V. V. M., S. Pola and P. Chetti
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 245 (2021) 118940
2
integral respectively. Eq. (2) suggests that the charge transfer rate
mainly depends on values of λ and V. λ is composed of internal and ex-
ternal reorganization energies, whose parameters are influenced by in-
tramolecular vibrations and surrounding medium consecutively. The
values of external λ are comparatively lower than those of internal λ
2.3.1. PZ1:4,6-dichloro-N -(6-methyl-2-pyridinyl)-1,3,5-triazine-2-amine
The mixture of cyanuric chloride (0.5 g. 2.71 mmol) and DIPEA
(0.3 mL, 2.71 mmol) in 25 mL THF was cooled to 0 °C under N atmo-
2
sphere. The previously cooled (0 °C) solution of 2-amino-6-methyl pyr-
idine in 25 mL THF was added dropwise to the above reaction mixture
[36]. Hence, we have calculated internal λ [total internal hole reorgani-
2
over a period of 15 min and stirred for 2 h under N . The reaction was
zation energy (λ
Eqs. (3) and (4) respectively.
h
) and electron reorganization energy (λ
e
)] by using
continued to stir at 0-5 °C till all the amine gets exhausted as indicated
by TLC. Then, THF was removed from the reaction mixture under re-
duced pressure. Further, the reaction mixture was extracted in ethyl ac-
etate (3×30 mL) and the organic layer was dried over anhydrous
λh ¼ λ1 þ λ2
ð3Þ
ð4Þ
2 4
Na SO , filtered and the solvent was evaporated under reduced pres-
sure to obtain a white residue. The residue is purified by silica column
chromatography (ethyl acetate/hexane: 1:8→1:7) to get a white solid
λe ¼ λ3 þ λ4
−
1
(
0.562 g, 81% yield). M.P: 132-135 °C.IR (KBr): 3234 cm (medium,
where
−
1
−1
-NH), 2924 cm
(medium, -CH
3
), 1606 cm
(medium, -C=N-),
): δ 9.47 (br s, 1H,
−1
1
1
250 cm (strong, -CH
3
). H NMR (500 MHz, CDCl
3
þ
þ
λ1 ¼ E ðG0Þ−E ðGþÞ
NH), 8.06 (m, J = 5 Hz, 1H,ArH), 7.70 (t, J = 5 Hz, 1H, ArH), 6.99 (d,
13
J = 5 Hz, 1H,ArH), 2.52 (s, 3H, CH
3 3
). C NMR (500 MHz, CDCl ): δ
0
0
λ2 ¼ E ðGþÞ−E ðG0Þ
163.66, 157.71, 149.26, 138.86, 120.17, 111.93, 23.80. EI-MS: Calculated
+
9 7 2 5
for C H Cl N is 255.01, found 255.82 (M ).
−
−
λ3 ¼ E ðG0Þ−E ðG−Þ
2
4
2
.3.2. PZ2:6-chloro-N ,N -bis-(6-methyl-2-pyridinyl)-1,3,5-triazine-2,4-
diamine
Cyanuric chloride (1 g, 5.42 mmol) was dissolved in 30 mL of THF in
a 100 mL round bottom flask and was added with DIPEA (~2 mL,
11.38 mmol) under N atmosphere at room temperature. Then 2-
0
0
λ4 ¼ E ðG−Þ−E ðG0Þ
0
In the above equations, where E (G
0
) is the energy of the neutral
(G+/−) is the energy of ion (cat-
+
/−
2
molecule in neutral geometry, E
ion/anion) in ionic geometry, E /−(G
+
amino-6-methyl pyridine (1.23 g, 11.38 mmol) was dissolved in
30 mL of THF and added dropwise to the above reaction mixture over
a period of 30 min. The reaction mixture was stirred at rt. under nitro-
gen for 8 h. The progress of the reaction was monitored by TLC. Then
THF was stripped off from reaction mixture by rotavaporization
followed by extraction of product in ethyl acetate (3×50 mL). The or-
0
) is the energy of ion (cation/
0
anion) in neutral geometry and E (G+/−) is the energy of the neutral
molecule in ionic geometry. Here hole and electron are represented by
subscripts h and e.
