(7-Dialkylamino-3-coumarinyl)pyrazolines – new effective push-pull photogenerators of acidity

Article abstract of DOI:10.1016/j.jphotochem.2017.09.072

(7-Dialkylamino-3-coumarinyl)pyrazolines and their julolidine analog have been synthesized and proved as new effective photogenerators of acidity. Having D-π-linker ?A conjugated system of push-pull type these compounds possess intensive absorption in visible region of electronic spectra, high photosensitivity and undergo photodehydrogenation with proton elimination in the presence of CCl₄ or C₂Cl₆ with a high speed.

Full text of DOI:10.1016/j.jphotochem.2017.09.072

Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 8–15
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
(7-Dialkylamino-3-coumarinyl)pyrazolines – new effective push-pull
photogenerators of acidity
*
V.F. Traven , D.A. Cheptsov, G.V. Vershinina, N.P. Solovjeva, T.A. Chibisova, S.M. Dolotov,
I.V. Ivanov
D. I. Mendeleev Russian University for Chemistry and Technology, Miusskaya st.3, 125047 Moscow, Russian Federation
A R T I C L E I N F O
A B S T R A C T
Article history:
(7-Dialkylamino-3-coumarinyl)pyrazolines and their julolidine analog have been synthesized and
Received 7 July 2017
Received in revised form 28 August 2017
Accepted 28 September 2017
Available online 7 October 2017
proved as new effective photogenerators of acidity. Having D-
p
-linker ꢀA conjugated system of push-
pull type these compounds possess intensive absorption in visible region of electronic spectra, high
photosensitivity and undergo photodehydrogenation with proton elimination in the presence of CCl4 or
C2Cl6 with a high speed.
Keywords:
© 2017 Elsevier B.V. All rights reserved.
Aryl(hetaryl)pyrazolines
Photodehydrogenation
Photogeneration of acidity
Fluorescence
Push-pull
p-system
1. Introduction
medium to control the hydrolytic activity of enzymes and
suppression of cancer cells in the treatment of cancer are already
The creation of methodology for the directed synthesis of
heterocyclic compounds with photochemical activity and the
required spectral characteristics is an important issue. Such
heterocyclic compounds include photogenerators of acidity
(PGA) ꢀ compounds that are capable of being transformed with
the release of acid during irradiation. The photogenerators of
acidity provide efficient application of optical methods for
recording information, monitoring of biochemical reactions and
design of new sensor systems.
Thus, development of high performance systems for recording
information requires the creation of multilayer polymer optical
discs, providing an increase in their data capacity tenfold
compared to current optical media [1–8]. Photofluorescent
recording media containing a fluorescent precursor have been
used in the most promising multilayer optical disks. Effective
fluorophores in their passive form are known as fluorescent
precursors. Generation of the fluorescence of such a fluorescent
precursor is caused by acid generated during phototransformation
of PGA [9–13].
known [17,18].
Typical PGA-s proposed for use in archival recording of
information and control of biochemical reactions are triarylsulfo-
nium and triarylmethane salts of certain organic and inorganic
acids, derivatives of sulfonic acids, nitrobenzaldehyde and nitro-
naphthalenaldehyde [7,8,10]. The disadvantage of these photo-
generators is their short-wave absorption and, as a consequence,
the need to use UV light for their phototransformation. Ultraviolet
irradiation in some cases is too hard and causes degradation of the
fluorescent precursor, or a biological object. Recently, (4-hydroxy-
3-coumarinyl)pyrazolines have been found as effective photo-
generators of acidity. The photodehydrogenation reaction was
applied for creation a new photofluorescent media for optical
information recording [19–21]. However, definite disadvantage of
these photogenerators of acidity is their ability to tautomeric
transformations, since hydroxy-form only has been suggested to
provide photogeneration of acidity.
Another intensively developing direction of the PGA application
is optical monitoring of biochemical reactions [14–16]. Examples of
successful application of photoactivating changes the pH of the
Withdrawal of 4-hydroxy-group from the forth position of
coumarin ring excludes ability of related pyrazolines to keto-enol
* Corresponding author.
E-mail address: valerii.traven@gmail.com (V.F. Traven).
https://doi.org/10.1016/j.jphotochem.2017.09.072
1010-6030/© 2017 Elsevier B.V. All rights reserved.

V.F. Traven et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 8–15
9
tautomerism but decreases notably rates of acidity photogenera-
tion.
In this study we have synthesized (7-diethylamino-3-coumar-
2. Experimental
2.1. Synthesis
inyl)pyrazolines 1 and their julolidine analog 2–new effective
photogenerators of acidity. As one can see,
The deuterated solvent (DMSO-d6) for NMR spectroscopy was
obtained from Merck. The lactone form of Rhodamine B was used
as precursor of fluorescent laser dye (high purity grade, Aldrich).
Hexachloroethane was used as a halogen-containing additive (high
purity grade, Aldrich). The other chemicals were Aldrich HPLC or
spectral grade and were used without further purification.
