Synthesis and photophysical properties of 1, 4-disubstituted naphthyloxymethyl-N-alkyl naphthimido-1,2,3-triazole

Article abstract of DOI:10.1007/s12039-014-0677-x

Regioselective synthesis of a series of 1,4-disubstituted of naphthoxymethyl-N-alkyl naphthalimide-1,2,3-triazoles employing click reaction is presented. Highly selective and efficient copper(I)-catalysed 1,3-dipolar cyclo addition between 1-naphthylpropargylic ether and azido alkyl naphthalimides yielded the title compounds in 74% to 94%. The structure of all the new 1,2,3-triazoles was characterized by ¹HNMR, ¹³C NMR, IR and Mass. The electronic absorption and emission studies revealed that the light absorbing and emitting chromophore is the naphthoxy moiety. There is no extensive delocalization of aromatic π-electrons in the active chromophore which exhibited lower quantum yields and lower Stokes shifts.

Full text of DOI:10.1007/s12039-014-0677-x

c
J. Chem. Sci. Vol. 126, No. 4, July 2014, pp. 1063–1074. ꢀ Indian Academy of Sciences.
Synthesis and photophysical properties of 1, 4-disubstituted
naphthyloxymethyl-N-alkyl naphthimido-1,2,3-triazole
J RAMCHANDER, N RAMESHWAR, T SHESHASHENA REDDY, GAJULA RAJU and
A RAM REDDY∗
Department of Chemistry, Osmania University, Hyderabad 500 007, India
e-mail: a_ramreddy@yahoo.com
MS received 3 December 2013; revised 13 February 2014; accepted 6 March 2014
Abstract. Regioselective synthesis of a series of 1,4-disubstituted of naphthoxymethyl-N-alkyl naphtha-
limide-1,2,3-triazoles employing click reaction is presented. Highly selective and efficient copper(I)-catalysed
1,3-dipolar cyclo addition between 1-naphthylpropargylic ether and azido alkyl naphthalimides yielded the
title compounds in 74% to 94%. The structure of all the new 1,2,3-triazoles was characterized by 1HNMR,13C
NMR, IR and Mass. The electronic absorption and emission studies revealed that the light absorbing and emit-
ting chromophore is the naphthoxy moiety. There is no extensive delocalization of aromatic π-electrons in the
active chromophore which exhibited lower quantum yields and lower Stokes shifts.
Keywords. Naphthylpropargylicether; azidonaphthalimides; 1,3-dipolar cycloaddition; regioselective.
polyphosphate. Bag, Kundu and Talukdar18 demon-
strated that click triazolenitrogens are binding sites
for the selective recognition of metal ions. They have
shown that triazolyl units are capable of installation
of fluorescence properties into a non-fluorescent pre-
cursor and also electronic coupling between a tri-
azole and a fluorophore gives rise to a modulated
emission response to the fluorophore, solvatochromism
and quantum yield. Triazole derivatives are known
to exhibit various pharmacological properties such as
anti-microbial,19 anti-inflammatory,20 cytotoxic,21 anti-
convulsant,22 analgesic23 and anti-viral.24 Triazoles
have also been incorporated in a wide variety of thera-
peutically interesting drugs including H1/H2 histamine
receptor and antimycotic drugs such as fluconazole,
itraconazole and voriconazole. On the other hand, het-
erocycles containing the naphthol nucleus also exhibit
various biological activities. For instance, 2-naphthol
derivatives have been reported as potential cognition
enhancers.25 2-Substituted-1-naphthol derivatives were
shown to inhibit the activities of cyclooxygenase and
5-lipooxygenase. 1-Naphthol derivatives were found
to possess potent anti-amnesic activity. Pharmacolog-
ical importance and electronic properties of both tria-
zoles and naphthol moiety have encouraged us to syn-
thesize a series of novel 1,4-disubstituted naphthyloxy
methyl-N-alkyl naphthimido-1,2,3-triazoles derivatives
containing a 1,2,3-triazole. The synthetic route uti-
lized the ‘click reaction’ which is a Cu(I)-catalysed
[3+2] cycloaddition popularized by Sharpless as the
1. Introduction
With increasing demand in developing fluorescent
chemosensors for the detection of biological and envi-
