Influence of the chemical structure and solvent polarity on the fluorescence of 3-aryl-7-benzoyl-pyrrolo [1,2-c]pyrimidines

Article abstract of DOI:10.1016/j.dyepig.2019.108023

Structure-fluorescence properties of new synthesized 3-aryl-7-benzoyl-pyrrolo[1,2-c]pyrimidines were measured in order to correlate the nature of the substituents with the absorption and emission features (absorption intensity, fluorescence quantum yield, Stokes shifts, fluorescence quenching in presence of inhibitors). The influence of the solvent on the fluorescence of the title compounds was investigated by multiple linear regressions, connecting the polarity of different solvents with the luminescent properties. Some of the new pyrrolo[1,2-c]pyrimidines show strong fluorescence in the blue region of the visible spectrum, making them potential candidates for OLED technology or advanced materials.

Full text of DOI:10.1016/j.dyepig.2019.108023

Journal Pre-proof
Influence of the chemical structure and solvent polarity on the fluorescence of 3-
aryl-7-benzoyl-pyrrolo [1,2-c]pyrimidines
Eleonora-Mihaela Ungureanu, Marian-Laurentiu Tatu, Emilian Georgescu, Cristian
Boscornea, Marcel-Mirel Popa, Gabriela Stanciu
PII:
S0143-7208(19)31400-7
DOI:
https://doi.org/10.1016/j.dyepig.2019.108023
DYPI 108023
Reference:
To appear in: Dyes and Pigments
Received Date: 15 June 2019
Revised Date: 8 October 2019
Accepted Date: 4 November 2019
Please cite this article as: Ungureanu E-M, Tatu M-L, Georgescu E, Boscornea C, Popa M-M, Stanciu
G, Influence of the chemical structure and solvent polarity on the fluorescence of 3-aryl-7-benzoyl-
pyrrolo [1,2-c]pyrimidines, Dyes and Pigments (2019), doi: https://doi.org/10.1016/j.dyepig.2019.108023.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of
record. This version will undergo additional copyediting, typesetting and review before it is published
in its final form, but we are providing this version to give early visibility of the article. Please note that,
during the production process, errors may be discovered which could affect the content, and all legal
disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier Ltd.

1
Influence of the chemical structure and solvent polarity on the fluorescence of 3-aryl-7-
benzoyl-pyrrolo[1,2-c]pyrimidines
2
3
4
5
Eleonora-Mihaela Ungureanua, Marian-Laurentiu Tatua,b, Emilian Georgescuc,
Cristian Boscornead, Marcel-Mirel Popae, Gabriela Stanciuf*
6
7
8
9
10
11
12
13
14
15
16
17
aDepartment of Inorganic Chemistry, Physical Chemistry and Electrochemistry, University
"Politehnica" of Bucharest, Gh. Polizu 1-7, 011061, Bucharest, Romania
bResearch-Development Institute for Non-Ferrous and Rare Metals (IMNR), 102 Biruintei
Blvd, 077145, Pantelimon, Romania
cChimcomplex Research Center, Uzinei Street 1, 240050, Ramnicu Valcea, Romania
dDepartment of Bioresources and Polymer Science University "Politehnica" of Bucharest,
Gh. Polizu 1-7, 011061, Bucharest, Romania
eCenter of Organic Chemistry “C. D. Nenitzescu”, Romanian Academy, Spl. Independentei,
202 B, 060023, Bucharest, Romania
fDepartment of Chemistry and Chemical Engineering, Ovidius University, Constanta, 124
Mamaia Blvd, 900527, Romania
18
19
20
21
*Corresponding authors. E-mail: gstanciu66@yahoo.com, Tel. +40 724936673
22
23
24
25
26
27
28
29
Abstract
Structure-fluorescence properties of new synthesized 3-aryl-7-benzoyl-pyrrolo[1,2-
c]pyrimidines were measured in order to correlate the nature of the substituents with the
absorption and emission features (absorption intensity, fluorescence quantum yield, Stokes
shifts, fluorescence quenching in presence of inhibitors). The influence of the solvent on the
fluorescence of the title compounds was investigated by multiple linear regressions,
connecting the polarity of different solvents with the luminescent properties. Some of the new
pyrrolo[1,2-c]pyrimidines show strong fluorescence in the blue region of the visible
spectrum, making them potential candidates for OLED technology or advanced materials.
30
31
32
Keywords: pyrrolo[1,2-c]pyrimidines, fluorescence, quantum yield, Stokes shift, solvent
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
polarity functions
1. Introduction
Fluorescence is an important property [1] of organic molecules, very useful in designing
advanced materials for practical applications such as OLEDs [2], dye-sensitized solar cells
[3,4], bioimaging [5], chemical sensors [6] or even for the study of supramolecular structures
by fluorescence resonance energy transfer [7]. Small nitrogen containing molecules from the
class of N-bridgehead heterocycles are promising candidates for important fluorescence
applications [8-10]. In this class, pyrrolo[1,2-c]pyrimidines have shown interesting biological
activity [11,12], the same heterocyclic moiety being found in the structures of several natural
compounds [13,14]. However, the literature is rather scarce in what concerns the
photophysical properties of these compounds, even if the interest in their synthetic strategies
is permanent [15-20]. Among the synthetic methods of the pyrrolo[1,2-c]pyrimidines, the
1,3-dipolar cycloaddition of the corresponding N-ylides has been found especially
advantageous [21-24].
The effect of the solvent on excitation and emission properties of organic compounds is also
a current subject of interest [25]. When the photon excites a molecule, a redistribution of
charges occurs. This can lead to the change of the dipole moment in the excited state, which
offers information about the molecule electronic structure and geometry. The method used
1

52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
for calculation of the dipole moment is based on the spectral shifts [26,27]. The position,
shape and intensity of the bands in excitation and emission spectra of a molecule change in
solvents with different polarity. This phenomenon can be attributed to the solvent – solute
interactions, which can be non-specific (electrostatic interaction) or specific (hydrogen
bonding) [28-31].
Organic molecules which have the property to change their colour in presence of solvents
with different polarity are potential candidates as environment-sensitive fluorescent probes
[1,2]. If the fluorophores possess photo-switching ability, they can be used as molecular
probes for super-resolution fluorescence microscopes [32,33].
Several electrochemical and fluorescence measurements [34-36] have been conducted in our
group as part of the general interest in finding and describing the applicative properties of
pyrrolopyrimidines. A series of 3-aryl-7-benzoyl-pyrrolo[1,2-c]pyrimidines in which the 3-
aryl ring is substituted with methoxy groups (which were proved to have high enhancing
effect on the photophysical features of pyrrolo[1,2-c]pyrimidines [35]) have been synthesized
and investigated. The compounds described in this paper have additional structural changes
given by substitution of the benzoyl moiety in C-7 [37,38]. The structural effect of
substitution was quantified by fluorescence properties (quantum yield, Stokes shifts and
fluorescence quenching). The correlation between substituents and excitation/fluorescence
spectra of the studied compounds are discussed herein. The influence of the solvent polarity
was also investigated.
71
72
73 2. Materials and methods
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
2.1. Equipment, materials and methods
Melting points were determined on Boëtius hot plate microscope. Elemental analysis was
carried out on COSTECH Instruments EAS32 apparatus. IR spectra were recorded in KBr
pellets on Bruker Vertex 70 ATR or Nicolet Impact 410 spectrometers. NMR spectra were
recorded on Varian Gemini 300 BB, operating at 300 MHz for 1H-NMR and 75 MHz for 13C-
NMR or on Bruker Advance III 400 instrument, operating at 400 MHz for 1H-NMR and 100
MHz for 13C-NMR. JASCO V550 spectrophotometer has been used to record UV-Vis
spectra. Quartz cuvettes with 1 cm optical path length where used for the measurements
performed in solution. Jasco FP6500 spectrofluorometer was used to measure excitation and
emission spectra applying a reading angle of 90º. Refractive indices were measured at 25oC
using Abbe refractometer (from CETI Belgium). Quantum yields were calculated using
quinine sulphate as standard [36]. The spectra were recorded in chloroform (CHCl3),
dichloromethane (CH2Cl2), acetonitrile (CH3CN) or dimethyl sulfoxide (DMSO) of
spectrophotometric quality. High resolution MS spectra have been recorded on Bruker Maxis
II QTOF spectrometer with electrospray ionization (ESI) in the positive mode.
2.2. Main characteristics of the new 3-aryl-7-benzoyl-pyrrolo[1,2-c]pyrimidines
92
93
94
95
96
97
98
99
The new pyrrolo[1,2-c]pyrimidines have been synthesized by a previously reported general
synthetic procedure based on the 1,3-dipolar cycloaddition reactions of N-heterocyclic ylides,
generated in situ from the corresponding N-heterocycle quaternary salts in the presence of
epoxides as acid scavengers and reaction medium, with activated acetylenes [39,40]. All
reactions have been performed in the presence of 1,2-epoxybutane at reflux temperature
starting from 2.5 mmol of pyrimidinium quaternary salts [21,23,24]. Their main
characteristics are given below.
2