Synthesis of (7-diethylamino-3-coumarinyl)pyrazolines
1 has
been carried out as it is shown in Scheme 1. 3-Acetyl 7-
diethylaminocoumarin 4 has been obtained as reported in [22].
It was then condensed with related benzaldehydes to get 3-
cinnamoyl-7-diethylaminocoumarins 5. Their reactions with
arylhydrazines have provided preparation of 1.
Synthesis of compound 2 has been carried out as it is shown in
Scheme 2 with the main intermediates 6–9.
structures 1 and 2 are specific for presence in their molecules
push-pull conjugated
substituted amino-function at position 7 of coumarin fragment
p
-systems
D
ꢀ
p
-linker
ꢀ
A, where
2.1.1. 3-Acetyl-7-diethylaminocoumarin 4
Compound 4 has been obtained by known procedure [22]: yield
50%, mp 151–152 ꢁC (ethanol), lit. [22], mp 151–153 ꢁC.
ꢀ strong electronodonor D is conjugated with pyrazoline C
¼
N
bond at position 3 ꢀ definite electronoacceptor A. From this point,
the structures 1 and 2 are very similar to structures of known laser
dyes ꢀ coumarin derivatives, for example, Coumarin 6 and
Coumarin 334.
2.1.2. 8-Hydroxyjulolidine 6
Compound 6 has been obtained by known procedure [23]: yield
20%, mp 128.5-130.5 ꢁC (ethanol), lit. [24], mp 126–130 ꢁC.
2.1.3. 9-Formyl-8-hydroxyjulolidine 7
Compound 7 has been obtained by known procedure [25]: yield
74%, mp 73–75 ꢁC, lit. [25], mp 73–74 ꢁC.
2.1.4. 10-Acetyl-2,3,6,7-tetrahydro-1H-pyrano[2,3-f]pyrido[3,2,1-ij]
quinoline-11(5H)-one 8
Ethyl acetoacetate (0.38 ml, 2.72 mmol) and a catalytic amount
of morpholine were added to
a suspension of 9-formyl-8-
hydroxyjulolidine (0.43 g, 2.00 mmol) in 15 ml of ethanol. The
resulting reaction mixture was heated under reflux for 3–5 h (end
of the reaction is monitored by TLC). The reaction mixture as an oil
was purified by column chromatography, followed by recrystalli-
zation from ethanol. Yield 41%, mp 180–181.5 ꢁC, lit. [26], mp 181–
182 ꢁC. MS (ES + ) calcd for C17H17NO3 m/z: 283.12, found m/z (%):
283.27 (45).
These laser dyes are famous for their excellent electronic
absorption and emission properties with extinction coefficients
e
near to 50 000 Molꢀ1cmꢀ1. (3-Coumarinyl)pyrazoline 3 that has no
amino function at position 7 of coumarin fragment was synthe-
sized for comparison of its spectral properties with that of
compounds 1 and 2.
2.1.5. Synthesis of 3-cinnamoyl-7-diethylaminocoumarins 5a-b and
compound 9
Equimolar amounts of the corresponding benzaldehyde and 3-
acetyl-7-diethylaminocoumarin 4 (or compound 8) in 15 ml of
butyl alcohol were stirred under reflux in the presence of catalytic
amount of piperidinium acetate for 6–15 h (end of the reaction is
monitored by TLC). The formed precipitate is filtered off and
recrystallized from ethanol.
Scheme 1. Synthesis of (7-diethylamino-3-coumarinyl)pyrazolines 1. Reagents and conditions: (a) 4-R1-C6H4CHO, Pip
(excess), AcOH, i-PrOH, reflux, 1–7 h.
ꢂ
AcOH, n-BuOH, reflux, 6–15 h; (b) 4-R2-C6H4NHNH2

10
V.F. Traven et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 8–15
Scheme 2. Synthesis of the compound 2. Reagents and conditions: (a) 1-bromo-3-chloropropane, Na2CO3, DMF, reflux; (b) POCl3, DMF, reflux; (c) ethyl acetoacetate,
morpholine, EtOH, reflux, 3–5 h; (d) PhCHO, Pip AcOH, n-BuOH, reflux, 6 h; (e) 4-CH3-C6H4NHNH2 (excess), AcOH, i-PrOH, reflux, 7 h.