ronmental analytes, modular approaches have offered
the possibility for rapidly constructing sensor molecu-
lar libraries. Among them, Cu(I)-catalysed azidealkyne
cyclo addition (CuAAC)1,2 represents one of the most
efficient approaches for chemical transformation to
create new fluorescent molecules with desired spec-
tral properties.3–13 The triazoles and substituted tria-
zoles on conjugation with oxadiazoles were developed
into organic light emitting diodes by Lee et al.14
who found that triazoles are efficient electron trans-
porting molecules. Ruan and co-workers15 have inves-
tigated the chemo-sensing ability of 1,4 and 1,5 mono-
and bi-substituted 1,2,3-triazoles and found that when
attached aromatic ring leads to extensive delocaliza-
tion of π-electrons reducing the energy gap of π-π*
transition. Further, they proved that these triazoles
are potential ligands because of their N3, N3 and
C5 are able to coordinate to metal centres. The lig-
and character of triazoles was further proved by Jia
et al. who exploited the naphthol–triazole system for
Al3+ detection, based on chelation-enhanced fluores-
cence technique.16 Czirok and co-workers17 investi-
gated the aminophthimide-based three-armed fluores-
cent triazole receptors fluorsensing of the nucleoside
∗For correspondence
1063

1064
J Ramchander et al.
key transformation to build up the triazole ring.26
Herein, we report the facile regioselective synthesis
of a series of naphthol-based 1,2,3-triazoles employ-
ing click reaction and their electronic absorption
and emission properties. Electronic absorption and
emission studies revealed that the electron transport-
ing ability of 1,4-disubstituted 1,2,3-triazoles did not
give a new fluorophore as the conjugation between
the two terminal substituents is prevented by the
sp3-hybridized atoms such as carbon, nitrogen and
oxygen.
spectrofluorophotometer with 5 nm excitation and
emission slit widths at 25◦C employing 1 cm path
length quartz cell. The relative fluorescence quantum
yield, ꢀ is evaluated by employing Eq. 1.
ꢀ
ꢁ ꢀ
ꢁ ꢀ
ꢁ
2
Iunk
Istd
Astd
nunk
nstd
ꢀunk = ꢀstd
,
(1)
Aunk
where ꢀ, ꢀstd,Iunk,Istd,Astd, Aunk, nunk and nstd are fluo-
rescence quantum yields, integral of the emission inten-
sities, the absorbance at the excitation wavelength and
refractive indexes of the corresponding solvents of the
unknown samples and the standard, respectively. 9,10-
diphenyl anthracene was used as standard in cyclohex-
ane solvent (ꢀ = 0.9).
2. Experimental
2.1 Materials and apparatus
2.2 General procedure for the synthesis
of naphthylpropargylicethers (III1-2)
Spectroscopic grade organic solvents were obtained
from Finar Chemicals. Starting and other chemicals and
reagents were purchased from Sigma–Aldrich unless
otherwise stated and were used without further purifica-
tion. Thin layer chromatography (TLC) was performed
on silica gel 60 F254 aluminum plates (Merck). The
reported melting points were uncorrected and deter-
mined in Polmon instrument (model No. MP-96). The
IR spectra were recorded on Bruker Infrared model
Naphthylpropargylic ethers were synthesized starting
from compound I as shown in scheme 1. Naphthyl-
propargylic ethers (III) were synthesized according to
reported procedure.27
2.3 General experimental procedure for the synthesis
of 1,4-disubstituted naphthyloxy methyl-N-alkyl
naphthimido-1,2,3-triazoles.(IV1-2 a-f)
1
Tensor-27. H NMR and 13C NMR were recorded
on a Bruker400 MHz Ultrashield spectrometer. The
ESI mass spectra were recorded on a VG micro
mass 7070-H. UV-vis spectra were recorded on Elico Compound III1−2 (2 mmol) and azides IXa−f (2 mmol)
SL 159 UV-VIS spectrophotometer. Steady state flu- were dissolved in 10 mL of DMF. To this mixture,
orescence was investigated on Shimadzu RF-5301PC CuSO4.5H2O (25 mg, 0.1 mmol) and sodium ascorbate
Here R = H-1, R = OCH3-2, n = a =2, b =3, c =4, d = 5, e = 6, f =8
Scheme 1. Synthesis of 1,4-disubstituted naphthyloxymethyl-N-alkylnaphthimido-1,2,3-triazoles.

