Synthesis and spectral properties of novel iminophosphoranes

Article abstract of DOI:10.1080/10426507.2016.1165677

Three new iminophosphoranes coded as FPZ1 (Ph–C≡C–C₆H₄–N = PPh₃), FPZ2 (Ph–N = P(C₆H₄–C≡C–Ph)₃) and FPZ3 (Ph–C≡C–C₆H₄–N = P(C₆H₄–C≡C–Ph)₃) were designed and synthesized by introducing different numbers of phenylene acetylene units to FPZ0 (Ph–N = PPh₃). The effect of structural modification was studied in detail analyzing the absorption spectra, the emission spectra, and the distributions of the electron density. The absorption spectra of the new iminophosphoranes are shown to be a linear combination of the spectra of each part by the artificial combinatorial absorption spectrum, which coincides with the real one. Most probably the individual parts can’t conjugate due to the tetrahedral structure. The probably formed excimer of FPZ0 and FPZ1 causes in their solid emission spectra an obvious bathochromic shift as compared to that of FPZ2 and FPZ3. The melting point data also showed that long branches of FPZ2 and FPZ3 will attenuate the interactions between the molecules. The results of quantum chemical calculations show that the electronic density in the HOMO of FPZ1, FPZ2, and FPZ3 is delocalized over the iminoaryl moieties. The electron density in the LUMO is delocalized over the triaryl phosphine moieties, but only concentrated on two branches, which directly determines the main direction of intramolecular charge transfer.

Full text of DOI:10.1080/10426507.2016.1165677

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Synthesis and Spectral Properties of Novel
Iminophosphoranes
Jing-Kun Fang, Zhimin Xu, Tengxiao Sun, Yu Fang, Zhengxi Yin & Shijun Wang
To cite this article: Jing-Kun Fang, Zhimin Xu, Tengxiao Sun, Yu Fang, Zhengxi Yin & Shijun
Wang (2016): Synthesis and Spectral Properties of Novel Iminophosphoranes, Phosphorus,
Sulfur, and Silicon and the Related Elements, DOI: 10.1080/10426507.2016.1165677
To link to this article: http://dx.doi.org/10.1080/10426507.2016.1165677
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Synthesis and Properties of Iminophosphoranes
Synthesis and Spectral Properties of Novel Iminophosphoranes
Jing-Kun Fang*, Zhimin Xu, Tengxiao Sun, Yu Fang, Zhengxi Yin and Shijun Wang
School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing
210094, People’s Republic of China
*Email: fjk_003@163.com
Abstract
Three new iminophosphoranes coded as FPZ1 (Ph--C≡C--C6H4--N = PPh3), FPZ2 (Ph--N =
P(C6H4--C≡C--Ph)3) and FPZ3 (Ph--C≡C--C6H4--N = P(C6H4--C≡C--Ph)3) were designed
and synthesized by introducing different number of phenylene acetylene units to FPZ0 (Ph--N =
PPh3). The effect of structural modification was studied in detail analyzing the absorption
spectra, the emission spectra and the distributions of the electron density. The absorption spectra
of the new iminophosphoranes are shown to be a linear combination of the spectra of each part
by the artificial combinatorial absorption spectrum, which coincides with the real one. Most
probably the individual parts can’t conjugate due to the tetrahedral structure. The probably
formed excimer of FPZ0 and FPZ1 causes in their solid emission spectra an obvious
bathochromic shift as compared to that of FPZ2 and FPZ3. The melting point data also showed
that long branches of FPZ2 and FPZ3 will attenuate the interactions between the molecules. The
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results of quantum chemical calculations show that the electronic density in the HOMO of
FPZ1, FPZ2 and FPZ3 is delocalized over the iminoaryl moieties. The electron density in the
LUMO is delocalized over the triaryl phosphine moieties, but only concentrated on two
branches, which directly determines the main direction of intramolecular charge transfer.
Keywords
Iminophosphorane; UV-Vis; fluorescence; tetrahedral structure; intramolecular charge transfer;
linear combination
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INTRODUCTION
Iminophosphoranes, also known as phosphazenes, phosphoranimines, or phosphine imides, are
organic compounds of general composition R3P = NR, in which a phosphorus atom is linked to a
nitrogen atom by a double bond and to three other atoms or groups by single bonds. This kind of
compounds was firstly reported in 19191, and studied in detail during the end of last century2.