100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
Ethyl 3-(2,4-dimethoxyphenyl)-7-(4-methylbenzoyl)pyrrolo[1,2-c]pyrimidine-5-carboxylate
3a: yellow crystals; 0.53 g (48 %). IR (ν, cm-1): 2985, 1686, 1612, 1572, 1523, 1472, 1408,
1349, 1327, 1299, 1257, 1206, 1087. 1H NMR (δ, 300 MHz, CDCl3):1.44 (t, 3H, J = 7.1 Hz,
CH3); 2.46 (s, 3H, CH3); 3.87, 3.97 (2s, 6H, 2MeO); 4.40 (q, 2H, J = 7.1 Hz, CH2); 6.57 (d,
1H, J = 2.5 Hz, H-3’); 6.64 (dd, 1H, J = 8.2, 2.5 Hz, H-5’); 7.33 (d, 2H, J = 8.8 Hz, H-2”, H-
6”); 7.76 (d, 2H, J = 8.2 Hz, H-3”, H-5”); 7.83 (s, 1H, H-6); 8.22 (d, 1H, J = 8.8 Hz, H-6’);
8.90 (d, 1H, J = 1.5 Hz, H-4); 10.52 (d, 1H, J = 1.5 Hz, H-1). 13C NMR (δ, 75 MHz, CDCl3):
14.7 (CH3); 21.7 (CH3); 55.6, 55.7 (2MeO); 60.4 (CH2); 99.0 (C-3’); 105.3 (C-5’); 106.6 (C-
5); 112.2 (C-4); 118.8 (C-1’); 122.2 (C-7); 129.5 (C-6, C-3”, C-5”); 130.1 (C-2”, C-6”);
132.3 (C-6’); 140.3 (C-1); 136.6, 140.6, 142.6, (C-4a, C-1”, C-4”); 147.5 (C-3);159.4, 162.2
(C-2’, C-4’); 163.9 (COO);185.0 (COAr). HRMS-ESI (m/z): [M+H]+ for C26H24N2O5, calcd.
445.17580, found 445.17590; Elem. anal.: calcd. for C26H24N2O5 (444,48): C 70.26, H 5.44,
N 6.30; found C 70.37, H 5.53, N 6.22.
Ethyl 3-(3,4-dimethoxylphenyl)-7-(4-fluorobenzoyl)pyrrolo[1,2-c]pyrimidine-5-carboxylate
3b: yellow crystals; 0.56 g (50 %). IR (ν, cm-1): 2949, 1697, 1618, 1597, 1505, 1476, 1411,
1330, 1270, 1229, 1197, 1151,1084. 1H NMR (δ, 300 MHz, CDCl3): 1.43 (t, 3H, J = 7.1 Hz,
Me); 3.95, 4.01 (2s, 6H, 2MeO); 4.41 (q, 2H, J = 7.1 Hz, CH2); 6.96 (d, 1H, J = 8.4 Hz, H-
5’); 7.21 (t, 2H, J = 8.5 Hz, H-3”, H-5”); 7.70 (d, 1H, J = 2.1 Hz, H-2’); 7.73-7.76 (m, 3H, H-
6’, H-6); 7.85-7.90 (m, 2H, H-2”, H-6”); 8.50 (d, 1H, J = 1.5 Hz, H-4); 10.49 (d, 1H, J = 1.5
Hz, H-1); 13C NMR (δ, 75 MHz, CDCl3): 14.6 (Me); 56.1 (2MeO); 60.6 (CH2); 106.7 (C-5);
107.4 (C-4); 109.8 (C-2’); 111.3 (C-5’); 115.7 (J= 22.0 Hz, C-3”, C-5”); 119.9 (C-6’): 122.0
(C-7); 129.4 (C-1’); 129.9 (C-6);131.5 (J= 8.1 Hz, C-2”, C-6”) 140.7 (C-1);135.3, 141.2,
149.4, 149.8, 151.1 (C-3, C-4a, C-3’, C-4’, C-1”); 165.1 (J = 251.9 Hz, C-4”); 163.7
(CO2Et); 183.7 (COAr). HRMS-ESI (m/z): [M+H]+ for C25H21FN2O5, calcd. 449.15073,
found 449.15095; Elem. anal.: calcd. for C25H21FN2O5(448.44): C 66.96, H 4,72, N 6.25;
found C 66.89, H 4.67, N 6.31.
Ethyl
3-(3,4-dimethoxylphenyl)-7-(2,4-dimethoxybenzoyl)pyrrolo[1,2-c]pyrimidine-5-
carboxylate 3d: yellow crystals; 0.57 g (47 %). IR (ν, cm-1): 1692, 1619, 1599, 1476, 1329,
1266, 1200.1H NMR (δ, 300 MHz, CDCl3): 1.42 (t, 3H, J = 7.1 Hz, Me); 3.84, 3.96, 4.00,
4.03 (4s, 12H, 4MeO); 4.40 (q, 2H, J = 7.1 Hz, CH2);6.57 (s, 1H, H-3”); 6.99 (d, 1H, J = 8.4
Hz, H-5’); 7.73 (d, 1H, J = 2.1 Hz, H-2’); 7.76-7.79 (m, 3H, H-6’, H-5”, H-6”); 7.53 (s, 1H,
13
H-6); 8.46 (d, 1H, J = 1.5 Hz, H-4); 10.52 (d, 1H, J = 1.5 Hz, H-1); C NMR (δ, 75 MHz,
CDCl3): 14.5 (Me); 56.0, 56.1, 56.2, 56.4 (4MeO); 60.4 (CH2); 96.7 (C-3”); 106.6 (C-5);
107.4 (C-4); 109.8 (C-2’); 111.2 (C-5’); 119.9 (C-6’):122.5 (C-7); 130.2, 133.7 (C-6, C-5”,
C-6”);140.7 (C-1);101.9, 129.4, 141.0, 149.3, 149.8, 150.9, 158.1, 158.6 (C-3, C-4a, C-1’, C-
3’, C-4’, C-1”, C-2”, C-4”); 163.7 (CO2Et); 182.5 (COAr). HRMS-ESI (m/z): [M+H]+ for
C27H26N2O7, calcd. 491.181278, found 491.05077; Elem. anal.: calcd. for C27H26N2O7
(490.50): C 66.11, H 5.34, N 5.71; found C 66.20, H 5.39, N 5.60.
Dimethyl 3-(2-methoxyphenyl)-7-benzoyl-pyrrolo[1,2-c]pyrimidine-5,6-dicarboxylate 3e:
yellow crystals; 0.43 g (39%). IR (ν, cm-1): 2945, 1746, 1697, 1626, 1518, 1490, 1448, 1382,
1344, 1303, 1265, 1202, 1167, 1108.1H NMR (δ, 300 MHz, CDCl3): 3.34, 3.91, 3.99 (3s, 6H,
3MeO); 7.06 (dd, 1H, J = 8.3, 1.1 Hz, H-3’); 7.13 (td, 1H, J = 7.8, 1.1 Hz, H-5’);7.41-7.61
(2m, 4H, H-4’, H-3”, H-4”, H-5”); 7.71-7.74 (m, 2H, H-2”, H-6”); 8.18 (dd, 1H, J = 7.8, 1.8
13
Hz, H-6’); 8.95 (d, 1H, J = 1.5 Hz, H-4); 10.30 (d, 1H, J = 1.5 Hz, H-1). C NMR (δ, 75
MHz, CDCl3): 51.7, 52.3, 55.6 (3MeO); 104.7 (C-5); 111.5 (C-3’); 113.5 (C-4); 120.2 (C-7);
121.1, 130.9, 131.0 (C-4’, C-5’, C-6’); 128.1, 128.6, 132.1 (C-2”, C-3”, C-4”, C-5”, C-6”);
125.5, 132.8, 138.9, 139.0 (C-4a, C-6, C-1’, C-1”); 139.7 (C-1); 147.9 (C-3); 157.9 (C-2’);
162.9, 164.5 (2COO); 186.3 (COAr). HRMS-ESI (m/z): [M+H]+ for C25H20N2O6, calcd.
445.13941, found 445.13861; Elem. anal.: calcd. for C25H20N2O6 (444.44): C 67.56, H 4.54,
N 6.30; found C 67.63, H 4.61, N 6.22.
3