ꢂ
2.1.6. 7-(Diethylamino)-3-[(2E)-3-phenylprop-2-enoyl]coumarin 5a
Yield 47%, mp.159–161 ꢁC. 1H NMR (500
Hz, CDCl3, (ppm.), J
(Hz)): 1.26 (t, 6H, N(CH2CH3)2, J = 7.3); 3.48 (q, 4H, N(CH2CH3)2,
J = 7.3); 6.53 (d, 1H, H(8), J = 2.4); 6.66 (dd, 1H, H(6), J = 2.4, J = 8.8);
J = 6.4, J = 12.2); 6.54 (d, 1H,
J = 2.4); 6.88-6.96 (m, 4H,
24)); 7.56 (d, 1H, (5), J = 8.9); 8.30 (s, 1H,
Hz, DMSO-d6, (ppm.)): 12.3 (2C); 20.0 (
63.1 ( ); 96.1 ( ); 108.0 ( ); 109.5 ( ); 112.0 (
(2 ); 127.2 ( ); 128.8 (2 ); 129.2 (2 ); 130.9 (
); 139.4 ( ); 139.6 ( ); 142.6 ( ); 150.8 (
=
(8), J = 2.4); 6.74 (dd, 1H,
(13,14,16,17)); 7.22-7.34 (m, 5H,
(4)). 13E NMR (126
); 44.1 (2 ); 45.1 ( );
); 113.0 (2
); 132.5 (
); 158.8 (
=
(6), J = 8.9,
;
d
=
=(20–
=
=
;
d
E
E
E
7.38-7.46 (m, 4
(d, 1H, H(11), J = 15.6); 8.15 (d, 1H, H(10), J = 15.6); 8.56 (s, 1H, H(4)).
13E NMR (126
Hz, CDCl3, (ppm.)): 11.9 (2 ); 44.8 (2 ); 96.4
); 108.3 ( ); 109.5 ( ); 116.5 ( ); 124.5 ( ); 128.2 (2
); 129.6 ( ); 131.2 ( ); 134.9 ( ); 142.8 ( ); 148.1 (
); 158.1 ( ); 160.3 ( ); 186.0 (
=,
=
(5,14,15,16); 7.67-7.71 (m, 2
=
,
=(13,17)); 7.84
E
E
E
E
E
E
E
E
E
E
); 125.7
); 134.0
E
E
E
;
d
E
E
(
E
E
E
E
E); 159.1 (E).
(
(2
(
E
E
E
E
E
E
E
); 128.2
); 152.3
MS (ES + ) m/z (%): 451.46 (68). HRMS calcd for C29H29N3O2Na+
E
E
E
E
E
(M + Na)+ 474.2152, found 474.2165.
E
E
E
E). MS (ES + ) calcd for C22H21NO3
m/z: 347.15, found m/z (%): 347.31 (62). The 1H NMR spectrum is
2.1.11. 7-(Diethylamino)-3-[1-(4-fluorophenyl)-5-phenyl-4,5-
dihydro-1H-pyrazol-3-yl]coumarin 1b
identical to the spectrum given in [27] (see Suppl. Data).
Yield 74%, mp. 186–187 ꢁC. 1H NMR (500
;
Hz, DMSO-d6,
d
2.1.7. 7-(Diethylamino)-3-[(2E)-3-[4-(methoxyphenyl)prop-2-enoyl]
coumarin 5b
(ppm.), J (Hz)): 1.13 (t, 6H, N(CH2CH3)2, J = 7.0); 3.16 (dd,1H,
=
A(25),
J = 6.7, J = 17.9); 3.45 (q, 4H, N(CH2CH3)2, J = 7.0); 3.94 (dd, 1H,
B(25), J = 12.2, J = 17.9); 5.38 (dd, 1H, (18), J = 6.7, J = 12.2); 6.55
(d,1H, (8), J = 2.3); 6.74 (dd,1H, (6), J = 8.9, J = 2.3); 6.95-7.02 (m,
4H, (13,14,16,17)); 7.24-7.36 (m, 5H, (20–24)); 7.56 (d, 1H, (5),
J = 8.9); 8.32 (s,1H, NMR (126 Hz, DMSO-d6, (ppm.)):
(4)). 13
12.3 (2 ); 44.1 (2 ); 45.2 ( ); 63.3 ( ); 96.1 ( ); 108.1 ( ); 109.5
); 111.5 ( ); 114.0 (d, 2 , J = 8.2); 115.3 (d, 2 , J = 21.8); 125.8
); 127.4 ( ); 128.9 (2 ); 130.0 ( ); 139.9 ( ); 141.1 (
); 144.6 ( ); 150.8 ( ); 155.8 (d, , J = 234.3); 156.1 (
Yield 28%, mp.169–171.5 ꢁC.1H NMR (500
;
Hz, CDCl3,
, N(CH2CH3)2, J = 7.0); 3.49 (q, 4 , N(CH2CH3)2,
, OCH3); 6.53 (d, 1 (8), J = 2.4); 6.66 (dd, 1
(6), J = 2.4, J = 8.9); 6.94 (d, 2 (14,16), J = 8.5); 7.45 (d,1 (5),
J = 8.9); 7.67 (d, 2 (13,17), J = 8.5); 7.84 (d, 1 (11), J = 15.6);
8.06 (d, 1 (10), J = 15.6); 8.56 (s, 1
(4)). 13
CDCl3, (ppm.)): 11.9 (2 ); 44.7 (2 ); 54.8 ( ); 96.3 (
109.4 ( ); 113.7 (2C); 116.7 ( ); 122.2 ( ); 127.7 (
); 142.8 ( ); 148.0 ( ); 148.0 ( ); 152.2 (
); 161.0 ( ); 185.9 (
d
(ppm.),
=
=
J (Hz)): 1.27 (t, 6
=
=
=
=
J = 7.0); 3.87 (s, 3
=
=,
=
=,
=
=
=
=
=,
=
=
,
=
=
E
E
;
d
=
,
=
=
,
E
=
E
E
E
E
E
=,
=
=
,
=
NMR (126
;
Hz,
(
(2
E
E
E
E
d
E
E
E
E
); 108.3 (
); 130.0 (
); 158.1 (
E
E
E
);
);
);
E
E
E
E
E
E
E
E
); 142.3
); 159.1
E
E
E
E
E
E
E
E
E
E
(
E
E
E
131.2 (
E
E
(E
). MS (ES + ) m/z (%): 455.33 (23). HRMS calcd for
160.3 (
). MS (ES + ) calcd for C23H23NO4 m/z:
C
28H26FN3O2Na+ (M + Na)+ 478.1901, found 478.1915.