Now, these compounds are applied in many fields, e. g. as superbases with non-metallic
non-ionic and low-nucleophilic characteristics3,4 (e.g. Schwesinger base), as intermediates in
organic synthesis5,6 (e.g. for the synthesis of Schiff bases) or as building blocks of polymers
known as polyphosphazenes7,8. The related phosphine imide ligands are widely used in
catalysis9-11
.
The most generally and widely used methods for the synthesis of iminophosphoranes
are the so-called Staudinger and Kirsanov reactions. In both methods a phosphine (PR3) is
used as the starting material, with the Staudinger reaction involving its direct oxidation
with an organic azide1. In the Kirsanov reaction the phosphine is firstly brominated and
subsequently treated with a primary amine in the presence of a base12.
As a simple iminophosphorane, phenylimino triphenylphosphorane (FPZ0) can be
easily synthesized from triphenyl phosphine and phenylazide by the Staudinger
reaction13. Iminophosphoranes possess a highly polarized P = N bond, with which makes
intramolecular charge transfer possible and can be applied in relevant fields.
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Comparing with the widely studied linear or planar optoelectronic molecules, FPZ0
is a three dimensional tetrahedral molecule, from which some special properties can be
expected. For example, the research of Dye-Sensitized Solar cells aims to avoid
aggregations introducing long alkyl chains to dye molecules in order to achieve three
dimensional structures14-16. In addition to its excellent electrical properties, the
triphenylamine unit was usually used for the same reason because of its tetrahedral
architecture17,18. Considering the structural characteristics of FPZ0 aggregation should be
suppressed without introducing bulky groups in these compounds.
Based on these results, we have planned to study the potential applications of FPZ0-like
compounds. The application of FPZ0 is restricted obviously for its limited π-conjugated system.
Here we report three novel arylimino phosphoranes with extended π-conjugated system as
compared to FPZ0. They are coded as FPZ1, FPZ2 and FPZ3 and are shown in Scheme 1.
Phenylene acetylene units were introduced with the purpose to extend π-conjugation. Spectral
properties and theoretical calculations were also carried out to investigate the characteristics of
these compounds.
RESULTS AND DISCUSSION
Structure Characterization
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Arylimino triarylphosphoranes FPZ1, FPZ2 and FPZ3 were characterized extensively by 1H,
13C and 31P NMR spectroscopy as well as by HRMS (see Supplementary Information). In the 13C
NMR spectra J-couplings between the carbon atoms and phosphorus are observed and their
values are similar to those observed for FPZ05. In the 31P NMR spectra the signals for FPZ1 (δ =
4.5), FPZ2 (δ = 1.6) and FPZ3 (δ = 2.6) indicate a structure similar to that of FPZ0 (δ = 2.95). In
the HRMS spectra the (M+H)+ peak was observed with the highest relative abundance, which
further supports the identity of FPZ1, FPZ2 and FPZ3.
Absorption Spectra
The absorption spectra of FPZ0 and the three new arylimino triarylphosphoranes FPZ1,
FPZ2 and FPZ3 in diluted CH2Cl2 solution (1.6 × 104 M for FPZ0 and FPZ1, 0.8 × 104 M for
FPZ2 and FPZ3) are shown in Figure 1. The relevant maxima are listed in Table 1. Compared to
the absorption spectrum of FPZ0 in CH2Cl2 the spectra of FPZ1, FPZ2 and FPZ3 are much
more intense based on the increase of the molar extinction coefficient ε and a bathochromic shift
is observed.
FPZ1 with a phenylene acetylene unit attached to phenyl imine part shows the most
significant bathochromic shift, 80 nm (λabs shifts from 255 nm to 335 nm), and log ε increases
from 4.19 to 4.54 compared with FPZ0. Compound FPZ2 with phenylene acetylene units
attached to the triphenyl phosphine part shows a bathochromic shift of 43 ~ 60 nm (two peaks
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are observed, 298 nm and 315 nm), and log ε increases from 4.19 to 4.96 and 4.97, respectively.
Compound FPZ3 with phenylene acetylene units attached to both phenyl imine and triphenyl
phosphine parts shows a bathochromic shift of 46 ~ 61 nm (two peaks are observed, 301 nm and
316 nm) and exhibits the highest ε value; log ε increases from 4.19 to 5.03 and 5.05,
respectively.