150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
Diethyl 3-(3-methoxyphenyl)-7-(3-nitrobenzoyl)pyrrolo[1,2-c]pyrimidine-5,6-carboxylate 3f:
yellow crystals; 0.66 g (51%). IR (ν, cm-1): 2986, 1732, 1707, 1619, 1530, 1493, 1439, 1340,
1224, 1197, 1118. 1H NMR (δ, 400 MHz, CDCl3): 1.09, 1.40 (2t, 6H, J = 7.1 Hz, 2CH3); 3.92
(s, 3H, MeO); 3.71, 4.37 (2q, 4H, J = 7.1 Hz, 2CH2); 7.03-7.06 (m, 1H, H-4’); 7.44 (t, 1H, J
= 7.8 Hz, H-5’); 7.66-7.75 (m, 3H, H-2’, H-6’, H-5”);8.04-8.07 (m, 1H, H-6”); 8.42-8.45 (m,
1H, H-4”); 8.57 (t, 1H, J = 1.8 Hz, H-2”); 8.65 (d, 1H, J = 1.5 Hz, H-4); 10.37 (d, 1H, J = 1.5
13
Hz, H-1). C NMR (δ, 100 MHz MHz, CDCl3): 13.5, 14.3 (2Me); 55.5 (MeO);61.0, 62.3
(2CH2), 105.7 (C-5); 108.9 (C-4); 112.5, 116.5 (C-2’, C-4’), 123.6 (C-4”); 126.4, 129.5 134.3
(C-2”, C-5”, C-6”); 119.3, 130.1 (C-5’, C-6’); 119.1, 133.8, 137.4, 140.1, 140.2, 150.6 (C-4a,
C-6, C-7, C-1’, C-1”, C-3”);140.3 (C-1);147.7 (C-3);160.2 (C-3’); 162.2, 164.0 (2COO);
183.5 (COAr); HRMS-ESI (m/z): [M+Na]+ for C27H23N3O8, calcd. 540.13774, found
540.13834; Elem. anal.: calcd. for C27H23N3O8 (517.49): C 62.66, H 4.48, N 8.12; found C
62.74, H 4.52, N 8.03.
Dimethyl
3-(2,4-dimethoxyphenyl)-7-(4-bromobenzoyl)pyrrolo[1,2-c]pyrimidine-5,6-
dicarboxylate 3g: yellow crystals;0.57 g (41%). IR (ν, cm-1): 2945, 1739, 1704, 1605, 1502,
1446, 1386, 1292, 1261, 1201, 1177, 1106.1H NMR (δ, 400 MHz, CDCl3): 3.41, 3.89, 3.90,
3.98 (2s, 6H, 2MeO); 6.58 (d, 1H, J = 2.5 Hz, H-3’); 6.66 (dd, 1H, J = 8.2, 2.5 Hz, H-5’);7.57
(d, 2H, J = 8.8 Hz, H-2”, H-6”); 7.62 (d, 2H, J = 8.8 Hz, H-3”, H-5”); 8.24 (d, 1H, J = 8.8
13
Hz, H-6’); 8.93 (d, 1H, J = 1.5 Hz, H-4); 10.25 (d, 1H, J = 1.5 Hz, H-1); C NMR (δ, 100
MHz MHz, CDCl3): 51.8, 52.5 (2Me); 55.5, 55.6 (MeO); 98.92 (C-4”) 104.5 (C-5); 105.3 (C-
4); 130.1, 132.2 (C-2”, C-3”, C-5”, C-6”); 112.1, 133.1 (C-5’, C-6’); 118.1, 119.6, 127.0,
137.7, 139.6 (C-4a, C-6, C-7, C-1’, C-1”); 139.7 (C-1);148.1 (C-3); 159.4 (C-2’); 162.4 (C-
4’); 162.9, 164.6 (2COO); 184.9 (COAr); ); HRMS-ESI (m/z): [M+H]+ for C26H21BrN2O7,
calcd. 553.06049; 555.05888, found 553.06020; 555.05848; Elem. anal.: calcd. for
C26H21BrN2O7 (553.36): C 56.43, H 3.82, N 5.06; found C 56.38, H 3.76, N 5.11.
Diethyl
3-(3,4-dimethoxylphenyl)-7-(3-nitrobenzoyl)pyrrolo[1,2-c]pyrimidine-5,6-
dicarboxylate 3h: yellow crystals; 0.57 g (43 %). (ν, cm-1): 2991, 1731, 1689, 1617, 1531,
1504, 1435, 1401, 1384, 1348, 1331, 1256, 1222, 1200. 1H NMR (δ, 400 MHz, CDCl3): 1.08,
1.39 (2t, 6H, J = 7.1 Hz, 2CH3); 3.98, 4.03 (2s, 6H, 2MeO); 3.70, 4.38 (2q, 4H, J = 7.1 Hz,
2CH2); 7.00 (d, 1H, J = 8.4 Hz, H-5’); 7.69 (t, 1H, J = 8.00 Hz, H-5”); 7.74-7.77 (m, 2H, , H-
2’, H-6’); 8.03-8.05, 8.42-8.44 (2m, 2H, H-4”, H-6”); 8.55 (t, 1H, J = 1.1 Hz, H-2”); 8.58 (d,
1H, J = 1.5 Hz, H-4); 10.35 (d, 1H, J = 1.5 Hz, H-1); 13C NMR (δ, 100 MHz MHz, CDCl3):
13.5, 14.2 (2Me); 56.0 (MeO);61.0, 62.2 (2CH2), 105.1 (C-5); 107.4 (C-4); 109.8, 111.3,
120.1 (C-2’ C-5’, C-6’); 123.6 (C-4”); 126.3, 129.5 134.3 (C-2”, C-5”, C-6”); 119.0, 128.8,
133.9, 140.3, 140.5, 149.4 (C-4a, C-6, C-7, C-1’, C-1”, C-3”);140.3 (C-1);147.6 (C-
3);150.3,151.3 (C-3’, C-4’); 162.3, 164.0 (2COO); 183.4 (COAr); HRMS-ESI (m/z): [M+H]+
for C28H25N3O9, calcd. 548.16636, found 548.16741; Elem. anal.: calcd. for C28H25N3O8
(531.51): C 63.27, H 4.74, N 7.91; found C 63.38, H 4.68, N 7.82.
Dimethyl 3-(3,4-dimethoxylphenyl)-7-(2,4-dimethoxybenzoyl)pyrrolo[1,2-c]pyrimidine-5,6-
dicarboxylate 3i: yellow crystals; IR (ν, cm-1): 1701, 1610, 1504, 1475, 1329, 1267, 1199. 1H
NMR (δ, 300 MHz, CDCl3): 3.47, 3.81, 3.89, 3.98, 3.99, 4.04 (6s, 18H, 6MeO); 6.49 (s, 1H,
H-3”); 7.01 (d, 1H, J = 8.4 Hz, H-5’); 7.73 (d, 1H, J = 2.1 Hz, H-2’); 7.76-7.79 (m, 3H, H-6’,
13
H-5”, H-6”); 8.52 (d, 1H, J = 1.5 Hz, H-4); 10.49 (d, 1H, J = 1.5 Hz, H-1); C NMR (δ, 75
MHz, CDCl3): 51.9, 52.6, 56.0 (2C) 56.1, 56.4 (6MeO); 96.0 (C-3”); 107.3 (C-4); 109.8 (C-
2’); 111.1 (C-5’); 120.0 (C-6’): 122.8 (C-7); 133.2, 133.4 (C-5”, C-6”); 139.8 (C-1); 101.2,
104.2, 120.6, 129.0, 140.5, 149.3, 150.3, 151.0, 158.7, 158.8 (C-3, C-4a, C-5, C-6, C-1’, C-
3’, C-4’, C-1”, C-2”, C-4”);162.9, 164.6 (2CO2Me);182.8 (COAr). Elem. anal.: calcd. for
C26H24N2O5: C 70.26, H 5.44, N 6.30; found C 70.42, H 5.65, N 6.17.
Dimethyl 3-(3-methylphenyl)-7-(3-nitrobenzoyl)pyrrolo[1,2-c]pyrimidine-5,6-dicarboxylate
3j: yellow crystals; 0.52 g (44 %). IR (ν, cm-1): 2955, 1747, 1709, 1620, 1600, 1530, 1496,
4

200
201
202
203
204
205
206
207
208
209
210
211
1447, 1424, 1387, 1339, 1248, 1209, 1119. 1H NMR (δ, 300 MHz, CDCl3): 2.47 (s, 3H, Me);
3.92 (s, 6H, 2MeO); 7.31-7.33 (m, 1H, H-4’); 7.42 (t, 1H, J = 7.6 Hz, H-5’); 7.70 (t, 1H, J =
8.0 Hz, H-3”);7.95-7.99 (m, 3H, H-2’, H-6’);8.03-8.06 (m, 1H, H-6”); 8.43-8.46 (m, 1H, H-
4”);8.56 (t, 1H, J = 1.8 Hz, H-2”); 8.61 (d, 1H, J = 1.5 Hz, H-4); 10.38 (d, 1H, J = 1.5 Hz, H-
1).13C NMR (δ, 75 MHz, CDCl3): 21.5 (Me); 52.0, 52.5 (2MeO); 105.3 (C-5); 108.6 (C-4);
123.5, 124.2 (C-4’, C-4”); 126.4, 131.1, 134.2 (C-2”, C-5”, C-6”); 127.7, 129.0, 129.5 (C-2’,
C-5’, C-6’); 119.1, 133.6, 136.0, 138.9, 140.2, 140.3, 151.3 (C-4a, C-6, C-7, C-1’, C-1”, C-
3’, C-3”);140.1 (C-1);147.7 (C-3);162.6, 164.3 (2COO); 183.4 (COAr). HRMS-ESI (m/z):
[M+H]+ for C25H19N3O7, calcd. 474.12958, found 474.13102; Elem. anal.: calcd. for
C25H19N3O7 (473.43): C 63.42, H 4.05, N 8.87; found C 63.35, H 4.13, N 8.76.
3. Results and Discussion
212 3.1. Synthesis of pyrrolo[1,2-c]pyrimidines
213
214
215
216
217
The pyrrolo[1,2-c]pyrimidines 3a-j have been synthesized (Scheme 1) starting from the
pyrimidinium bromides 1 by 1,3-dipolar cycloaddition with the alkyne dipolarophiles 2 in
1,2-epoxybutane as reaction medium and acid scavenger [21,23,24]. Their structures are
presented in Table 1. In view of future exploitation of these compounds in the field of bio-
imaging investigations a study of their photophysical properties has been undertaken.
218
219
220
221
222
Scheme 1. Synthesis of the pyrrolo[1,2-c]pyrimidines 3a-j
Table 1. Substituents of the pyrrolo[1,2-c]pyrimidines and their melting points
Compound R1
R2
R3
CO2Et
CO2Et
CO2Et
R4
H
H
H
H
m.p.(oC)
197-199
223-225
193-195*
238-241
2,4-diMeO-C6H3 4-Me-C6H4
3,4-diMeO-C6H3 4-F-C6H4
3,4-diMeO-C6H3 4-Me-C6H4
3a
3b
3c
3d
3,4-diMeO-C6H3 2,4-diMeO-C6H3 CO2Et
2-MeO-C6H4
3-MeO-C6H4
2,4-diMeO-C6H3 4-Br-C6H4
3,4-diMeO-C6H3 3-NO2-C6H4
C6H5
3-NO2-C6H4
CO2Me CO2Me 166-168
CO2Et CO2Et 180-182
CO2Me CO2Me 209-211
CO2Et CO2Et 221-223
3e
3f
3g
3h
3,4-diMeO-C6H3 2,4-diMeO-C6H3 CO2Me CO2Me 201-203
3-Me-C6H4 3-NO2-C6H4 CO2Me CO2Me 230-231
3i
3j
223
224
*reference [24]
225 3.2. UV-Vis and fluorescence spectra
226
227
228
229
230
231
232
The photophysical properties of compounds 3a-j have been studied in different solvents.
Figures 1 and 2 show their absorption and emission spectra, respectively, in chloroform, and
Table 2 gives their spectral parameters. The spectra of the compounds were initially
measured in chloroform. Compounds 3a-d (group (a) in Table 2) have clearly shown higher
fluorescence than compounds 3e-j (group (b) in Table 2) (Figure 1). Consequently, the
studied compounds were divided into two groups (Table 2): (a) and (b), according to the
substituent R4 at C-6 of the pyrrolo[1,2-c]pyrimidine framework: R4 = -H for group (a) and
5