377.16, found m/z (%): 377.36 (100). The 1H NMR spectrum is
identical to the spectrum given in [28] (see Suppl. Data).
2.1.12. 7-(Diethylamino)-3-[1,5-diphenyl-4,5-dihydro-1H-pyrazol-3-
yl]coumarin 1c
2.1.8. 5-[(2E)-3-Phenylprop-2-enoyl]-3-oxa-13-azatetracyclo
Yield 40%, mp. 179–181 ꢁC. 1H NMR (500
;
Hz, DMSO-d6,
, N(CH2CH3)2, J = 7.0); 3.17 (dd, 1
A(25), J = 6.4, J = 18.0); 3.45 (q, 4H, N(CH2CH3)2, J = 7.0); 3.95 (dd,
d
=,
[7.7.1.02,7.013,17]heptadeca-1,5,7,9(17)-tetraen-4-one 9
(ppm.), J (Hz)): 1.14 (t, 6
=
Yield 35%, mp. 229–231 ꢁC.1H NMR (500
;
Hz, CDCl3,
(8,9)); 2.73-2.94 (m, 4 (6.11)); 3.29-
(8,9)); 7.01 (broad. s, 1 (18)); 7.36-7.41 (m, 3
(5,17,19)); 7.68 (d, 2 (16,20), J = 7.0); 7.81 (d, 1 (14),
J = 15.6); 8.19 (d, 1 (13), J = 15.6); 8.46 (s, 1 NMR
(4)). 13
(126 Hz, CDCl3, (ppm.)): 20.0 ( ); 20.2 ( ); 27.1 ( ); 27.4 ( );
50.0 ( ); 50.4 ( ); 105.7 ( ); 108.6 ( ); 115.4 ( ); 119.6 ( ); 125.3
); 127.7 (2 ); 128.66 ( ); 128.73 (2 ); 130.0 ( ); 135.6 ( );
142.7 ( ); 148.7 ( ); 153.7 ( ); 158.8 ( ); 161.3 ( ); 186.8 ( ). MS
d
(ppm.), J
=
(Hz)): 1.92-2.03 (m, 4
3.39 (m, 4
=
,
=
=
,
=
1H,
=
B(25), J = 12.2, J = 18.0); 5.42 (dd, 1H, H(18), J = 6.4, J = 12.2);
=,
=
=
,
=
=
,
6.55 (d, 1H, H(8), J = 2.4); 6.71 (t, 1H, H(15), J = 7.3); 6.75 (dd, 1H, H
(6), J = 8.9, J = 2.4); 6.98-7.16 (m, 4H, H(13,14,16,17)); 7.24-7.35 (m,
=
=
=
,
=
=, =
=
,
=,
=
E
5H,
NMR (126
); 62.8 (
118.5 ( ); 125.7 (2
); 142.5 (
=
(20–24)); 7.57 (d, 1H,
Hz, DMSO-d6,
); 96.1 ( ); 108.1 (
); 127.3 (
); 144.1 (
=
(5), J = 8.9); 8.33 (s, 1H,
(ppm.)): 12.3 (2 ); 44.1 (2
); 109.5 ( ); 111.6 ( ); 112.9 (2
); 128.9 (2
); 150.8 (
=
(4)). 13E
); 45.0
;
E
d
E
E
E
E
;
d
E
E
E
E
E
E
E
E
(
E
E
E
E
E
E
E
E
E);
E);
E);
(
E
E
E
E
E
E
E
E
E
); 128.7 (2
E
); 130.0 (
E
E
E
E
E
E
139.7 (
E
E); 144.4 (
E); 156.0 (
(ES + ) m/z (%): 371.32 (100). HRMS calcd for C24H21NO3Na+
159.2
(E). MS (ES + ) m/z (%): 437.42 (41). HRMS calcd for
(M + Na)+ 394.1414, found 394.1407.