It is not surprising that the ε value increases when the number of phenylene acetylene units
is increased. The ability of harvesting light is improved by expanding the range of π-conjugation
in arylimino triarylphosphoranes. Nevertheless, we did not expect FPZ1 to showed the largest
λabs value. It should be noted that a shoulder was observed in the absorption spectrum of FPZ3,
in which a phenylene acetylene unit attached to phenyl imine is present, the same as in case of
FPZ1.
To investigate the relationship between molecular structure and absorption spectra, an
artificial absorption spectrum was generated. The absorption spectrum of FPZ1 plus the
absorption spectrum of FPZ2 and then minus the absorption spectrum of FPZ0 should give the
“combined” absorption spectrum of FPZ3, which is shown in Figure 2.
It is evident that the artificial absorption spectrum fits well to the real one, which means that
the absorption spectra of arylimino triarylphosphoranes can be viewed as a linear combination of
each part. This should be attributed to the tetrahedral structure, which prevents the individual
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π-systems from conjugation. Based on the above results, it is easier to control tuning of the
absorption spectra of this kind of compounds as compared to linear and planar molecules, as only
the partial structure rather than whole molecule needs to be considered.
Emission Spectra
The emission spectra of the three arylimino triarylphosphoranes FPZ1, FPZ2 and FPZ3 in
diluted solutions of CH2Cl2 (1.0 × 106 M) are shown in Figure 3. The corresponding data are
listed in Table 1. The emission spectrum of FPZ0 is too weak to give credible data.
Compound FPZ1 with a phenylene acetylene unit attached to the phenyl imine part shows
the emission peak at longest wavelength (λem = 369 nm). The emission spectra of FPZ2 and
FPZ3 display a similar hypsochromic shift compared to FPZ1 and two peaks are observed for
FPZ3.
The emission spectra of FPZ0 and the three new arylimino triarylphosphoranes FPZ1,
FPZ2 and FPZ3 in the solid state were further recorded and are shown in Figure 4. The
respective data are listed in Table 1. It is interesting to note, that the wavelength (λsolid) of the
maxima for FPZ0 and FPZ1 show a bathochromic shift of about 120 nm as compared to λsolid of
FPZ2 and FPZ3. Most probably the solid emission spectra of FPZ0 and FPZ1 were produced
from the corresponding excimers and the emission spectra of excimers are expected to display a
bathochromic shift. For an excimer to be formed a sandwich-like structure is necessary19. The
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long branches of FPZ2 and FPZ3 prevent the forming an excimer and thus only the emission
spectra of the monomer in the range of shorter wavelength can be observed.
This can also be proved by the melting point. Typically, higher molecular weight molecules
with similar structure will show higher melting points. However the melting points of FPZ0 and
FPZ1 (134-135 C and 182-183 C) with lower molecular weight are significantly higher than
those of FPZ2 and FPZ3 (90-92 C and 96-98 C) with higher molecular weight. The reason is
that the long substituents of FPZ2 and FPZ3 will attenuate the interactions between the
molecules, which stabilize the crystal packing, finally leading to a lower melting point.
Theoretical Calculations
To obtain insight into the geometrical and photophysical properties molecular orbital
calculations of FPZ1, FPZ2 and FPZ3 were carried out using DFT methods with the Gaussian
09 program. The calculations were performed with the B3LYP exchange correlation functional
under 6-31G (d) basis set.
The distribution of the electron density in the HOMO and LUMO of the three arylamino
triarylphosphoranes is shown in Figure 5. It can be seen that the electron density in the HOMOs
of FPZ1, FPZ2 and FPZ3 is delocalized over the aryl imine moiety, while the electron density
in the LUMO is delocalized over the triaryl phosphine moiety.
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Furthermore, it becomes evident, that the electron density of the LUMO of the three
arylimino triarylphosphoranes is concentrated only on two branches, instead of the three
branches as we expected. This characteristic directly determines the main direction of the
intramolecular charge transfer and influences the spectral properties significantly. This
phenomenon is responsible for some interesting results and has been reported20. As discussed
above, arylimino triarylphosphoranes have a potential for application in the field of
optoelectrical materials, in which electron mobility in the excited states is of great importance.