233
234
235
236
237
238
239
240
241
242
243
244
245
R4 = -COOMe(or -COOEt) for group (b). This division agrees with the entire range of
fluorescence properties, as it will be shown below.
The absorption spectra of compounds 3a-j (Figure 1) display two main domains. In the first
domain, the maximum wavelength λabs1 varies in the range 242-275 nm and corresponds to
conformers with a lower conjugation, by not-involving the R1 group in the conjugation due to
the rotation outside the plane related to the pyrrolo[1,2-c]pyrimidine cycle.
In the second one, , the maximum wavelength λabs2 varies between 386 and 405 nm and
corresponds to compounds with a larger conjugation chain, in which the substituent R1 also
participates. The ratio of the two types of conformers varies in both groups depending of the
structure of R1 and also of R3.
The values of the extinction coefficient (ε) for each compound at the main wavelengths (ε1 at
λmax1 and ε2 at λmax2) are given in Table 2. The extinction coefficients were calculated using
the slopes of linear absorbance - concentration dependences.
246
247
248
249
250
251
252
253
254
255
256
Figure 1. Absorption spectra of chloroform solutions (5µmol/L) for compounds 3a-j
unsubstituted at C-6 (group (a)) and with an ester COOR attached to C-6 (group (b))
The emission spectra, recorded in chloroform for the compounds 3a-j are shown in Figure 2.
The emission spectra were obtained by exciting the molecules at λabs2 at which a higher
intensity of the fluorescence was obtained (as shown in Figure 2 inset for compound 3c :
fluorescence(λabs2) > fluorescence(λabs1).
A main emission band can be seen in the region 437–463 nm, corresponding to the blue
region of the visible spectrum. The spectroscopic features for fluorescence of 3a-j are
summarized in Table 2 together with the wavelengths for the main UV-Vis bands (λabs1, λabs2
and extinction coefficients (ε1, ε2).
)
6

257
258
259
260
261
262
263
Figure 2. Emission spectra in chloroform solutions (1µmol/L) of compounds 3a-j with (a) R4
= H (group (a)) and (b) R4 = COOR (group (b)); Figure 2a inset: fluorescence emission for
different absorption wavelengths: λabs1 = 275 nm (red) and λabs2 = 397 nm (black) for
compound 3c.
Table 2 Absorption and fluorescence parameters for compounds 3a-j in chloroform solutions
(10-6 M)*. Compounds of type a and b are on pink and blue backgrounds, respectively
R4
%
%
Emission
intensity
λabs1
(nm)
λabs2
(nm)
λem
(nm)
*
*
∆
ν 1
∆ν 2
Cpd
ε1
ε2
(cm-1) (cm-1)
H
H
H
H
268 23300
265 25200
275 29090
258 42300
261 44620
252 39520
242 42770
250 61060
242 25600
268 56200
396 39100
400 36800
397 47900
405 53800
386 46960
390 50630
392 57930
395 65910
396 27850
388 47200
462 15668
462 16091
3608
3355
3355
1808
6786
7088
6957
3387
3030
7116
158.12
109.10
238.75
289.58
36.83
7.72
21.78
1.84
131.40
5.83
3a
3b
3c
3d
3e
3f
3g
3h
3i
a
b
458 14530
437 15876
463 16716
539 21130
440 18595
456 18070
450 19100
535 18622
CO2Me
CO2Et
CO2Me
CO2Et
CO2Me
CO2Me
3j
*
264
265
Extinction coefficient (in L/mol/cm calculated from the linear correlation between absorbance and
concentration)
266
267
268
269
270
271
272
273
274
275
276
Table 2 shows the absorption and emission spectra parameters in chloroform for the
compounds 3a-j. An important change of the emission spectra of compounds 3a-j was
noticed upon the variation of the substituent R4 (Table 2). The presence of an ester group
attached to the pyrrolo[1,2-c]pyrimidine framework at C-6 (R4) dramatically decreases the
emission intensity in all compounds from group b (Figure 2b), compared to the unsubstituted
ones (Figure 2a), as it can be seen also from Table 2. This behaviour is similar in all studied
solvents (Table 4). The 7-benzoyl-pyrrolo[1,2-c]pyrimidine could present a zwitterionic
structure in which the opposite charges are in close contact, and in which there is a clear
coplanarity (due to the exocyclic double bond) between the pyrrolo[1,2-c]pyrimidine
framework and the benzoyl at C-7 (Scheme 2).
_
O
O
N
N
R2
+
N
R2
R1
R1
N
H or COOR
H or COOR
R3
R3
277
278
Scheme 2. Proposed zwitterionic structure of the 3-aryl-7-benzoyl-pyrrolo[1,2-
279
280
281
282
283
284
285
286
287
288
289
c]pyrimidine framework
The decrease of quantum yield (QY) in case of compounds 3e-j from group (b) with respect
to compounds 3a-d from group (a) could be caused by the electronic withdrawing effect of
the supplementary ester group, which tends to affect the charge distribution within the
pyrrolopyrimidine fluorophore, and by the steric effects which should be accounted, such as
the influence on conjugation degree between the pyrrolo[1,2-c]pyrimidine framework and the
benzoyl core attached to C-7.
3.3 Influence of substituents on the absorption spectra
Influence of R1 on the absorption spectra
7

290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
When the substituent attached to C-3 (R1) varied, important changes in UV-Vis spectra were
observed (Table 2). For instance, comparing compounds 3a and 3c, which differ by the
positions of the methoxy groups, the extinction coefficient increased from 23300 to 29090 for
λmax1, and from 39100 to 47900 for λmax2. Also, this comparison indicates a shift of λmax1 from
268 to 275 nm, while for λmax2, of only 1 nm (from 396 to 397). The increase of the extinction
coefficient value for 3c with respect to 3a may be attributed to the decrease in the steric
constraints in case of meta (in 3c) substitution vs ortho (in 3a). Also, compound 3h has ε1 and
ε2 values greater than 3f (61060> 39520; 65910> 50630). These values may be explained by
the substitution pattern, an MeO group in ortho position may influence the electron
distribution within the fluorophore pyrrolo[1,2-cpyrmidine] (oxygen in MeO possesses a lone
pair of electrons) and thus causing a loss in fluorescence by non-radiative effects.
Influence of R2 on the absorption spectra
Changing the benzoyl moiety on C-7 yields important absorbance variations, as it results
from the comparison between compounds 3b and 3c (with the same R1, R3 and R4
substituents, but with 4-F and 4-CH3, respectively). The extinction coefficients increase from
25200 to 29090 for λmax1, and from 36800 to 47900 for λmax2. Also, shifts of λmax1 from 265 to
275 nm, and λmax2 from 400 to 397 nm occur. The increase of extinction coefficient values for
3c relatively to 3b can be explained by the opposite electronic effects of substituent at the
aromatic ring (electron donor for 4-Me and electron withdrawing for 4-F).
Based on similar electronic effect consideration, the conjugation in the zwitterionic structure
would be easily extended to the phenyl ring of the benzoyl moiety, when a mild electron
donor such as a methyl group is present, but it would be more difficult to achieve such
conjugation, when a strong electron withdrawing substituent, such as a fluorine atom, is in
the 4- position of the aromatic ring of R2.
Influence of R4 on the absorption spectra
By comparing the compounds 3d and 3i, which have the same substituents R1 and R2, it is
found that the introduction of an ester group CO2Me (R4) determines the decrease in the
values of the extinction coefficient from 42300 to 25600 for λmax1, and from 53800 to 27850
for λmax2. Also, shifts of λmax1 from 258 to 242 nm, and of λmax2 from 405 to 396 nm occur.
The other values in Table 2 are difficult to be attributed to the effects of substituents, due to
the complexity of the structures and of the electronic effects involved.
3.4 Influence of substituents on fluorescence spectra
QY values were compared for similar structures to assess the influence of R1, R2, R3 and R4
on the fluorescence of the pyrolo[1,2-c]pyrimidines. For the scope of investigation, the
structures of the compounds were virtually assigned as pyrrolo[1,2-c]pyrimidine fluorophore
connected to two other fluorophore entities (F1 and F2), as depicted in Figure 3. The first
fluorophore entity (F1) is a phenyl ring substituted with methoxy groups, and the second one
is a substituted benzoyl moiety (F2).
O
F2
N
R2
F1
R1
N
R4
R3
333
8

