPTPPZn
is more difficult than NPPTPPNi and NPPTPPCu. On the con-
trary, the oxidation of NPPTPPZn is easier than NPPTPPNi
and NPPTPPCu. This shows that the redox of porphyrin ring
is correlated to the electron density of the conjugated system.
Increasing the electron density of the porphyrin ring makes the
reduction potentials negative shift.
Three reductions of NPPTPPMnCl are observed. The first,
at E1/2 = –0.636 V is not reversible (|Epa − Epc| = 395 mV),
which corresponds to the reaction Mn (III)/Mn (II). The second
occurs at –1.722 V and can be assigned to the formation of the
anion radical. The third, at Epc = –2.411 V, is coupled with an
oxidation peak at Epa = –2.182 V, and the ratio of ipa/ipc is much
lower than 1.0, suggesting an EC mechanism.
The cyclic voltammogram of NPPTPPFeCl is shown in Fig-
ure 4. The reduction of E1/2 = –1.380 V corresponds to the for-
mation of the anion radical and the oxidation of E1/2 = 0.832 V
corresponds to the formation of the cation radical. Figure 4 also
shows cyclic voltammogram obtained for the Fe(III)/Fe(II) cou-
ple of NPPTPPFeCl. On the negative potential sweep, one broad
FIG. 5. The cyclic voltammograms of free-base porphyrin-nicacid dyads with
different substituent groups.
Gouterman.[21] The differences between the first and second
ring reduction are 0.322, 0.347, and 0.316 V for NPPTMPP,
NPPTPP, and NPPTCPP, respectively, and the values are very
close to that of the TPP (0.35 V).[22]
Compared to NPPTPP, the redox potentials of NPPTMPP
shifted to the negative direction while the NPPTCPP shifted
positively. This can be explained by the effect of substituents.
The attachment of an electron-donating group (–OCH3) at para
position on phenyl ring will increase the electron density of
porphyrin ring, which makes it easier to oxidized and harder
to reduced. On the contrary, the electron-withdraw group (–Cl)
will decrease the electron density of porphyrin ring, so it is
easier to reduced and harder to oxidize.
anodic process (Epc = –0.650 V) and two cathodic peaks (Epa
=
–0.137, –0.485 V) are observed. The existence of NPPTPPFeCl
in DMF containing TBAP as supporting electrolyte is very com-
plicated because Cl–, ClO4 , and DMF may coordinate to Fe
–
atom.
In the solvent DMF, NPPTPPCo exhibits a somewhat un-
usual wave for the Co(III)/Co(II) reduction. Although the waves
corresponding to Co(III)/Co(II) redox process are well defined,
those due to Co(III)/Co(II) are not. As we can see from the
figure, the cathodic wave and anodic wave are ill defined, the
height of the wave is small and the separation of the cathodic
and anodic wave is broad. This phenomenon might be caused by
the axis coordination of the metallporphyrin.[20] The complex of
NPPTPPCo may coordinate with electrolyte anion or DMF to
form an ion pair. The removal of ClO4– or DMF during reduc-
tion should result in a lower rate constant, because the activation
energy needed to separate coordination anion from cobalt atom
increased.
Fluorescence Spectra
Effect of the central metal ion
Figure 6 shows the emission spectra of NPPTPP and its
complexes in CHCl3 and the excitation wavelength is 420 nm.
From Figure 6, we can see that the fluorescence intensities of
the ligand and the complex NPPTPPZn are much higher than
Effects of the substituent groups
TABLE 3
The cyclic voltammetry spectra of free-base porphyrins with
different substituent groups are shown in Figure 5 and a sum-
mary of the half-wave potentials is listed in Table 3. We can
see that NPPTPP undergoes two quasi-reversible oxidation and
two quasi-reversible reductions for a scan rate of 0.1 V/S and
the compounds of NPPTCPP and NPPTMPP undergo one ir-
reversible oxidation, one quasireversible oxidation, and two
quasireversible reductions in the range of the solvent. The dif-
ferences in E1/2’s between the first ring oxidation yielding π
cation radicals and the first ring reduction yielding π anion rad-
icals are 2.164, 2.237, and 2.251 V for NPPTMPP, NPPTPP,
and NPPTCPP, respectively, which are in good agreement with
E1/2ox(1) − E1/2red(1) = 2.25 0.15 V obtained by Zerner and
Half-wave electrochemical redox data of free-base
porphyrin-nicacid dyads with different substituents (vs.