CONCLUSIONS
In summary we have prepared three new iminophosphoranes (FPZ1, FPZ2 and FPZ3) by
introducing different numbers of phenylene acetylene units to FPZ0. The absorption spectra of
the new compounds show that the molar extinction coefficients increase when the number of
phenylene acetylene units is increased. This means,that the abilities of harvesting light is
strengthened along with expanding π-conjugation range. The artificially generated absorption
spectrum fits well to the real one indicating that the absorption spectra of arylimino
triarylphosphoranes can be viewed as a linear combination of of the spectra of each part. This is
most probably due to thei tetrahedral structure, which prevents teh individual π-systems from
conjugation. Thus, it is easier to tune the absorption spectral range of this kind of compounds
than of linear and planar molecules, as only the partial structure rather than whole molecule
needs to be considered. The solid emission spectra of FPZ0 and FPZ1 show a bathochromic
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shift of about 100 nm compared with FPZ2 and FPZ3. Most probably the solid emission spectra
of FPZ0 and FPZ1 are produced by excimers, which is expected to cause such a bathochromic
shift. A sandwich-like structure is necessary to form an excimer. Because of the crowded
architecture of FPZ2 and FPZ3 only the emission spectra of the monomers can be observed for
these compounds in the solid state. The melting point data also show that the long branches of
FPZ2 and FPZ3 will attenuate the interactions between the molecules, leads to a lower melting
point.
Results of theoretical calculations for FPZ1, FPZ2 and FPZ3 show that the electron density
of the HOMO is delocalized over the aryl imine moieties. In the case of the LUMO the electron
density is distributed over the triaryl phosphine moieties and is concentrated only on two
branches instead of three, which directly determines the main direction of the intramolecular
charge transfer. Arylimino triarylphosphoranes may have a potential of application in the field of
optoelectrical materials, in which usually electron mobility in the excited state is of great
importance. Further studies on possible applications of arylimino triarylphosphoranes in the field
of optoelectrical materials are in progress.
EXPERIMENTAL
Materials and Equipments
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All reactions were carried out under an atmosphere of nitrogen with freshly distilled
solvents. All reagents were obtained from commercial sources and used as received, unless
otherwise noted. Ethyl ether was dried over sodium/benzophenone and distilled before used.
Other solvents such as toluene and diisopropylamine were distilled from CaH2. 1H and 13C NMR
spectra were recorded at room temperature with a JEOL Lambda 500 instrument and calibrated
with tetramethylsilane (TMS) as an internal reference. 31P NMR spectra were recorded at room
temperature with a Bruker AvanceTM III 500 instrument and are refered to 85 5 H3PO4 as
external standard. HRMS spectra were recorded with a Waters Q-TOF MicroTM instrument.
UV-VIS absorption and emission spectra were recorded with a HITACHI U-3310 and a JASCO
FP-6600 instrument at room temperature, respectively. The Supplemental Materials contains
sample 1H, 13C, 31P and HR-MS spectra o the products (Figures S 1 -- S 12).
Synthesis and Characterization
In order to investigate the properties of iminophosphoranes with substituents having an
extended π-conjugated system phenylene acetylene units were introduced into FPZ0. The
synthetic routes for the arylimino triarylphosphoranes FPZ1, FPZ2 and FPZ3 are shown in
Scheme 1. Compound FPZ0 and 1-azido-4-(phenylethynyl)benzene (1) were synthesized
according to the corresponding literature methods21, 22. The final step was a Staudinger reaction
between the tertiary phosphines and respective organic azides in diethyl ether.
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Synthesis of FPZ1
1-Bromo-4-(phenylethynyl)benzene (2)
To a flask were added phenylacetylene (204 mg, 2.0 mmol), 4-bromotriphenylamine (566 mg,
2.0 mmol), Pd(PPh3)4 (116 mg, 0.1 mmol), CuI (19 mg, 0.1 mmol), diisopropylamine (5 mL) and
toluene (15 mL) and the mixture was stirred at room temperature overnight. Then the reaction
mixture was poured into aqueous NH4Cl and extracted with CH2Cl2, the organic layer was
washed with brine and dried over MgSO4. After filtration, solvents were evaporated. The crude
product was subjected to column chromatography (SiO2; eluent: hexane) to give 466 mg of 2 as a
white powder in 90.7% yield. 1H NMR (500 MHz, CDCl3):  = 7.35-7.36 (m, 3H), 7.39 (d, J =
8.0 Hz, 2H), 7.48 (d, J = 8.0 Hz, 2H), 7.51-7.53 (m, 2H); 13C NMR (125 MHz, CDCl3):  =
88.3, 90.5, 122.2, 122.5, 122.9, 128.4, 128.5, 131.6, 131.6, 133.0. HRMS (ESI+): Calcd for
(M+H)+ C14H10Br: 256.9966, found: 256.9976.