334
335
336
337
Figure 3. Schematic representation of fluorophore entities of pyrrolo[1,2-c]pyrimidines
Table 3 Fluorescence yield (QY) and KSV values of quenching for compounds 3a-j in
chloroform solutions (10-6 M)
R1
R2
R4
λem
QY*a
(%)
*b
Cpd
KSV
(nm)
462
462
458
437
2,4-diMeO-C6H3
3,4-diMeO-C6H3
3,4-diMeO-C6H3
3,4-diMeO-C6H3
2-MeO-C6H4
4-Me-C6H4
4-F-C6H4
4-Me-C6H4
2,4-diMeO-C6H3
C6H5
3-NO2-C6H4
4-Br-C6H4
3-NO2-C6H4
H
H
H
H
51.77
38.26
61.35
42.40
11.04
2.64
6.63
2.99
27.46
3.24
928
367
638
885
307
160
287
79
3a
3b
3c
3d
3e
3f
3g
3h
3i
(a)
(b)
CO2Me 463
CO2Et 539
CO2Me 440
CO2Et 456
3-MeO-C6H4
2,4-diMeO-C6H3
3,4-diMeO-C6H3
3,4-diMeO-C6H3
3-Me-C6H4
2,4-diMeO-C6H3 CO2Me 450
3-NO2-C6H4
644
242
CO2Me
535
3j
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
*a quinine sulphate standard; *b calculated from the quenching experiments in presence of benzoquinone
Influence of R1 on the fluorescence spectra
Important variations of the QY are produced by changing the position of substituent R1 on the
phenyl ring (F1) attached to C-3 (see Table 2, 3). By comparing the quantum yields of
compounds 3a (2.4-diMeO substituted) and 3c (3,4-diMeO substituted), it was found that the
relative position of the two methoxy groups influences the emission spectra. The QY value
for 3a (51.77%) is smaller than for 3c (61.35%), due to the steric hindrance that diminishes
the conjugation in the structure of F1 (see above).
Comparing the compounds 3f and 3h, which have the same substituents R2, R3, R4, the
quantum yield was found to slightly increase (2.99%) in compound 3h, due to the presence of
an additional MeO- group attached to the C-3 phenyl ring (F1), while for compound 3f was
of 2.64%.
Influence of R2 on the fluorescence spectra
The QY values for compounds 3b and 3c were compared, in order to evaluate this influence
of the R2 substituent on fluorescence. These compounds have the same R1, R3 and R4
substituents, but different R2 substituents, 4-F-C6H4- and 4-Me-C6H4- , respectively. When
the fluorine atom is replaced by Me group, the value of the QY significantly increases (from
38% to 61%). This indicates the growth of conjugation inside the pyrrolo[1,2-c]pyrimidine
fragment due to the donor effect of the methyl group. Conversely, that of F decreases the
conjugation (due to its electron withdrawing effect).
The confirmation of the contribution of the substituted benzoyl moiety (F2) to fluorescence
has been done because the presence of two electron donating methoxy groups in compound
3d lead to higher QY than that of 3b.
The QY value for 3i (27.46%) increases more than 10 times, compared to that for 3h
(2.99%), due to the different electronic effects of the two dimethoxy (electron donor) groups
from 3i and nitro (electron withdrawing) group from 3h. In the same time, the nitro group
induces a shift toward lower wavelengths (hypsochromic effect), while the methoxy groups
induce a shift toward higher wavelengths (bathochromic effect).
It was also noticed that the presence of the Br atom on the benzoyl fragment (in compound
3g) decreases the fluorescence intensity of the compound 3g to 6.63%. The unsubstituted
aromatic ring on F2 (R2 = -C6H5) would be expected to have QY > 11.04% (value
corresponding to the compound 3e), as in the case of comparison between compound 3f and
3h (where an additional group on F1 leads to the increase in QY value: QY = 2.64% for 3f,
9

373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
and QY = 2.99% for 3h). In case of compound 3g, the decrease of QY compared to a
hypothetical parent compound with R2 = 4-Br-C6H4 (with the same F1) is explained by the
internal effect of fluorescence quenching by heavy atoms (Br).
Influence of R3 on the fluorescence spectra
The R3 substituent varies slightly along the series of compounds (-COOMe or -COOEt).
Upon comparing compounds 3f and 3j, which have the same F2, and F1 substituted in meta-
position (thus expecting a weak influence on conjugation), both having R4 ≠ H, it can be
noticed that the quantum yields are similar. It can be concluded that the presence of a
carboetoxy or carbomethoxy group (R3) does not have a major influence on the emission
intensity and absorption wavelength.
Influence of R4 on the fluorescence spectra
The introduction of a substituent in position 6 of the pyrrolo[1,2-c]pyrimidine ring
determines the decrease in quantum yield, as seen in Table 3 for all studied compounds.
Compounds 3a-d, unsubstituted in position 6, have all without exception quantum yields
greater than compounds 3e-j, substituted in this position, regardless the nature of the other
substituents (R1, R2, R3). Comparing the compound 3d, unsubstituted in position 6, with
compound 3i, substituted in 6, with the same substituents R1 and R2, a decrease in quantum
yield from 42.4% to 27.46% is observed. This decrease may be determined by the electron
withdrawing effect of the ester group and also by its steric effect, which influences the degree
of conjugation between pyrrolo[1,2-c]pyrimidine and the benzoyl attached to C-7.
3.5. Fluorescence quenching
Fluorescence quenching is a property that can be linked to important applications, such as
investigation of supramolecular assemblies [41]. The fluorescence quenching of the new
synthesized compounds has been examined using 1,4-benzoquinone (BQ) as inhibitor. In the
presence of BQ, a decrease of fluorescence intensity occurs, as shown for the compound 3d
(Figure 4a-inset). The quenching (F0/F) was calculated as the ratio of the solution
fluorescence without BQ (F0) and in presence of BQ (F), for increasing concentrations of BQ.
F0/F vs [BQ] plots obtained for all the compounds 3a-j (Figure 4) are liniar. These plots
predict the occurrence of collisional quenching of fluorescence [42].
404
405
406
407
408
409
Figure 4. F0/F vs [BQ] plot in 10−6 mol/L CHCl3 solutions of compounds 3a-d with R4 = H
(a) and 3e-j with R4 = COOR (b); Figure 4a inset: fluorescence quenching spectra of 3d
The spectroscopic features for the fluorescence of 3a-j compounds with the substituent R4
attached to C-6 of the pyrrolo[1,2-c]pyrimidine framework can be summarized from Table 2
and 3:
10

410
411
412
413
414
415
416
417
418
419
420
421
422
423
•
The wavelengths for the main fluorescence (λem) are smaller for compounds of the
group (a) with R4 = H than those substituted with R4 = COOMe or COOEt from the
group (b), being situated in the blue region;
Stokes shifts are smaller for compounds of the group (a) than those of the group (b),
∆ν2 being at least 3 times smaller than ∆ν1;
Quantum yield (QY) is at least 2 times bigger for compounds of group (a) than those
of group (b); QY varies between 42% and 61% for compounds 3a-d, and between 2%
and 27% for compounds 3e-j.
Stern-Volmer constant (KSV) is generally bigger for compounds of group (a) than
those of group (b).
•
•
•
•
•
Important changes of QY and KSV occur when F1 and F2 structures vary.
The study of each substituent's effects on the spectral properties allows the prediction
of the functional groups that will lead to the best values for quantum yields and KSV.
424
425
426
427
428
429
430
431
432
433
434
3.6. Influence of solvent on photophysical properties
The photoluminescence of organic fluorophores in solutions is influenced by solvent polarity
[43]. To evaluate this influence, the UV-Vis and fluorescence spectra of the new synthesized
compounds were recorded in solvents with various dielectric constant (ε) and refractive index
(n). To identify the link between the solvent properties and the spectral characteristics, the
spectra have been recorded in different solvents: chloroform (CHCl3), dichloromethane
(CH2Cl2), acetonitrile (CH3CN), and dimethyl sulfoxide (DMSO). The data obtained in
chloroform are given in Table 2, and the data obtained in dichloromethane, acetonitrile and
dimethyl sulfoxide are resumed in Table 4. For instance, the influence of solvent on
absorption and emission spectra, in case of compound 3g, is depicted in Figure 5.
435
436
Figure 5. Absorption (a) and emission (b) spectra for compound 3g (10-6 mol/ L) in solvents
437
438
439
440
441
442
443
444
445
with different polarity: chloroform, dichloromethane, acetonitrile, DMSO
The change of the solvent leads to important variations of absorption and fluorescence
maximum wavelength and intensity. This compound has the biggest red shift of the emission
wavelength from 440 nm (in CHCl3) to 557 nm (in DMSO). A bathochromic shift of the
emission peaks can be seen when passing from CHCl3 to CH2Cl2, CH3CN, DMSO (Tables 2-
4). This suggests the implication of photo-induced intramolecular charge transfer (ICT) in the
singlet excited state with larger dipole moment, as expected [44].
11