Synthesis of naphthlimide-based triazoles
1065
(39 mg, 0.2 mmol) aqueous solution were added and 400 MHz)δ 7.79 (t, 2H), 8.45–8.43 (m, 4H), 11.71 (bs,
stirred at 80◦C for 12 h. The reaction mixture was 1H, D2O exchanged). ESI–MS: m/z 198[M+H]+.
poured into 25 mL of water and was extracted with
CHCl3 (3 × 25 mL). The organic layers were combined,
2.7b 2-(4-bromobutyl)-1H-benzo[de]isoquinoline-
and washed with water (20 mL) and dried over anhy-
1,3(2H)-dione (VIII c): Yield 88.4%; M.p. 100–103◦C;
drous Na2SO4. The solvent was evaporated in vacuo to
give the crude product. The crude product was purified
by column chromatography using hexane: ethylacetate
(9:1–6:4%) as eluent to afford the pure product.
IR (KBr): 3095, 1697, 1664, 1588 cm−1.1HNMR
(CDCl3, 400 MHz): 1.87–2.03 (m 4H), 3.47 (t, 2H),
4.23 (t, 2H), 7.75 (t, J = 8 Hz, 2H), 8.21 (d, J = 8.4 Hz,
2H), 8.60 (d, J = 7.2 Hz, 5H).13CNMR (DMSO-
d6,400 MHz) δ 164.15, 133.96, 131.54, 131.25, 128.10,
2.4 General procedure for the synthesis
of N-(ω-azidoalkyl)-1,8-naphthalimide (IXa-f)
126.93, 122.53, 39.34, 33.18, 30.25, 26.89. ESI–MS:
m/z332 [M+H]+.
One equivalent of N-(ω-bromoalkyl)-1,8-naphthali-
mide (VIIIa−f ) was dissolved in DMF mix and two
equivalents of sodium azide were added to it. The mix-
ture was stirred at 80◦C for 12 h. After completion of
the reaction, DMF was removed in vacuo and poured
into ice cold water, extracted with chloroform. After
evaporation of chloroform, the pure compound was
collected.
2.7c 2-(5-bromopentyl)-1H-benzo[de]isoquinoline-
1,3(2H)-dione (VIII d): Yield 87.2%; M.p. 118–
120◦C; IR (KBr): 3060, 2954, 1695, 1660, 1589,
1512 cm−1.1HNMR (CDCl3, 400 MHz) δ 1.58–1.63
(m, 2H),1.75–1.83 (m, 2H), 1.93–2.00 (m, 2H), 3.45
(t, J = 6.8 Hz, 2H), 4.21 (t, J = 7.6 Hz, 2H), 7.78
(t, J = 7.6 Hz, 2H), 8.23 (d, J = 8.0 Hz, 2H), 8.62
(d, J = 7.4 Hz, 2H). ESI–MS: m/z:346 [M+H]+.
2.5 General procedure for the synthesis
of N-(ω-bromoalkyl)-1,8-naphthalimide (VIIIa-f)
2.7d 2-(6-bromohexyl)-1H-benzo[de]isoquinoline-1,3
(2H)-dione (VIII e): Yield 85.8%; M.p. 90–94◦C;
IR (KBr): 3061, 2954, 2932, 1694, 1662, 1587,
To a solution compound VI (0.5 gm, 1 mmol) in acetoni-
trile (30 mL), anhydrous potassium carbonate (553 mg,
4 mmol) and terminal dibromoalkane (561 mg, 3 mmol)
were added and the mixture was refluxed for 12 h.