Tris(4-(phenylethynyl)phenyl)phosphine (3)
To a flask were added 2 (514 mg, 2.0 mmol) and THF (20 mL). n-BuLi (1.2 mL, 1.6 M in
hexane, 1.9 mmol) was added at -78 C and the mixture was stirred at this temperature for 0.5 h.
Phosphorus tribromide (135 mg, 0.5 mmol) and borane tetrahydrofuran complex solution (0.6
mL, 1.0 M in THF, 0.6 mmol) was added to the reaction mixture and the mixture was stirred at
-40 C for 2 h. Diethylamine (5 mL) was added after evaporation of the solvents and the mixture
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was stirred at 45 C for 4 h. Then the reaction mixture was poured into aqueous NH4Cl and
extracted with CH2Cl2, the organic layer was washed with brine and dried over MgSO4. After
filtration, the solvents were evaporated. The crude product was subjected to column
chromatography (SiO2; eluent: hexane / CH2Cl2, 2 : 1) to give 119 mg of 3 as a white powder in
42.3% yield. 1H NMR (500 MHz, CDCl3):  = 7.29 (t, J = 8.0 Hz, 6H), 7.35-7.37 (m, 9H),
7.51-7.55 (m, 12H); 13C NMR (125 MHz, CDCl3):  = 87.4, 90.1, 122.6 (d, JPC = 7.1 Hz),
127.6, 128.4, 128.8, 132.1, 132.2, 135.9 (d, JPC = 19.6 Hz), 136.9 (d, JPC = 10.7 Hz). HRMS
(ESI+): Calcd for (M+H)+ C42H28P: 563.1929, found: 563.1940.
Synthesis of FPZ1
To a flask were added triphenylphosphine (131 mg, 0.5 mmol), 1 (131 mg, 0.6 mmol) and
diethyl ether (10 mL) and the mixture was refluxed for 2 h. Then the reaction mixture was
poured into water and extracted with CH2Cl2, the organic layer was washed with brine and dried
over MgSO4. After filtration the solvents were evaporated and the residue was recrystallized
from ethanol to give 199 mg of 2 as an earthy yellow powder in 87.8% yield. Mp 182-183 C; 1H
NMR (500 MHz, CDCl3):  = 6.75 (d, J = 8.0 Hz, 2H), 7.20 (d, J = 8.0 Hz, 2H), 7.24-7.29 (m,
3H), 7.44-7.46 (m, 8H), 7.53 (t, J = 7.0 Hz, 3H), 7.72-7.76 (m, 6H); 13C NMR (125 MHz,
CDCl3):  = 87.4, 91.0, 110.9, 123.2 (d, JPC = 18.0 Hz), 124.3, 127.2, 128.1, 128.7 (d, JPC
=
11.8 Hz), 130.4 (d, JPC = 98.6 Hz), 131.2, 131.8 (d, JPC = 2.5 Hz), 132.3 (d, JPC = 1.5 Hz), 132.5
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(d, JPC = 9.8 Hz), 152.2 (d, JPC = 2.5 Hz); 31P NMR (202 MHz, CDCl3):  = 4.5; HRMS (ESI+):
Calcd for (M+H)+ C32H25NP: 454.1725, found: 454.1736.
Synthesis of FPZ2
To a flask were added 3 (169 mg, 0.3 mmol), azidobenzene (87 mg, 0.4 mmol) and diethyl ether
(10 mL) and the mixture was refluxed for 2 h. Then the reaction mixture was poured into water
and extracted with CH2Cl2, the organic layer was washed with brine and dried over MgSO4.
