Journal of Alloys and Compounds 380 (2004) 396–404
Spectroscopic properties of porphyrins and effect of
lanthanide ions on their luminescence efficiency
R. Wiglusz a , J. Legendziewicz a,∗ , A. Graczyk b , S. Radzki c ,
P. Gawryszewska a , J. Sokolnicki a
a
Faculty of Chemistry, University of Wrocław, 50-383 Wrocław, Poland
Institute of Optoelectronics, Military Technical University, Warsaw, Poland
Faculty of Chemistry, M. Curie-Skłodowska University of Lublin, 20-031 Lublin, Poland
b
c
Abstract
Spectroscopic properties of H2 TPP porphyrin and Tb(III)TPP(acac) in solid and methanolic solutions have been compared. Emission from
the S1 singlet state of Tb(III)TPP(acac) have been recorded at 296 and 77 K. Spectroscopic investigations of new types of porphyrins soluble
in organic solvents (e.g. methanol), PP(AA)2 , and porphyrins soluble in water, PP(AA)2 (Arg)2 (where AA, alanine or serine; Arg, arginine),
are presented. Interaction of PP(AA)2 with lanthanide ions (Yb(III), Eu(III)) has been studied. It has been found that the lanthanide (III) ions
decrease efficiency of the porphyrin emission. For the alanine derivative, the stronger losses are caused by the Eu(III) ions as compared to the
Yb(III) ions. On the other hand, the emission quenching by both lanthanide ions is similar in the case of the serine derivative. Influence of the
Pr(III) and Eu(III) ions on the PP(AA)2 (Arg)2 emission has also been investigated. An unexpected increase of the porphyrin emission intensity
has been observed in solution for the lowest concentration of Pr(III) added, whereas the Eu(III) ions quench the emission in the full range
of its concentration. The observed phenomena are analyzed, and the mechanisms of the excited-state dynamics in which the f-excited states
take part in the porphyrin emission quenching are considered. It has been found that the lanthanide ions influence the absorption spectrum as
well as the relative intensities of the respective bands in the emission spectra. The luminescence intensities of these porphyrins as a function
of pH, the concentration and the type of the porphyrine substituent have been analyzed. Significant influence of the above factors on the
emission properties of the porphyrins has been found and discussed. Efficiency of the emission has been determined for these M-porphyrin
systems in comparison to the free porphyrins in methanol solutions. The observed effects can be explained by formation of polymeric chains
and decrease of face-to-face agglomeration that leads to effective quenching.
© 2004 Published by Elsevier B.V.
Keywords: Photophysics of the Ln(III):porphyrin systems; New types of porphyrins; Water-soluble porphyrins; UV–Vis spectroscopy; Lanthanide(III) ions
1. Introduction
Porphyrins attract large attention because of their role in
the human body, ability to accumulate in many kinds of cancer cells, as well as magnetic and optical properties. These
features make them useful in cancer medicine and photodynamic therapy [1–3]. The porphyrins are molecules, whose
physicochemical properties can be easily adjusted by modifications of the electronic distribution on the aromatic ring
through peripheral substitutions that plays an important role
in many biological systems and in photochemistry [4–6].
For example, the existence of such complexes is crucial for
∗ Corresponding author. Tel.: +48-71-3204-300;
fax: +48-71-3282-348.
E-mail address: [email protected] (J. Legendziewicz).
0925-8388/$ – see front matter © 2004 Published by Elsevier B.V.
doi:10.1016/j.jallcom.2004.03.065
transport of oxygen (hemoglobin), solar energy transfer
(chlorophyll), and electron transfer (cytochrome oxidase)
[7,8].
Many porphyrins are known to dimerize and further
agglomerate in aqueous solutions. A series of water-soluble
porphyrins can be derived from porphyrin precursors insoluble in water by introducing ionic groups such as –COO− ,
–SO3 − , =N–CH3 + , or –N(CH3 )3 + . These so-called peripheral charge groups change chemical, spectral, and redox
properties of the compounds and their metal complexes
[9–11].