446
447
Table 4. Several photophysical parameters for compounds 3a-j in solutions (10-6 M) with
different solvents (S)
Solvent
Dichloromethane
Acetonitrile
Dimethyl sulfoxide
%
%
%
λabs
ε
λem
QY λabs
ε
λem
QY λabs
ε
λem
QY
∆
ν
∆
ν
∆ν
nm L/mol/ nm (cm-1) (%) (nm) L/mol/ (nm) (cm-1) (%) (nm) L/mol/ (nm) (cm-1) (%)
Compound
cm
246 24300 466 19191 25.98 270 43400 468 15669 29.80 289 15500 468 13234 51.51
397 43000 3729 390 29700 4273 395 31800 3948
244 122800 466 19524 5.67 244 17600 469 19661 10.7 290 14000 470 20390 21.74
398 197100 3666 395 27600 3994 390 31600 4364
266 89000 468 16226 20.99 266 20900 481 16226 52.60 292 25000 492 12833 87.26
397 148600 3821 393 39600 4077 390 49300 4227
240 34100 438 18835 17.90 252 44300 439 16903 3.89 295 13200 467 11476 40.16
402 44100 2284 400 83100 2666 395 40300 3219
242 36900 470 19392 0.80 248 21500 525 21347 2.88 291 15600 457 12482 4.66
394 39200 3007 375 24800 7691 378 25000 4573
246 22900 437 17767 0.84 246 81600 428 17285 1.74 290 19600 435 11494 0.80
386 17700 3023 380 59500 2951 390 25500 2652
245 21000 459 19029 10.07 277 64100 555 18083 0.50 290 18400 557 16529 5.64
388 29800 3986 391 85600 7557 395 22400 7363
245 40100 460 18886 0.14 244 47300 465 20019 2.29 290 26400 455 19688 0.60
394 37400 3007 390 38600 4352 388 44900 34672
245 27800 460 19927 12.33 240 44000 468 20299 8.84 270 46300 470 15760 6.80
394 32500 3836 391 38700 4207 396 49700 3513
245 50300 457 18934 1.29 245 43200 520 21585 1.64 290 23400 536 15826 2.03
387 42100 3957 382 33600 6947 385 27600 7317
cm
cm
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
The comparison of spectral parameters (Tables 2 - 4) shows that the investigated pyrrolo[1,2-
c]pyrimidines 3a-j have fluorescence quantum yields with significant variations (from 0 to
about 90 %), which are very much dependent on solvent.
The common behaviour of the new synthesized compounds is a shift of the emission peaks to
lower wavelengths (hypsochochromic shift) with the increase of solvent polarity, from 6 nm
in case of compound 3a, to 117 nm for compound 3g. This is a typical tendency found for
these compounds, when ICT occurs upon excitation (solvatochromic behaviour) and leads to
a charge-separated (highly polar) emitting state, which can be stabilized by polar solvents.
The emission wavelength increases with the solvent polarity (red shift). This behaviour leads
to the conclusion that ICT is polar for the excited state, with a large dipole moment. This
state is understandably very stable when the solvent is polar.
Figure 5 shows that the change of the solvent has no major impact on the absorption spectra,
but it has a significant effect on fluorescence intensity and wavelength. The values from
Table 2 -4 confirm this behaviour for all compounds.
To rationalize the obtained results for the influence of solvent on fluorescent properties of the
studied compounds (Stokes shifts, etc.), solvent polarity function (∆ƒ) expressed by Lippert-
Mataga equation (1) [45] has been examined. The solvent polarity values have been
calculated using equation (2).
2
2(µe
−
µ g )
(1)
(2)
∆
ν st
=
∆f + Const.
hca 3
ε
−1
n2 −1
∆f
=
−
2n2 +1
2ε +1
is the Stokes shift (cm-1), h is Planck's constant, c is the vacuum light speed, a is
∆
ν
st
466
467
468
469
470
471
where
the radius of Onsager cavity, ε and n are, respectively, the dielectric constant and refractive
index of the solvent. µe and µg are the compound dipole moment in excited and ground states,
respectively, while ∆ƒ is the solvent orientation polarizability. ∆ƒ reflects the electron
mobility and dipole moment of the solvent molecule. The changes in the dipole moment (∆µ
= µe- µg) were calculated using Lippert-Mataga method [46].
12

472
473
474
475
476
477
Bakhshiev's (Eq. 3) and Kawski-Chamma-Viallet’s (Eq. 6) equations [47] were used to
calculate the dipole moments in the fundamental and excited states for each compound 3a-j.
By plotting Stokes shift (νabs
- νem) vs solvent polarity function F1 (Figure 7a), S1 has been
calculated using equation (3). Plotting the average sum of the absorption-emission maxima vs
F2 [48] (Figure 7b), allowed the calculation of S2 using equation (8).
(3)
νabs - νem = S1·F1(D, n) + const.
478
479
480
In (3), νabs and νem are the wave numbers (cm-1) for excitation and emission maxima,
respectively, F1 (orientation solvent polarity function), and S1 being defined as in equations
(4) and (5):
2
2
(4)


2n + 1
ε
− 1 n − 1
F1 (
ε
, n) =
−




n2 + 2
ε
+ 2 n2 + 2
2
(5)
2
µ
−
µg
)
(
e
S1 =
hca3
(6)
(7)
(
νabs
+ νem)/2 = -S2·F2(ε, n) + const.
481
F2 and S2 were defined as in equations (7) and (8):





1
3
n4 −1
F2 (
ε
,n) = F (
ε
,n) +
1
2
2 (n2 + 2)2

2
µ2 µg2
−
(8)
(
)
e
S2 =
hca3
482
483
484
485
486
487
488
Looking at the differences between the dipole moments ∆µ, given in Table 5 (calculated for
all studied compounds), the compound 3c has the smallest value of the difference between
the µg, and µe. That is why, this compound has been selected to estimate the solvent influence
on fluorescence properties for the studied compounds, through the dependence of Stokes
shifts on solvent polarity (Figure 6). The R2 value (0.973) from Figure 6 for the linear
dependence of ∆υ vs ∆f shows a good correlation.
489
490
491
492
493
Figure 6. Dependence of Stokes shift values (∆υ) on orientation solvent polarity (∆f) in
different solvents for compound 3c
Table 5. Calculated values for ∆µ (∆µ = µe- µg) between the ground (µg) and excited (µe)
494
dipole moments for the compounds using equations (1), (2), (3) and (6)
13

Group
(a)
Compound
∆µ (D)
3.64
µg (D)
2.83
2.42
4.32
3.11
µe (D)
6.47
7.64
4.7
3a
3b
3c
5.21
0.38
2.08
5.16
3d
3e
3f
3g
3h
3i
10.24
0.82
11.84
5.32
9.27
4.88
3
13.24
4.89
16.17
9.48
9.68
7.52
4.06
4.35
4.15
0.2
(b)
2.63
3j
495
496
497
498
499
500
501
In Figure 7, the variation of Stokes shift ∆υ with F1 (a), and of the average value between
absorption - emission maximum wavelength shifts with F2 (b) are shown, respectively, for
compound 3c. Figure 7b shows the dependence of the average value between absorption –
emission maximum wavelength shifts ∆υ vs the solvent polarity (F2), for the compound 3c,
used to evaluate S2 for the compound 3c. The correlation coefficient obtained has a small
value (R2 = 0.422) attributed to the specific interaction between solute and solvent [49]. The
more polar solvent, acetonitrile, stabilizes better the excited state of a compound, when the
dipole moment of the solute in the excited state is bigger than that in the ground state.
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
Figure 7. Stokes shift variation with F1 (a) and the average value between absorption and
emission maximum wavelength shifts with F2 (b), respectively, for compound 3c
The calculated properties (F1, F2, etc.) for all the pyrrolo[1,2-c]pirimidines were examined in
correlation with the experimental values, to describe the solvent influence on fluorescence
properties of the investigated compounds. The overall effects of the solvent on optical
properties (absorption and emission) were analyzed by Kamlet-Taft solvatochromic equation
(Eq. 9) [50]. In (9), π* is the solvent polarizability, β is the hydrogen bond acceptor (HBA)
ability, α is the hydrogen bond donor ability (HBD). The coefficients s, b, and a are constants
characteristic for the solute. Their absolute value and sign reflect the contribution of the
corresponding solvent-solute interactions on the investigated property (such as electronic
transition energy). ν and ν0 represent the solvent-dependent property under study, for instance
λmax value in the UV-Vis spectrum.
ν = β + a α
ν0 + s π * +b
(9)
517
The solvents parameters π*, α, and β, are given in Table 6 [44].
14

518
519
Table 6. Solvent polarity parameters [44]
Solvent
∆f
π*
β
α
Chloroform
Dichloromethane
DMSO
0.15
0.21
0.26
0.30
0.69
0.73
1.00
0.66
0.10
0.10
0.76
0.19
0.20
0.13
0.00
0.40
Acetonitrile
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
The data obtained after the calculation using equation (9) by multiple linear regression
analysis, for solvatochromic parameters for all compounds 3a-j, are presented in Tables 7 and
8. The multiple linear regression in Figure 8 shows a good correlation between the calculated
and experimental data. The values of a and b coefficients present smaller values than s
coefficients, which indicates that the ability of the solvent to donate or accept hydrogen
bonds is weaker than the solute-solvent dipole-dipole interactions.
For the compounds with positive values of s and a coefficients (Table 7), it is expected a
bathochromic shift of the emission wavelength with the solvent polarity increase. This is
seen in Table 4, for compound 3d (which has positive s and a coefficients, s = 10.72 and a =
4.55). It shows a positive solvatochromic behaviour (λem (nm) is 438, 439, and 467 in DCM,
CH3CN and DMSO, respectively). A stabilization of the electronic excited state relatively to
the ground state occurs in this case. If the coefficient b is negative, a hypsochromic shift
occurs, that indicates the stabilization of the ground state, relatively to the electronic excited
state.
535
536
Figure 8. Experimental (υexp) vs. calculated (υcalc) values of Stokes shifts for compounds 3a-j
537
538
539
540
from Eq. (9)
Table 7. Coefficients of solvatochromic parameters for compounds 3a-j calculated by
multiple linear regression using equation (9)
Group
Compound
υ0 (cm-1)
s (103)
-14630
b (103)
4720
a (103)
-5710
3a
3b
3c
32410
31640
44870
-13620
-34410
4290
-5130
(a)
10660
-13280
3d
3e
3f
3g
3h
3i
11180
11180
14950
1650
19660
47410
19010
10720
10720
5380
29070
3120
-3660
-3660
-2050
-12370
-2390
11580
470
4550
4550
1560
6930
1780
(b)
-34480
-500
-12800
-290
3j
541
15