2.3. Synthesis and characterization
2 4
ganic layer was dried over anhydrous Na SO , filtered and was concen-
trated under reduced pressure to obtain a red-colored residue. The
residue was purified by using column chromatography using silica gel
The molecules under investigation are presented in Scheme 1. The
synthetic protocols of PZ and AZ series of molecules are shown in
Figs. 1 and 2 respectively. The synthetic strategies follow simple nucle-
ophilic substitution reactions in the presence of a suitable base, solvent
and temperature, which are reported in previous literature [37–44] and
are carried out with slight modifications.
(
7
ethyl acetate/hexane: 1:5→1:4) to obtain pale yellow solid (1.29 g,
−1
−1
3% yield).M.P: 165-170 °C. IR (KBr): 3232 cm -3116 cm (br, me-
−
1
), 1737 cm−1 (medium, -C=
)· H NMR (500 MHz, CDCl ): δ 8.03 (br s,
H, ArH), 7.56 (br s, 2H, ArH), 6.85 (d, J = 10 Hz, 2H, ArH), 2.45 (s,
dium, -NH), 2924 cm (medium, -CH
N), 1273 cm (strong, -CH
2
6
1
3
3
−1
1
3
3
In the AZ series, the synthesis proceeded from mono- to di- to tri-
substitution without any difficulty by increasing the temperature of re-
action as shown in Fig. 2. But in the case of PZ series, mono- and di- sub-
stitution occurred readily, while the third substitution was prevented at
position 6 of 1,3,5-triazine due to the increased electron density at car-
bon present in the position 6 (due to electron donation by already
substituted two pyridine rings), which is no longer can be attacked by
nucleophiles. Though trisubstitution is attempted by means of varying
temperature of reaction from room temperature to refluxing tempera-
tures in tetrahydrofuran for extended time scale (24–36 h), the disub-
stituted molecule remained inert to trisubstitution. The detailed
procedures are described in the following discussion. The characteriza-
13
3 3
H, CH ). C NMR (500 MHz, CDCl ): δ169.91, 163.59, 157.22, 150.49,
38.29, 118.79, 111.50, 23.88. ESI-MS: Calculated for C15
27.10, found 328.07 (M + H) .
H
14ClN
7
is
+
2.3.3. AZ1:4,6-dichloro-N-phenyl-1,3,5-triazine-2-amine
2 3
The mixture of cyanuric chloride (1 g, 5.42 mmol) and K CO (0.75 g,
5.42 mmol) were taken in a 100 mL rb containing 30 mL toluene and
o
o
were cooled to 0 C. To this reaction mixture, a previously cooled (0
C) solution of aniline (~0.5 mL, 5.42 mmol) in 20 mL of toluene was
added dropwise over a period of 15 min. Further, the reaction was
stirred at 0-5 °C for 2 h to obtain a white precipitate and until all aniline
gets exhausted as indicated by TLC. Toluene was removed from the re-
action mixture under reduced pressure. The product was extracted in
1
13
tion data ( H NMR, C NMR, Mass and IR spectra) of PZ1, PZ2, AZ1, AZ2
and AZ3 are provided in Figs. S1-S20 (supporting information).
Cl
Cl
N
N
NH2
Cl
N
N
NH2
N
N
N
N
, DIPEA
N
N
, DIPEA
o
THF, 0 C, N , 2 hrs
THF, RT, N , 8 hrs H C
N
N
H
N
N
H
N
CH3
2
2
3
Cl
N
H
N
CH3
Cl
Cl
PZ2
PZ1
Fig. 1. The synthetic pathway of PZ1 and PZ2.
3