A new generation of two types of porphyrins [(PP(AA)2
and PP(AA)2 (Arg)2 ] substituted at the porphyrin ring by
different amino acids (Ala, Ser) were synthesized [12], and
their selected spectral data in water and methanol solutions
have been recently reported. The quantum yields of the
R. Wiglusz et al. / Journal of Alloys and Compounds 380 (2004) 396–404
emission and the singlet oxygen for the above-mentioned
porphyrins in methanol solutions have been studied [13,14].
The spectroscopic investigations of the second type of porphyrin H2 TPP and metalloporphyrin TbTPP(acac) have been
the object of our previous investigations [15,16]. The aim
of the present work is to focus on the photophysics of the
water-soluble porphyrins and the lanthanide ions influence
on their emission efficiency.
397
N
NH
N
HN
2. Experimental
(a)
The complex TbTPP(acac) was obtained according to the
method described in [17]. The porphyrin H2 TPP was purchased from Aldrich (Fig. 1a). Di-amino acid derivatives of
porphyrins, PP(Ser)2 (Arg)2 , PP(Ala)2 (Arg)2 , PP(Ser)2 , and
PP(Ala)2 (Fig. 1b and c), were obtained according to the
patented methods [18,19]. Ala, Arg, and Ser denote alanine,
serine, and arginine amino acids. Absorption spectra were
measured at 293 K with a Cary-Varian 500 Scan spectrophotometer in the spectral range 250–700 nm. Excitation and
emission spectra were obtained at 293 and 77 K using an
SLM Aminco SPF 500 spectrofluorometer equipped with a
300 W xenon arc lamp and an Acton Research Corporation
Spectra-Pro 750 monochromator equipped with a Hamamatsu R928 photomultiplier tube as a detector (resolution
0.01 nm) and a 450 W xenon arc lamp.
O
R =
CH3
OH
HO
NH
R
Ser
R
CH3
NH
or
N
O
H3C
R =
N
OH
HN
NH
CH3
H3C
Ala
CH2
CH2
O
H
O
H
(b)
O
R =
3. Results and discussion
Electronic absorption and emission spectra of porphyrins
are sensitive to processes such as metallation, protonation
(pH), substitution, or dimerization, which make porphyrins
useful sensors of their environmental surroundings. Fig. 2
shows absorption spectra of free porphyrins (H2 TPP) and
TbTPP(acac) in Nujol. The spectra differ in respect of the
positions and the intensity ratios of the four Q band components (Qy(1,0) , Qy(0,0) , Qx(1,0) , Qx(0,0) [20]), as well as
the molar absorption coefficients. The Soret band of the free
porphyrin consists of two components (395.2 and 415.6 nm)
and TbTPP(acac) exhibit only one (414.6 nm) but the shift
between main components is not significant. These changes
arise from metalation and substitution of porphyrin that
cause different symmetry of both compounds. In our earlier
paper [15], we proved D4h (4mmmm) symmetry and D2h
(mmm) symmetry for H2 TPP.
Agglomeration, typical phenomenon for solid-state porphyrins, is well manifested in the spectrum of TbTPP(acac)
by significant broadening of the Soret band (see Fig. 2).
It is well known that solid porphyrins and their derivatives do not exhibit emission because of the concentration
quenching. Dissolved ones yield bright emission occurring
in the red region of the spectrum. For this reason, further investigations have been carried out in methanolic or aqueous
solutions.
CH3
OH
HO
NH
R
Ser
R
CH3
NH
or
N
O
R =
N
H3C
OH
HN
NH
CH3
H3C
Ala
O
O
CH2
CH2
CH2
CH2
COO H
C NH3 +
COO + H3N
H
C
CH2
CH2
CH2
CH2
CH2
CH2
NH
O
NH
NH2
NH
O
H2N
NH
(c)
Fig. 1. Structural formulas of (a) H2 TPP, (b) PP(AA)2 and (c)
PP(AA)2 (Arg)2 ; AA, Ser and Ala.