542
Table 8. Contribution of solvatochromic parameters coefficients from equation (9)
Group
Compound
Pπ
Pβ
Pα
3a
3b
3c
0.58
0.59
0.59
0.19
0.19
0.18
0.23
0.22
0.23
(a)
3d
3e
3f
3g
3h
3i
0.61
0.57
0.60
0.60
0.43
0.40
0.59
0.21
0.19
0.23
0.26
0.32
0.37
0.20
0.18
0.24
0.17
0.14
0.24
0.23
0.22
(b)
3j
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
The solvatochromic parameters contributions of the new compounds are presented in Table 8.
The obtained values indicate that the solvatochromic behaviour of investigated [1,2-
c]pyrimidines is mainly influenced by the solvent polarizability (Pπ*). The hydrogen bond
acceptor ability, or hydrogen bond donor ability of the solvents, have smaller influence on the
solvatochromic properties of compounds 3a-j. However, for compound 3i, Pπ and Pβ have
close values. These values could be correlated to the other values of the parameters: QY
values decrease with the increasing of the solvent polarity (Table 4).
4. Conclusions
The new synthesized [1,2-c]pyrimidines present blue fluorescence, some of them showing
high quantum yields. The substituent effects on absorption and fluorescence parameters of
these derivatives were discussed. It was shown that the presence and position of the methoxy
or methyl groups on the phenyl ring in position 3, or on the benzoyl group in position 7, have
a strong influence on the fluorescence of compounds. The presence of an ester group grafted
on C-6 atom of the pyrrolopyrimidine dramatically reduces the fluorescence. The
examination of UV-Vis and fluorescence spectra of the new compounds, in close connection
with the substituent nature (halogen, methyl, methoxy and nitro), has revealed that these
spectra are also function of solvent properties. The interaction of these compounds with
solvents having different polarity (chloroform, dichloromethane, acetonitrile or dimethyl
sulfoxide) has been investigated through correlation of the absorption and fluorescence
features with solvent polarity functions. Solvent parameters (polarity, basicity, and acidity)
contribution onto solvent-solute interactions has been evaluated. Solvent polarity has been
found to be the most important parameter which influences the emission spectra of these
compounds - potential candidates for OLED technology and fluorescent probes. Further
studies directed to the electrochemical properties of all these compounds are in progress for
practical applications (e.g. chemical sensors).
569
570
571
Acknowledgement
572
573
574
575
576
577
578
579
Access to research infrastructure developed in the “Petru Poni” Institute of Macromolecular
Chemistry through the European Social Fund for Regional Development, Competitiveness
Operational Programme Axis 1, Project InoMatPol (ID P_36_570, Contract 142/10.10.2016,
cod MySMIS: 107464) is gratefully acknowledged.
References
[1]. Valeur B. Molecular Fluorescence: Principles and Applications. Wiley-VCH, Weinheim
GE. 2000
16

580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
[2]. Chen D, Su SJ, Cao Y. Nitrogen heterocycle-containing materials for highly efficient
phosphorescent OLEDs with low operating voltage. J Mater Chem. 2014; C2: 9565-9578.
doi: 10.1039/C4TC01941E
[3]. Yen YS, Ni JS, Lin TY, Hung WI, Lin JT. Imidazole-Based Sensitizers Containing
Double Anchors for Dye-Sensitized Solar Cells. Eur J Org Chem. 2015; 33: 7367-7377. doi:
https://doi.org/10.1002/ejoc.201501131
[4]. Ooyama Y, Uenaka K, Ohshita J. Development of D–π–A Fluorescent Dyes with a 3-
Pyridyl Group as Electron-Withdrawing Anchoring Group for Dye-Sensitized Solar Cells.
Eur J Org Chem. 2015; 17: 3713-3720. doi: https://doi.org/10.1002/ejoc.201500341
[5]. Firmino ADG, Goncalves MST. Bifunctionalised long-wavelength fluorescent probes for
biological
applications.
Tetrahedron
Lett.
2012;
53:4946-4950.
doi:
10.1016/j.tetlet.2012.07.004
[6]. Zhang Y, Yan Y, Chen S, Gao Z, Xu H. ‘Naked-eye’ quinoline-based ‘reactive’ sensor
for recognition of Hg2+ ion in aqueous solution. Bioorg Med Chem Lett. 2014; 24: 5373-
5376. doi: https://doi.org/10.1016/j.bmcl.2014.10.052
[7]. Suresh M, Mandal AK, Suresh E, Das A. First demonstration of two-step FRET in a
synthetic supramolecular assembly. Chem Sci. 2013; 4: 2380-2386. doi:
10.1039/C3SC50282A
[8]. Ying W, Yang J, Wielopolski M, Moehl T. Moser JE, Comte P, Hua J, Zakeeruddin, SM,
Tian H, Gratzel M. New pyrido[3,4-b]pyrazine-based sensitizers for efficient and stable dye-
sensitized solar cells. Chem Sci. 2014; 5: 206-214. doi: 10.1039/C3SC51844B
[9]. Huckaba AJ, Giordano F, McNamara LE, Dreux KM, Hammer NI, Tschumper GS,
Zakeeruddin SM, Gratzel M, Nazeeruddin MK, Delcamp JH. Indolizine-based donors as
organic sensitizer components for dye-sensitized solar cells. Adv Energ Mater. 2014;
5:1401629. doi: https://doi.org/10.1002/aenm.201401629
[10]. Dumitrascu F, Vasilescu M, Draghici C, Caproiu MT, Barbu L, Dumitrescu DG. New
fluorescent indolizines and bisindolizinylethylenes. Arkivoc. 2011; (x): 338-350. doi:
10.3998/ark.5550190.0012.a28
[11]. Kristafor S, Kraljevic TG, Ametamey SM, Cetinac M, Ratkajd I, Haceke RT, Pavelic
SK, Malic, SR. Syntheses and Antitumor Evaluation of C(6)-Isobutyl- and C(6)-Isobutenyl-
Substituted Pyrimidines, and Dihydropyrrolo[1,2-c]pyrimidine-1,3-diones. Chem Biodivers.
2011; 8: 1455-1469. doi: https://doi.org/10.1002/cbdv.201000202
[12]. Kim JT, Hamilton AD, Bailey CM, Domoal RA, Wang L, Anderson KS, Jorgensen
WL. FEP-guided selection of bicyclic heterocycles in lead optimization for non-nucleoside
inhibitors of HIV-1 reverse transcriptase. J Am Chem Soc. 2006; 128: 15372-15373. doi:
10.1021/ja066472g
[13]. Bondu S, Genta-Jouve G, Leiros M, Vale C, Guigonis JM, Botana LM, Thomas OP.
Additional bioactive guanidine alkaloids from the Mediterranean sponge Crambecrambe.
RSC Adv. 2012; 2: 2828-2835. doi: 10.1039/C2RA00045H
[14]. Perry NB, Ettouati L, Litaudon M, Blunt JW, Munro MHG, Parkin S, Hope H.
Alkaloids from the antarctic sponge Kirkpatrickiavarialosa.: Part 1: Variolin b, a new
antitumour and antiviral compound. Tetrahedron. 1994; 50: 3987-3992. doi:
https://doi.org/10.1016/S0040-4020(01)89673-3
[15]. Alvarez M, Fernandez D, Joule JA. Synthesis of 1,2-dihydropyrrolo[1,2-c]pyrimidin-1-
ones. J Chem Soc Perkin Trans. 1999; 3: 249-256. doi: 10.1039/A809280J
[16]. Weidner H, Michaels FM, Beltman DJ, Montgomery CJ, Wadsworth DH, Briggs BT, L.
Picone M. Indolizines. 5. Preparation and structural assignments of azaindolizinols. J Org
Chem. 1991; 56: 5594-5598. doi: 10.1021/jo00019a024
17