After completion of the reaction, anhydrous potassium
carbonate was removed by filtration and the solvent
was evaporated under reduced pressure to get the crude
product. This was further purified by column chro-
matography (10% EtOAc-hexane) to afford the com-
pound VIII a–f.
1
1512 cm−1. HNMR (CDCl3, 400 MHz) δ 1.41–1.59
(m, 4H),1.69-1.79 (m, 2H), 1.84–1.93 (m, 2H), 3.37
(t, J = 6.79 Hz, 2H), 4.14 (t, J = 7.6 Hz, 2H), 7.73
(t, J = 7.93 Hz, 2H), 8.16 (d, J = 8.03 Hz, 2H), 8.55
(d, J = 7.36 Hz, 2H).13CNMR (DMSO-d6,400 MHz)
δ = 26.39, 28.01, 32.87, 33.28, 40.33, 123.19, 126.92,
128.44, 131.10, 133.65, 164.14. ESI–MS: m/z360
[M+H]+.
2.7e 2-(8-bromooctyl)-1H-benzo[de]isoquinoline-1,3
(2H)-dione (VIII f): Yield 80.6%: M.p. 70–
75◦C; IR (KBr): 3061, 2934, 1697, 1661, 1588,
1510 cm−1.1HNMR (CDCl3, 400 MHz) δ 1.30–1.44
(m, 8H),1.69–1.77 (m, 2H), 1.80–1.87 (m, 2H), 3.39 (t,
J = 6.8 Hz, 2H), 4.17 (t,J = 7.6 Hz, 2H), 7.75 (t, J =
7.2 Hz, 2H), 8.20 (d,J = 8.0 Hz, 2H), 8.59(d, J =
7.2 Hz, 2H). 13CNMR (DMSO-d6,400 MHz) δ 26.93,
28.01, 28.06, 28.55, 29.02, 32.77, 33.58, 40.34, 122.91,
126.82, 128.20, 131.02, 131.63, 133.61, 164.06.
ESI–MS: m/z 374 [M+H]+.
2.6 Synthesis of 1H-benzo
[de]isoquinoline-1,3(2H)-dione (VI)
1,8-Naphthalic anhydride (V)(1 g, 5.07 mmol) was
taken in ammonia solution (60 mL) and stirred at 100◦C
for 12 h. After cooling, a yellowish solid was obtained,
to this 200 mL of ice cold water was added and fil-
tered at pump. The solid product was dried in oven at
100◦C. The compound is characterized by IR, 1HNMR
and mass spectra.
2.7 Spectral data
2.7f N-(ω-azidoalkyl)-1, 8-naphthalimide (IXb): M.p.
2.7a 1H-benzo [de]isoquinoline-1,3(2H)-dione (VI): 128◦C; HNMR (CDCl3, 400 MHz) δ 2.09 (m, 2H),
Yield 91.7%; M.p. 262–264◦C; IR (KBr): 3440, 3059, 3.45 (t, J = 6.8 Hz, 2H), 4.36 (t, J = 6.4 Hz, 2H), 7.78
1701, 1676, 1622, 1586 cm−1. 1HNMR (CDCl3, (t, J = 7.6 Hz, 2H), 8.23 (dd, J1 = 1.2 Hz, J = 8.4 Hz,
1

1066
J Ramchander et al.
2H), 8.61 (dd, J1 = 0.8 Hz, J = 7.2 Hz, 2H). ESI–MS:
m/z 303 [M+Na]+.
125.86, 126.48, 127.49, 134.49, 152.67, 153.91,
155.11, 161.25, 161.69. ESI–MS: m/z 477 [M+H]+.