In Fig. 3, we plot excitation spectrum of TbTPP(acac)
dissolved in methanol. Comparing to the absorption spectrum of the solid complex, one can observe appearance of
the additional component on the blue shoulder of the Soret
band and some differences in the intensity distribution of
398
R. Wiglusz et al. / Journal of Alloys and Compounds 380 (2004) 396–404
2.0
Soret band
414,6
B(0,0)
(II)
1.5
Absorbance
(I)
250
Q band
1.0
300
350
400
Qy(1,0)
450
500
Qy(0,0) Qx(1,0)
508,2 538,6 566,4
415,6
Q(1,0)
478,6
550
550,9
508,2
600,8
600
650
700
Qx(0,0)
660
Q(0,0)
(II)
589,6
0.5
(I)
395,2
500
550
600
650
700
(II)
(I)
0.0
350
400
450
500
550
600
650
700
Wavelength [nm]
Fig. 2. Absorption spectra of TbTPP(acac) (I) and H2 TPP (II) in nujol.
the Q band components. These changes are due to the
agglomeration in the solid state as it has been mentioned
above. On the other hand, the effect of surface quenching is
also observed in the Soret band as the minimum at 425 nm.
The solid complex has a maximum at this energy in the absorption spectrum. The excitation spectrum correlates quite
good with the absorption spectrum of the Tb(III) complex
in methanol [15] in the area of the Q band. The changes
in the distribution of the Q band components, mainly Q(1,
0) suggest competition between the quenching and the
internal conversion processes in populating of the emitting
level. Partial dissociation and racemization processes of the
porphyrin can also play certain role [21,23]. At this stage
of the investigations, it is difficult to evaluate the net effect
of the respective processes. Such studies will be the subject
of our forthcoming paper.
Fig. 4 presents room temperature emission spectra for
methanolic solutions of TbTPP(acac) (I) and H2TPP (II) at a
concentration of about 10−5 M. Both spectra display typical
porphyrin emission and are very similar, with the exception
10
Soret band
411
em
= 650 nm
Intensity (arb. units)
8
B(0,0)
6
4
Q band
393
Q (1,0)
Q (0,0)
2
514
551
430
597
0
350
400
450
500
550
Wavelength [nm]
Fig. 3. Excitation spectrum of TbTPP(acac) in CH3 OH, c = 10−5 M.
600
R. Wiglusz et al. / Journal of Alloys and Compounds 380 (2004) 396–404
λexc = 400 nm
651,5
(I)
(II)
650,8
399
λexc = 400 nm
Q(0,0)
Intensity (arb. units)
Q(0,0)
Q(0,1)
Q(0,1)
713,8
713,5
605
600
650
700
750
600
Wavelength [nm]
650
700
750
Wavelength [nm]
Fig. 4. Emission spectra of TbTPP(acac) (I) and H2 TPP (II) in CH3 OH at 293 K, c = 10−5 M.
of the extra band at 605 nm for (I). At 77 K (Fig. 5), the compounds still exhibit emission from the S1 singlet state of the
porphyrin, independently of the excitation wavelength. This
implies that at 77 K, the rate of the S2 → S1 internal conversion can be reached, involving the 5 D4 level of the Tb(III)
ion as it can be seen from energy-level diagram. Also, dissociation can be efficient enough to give efficient emission
of the free porphyrin. Moreover, we do not consider the role
of the ␤-diketonate singlet and triplet states in the photoluminescence of the Tb(III) complex because of the large
distance between them and the porphyrine ring. Presumably,
(I)
the Tb(III) states mediate in the energy transfer process, but
in this case, the mechanism becomes much more complex.
In our investigations, we have also focused on determination of how the addition of the Eu(III) and Tb(III) ions to the
methanolic solutions containing porphyrins having peripheral substituents (PP(Ala)2 and PP(Ser)2 ) influences their
emission efficiency.