C
28H27N3O2K+ (M + K)+ 476.1735, found 476.1722.
2.1.9. Synthesis of 1,5-diaryl-(7-diethylaminocoumarin-3-yl)
pyrazolines 1a-e, 2 and 3
2.1.13. 7-(Diethylamino)-3-[5-(4-methoxyphenyl)-1-phenyl-4,5-
dihydro-1H-pyrazol-3-yl]coumarin 1d
The mixture of 3-cinnamoylcoumarin derivative (2.88 mmol),
the corresponding arylhydrazine (10 mmol) and catalytic amount
of glacial acetic acid in 30 ml of isopropyl alcohol were heated at
reflux for 1–7 h (the end of the reaction is determined by TLC). The
formed precipitate is filtered off and purified by column
chromatography or recrystallization from toluene or ethanol.
Yield 63%, mp. 155–157 ꢁC. 1H NMR (500
;
Hz, DMSO-d6,
d
(ppm.), J (Hz)): 1.14 (t, 6H, N(CH2CH3)2, J = 7.0); 3.15 (dd,1H,
J = 6.4, J = 18.0); 3.46 (q, 4
3.90 (dd, 1H, B(25), J = 12.2, J = 18.0); 5.36 (dd, 1H,
J = 12.2); 6.55 (d, 1H, (8), J = 2.3); 6.70 (t, 1H, (15), J = 7.3); 6.75
(dd,1H, (6), J = 8.9, J = 2.3); 6.87-7.00 (m, 4H, (13,17,21,23)); 7.12-
7.20 (m, 4H, (14,16,20,24)); 7.57 (d, 1H, (5), J = 8.9); 8.32 (s, 1H,
(4)). 13E NMR (126
Hz, DMSO-d6, (ppm.)): 12.3 (2C); 44.1
=
A(25),
=
, N(CH2CH3)2, J = 7.0); 3.71 (s, 3H, OCH3);
=
=(18), J = 6.4,
=
=
=
=
=
=
2.1.10. 7-(Diethylamino)-3-[1-(4-methylphenyl)-5-phenyl-4,5-
=
;
d
dihydro-1H-pyrazol-3-yl]coumarin 1a
(2C); 45.0 (C); 55.0 (C); 62.4 (C); 96.1 (C); 108.1 (C); 109.5 (C); 111.7
(C); 113.0 (2C); 114.3 (2C); 118.4 (C); 126.9 (2C); 128.7 (2C); 129.6
(C); 134.4 (C); 139.6 (C); 144.1 (C); 144.4 (C); 150.8 (C); 156.0 (C);
158.4 (C); 159.2 (C). MS (ES + ) m/z (%): 467.47 (41). HRMS calcd for
Yield 73%, mp. 179–181 ꢁC. 1H NMR (500
;
Hz, DMSO-d6,
(ppm.), J (Hz)): 1.13 (t, 6H, N(CH2CH3)2, J = 7.0); 2.16 (s, 3H, CH3);
3.14 (dd, 1H, A(25), J = 6.4, J = 17.7); 3.45 (q, 4H, N(CH2CH3)2,
J = 7.0); 3.92 (dd, 1H, B(25), J = 12.2, J = 17.7); 5.38 (dd, 1H, (18),
d
=
=
=
C
29H29N3O3K+ (M + K)+ 506.1841, found 506.1829.

V.F. Traven et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 8–15
11
2.1.14. 7-(Diethylamino)-3-[1-(4-methoxyphenyl)-5-phenyl-4,5-
dihydro-1H-pyrazol-3-yl]coumarin 1e
Eclipse (Varian) spectrofluorimeter (Australia). Photo-irradiation
was carried out using an L 5283 xenon lamp (HAMAMATZU lamp).
1H and 13C NMR spectra were registered on a spectrometer “Bruker
Avance” (500 MHz) in DMSO-d6. As internal standard SiMe4 was
used, or the signal of the residual protons and 13C carbon solvent
relative to SiMe4 (DMSO-d6–dH 2.50 ppm, dE 39.5 ppm; CDCl3–dH
7.27 ppm, dC 77.0 ppm; acetone-d6–dH 2.05 ppm, dE 29.9 ppm).
Mass spectra were obtained on a mass spectrometer “Thermo
Scientific” (ISQ LT Single Quadrupole Mass Spectrometer) by
electron impact at an energy of ionizing electrons 70 eV. High
resolution mass spectra were registered on the “Bruker micrOTOF
II” by electrospray ionization (ESI). Analytical thin layer chroma-
tography was performed on silica gel plates (Merck, Kieselgel 60,
0.25 thickness) with F254 indicator. Column chromatography was
performed on silica gel (Merck, Kieselgel 60, 70–230 mesh).