2.7j 2-{5-[4-(naphthalen-1-yloxymethyl)-[1,2,3]triazol-
1yl]pentyl]-benzo[de]isoquinoline-1,3-dione(IV1−d ):
M.p. 108–110◦C; IR (KBr): 3141, 3057, 2951, 2872,
2598, 2119, 1957, 1873, 1778, 1697, 1658, 1591, 1509,
1437, 1342, 1240, 1154, 1067 cm−1.1HNMR (DMSO-
d6,400 MHz): δ = 1.3 (m, 2H) 1.7(m, 2H), 1.9(m, 2H),
4.0 (t , J = 7.6 Hz, 2H), 4.4 (t, J = 7.2 Hz, 2H), 5.3 (s,
2H), 7.0 (d, J = 7.2 Hz, 1H), 7.1 (d, J = 7.2 Hz, 1H),
7.4(t, J = 8.4 Hz, 1H), 7.5 (t, J = 2.4 Hz, 2H), 7.8 (t,
J = 8.4 Hz, 2H), 8.12 (d, J = 8 Hz, 2H), 8.3 (s, 1H),
8.4(d, J = 8 Hz, 2H), 8.5 (d, J = 7.2 Hz, 2H).13CNMR
(DMSO-d6,400 MHz) δ 28.62, 32.13, 34.65, 54.49,
61.08, 67.00, 83.66, 110.96, 125.50, 125.86, 127.12,
130.50, 130.70, 131.15, 131.33, 132.31, 132.45,
132.64, 132.72, 135.85, 136.40, 139.23, 139.42,
158.70, 168.52. ESI–MS: m/z 491 [M+H]+.
2.7g 2-(2-(4((naphthalen-1-yloxy)methyl)-1H-1,2,3-
triazol-1-yl)ethyl)-1H-benzo[de]isoquinoline-1,3(2H)-
dione (IV1−a): M.p. 166–168◦C; IR (KBr): 3067,
2958, 2871, 1991,1953,1908, 1698, 1652,1623,
1588, 1512, 1438,1406, 1380, 1347, 1321, 1260,
1234, 1177, 1144, 1079, 1032 cm−1. 1H NMR
(DMSO-d6,400 MHz): δ 4.1(t, J = 6.8 Hz, 2H), 4.8 (t,
J = 6 Hz, 2H), 4.9 (s, 2H), 6.8 (d, J = 7.6 Hz, 1H), 6.9
(d, J = 7.2 Hz, 1H), 7.5(t, J = 2 Hz, 2H), 7.8 (t, J =
7.6 Hz, 2H), 8.1 (t, J = 6 Hz, 1H), 8.2 (s, 1H), 8.3 (d,
J = 6 Hz, 2H), 8.4 (d, J = 7.6 Hz, 2H), 8.4 (d, J =
7.2 Hz, 2H).13CNMR (DMSO-d6,400 MHz)δ 40.17,
42.38, 60.02, 110.90, 111.71, 122.41, 122.81, 125.68,
126.78, 127.96, 129.41, 131.03, 131.38, 131.92,
133.92, 135.78, 136.75, 139.30, 139.52, 147.92,
158.21, 164.41. ESI–MS:m/z 449 [M+H]+.