In Fig. 6, we show the S1 emission spectra of both compounds in methanol, before and after addition of the lanthanide ions. One can note a distinct difference between the
free porphyrin emission (Fig. 4 (I)) and the substituted one
1 λexc = 413.5 nm
644,95
(II)
2 λexc = 383 nm
1 λexc = 400 nm
646,5
2 λexc = 383 nm
8
Q(0,0)
Q(0,0)
Intensity (arb. units)
1
1
6
Q(0,1)
2
Q(0,1)
4
711
713,2
2
2
0
550
600
650
Wavelength [nm]
700
750
550
600
650
700
Wavelength [nm]
Fig. 5. Emission spectra of TbTPP(acac) (I) and H2 TPP (II) in CH3 OH at 77 K, c = 10−5 M.
750
400
R. Wiglusz et al. / Journal of Alloys and Compounds 380 (2004) 396–404
1 PP(Ala) c = 6.1*10 M
1 PP(Ala) c = 6.1*10
Q(0,0)
2 PP(Ser) c = 5.64*10 M
3 PP(Ala) : Yb (1:1) c = 6.1*10 M
Intensity (arb. units)
Q(0,0)
625
4 PP(Ala) : Eu (1:1) c = 6.1*10 M
2 PP(Ala) : Yb (1:1) c = 6.1*10 M
1 3 PP(Ala) : Eu (1:1) c = 6.1*10 M
2, 3
5 PP(Ser) : Yb (1:1) c = 5.64*10 M
4 PP(Ala) : Yb (1:1) c = 6.1*10 M after 12h
5 PP(Ala) : Eu (1:1) c = 6.1*10 M after 12h
6 PP(Ser) : Eu (1:1) c = 5.64*10 M
λexc = 400 nm
λexc = 400 nm
1
624,4
Q(0,1)
Q(0,1)
3
689,5
4
579,4
4
2
5, 6
5
646,6
550
600
650
700
750
550
600
Wavelength [nm]
650
700
750
Wavelength [nm]
Fig. 6. Emission spectra of the (a) PP(Ser)2 :Ln(III) and PP(Ala)2 :Ln(III) after 12 h in methanol; (b) emission spectra of the PP(Ala)2 :Ln(III).
with regard to a number of the components, their spectral
positions, and also their relative intensities. Moreover, the
emission intensity of the porphyrin substituted by Ala is
much higher than that for the Ser substituent. The spectra
are dominated by the Q(0,0) band, which is blue-shifted by
about 25 nm compared to the spectrum of the unsubstituted
porphyrin. Appearance of the additional band centered at
580 nm should also be noted. It is not surprising because it is
known that intensity and spectral position of the Q(0,0) band
are very sensitive to peripheral substituents. Such changes in
5
(a)
1 PP2ml
2 PP2ml +0.2mlPrCl3
578,8
578,8
3 PP2ml +0.4mlEuCl3
1
6
4 PP2ml +0.6mlPrCl3
4
1 PP2ml
2 PP2ml +0.2mlEuCl3
(b)
3 PP2ml +0.4mlPrCl3
2
Intensity (arb. units)
the area of the Q(0,0) band in different solvents for different
porphyrins have been reported by Makarska et al. [22]. The
observed effect can result from changes of the charge distribution in the porphyrine ring as well as from the degree
of the agglomeration and its mechanism.