628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
[17]. Copar A, Stanovnik B, Tisler M. A new approach for the synthesis of fused pyrroles.
The synthesis of acyl substituted pyrrolo[1,2-x]azines. J Heterocycl Chem. 1993; 30: 1577-
1579. doi: https://doi.org/10.1002/jhet.5570300621
[18]. Baumann M, Rodriguez-Garcia AM, Baxendale IR. Flow synthesis of ethyl
isocyanoacetate enabling the telescoped synthesis of 1,2,4-triazoles and pyrrolo[1,2-
c]pyrimidines. Org Biomol Chem. 2015; 13: 4231-4239. doi: 10.1039/C5OB00245A
[19]. Minguez Ortega JM, Vaquero Lopez JJ, Garcia-Navio JL, Alvarez-Builla J. Improved
synthesis of pyrrolo[1,2-c]pyrimidine and derivatives. Tetrahedron Lett. 1996; 37: 4263-
4266. doi: https://doi.org/10.1016/0040-4039(96)00812-X
[20]. Romashin YN, Liu MTH, Nijjar SS, Attanasi OA. Arylchlorocarbenes in the synthesis
of heterocycles containing two nitrogen atoms. Chem Commun. 2000; 1147-1148. doi:
10.1039/B002940H
[21]. Iuhas PC, Georgescu F, Georgescu E, Draghici C, Caproiu MT. Regiochemistry of the
1,3-dipolar cycloaddition of some N-heterocyclic cycloimmoniumylides to unsymmetrical
alkynes. Rev Roum Chim. 2002; 47: 333-338.
[22]. Mangalagiu GC, Mangalagiu II, Olariu RI, Petrovanu MG. 4-Methylpyrimidinium
ylides II: Selective reactions of pyrimidinium ylides with activated alkynes. Synthesis. 2000;
14: 2047-2050. doi: 10.1055/s-2000-8731
[23]. Georgescu E, Georgescu F, Draghici C, Cristian L, Popa MM, Dumitrascu F. Fast and
green one-pot multicomponent synthesis of a library of pyrrolo [1,2-c]pyrimidines under
microwave irradiation. Comb Chem High T Scr. 2013; 16: 851-857. doi:
10.2174/13862073113169990050
[24]. Georgescu E, Georgescu F, Popa MM, Draghici C, Tarko L, Dumitrascu F. Efficient
one-pot, three-component synthesis of a library of pyrrolo[1,2-c]pyrimidine derivatives.
ACS Comb Sci. 2012; 14: 101-107. doi: 10.1021/co2002125
[25]. Bhavya P, Melavanki R, Manjunatha MN, Koppal V, Patil NR, Muttannavar VT.
Solvent effects on the photophysical properties of coumarin dye. AIP Conference
Proceedings 1953, 080022 (2018). doi: https://doi.org/10.1063/1.5032828
[26]. Melavanki RM, Patil HD, Umapathy S, Kadadevaramath JS. Solvatochromic Effect on
the Photophysical Properties of Two Coumarins. J. Fluoresc., 2012; 22, 137-144. doi:
https://doi.org/10.1007/s10895-011-0939-7
[27]. Yang S, Liang X, Zhao Y, Fan J. Solvent effect on the absorption and fluorescence of
ergone: Determination of ground and excited state dipole moments. Spectrochim. Acta A,
2013; 102, 194-199. doi: 10.1016/j.saa.2012.10.013
[28]. Nagachandra KH, Mannekutla JR, Amarayya SM, Inamdar SR. Solvent effect on the
spectral properties of dipolar laser dyes: Evaluation of ground and excited state dipole
moments. Eur. J. Chem., 2012;3 (2), 163-171. doi: 10.5155/eurjchem.3.2.163-171.538
[29]. Deepa HR, Thipperudrappa J, Suresh Kumar HM. Effect of solvents on the
spectroscopic properties of LD-489 & LD-473: estimation of ground and excited state dipole
moments by solvatochromic shift method. Spectrochim. Acta A, 2013; 108, 288-294. doi:
10.1016/j.saa.2013.01.084
[30]. Mostafa S, El-Sadek M, Alla EA. Spectrophotometric determination of ciprofloxacin
and pefloxacin through charge transfer complexation. J. Pharmacol. Biomed. Anal., 2002; 27,
133-142. doi: https://doi.org/10.1016/S0731-7085(01)00524-6
[31]. Subhani MS, Bhatti NK, Mohammed M, Khan Turk AY. Spectroscopic Studies of
Charge-Transfer Complexes of 2,3-Dichloro-5,6-Dicyano-P-Benzo-Quinone. J. Chem., 2000;
24, 223-230.
[32]. Yang J, Cao Y, He JH, Yang T, Kim X, Peng X, Kim JS. Macro-/micro-environment-
sensitive chemosensing and biological imaging. Chem Soc Rev., 2014; 43, 4563-4601. doi:
10.1039/C4CS00051J
18

678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
[33]. Klymchenko AS. Solvatochromic and fluorogenic dyes as environment-sensitive
probes: design and biological applications. Acc Chem Res, 2017; 50, 366-375. doi:
10.1021/acs.accounts.6b00517
[34]. Tatu L, Georgescu E, Boscornea C, Ungureanu EM. Synthesis and fluorescence of 1-[7-
(4-nitrobenzoyl)-3-(biphenyl-4-yl)pyrrolo[1,2-c]pyrimidin-5-yl]ethanone. UPB Bull Sci.
2015; 77: 49-58.
[35]. Tatu ML, Georgescu E, Boscornea C, Popa MM, Ungureanu EM. Synthesis and
fluorescence of new 3-biphenylpyrrolo[1,2-c]pyrimidines. Arab J Chem. 2016; 10: 643-652.
doi: https://doi.org/10.1016/j.arabjc.2016.09.013
[36]. Tatu ML, Harja F, Ungureanu EM, Georgescu E, Popa MM. Electrochemical
characterization of some pyrrolo[1,2-c]pyrimidine derivatives. Rev Chim (Buc). 2018; 69:
499-506.
[37]. Tatu ML, Spectral and electrochemical studies of several pyrrolopyrimidines.
Universitatea Politehnica Bucuresti. 2017, PhD Thesis
[38]. Zugravescu I, Georgescu F, Chiraleu F, Filip P I, Georgescu E. Pyrimidinium-ylides. I.
The synthesis and the stability of some 4-phenylpyrimidinium-ylides. Rev Chim (Buc) vol.
31, 1980, p 11-13.
[39]. Georgescu E, Druta I, Petrovanu M. Dipolar derivatives in the quinazoline series. I. The
synthesis of pyrrolo[1,2-c]quinazolines. Rev. Roum. Chim. vol. 26, 1981, p 109-116
[40]. Georgescu F, Chiraleu F, Georgescu E, Zugravescu I. Pyrimidinium-ylides. II. The
reactions of several carbanion-monosubstituted 4-phenylpyriminium-ylides with activated
acetylenes. Rev. Roum. Chim. vol. 26, 1981, p 879-885
[41]. Wang C, Huang J, Ye J. Binding of aromatic anion amphiphile to phospholipid
vesicles: a fluorescence study. Colloids Surf A. 2002; 204: 125-129. doi:
https://doi.org/10.1016/S0927-7757(01)01133-5
[42]. Lakowicz JR. Principles of Fluorescence Spectroscopy. Springer-Verlag US. 2006; 277-
290.
[43]. Raikar US, Renuka CG, Nadaf YF, Mulimani BG, Karguppikar AM Soudagar MK.
Solvent effects on the absorption and fluorescence spectra of coumarins 6 and 7 molecules:
determination of ground and excited state dipole moment, Spectrochim. Acta A. 2006; 65:
673-677. doi: https://doi.org/10.1016/j.saa.2005.12.028
[44]. Ziołek M, Filipczak K, Maciejewski A. Spectroscopic and photophysical properties of
salicylaldehyde azine (SAA) as a photochromic Schiff base suitable for heterogeneous
studies.
Chem
Phys
Lett.
2008;
464:
181-186.
doi:
https://doi.org/10.1016/j.cplett.2008.09.030
[45]. Abboud JM, Kamlet MJ, Taft RW, (1977) Regarding a generalized scale of solvent
polarities. J Am Chem Soc. 1977; 99: 8325-8327. doi: 10.1021/ja00467a039
[46]. Zakerhamidia MS, Ghanadzadeha A, Tajalli H, Moghadamb M, Jassas M. Hosseininiaa
R. Substituent and solvent effects on the photo-physical properties of some coumarin dyes.
Spectrochimica Acta A. 2010; 77: 337-334. doi: https://doi.org/10.1016/j.saa.2009.12.060
[47]. Kawski A. On the Estimation of Excited-State Dipole Moments from Solvatochromic
Shifts of Absorption and Fluorescence Spectra. Z Naturforsch. 2002; 57: 255-262. doi:
https://doi.org/10.1515/zna-2002-0509
[48]. Pannipara M, Asiri AM, Alamry KA, Salem IA, El-Daly SA. Spectral behavior and
photophysical parameters of (2Z)-3-[4-(dimethylamino) phenyl]-2-(4-fluorophenyl) prop-2-
ene-nitrile (DPF) in different media. J Luminesc. 2015; 157: 163-171. DOI:
https://doi.org/10.1016/j.jlumin.2014.08.053
[49]. Liu L, Sun Y, Wei S, Hu X, Zhao Y, Fan J. Solvent effect on the absorption and
fluorescence of ergone: Determination of ground and excited state dipole moments.
Spectrochim Acta A. 2012; 86: 120-123. DOI: https://doi.org/10.1016/j.saa.2011.10.016
19

728
729
730
[50]. Kamlet MJ, Taft RW. The solvatochromic comparison method. I. The beta-scale of
solvent hydrogen-bond acceptor (HBA) basicities. J Am Chem Soc. 1976; 98: 377-383. doi:
10.1021/ja00418a009
20

Highlights
•
•
New 3-arylpyrrolo[1,2-c]pyrimidines substituted at C3 and C7 were synthesized. 79
Their absorption spectra display two main absorption domains, and blue fluorescence
appeared.95
•
•
•
The excitation and emission spectra were recorded in different solvents.74
The dipole moments have been calculated using the solvent polarity functions. 79
The fluorescence is influenced by substituents (halogen, methyl, methoxy and NO2). 85