Ag/Ag+) in CH2Cl2
Compound
O2
O1
R1
R2
O1-R1 R1-R2
NPPTMPP 0.806 0.638 −1.526 −1.858 2.164 0.322
(0.857a)
NPPTPP
1.030a 0.778 −1.509 −1.856 2.237 0.347
NPPTCPP 0.987a 0.799 −1.452 −1.876 2.251 0.316
aValue given is Epa; O1 and O2 are the half wave potentials of the
first and second oxidation, respectively; R1 and R2 are the half wave
potentials of the first and second reduction, respectively.

PORPHYRIN-NICACID DYADS
163
TABLE 4
Emission spectral data of free-base porphyrin-nicacid dyads
with different substituents
Compounds
Qx(0,0)
Qx(1,0)
ꢀf
NPPTMPP
NPPTPP
NPPTCPP
654
650
649
714
710
712
0.164
0.142
0.074
fluorescent bands of NPPTPP, the Q (0, 0) peaks of NPPTMPP
and NPPTCPP have shifted to the red region by 4 nm and to the
blue region by 1 nm respectively. As we can see from Figure 7
and Table 4, when attached an electron-donating group (–OCH3)
on porphyrin ring, the fluorescence intensity and the quantum
yield decreased while the attachment of an electron-withdraw
group (–Cl) increase the fluorescence intensity and the quantum
yield. This is because the electron-donating group strength the
conjugate ability of the porphyrin π system while the electron-
withdraw group’s effect is contrary. We also noticed that the
quantum yield of NPPTCPP has changed a lot compared with
NPPTPP whereas that of the NPPTMPP has changed a little,
which indicates that the effect of electron-withdrawing group
ring is more obvious than electron-donating group.
FIG. 6. The fluorescence spectra of NPPTPP and its metal complexes.
other transition metal complexes. The result is same with the
reference[23] and confirmed that the transition metal on the center
of porphyrin ring quenches the fluorescence of porphyrin.
Effects of the substituent groups
Figure 7 shows the emission spectra of free-base porphyrins
with different subsituents in CHCl3 and the emission spectral
data are given in Table 4. There are fluorescence of the S2 (Soret
band) and the S1 (Q band) in porphyrin ligands. The fluorescence
of S2→S0 is too weak to be observed in this work. Fluorescence
spectra of NPPTPP, NPPTMPP and NPPTCPP are similar in
shape and consist of two bands, Q (0, 0) and Q (0, 1). The Q
(0, 0) fluorescent bands are at 650, 654, and 649 nm and Q (0,
1) fluorescent bands are at 710, 714, and 712 nm for NPPTPP,
NPPTMPP, and NPPTCPP, respectively. Compared with the
CONCLUSION
Here we studied the cyclic voltammetry, fluorescence spec-
tra, and RR spectra of the nicacid linked porphyrin dyads and
their metal complexes. The RR bands of the compounds are
assigned and the study showed that with increasing core size on
going through Ni, Co, Cu, Zn complexes results in significantly
downshifted frequencies. The cyclic voltammetry of Mn, Fe,
and Co complexes are different from the porphyrin ligand and
other metal complexes, which show not only the redox of por-
phyrin ring, but also the redox of metal ion. The attachment of
an electron-donating group or an electron-withdraw group has
different effect on the redox potentials and fluorescence spectra.
The fluorescence intensity of NPPTPPZn is much higher than
other transition metal complexes.
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