Addition of the Eu(III) or Yb(III) ions decreases the emission intensity of the porphyrine compounds. Emission of the
serine compound is decreased by both ions to similar degree and this process is time independent. In case of the alanine compound, the emission quenching appeared to be time
4 PP2ml +0.6mlEuCl3
5 PP2ml +0.8mlPrCl3
5 PP2ml +0.8mlEuCl3
6 PP2ml +1.0mlPrCl3
6 PP2ml +1.0mlEuCl3
7 PP2ml +1.2mlPrCl3
7 PP2ml +1.2mlEuCl3
1
3
4
Q(0,0)
Q(0,0)
2
2
3
623,4
623,4
Q(0,1)
2
4
1
Q(0,1)
3
5
4
678
678
6, 7
5, 6, 7
0
0
550
600
650
Wavelength [nm]
700
750
550
600
650
700
750
Wavelength [nm]
Fig. 7. Influence of the (a) Pr(III) and (b) Eu(III) ions concentration in the aqueous solution on emission intensity of PP(Ser)2 (Arg)2 .
R. Wiglusz et al. / Journal of Alloys and Compounds 380 (2004) 396–404
-3
(a)
623,5
2
Q(0,0)
1 c = 10 M pH = 3.62
-4
2 c = 10 M pH = 4.37
-5
3 c = 10 M pH = 7.71
-6
4 c = 10 M pH = 8.49
30000
porphyrin
Eu(III)
D4
S2
25000
-1
P1
P0
20000
S1
15000
5
3
5
D1
5
D0
1
D2
B (Soret)
band
S1 emission
Q band
10000
5000
3
S0
0
7
H4
F0
F6
the porphyrins (see Scheme 1), and for this reason, their
role in mediation of the S2 → S1 internal conversion should
be considered. First of all, the role of the mediating metal
ion excited states could be different for different ions. Furthermore, the f–d transition energy level of the Pr(III) ion,
which is located above the S2 singlet state of the porphyrin
can feed energy to the porphyrin more efficiently at lower
concentrations of the metal ions. At the higher Pr(III) ion
concentrations, we have to consider the dimerization and
agglomeration processes causing quenching of the emission
by possible energy migration through the porphyrin rings.
-3
(b)
408,3
Soret band
2
B(0,0)
1 c = 10 M pH = 3.62
-4
2 c = 10 M pH = 4.37
-5
3 c = 10 M pH = 7.71
-6
4 c = 10 M pH = 8.49
λem = 622 nm
Q band
508,2
544,5 568,8
405,3
3
3
621,7
4
4
1
1
700
7
Scheme 1. Energy-level diagram of the excited states of porphyrin, Pr(III),
Eu(III), and Tb(III).
583,5
650
D4
S2 emission
622
Wavelength [nm]
D3
P2
Q(0,1)
600
5
3
582,6
550
Tb(III)
3
λexc = 400 nm
Intensity (arb. units)
Pr(III)
5
Energy [cm ]
dependent (see Fig. 6). Directly after addition of the lanthanide ions, the emission is analogously quenched, but after
some time, Eu(III) causes higher decrease of the emission
intensity. Subtle differences in the emission can be caused
by different energies of the excited states of the ions and also
by different positions of their C–T states. It is worth noting
that no emission was detected from the lanthanide(III) ions.
We have also examined influence of addition of the Pr(III)
and Eu(III) ions on spectroscopic properties of the porphyrin
derivatives possessing arginine as a peripheral substituent
(PP(Ser)2 (Arg)2 , PP(Ala)2 (Arg)2 ) in aqueous solutions.
Fig. 7 shows the S1 emission spectra for PP(Ser)2 (Arg)2
before and after addition of the lanthanide(III) ions. It
should be noted that the band centered at 580 nm exceeds
in intensity the Q(0,0) band, whereas their spectral positions
remain unaffected as compared to the spectrum of the free
porphyrin. It leads to the conclusion that the second substituent of the porphyrin can influence only the intensity of
the bands [22].
As it can be seen, the emission intensity of the porphyrin
exhibits strong dependence on concentration of the lanthanide ions. It increases as the concentration of the Pr(III)
ions increases, reaches maximum, and then decreases (see
Fig. 7a). However, addition of the Eu(III) ions causes immediate decrease of the emission intensity (see Fig. 7b).
Apparently, presence of the Pr(III) and Eu(III) ions in the
solutions influences the S1 porphyrin emission intensity,
which was reported for the first time by us [16]. The question arises why that influence is different for the different
Ln(III) ions (i.e. Pr(III) and Eu(III)).