2.7k 2-(6-(4-((naphthalen-1-yloxy)methyl)-1H-1,2,3-
triazol-1yl)hexyl)-1H- benzo[de]isoquinoline-1,3(2H)-
dione(IV1−e): M.p. 98–100◦C; IR (KBr): 3058, 3012,
2938, 2861, 1697, 1658, 1625, 1587, 1508, 1460,
1440, 1390, 1346, 1268, 1236, 1175, 1098, 1069,
1021 cm−1.1HNMR (DMSO-d6,400 MHz) δ = 1.2 (m,
2H) 1.3 (m, 2H), 1.6 (m, 2H), 1.8 (m ,2H) 4.0 (t, J =
7.2 Hz, 2H), 4.4 (t, J = 6.8 Hz, 2H), 5.3 (s,2H), 7.1 (d,
J = 6.8 Hz, 1H), 7.4(t, J = 8.0 Hz, 1H), 7.1 (t, J =
2.4 Hz, 2H), 7.8 (t, J = 8.0 Hz, 2H), 8.1 (d, J =
8.4 Hz, 2H), 8.1 (d, J = 8.4 Hz, 1H), 8.3(s, 1H), 8.4
(d, J = 8.0 Hz, 2H), 8.4 (d, J = 7.2 Hz, 2H). 13CNMR
(DMSO-d6,400 MHz) δ 27.33, 27.55, 30.00, 31.12,
54.81, 60.94, 66.98, 110.37, 125.36, 125.42, 125.74,
126.61, 126.79, 127.20, 130.06, 130.20, 130.71,
131.38, 132.30, 132.64, 135.71, 136.33, 138.99,
139.14, 139.17, 158.70. ESI–MS:m/z 505 [M+H]+.
2.7h 2-(3-(4-((naphthalen-1-yloxy)methyl)-1H-1,2,3-
triazol-1-yl)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-
dione (IV1−b): M.p. 76–78◦C; IR (KBr): 3441, 3163,
3053, 2946, 2870, 2600, 2508, 2413, 2265, 2094, 1957,
1871, 1776, 1701, 1656, 1580, 1509, 1460, 1386, 1340,
1270, 1237, 1155, 1097, 1052 cm−1.1H NMR (DMSO-
d6,400 MHz) δ 2.5(m, 2H), 4.81(t, J = 6.8 Hz, 2H), 4.5
(t, J = 7.2 Hz, 2H) 5.3 (s, 2H), 7.1 (d, J = 7.2 Hz, 1H),
7.4 (d, J = 7.2 Hz, 1H), 7.5(t, J = 2 Hz, 2H), 7.8 (t, J =
7.6 Hz, 2H), 8.1 (t, J = 6 Hz, 1H), 8.3 (d, J = 6 Hz,
2H), 8.3 (s, 1H), 8.4 (d, J = 8.4 Hz, 2H), 8.5(d, J =
6.8 Hz, 2H).13CNMR (DMSO-d6, 400 MHz) δ 30.42,
52.94, 54.51, 67.03, 110.99, 111.07, 125.51, 126.79,
127.36, 129.53, 129.65, 130.13, 130.50, 131.35,
131.66, 132.65, 135.87, 136.47, 139.25, 139.46,
147.93, 158.74, 168.78, ESI–MS: m/z 462 [M+H]+.
2.7l 2-{8-[4-(naphthalen-1-yloxymethyl)-[1,2,3]triazol-
1yl]octyl]benzo[de]isoquinoline-1,3-dione(IV1−f )::
M.p. 78–80◦C; IR (KBr): 3050, 2929, 2851, 2599,
2.7i 2-(4-(4-((naphthalen-1-yloxy)methyl)-1H-1,2,3-
triazol-1-yl)butyl)-1H-benzo[de]isoquinoline-1,3(2H)-
dione (IV1−c): M.p. 78–80◦C; IR (KBr): 3142, 3059, 2417, 2118, 1968, 1914, 1872, 1786, 1698, 1662,
2921, 2852, 1716, 1615, 1509, 1441, 1390, 1268, 1238, 1591, 1508, 1438, 1345, 1267, 1238, 1154, 1098,