Photo-irradiation was carried out using an L 5283 xenon lamp
(HAMAMATZU lamp) through an optical fiber of 1 m length and a
light filter to select light in UV region at 360 nm and in the visible
region at 420 nm with corresponding glass filters. The distance
between the optical fiber and the sample is 20 mm
Rate constants of photodehydrogenation reactions were found
by graphics method with use of linear form of the first order
reaction. Changes of optical densities of the pyrazolines have been
used in the region of 0.2-0.8 for the rate constants calculations. The
average rate constants given in Tables 1 and 2 are obtained from
four convergent results with accuracy 5% (see Supplementary data
for more detail).
Quantum mechanical calculations were carried out with
GAMESS suite of programs [29]. Geometry optimization and
calculations of the energy was carried out with Density Functional
Theory (DFT) [30] using the Becke’s hybrid exchange functional
and non-local, correlation functional of Lee, Yang and Parr (B3LYP)
[31] and 6–31 + +G(d,p) basis set. The ionization potential of the
pyrazoline was evaluated as the energy difference between the
corresponding cation radical and the neutral molecule.
Yield 69%, mp. 192–194 ꢁC. 1H NMR (500
;
Hz, DMSO-d6,
d
(ppm.), J (Hz)): 1.14 (t, 6H, N(CH2CH3)2, J = 7.0); 3.13 (dd,1H,
J = 7.3, J = 17.7); 3.45 (q, 4
3.92 (dd, 1H, B(25), J = 12.2, J = 17.7); 5.32 (dd, 1H, H(18), J = 7.3,
J = 12.2); 6.54 (d, 1H, H(8), J = 2.4); 6.73-6.95 (m, 5H,
(6,13,14,16,17)); 7.23-7.35 (m, 5H, H(20–24)); 7.56 (d, 1H, H(5),
J = 8.9); 8.29 (s, 1H, H(4)). 13
NMR (126 Hz, DMSO-d6, (ppm.)):
12.3 (2C); 44.1 (2 ); 45.1 ( ); 55.2 ( ); 63.9 ( ); 96.1 ( ); 108.1
); 111.9 ( ); 114.3 (2 ); 114.3 (2 ); 125.9 (2
); 129.9 ( ); 135.0 ( ); 139.3 ( ); 142.6 (
); 152.6 ( ); 155.9 ( ); 159.2 (
=A(25),
=
, N(CH2CH3)2, J = 7.0); 3.64 (s, 3H, OCH3);
=
H
E
;
d
E
E
E
E
E
(E
(E
(E
); 109.4 (
); 128.8 (2
); 150.7 (
E
E
E
E
E
); 127.3
E
E
E
E
E); 143.5
E
E
E
E). MS (ES + ) m/z (%):
467.47 (47). HRMS calcd for C29H29N3O3K+ (M + K)+ 506.1841, found
506.1820.
2.1.15. 3-[1-(4-Methylphenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-3-
yl]coumarin 3
Yield 91%, mp. 208–210 ꢁC. 1H NMR (500
;
Hz, DMSO-d6,
(ppm.), J (Hz)): 2.17 (s, 3H, CH3); 3.20 (dd, 1H, A(25), J = 6.4,
J = 17.7); 3.98 (dd, 1H, B(25), J = 12.5, J = 17.7); 5.50 (dd, 1H, H(18),
d
=
=
J = 6.4, J = 12.5); 6.94-6.99 (m, 4H, H(13,14,16,17)); 7.25-7.41 (m, 7H,
H(6,8,20-24)); 7.58-7.62 (m, 1H, H(7)); 7.82 (dd, 1H, H(5), J = 7.6,
J = 1.5); 8.46 (s, 1H, H(4)). 13
E NMR (126 ;Hz, DMSO-d6, d (ppm.)):
20.2 (C); 44.6 (C); 63.4 (C); 113.6 (2C); 116.0 (C); 119.4 (C); 120.2
(C); 124.9 (C); 125.9 (2C); 127.6 (C); 128.2 (C); 128.8 (C); 129.1 (C);
129.5 (2C); 131.9 (
E
); 136.3 (
); 158.3 (
E); 138.2 (E); 141.5 (E); 142.4 (E);
142.7 (
E
); 153.0 (
E
E
). MS (ES + ) m/z (%): 380.29 (25).
HRMS calcd for C25H20N2O2K+ (M + K)+ 419.1156, found 419.1167.