The 3 P- and 5 D-excited state manifolds of Pr(III) and
Eu(III) are located between the S2 and S1 singlet states of
401
750 300
350
400
450
500
550
Wavelength [nm]
Fig. 8. (a) Emission and (b) excitation spectra of PP(Ala)2 (Arg)2 in the function of concentration.
600
402
R. Wiglusz et al. / Journal of Alloys and Compounds 380 (2004) 396–404
-3
(a)
1 c = 10 M pH = 3.46
-4
2 c = 10 M pH = 4.26
-5
3 c = 10 M pH = 7.03
-6
4 c = 10 M pH = 7.25
619,6
Q(0,0)
-3
(b)
1 c = 10 M pH = 3.46
-4
2 c = 10 M pH = 4.26
-5
3 c = 10 M pH = 7.03
-6
4 c = 10 M pH = 7.25
402,3
Soret band
3
B(0,0)
3
λem = 622 nm
Intensity (arb. units)
λexc = 400 nm
Q band
Q(0,1)
507,3
543,6
567
680,2
412,2
2
326,4
623,2
378,6
2
578,2
684,1
4
619,6 4
1
1
550
600
650
700
750 300
350
Wavelength [nm]
400
450
500
550
600
Wavelength [nm]
Fig. 9. (a) Emission and (b) excitation spectra of PP(Ser)2 (Arg)2 in the function of concentration.
As the concentration of the metal ions in the solutions increases, the latter processes start to dominate and the emission intensity decreases.
The above-mentioned facts suggest that the lanthanide
ions may play other roles in the energy dissipation than only
the direct participation in the S2 → S1 internal conversion.
Most probably their role, besides the energy transfer from
the f–d energy level to the S2 singlet state, might be related
to changes in the organization of the species in the solution.
1 pH = 0.20
2 pH = 1.50
3 pH = 3.71
4 pH = 6.60
5 pH = 8.49
6 pH = 10.66
7 pH = 11.80
(a)
7
Q(0,0)
Intensity (arb. units)
1
Another factor influencing absorption and emission spectra of porphyrins is pH. Recently, Dargiewicz et al. [23]
showed the relation between pH and changes in the absorption spectra of porphyrines in different media (water,
alcohol, silica sol-gel). The authors suggest the potential
applications of films (obtained by the dip-coating method)
containing cationic water-soluble porphyrins as the pH
sensors. In our investigations, we have examined the influence of pH on the emission spectra of PP(Ala)2 (Arg)2
(b)
1 pH = 0.20
2 pH = 1.50
3 pH = 3.71
4 pH = 6.60
5 pH = 8.49
6 pH = 10.66
7 pH = 11.80
7
Soret band
1
B(0,0)
λem = 622 nm
λexc = 400 nm
Q(0,1)
2
2
6
Q band
6
43
5
5
550
600
3
4
650
Wavelength [nm]
700
750 300
350
400
450
500
550
Wavelength [nm]
Fig. 10. (a) Emission and (b) excitation spectra of PP(Ala)2 (Arg)2 in the function of pH, c = 10−6 M.
600
R. Wiglusz et al. / Journal of Alloys and Compounds 380 (2004) 396–404
(a)
1 pH = 0.30
2 pH = 2.10
3 pH = 3.60
4 pH = 6.80
5 pH = 7.25
6 pH = 10.66
7 pH = 12.00
1
Q(0,0)
Intensity (arb. units)
2
403
1 pH = 0.30
2 pH = 2.10
3 pH = 3.60
4 pH = 6.80
5 pH = 7.25
6 pH = 10.66
7 pH = 12.00
(b)
1
Soret band
B(0,0)
2
6
λexc = 400 nm
λem = 622 nm
7
Q(0,1)
7
6
Q band
3
3
5
5
4
550
4
600
650
750 300
700
350
400
450
500
550
600
Wavelength [nm]
Wavelength [nm]
Fig. 11. (a) Emission and (b) excitation spectra of PP(Ser)2 (Arg)2 in the function of pH, c = 10−6 M.