After filtration the solvents were evaporated. The crude product was subjected to column
chromatography (SiO2; eluent: hexane / CH2Cl2, 2 : 1) to give 165 mg of 3 as a yellow powder in
84.3% yield. Mp 96-98 C; 1H NMR (500 MHz, CDCl3): 6.70 (t, J = 7.5 Hz, 1H), 6.81 (d, J =
8.5 Hz, 2H), 7.05 (t, J = 7.5 Hz, 2H), 7.34-7.37 (m, 9H), 7.53-7.55 (m, 6H), 7.60 (d, J = 8.5 Hz,
3H), 7.61 (d, J = 8.5 Hz, 3H), 7.73 (d, J = 8.5 Hz, 3H), 7.75 (d, J = 8.5 Hz, 3H); 13C NMR (125
MHz, CDCl3):  = 88.4 (d, JPC = 2.1 Hz), 92.2, 117.8, 122.6, 123.4 (d, JPC = 17.5 Hz), 127.1 (d,
JPC = 3.1 Hz), 128.4, 128.7, 128.8, 130.2 (d, JPC = 99.6 Hz), 131.6, 131.7, 132.4 (d, JPC = 9.8
Hz), 150.4 (d, JPC = 2.6 Hz); 31P NMR (202 MHz, CDCl3):  = 1.6; HRMS (ESI+): Calcd. for
(M+H)+ C32H25NP: 654.2351, found: 654.2361.
Synthesis of FPZ3
To a flask were added 3 (169 mg, 0.3 mmol), 1 (88 mg, 0.4 mmol) and diethyl ether (10 mL) and
the mixture was refluxed for 2 h. Then the reaction mixture was poured into water and extracted
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with CH2Cl2, the organic layer was washed with brine and dried over MgSO4. After filtration the
solvents were evaporated. The crude product was subjected to column chromatography (SiO2;
eluent: hexane / CH2Cl2, 2 : 1) to give 203 mg of 3 as an orange powder in 89.6% yield. Mp
90-92 C; 1H NMR (500 MHz, CDCl3):  = 6.77 (d, J = 8.0 Hz, 2H), 7.21-7.29 (m, 5H), 7.34 (t,
J = 7.0 Hz, 9H), 7.46 (d, J = 7.0 Hz, 2H), 7.53-7.55 (m, 6H), 7.60-7.62 (m, 6H), 7.69-7.74 (m,
6H); 13C NMR (125 MHz, CDCl3):  = 87.6, 88.3 (d, JPC = 2.1 Hz), 90.9, 92.5, 111.6, 122.4,
123.3 (d, JPC = 18.1 Hz), 124.2, 127.26 (d, JPC = 3.1 Hz), 127.29, 128.2, 128.4, 128.8, 129.5 (d,
JPC = 99.8 Hz), 131.2, 131.69 (d, JPC = 12.4 Hz), 131.72, 132.3 (d, JPC = 10.3 Hz), 132.4, 151.4
(d, JPC = 2.0 Hz); 31P NMR (202 MHz, CDCl3):  = 2.6; HRMS (ESI+): Calcd for (M+H)+
C32H25NP: 754.2664, found: 754.2675.
ACKNOWLEDGMENT
This work was financially supported by the Natural Science Foundation of Jiangsu Province
under Grant No. BK20140780.
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22. Tomioka, H.; Sawai, S. Org. Biomol. Chem. 2003, 1, 4441–4450.
1664–1675.
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Table 1 Absorption and fluorescence data of compound FPZ0 - FPZ3
compound
FPZ0
λabs/nm(log ε)
255 (4.19)
λex/nm
-
λem/nm
-
λsolid/nm
452; 472
451; 470
352
335 (4.54)
335
298
301
369
FPZ1
298 (4.97); 315 (4.96)
301 (5.03); 316 (5.05)
331
FPZ2
332; 347
342; 361
FPZ3
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120000
100000
80000
60000
40000
20000
0
FPZ0
FPZ1
FPZ2
FPZ3
250
300
350
400
450
Wavelength(nm)
Figure 1 Absorption spectra of compounds FPZ0 - FPZ3
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1.0
FPZ3
FPZ1 + FPZ2 - FPZ0
0.5
0.0
250
300
350
400
450
Wavelength(nm)
Figure 2 The absorption spectrum of FPZ3 and the spectrum resulting from a linear combination
of the spectra of FPZ0 - FPZ2
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1.0
0.5
0.0
FPZ1
FPZ2
FPZ3
350
400
450
500
Wavelength(nm)
Figure 3 Emission spectra of compounds FPZ1 - FPZ3
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FPZ0
FPZ1
FPZ2
FPZ3
1.0
0.5
0.0
350
400
450
500
550
Wavelength(nm)
Figure 4 Solid emission spectra of compounds FPZ0 - FPZ3
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HOMO
LUMO
FPZ1
FPZ2
FPZ3
Figure 5 HOMO and LUMO orbitals for compounds FPZ1, FPZ2 and FPZ3
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Scheme 1 Synthetic route to compounds FPZ1, FPZ2 and FPZ3
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