2.1.16. 5-[1-(4-Methylphenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-3-
yl]-3-oxa-13-azatetracyclo-[7.7.1.02,7.013,17]heptadeca-1(17),2
(7),5,8-tetraen-4-one 2
Yield 66%, mp. 236–237,5 ꢁC. 1H NMR (500
;
Hz, DMSO-d6,
(7,10)); 2.17 (s, 3 E=3); 2.72-
(6,11)); 3.15 (broad. dd, 1 A(28)); 3.28-3.31 (m,
(8,9)); 3.93 (dd, 1 B(28), J = 12.5, J = 17.7); 5.33 (dd, 1
(21), J = 7.0, J = 12.5); 6.89 (d, 2 (16,20), J = 8.4); 6.95 (d, 2
(17,19), J = 8.4); 7.14-7.34 (m, 6 (5,23,24,25,26,27); 8.19 (s,1
(4)). 13
NMR (126 Hz, DMSO-d6,
); 20.8 ( ); 26.9 ( ); 45.2 ( ); 48.9 (
); 107.9 ( ); 110.7 ( ); 113.0 (2 ); 118.7 (
); 127.72 (2 ); 128.9 (2 ); 129.2 (
); 144.1 ( ); 146.2 (
d
(ppm.), J (Hz)): 1.89-1.92 (m, 4
2.76 (m, 4
=
,
=
=,
=,
=
=, =
4
=,
=
=,
=
=
,
3. Results and discussion
=
=
=
=
,
=
=,
=
,
=
=
,
3.1. Electron absorption spectra
E
;
d
(ppm.)): 19.7 (
); 49.4 (
); 125.8 (2
); 139.6 ( ); 142.1 (
); 159.4 (
E
); 19.9 (
); 63.2 (
E
E
E
E
);
);
);
);
20.0 (
105.0 (
127.71 (
142.7 (
E
E
E
E
E
E
Pyrazolines 1a-e containing 7-diethylamino-function in cou-
marin fragment show significant bathochromic shift and definite
increase of intensity of the longest wave-length bands in electronic
absorption spectra. This conclusion comes from comparison of
their spectral data with that of the compound 3 which has no such
function. Positions of the bands labsmax, values of their extinction
E
E
E
E
E
E
E
E
E
E
E
E
E); 151.0 (
E
); 158.9 (
E
E). MS
(ES+) m/z (%): 475.46 (51). HRMS calcd for C31H29N3O2K+ (M + K)+
514.1891, found 514.1887.
coefficients e, positions of the emission bands l
em, photodehy-
2.2. Measurements
drogenation reaction rate constants k1 of new pyrazolines 1-3
measured in toluene and acetone are given in Table 1.
Electronic absorption spectra were recorded on an APELP-
D_303UV spectrometer (China) and fluorescent spectra ꢀ on Cary
Comparison of absorption spectra of the compounds 1a, 2 and 3
is shown in Fig. 1. As expected, spatial fixation of the amino
Table 1
Electronic absorption (position labsmax and value of extinction coefficient em) properties, photodehydrogenation
e of the longest wave-length band) and emission (position l
reaction rate constants k1 of new pyrazolines 1-3 in toluene and acetone.
comp.
Solvent
Toluene
Acetone
labsmax, nm
e
, Mꢀ1 cmꢀ1
l
em, nm
k110ꢀ4, sꢀ1
labsmax, nm
e
, Mꢀ1 cmꢀ1
l
em, nm
k110ꢀ4, sꢀ1
1a
466
468
464
462
470
472
462
27873
30294
25625
28884
14842
26953
22667
578
567
567
570
595
579
578
773.3
496.0
453.0
506.0
868.8
865.5
9.0
460
452
456
436
462
470
438
35554
34747
36555
32254
24794
39415
16055
582
571
569
578
604
590
599
955.8
1b
1c
1d
1e
2
2702.7
3778.8
2722.5
1307.8
4036.2
11.4
3

12
V.F. Traven et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 8–15
significant side reactions. Similar changes along irradiation of 1b-e
can be seen in the emission spectra as well: weak emission of
starting pyrazoline gradually decreases and stronger emission of
formed pyrazole goes up (Fig. 2, right).
By measurement of the pyrazoline absorption changes we have
evaluated the rates of pyrazolines 1 ꢀ3 photodehydrogenation
reaction. Measured kinetic data have been approximated by the
first order kinetics [19]. The calculated rate constants k1 are shown
in Table 1. One can see that pyrazolines having 7-amino-function
show much higher rates of phototransformation. As expected,
pyrazoline 2 shows the maximal rate of photodehydrogenation:
rate constant of the compound 2 reaction in acetone increases 354
times in comparison with that of pyrazoline 3. Thus, spatial
fixation of the 7-amino function in julolidine pyrazoline 2 creates
the most favorable conditions for the transfer of electronic density
from the donor fragment, the nitrogen atom
(p-symmetry
unshared pair of which is strictly fixed) on the acceptor pyrazoline
fragment. In julolidine pyrazoline 2 fully is realized, thereby, the
push-pull nature of the electronic excitation of acidity photo-
generation.