and PP(Ser)2 (Arg)2 in aqueous solutions and the results are
shown in Figs. 8 and 9. The highest emission intensities for
both compounds have been found for the extreme values
of pH (acidic and basic). For acidities close to the neutral,
the emissions are almost completely quenched. Moreover,
for the lowest pH values (0.2–0.3), the Q(0,0) and Q(0,1)
bands in the emission spectra move to the higher energies,
whereas for the other values of pH, they remain unaffected.
Concentration of the substituted porphyrins in solutions affects not only their emission intensities but also the Soret/Q
(b)
Integrated intensity
(a)
bands intensity ratios in the excitation spectra (Figs. 8b and
9b). This characteristic fact, observed for the higher concentrations, can be related to the self-absorption phenomenon,
which causes decrease of the Soret band intensity.
Although, in general, the influence of pH on the emission intensity is similar for both compounds, the highest intensity has been recorded for PP(Ala)2 (Arg)2 at basic pH
and for PP(Ser)2 (Arg)2 at acidic pH. To better understand
these differences arising from different compositions of the
compounds, one has to take into consideration the following
0
2
4
6
pH
8
10
12
0
2
4
6
8
10
12
pH
Fig. 12. Integrated intensity of the emission vs. pH for (a) PP(Ala)2 (Arg)2 and (b) PP(Ser)2 (Arg)2 .
404
R. Wiglusz et al. / Journal of Alloys and Compounds 380 (2004) 396–404
equilibria, which porphyrins undergo in solutions:
H4 P2+ ↔ H3 P+ + H+
(1)
H3 P+ ↔ H2 P + H+
(2)
H2 P ↔ HP− + H+
(3)
HP− ↔ P2− + H+
(4)
From the above relations, we can draw the conclusion
that for the extreme pH values of the solutions, there exist
mostly protonated or deprotonated forms of the porphyrins,
which, according to Figs. 8 and 9, exhibit the most intensive
emissions. Actual equilibria in the solutions for the systems
under study are more complex because the peripheral groups
are involved in the protonation processes too.
Figs. 10–12 demonstrate the relations between the concentrations of both compounds in solutions and pH. As it
can be seen, for the same concentration the pH values depend on the porphyrin derivatives and are always more basic for Ala. This fact is not surprising as it is apparent that
pH of the solution depends on the degree of dissociation of
the substituted porphyrins and the type of the amino acid
substituent, which undergoes protonation/deprotonation to a
different extent. Addition of acids or bases in order to obtain the same pH of the solutions of both compounds affects
the natural equilibrium to a different degree. Thus, depending on pH, we obtain more or less protonated forms of the
porphyrins, which in turn produce more or less intensive
emissions.
4. Summary
1. Absorption spectra of solid TbTPP(acac) and H2 TPP are
comparable with the excitation spectra of these compounds in alcoholic solution, which confirms their compositions.
2. The change of the concentration of the free porphyrin
strongly affects the emission spectrum as a result of a
different degree of the agglomeration and concentration
quenching.
3. The emission intensity of the porphyrin depends on the
Pr(III) ion concentrations in the solutions. It increases as
the concentration of the Pr(III) ions increases, reaches a
maximum, and then decreases.
4. The efficiencies of the luminescence in methanol for
the amino acid derivatives of the porphyrins have been
determined. The efficiencies decrease from PP(Ala)2 to
PP(Ser)2 , and the emission is quenched by the lanthanide
ions Yb(III) and Eu(III). The efficiency of the emission
quenching depends on electronic structure of the metal
ions and the type of the porphyrin.
5. Changes of pH of aqueous solution of PP(AA)2 (Arg)2
considerably influence the intensities of the Soret and Q
band as well as emission spectra.
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