Fig. 1. Electronic absorption spectra of the compounds 3 (1), 1a (2) and 2 (3) in
acetone.
function in the julolidine fragment of pyrazoline 2 provides the
maximal effect on the spectral properties due to the best
geometrical conditions for the conjugation of occupied pz-orbital
(7-Diethylamino-3-coumarinyl)pyrazolines 1a-e and 2 do not
contain hydroxy-function at the position 4 of coumarin ring. As a
result, in opposite to (4-hydroxy-3-coumarinyl)pyrazolines [32],
these pyrazolines are not able to undergo keto-enol tautomeric
transformations which hinder phototransformations. However,
definite changes in the compound 1d electronic spectra recorded
in solvents with different ratio (between 100% toluene and 100%
DMF) can be seen in Fig. 3 at 390–450 nm. These changes, probably,
are due to transitions between highly polarized pyrazoline push-
pull form and its nonpolar form. Similar transitions have been
earlier suggested [33]. Anyhow, in opposite to keto-enol tautom-
erism of the (4-hydroxy-3-coumarinyl)pyrazolines mentioned
above [19] these probable transitions do not hinder photo-
dehydrogenation reaction in any extent: rate constants k1 of
photodehydrogenation of pyrazoline 1d in DMF is even higher that
in toluene (0,0710 sꢀ1and 0,0478 sꢀ1respectively).
of nitrogen atom, coumarin
pyrazoline C
p-system and vacant p*-orbital of
Nꢀꢀbond. Bathochromic shift of the longest-wave
¼
absorption band of compound 2 compared to pyrazoline 3 is more
pronounced in acetone and equal to 32 nm as well as extinction
coefficient of the longest wave-length band goes up from
16055 Mꢀ1
ꢂ
cmꢀ1 to 39415 Mꢀ1 cmꢀ1
.
ꢂ
3.2. Photochemical reaction
Obviously, due to the increase in the absorption intensity,
compounds 1 and 2 differ considerably from pyrazoline 3 by higher
photosensitivity. (7-Diethylamino-3-coumarinyl)pyrazolines 1a-e
have been irradiated at
l= 380–465 nm in CCl4 or in different
solvents in the presence of C2Cl6. As example, the changes of
electronic absorption (left) and emission (right) spectra of
pyrazoline 1a upon irradiation of its solution in toluene in the
presence of hexachloroethane are shown in Fig. 2. A gradual
decrease of pyrazoline absorption intensity at
425–470 nm and the appearance of a shorter wavelength of
maximum absorption at 300–400 nm, which refers to the
absorption of the formed pyrazole. In all cases the spectral curves
form isobestic point showing that photochemical transformation
of pyrazoline into related pyrazole does not accompanied by any
Fig. 2. Electronic absorption (left) and emission (right) spectra of pyrazoline 1a in toluene in the presence of C2Cl6 before (1) and after (to 11) irradiation.

V.F. Traven et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 8–15
13
Fig. 4. Electronic absorption spectra of pyrazoline 1d in DMF in the presence of
Rhodamine B lactone form and C2Cl6 before (1) and after (to 13) irradiation.
Fig. 3. Absorption spectra of pyrazoline 1d in different toluene-DMF compositions:
1–100% toluene; 2–toluene-DMF (4: 1); 3–toluene-DMF (3: 2); 4–toluene-DMF (2:
3); 5–toluene-DMF (1: 4); 6–100% DMF.
As in the case of other pyrazolines, photodehydrogenation of (7-
dialkylamino-3-coumarinyl)pyrazolines is accompanied by elimi-
nation of proton. Increasing medium acidity during irradiation of
pyrazolines 1 in the presence of Rhodamine B lactone form in DMF
leads to appearance of intensive absorption of formed open form of
the laser dye (Scheme 4, Fig. 4).
Rates of pyrazolines 1a-e photodehydrogenation reaction
definitely depend also on the pyrazoline structure. We have found
that the ln k1 values of pyrazolines photodehydrogenation
correlate well with values of the calculated first ionization
potentials IP1.
Rates of the pyrazolines 1 photodehydrogenation definitely
depend on the solvent polarity. Thus, the measured rate constants
k1 are much higher in polar acetone than those in nonpolar
toluene. Presumably this is due to formation of charged
intermediates during photodehydrogenation reaction as it has
been previously assumed for CCl4 [19] (Scheme 3). Polar solvents
solvate better these intermediates, thus increasing the reaction
rate.
Scheme 3. Presumptive mechanism of photodehydrogenation of the pyrazolines.
Scheme 4. Opening of the Rhodamine B lactone form by (7-dialkylamino-3-coumarinyl)pyrazolines.

14
V.F. Traven et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 8–15
Table 2
irradiation of pyrazolines in the presence of Rhodamine B lactone
form leads to appearance of intensive absorption of formed open
form of the laser dye.
Photodehydrogenation rate constants (ln k1) in toluene and ionization potentials
values (IP1, eV) of new pyrazolines 1a-e and 2.
of compound
1a
1b
1c
1d
1e
2
k110ꢀ4, sꢀ1
ln k1
IP1, eV
Acknowledgment
733.3
496.0
453.0
506.0
868.8
865.5
ꢀ2.56
ꢀ2.66
ꢀ3.18
ꢀ2.62
ꢀ2.44
ꢀ2.45
5.37
5.53
5.62
5.38
5.24
5.23
This work was funded by the Russian Science Foundation
(RSCF), grant no. 17-13-01302.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at https://doi.org/10.1016/j.jphoto-
chem.2017.09.072.
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