1147, 1097, 1070 cm−1.1HNMR (DMSO-d6,400 MHz) 1051 cm−1.1HNMR (DMSO-d6,400 MHz) δ 1.2 (m,
δ 1.8(m, 2H), 2.1(m, 2H), 4.0 (t, J = 6 Hz, 2H) 4.4 8H) 1.6 (m, 2H), 1.8 (m, 2H), 4.0 (t , J = 7.6 Hz, 2H)
(t, J = 6.8 Hz, 2H), 5.4 (s, 2H), 6.1(s, 1H), 6.8 (m, 4.3 (t,J = 7.2 Hz, 2H), 5.3 (s, 2H), 7.0 (d, J = 7.6 Hz,
2H), 6.9(d, J = 7.6 Hz, 1H), 7.4 (m, 5H), 7.7 (s, 1H), 1H), 7.1 (d, J = 7.6 Hz, 1H), 7.4(t, J = 2.4 Hz, 1H), 7.5
7.8(d, J = 7.6 Hz, 1H),8.0 (s, 1H), 8.2 (d, J = 8 Hz, (t, J = 2.4 Hz, 2H), 7.8 (t, J = 7.6 Hz, 2H), 8.1 (d, J =
2H).13CNMR (DMSO-d6,400 MHz) δ 25.99, 27.00, 8.4 Hz, 2H), 8.3 (s, 1H), 8.4(d, J = 7.6 Hz, 2 H), 8.4
31.93, 50.07, 67.42, 101.27, 105.38, 111.85, 112.38, (d, J = 7.2 Hz, 2H).13CNMR (DMSO-d6,400 MHz)
113.58, 120.82, 121.96, 125.27, 125.56, 125.62, δ 31.02, 31.63, 32.65, 33.46, 33.73, 34.92, 54.79,

Synthesis of naphthlimide-based triazoles
1067
60.95, 66.96, 110.41, 125.36, 125.74, 126.79, 127.24, 131.03, 131.06, 131.52, 152.56, 154.17, 158.47,
130.09, 130.19, 130.29, 130.91, 131.32, 131.87, 159.93, 165.34, 166.77, 166.81. ESI–MS: m/z 507
132.30, 132.64, 135.71, 136.36, 139.02, 139.16, [M+H]+.
158.70, 168.49. ESI–MS: m/z 533 [M+H]+
2.7p 2-(5-(4-((4-methoxynaphthalen-yloxy)methyl)-1H-
2.7m 2-(2-(4((4-methoxynaphthalen-1-yloxy)methyl)-
1H-1,2,3-triazol-1-yl)ethyl)-1H-benzo[de]isoquinoline-
1,2,3-triazol-1-yl)pentyl)-1H-benzo[de]isoqunolene-1,3
(2H)-dione(IV2−d): M.p. 108–110◦C; IR (KBr): 3131,
1,3(2H)-dione (IV2−a): M.p. 120–122◦C; IR (KBr): 3067, 2947, 2853, 1950, 1781, 1696, 1658, 1592, 1463,
2923, 2853, 1696, 1658, 1624, 1591, 1462, 1440, 1381, 1388, 1272, 1237, 1099, 1049 cm−1.1H NMR (DMSO-
1344, 1272, 1236, 1152, 1095, 1048 cm−1.1HNMR d6,400 MHz) δ 1.3 (m, 2H) 1.7(m, 2H), 1.9(m, 2H),3.9
(DMSO-d6,400 MHz) δ 3.6 (d, J = 4.4, 2H), 3.9 (s,3H) (s, 3H), 4.0 (t , J = 7.2 Hz, 2H) 4.4 (t, J = 6.8 Hz, 2H),
4.1(d, J = 6.8 Hz, 2H), 4.9 (s,2H), 6.8 (d, J = 7.6 Hz, 5.2 (s, 2H), 6.8 (d, J = 8.4 Hz, 1H), 7.0 (d, J = 8.4 Hz,
1H), 6.9 (d, J = 7.2 Hz, 1H), 7.5(t, J = 2 Hz, 2H), 1H), 7.5(t, J = 4 Hz, 2H), 7.8 (t, J = 7.2 Hz, 2H), 8.0
7.8 (t, J = 7.6 Hz, 2H), 8.1 (d, J = 6 Hz, 2H), 8.2 (d, J = 1.6 Hz, 2H), 8.3 (s, 1H), 8.4(d, J = 8.4 Hz,
(s, 1H), 8.4 (d, J = 7.6 Hz, 2H), 8.4 (d, J = 6 Hz, 4H).13CNMR (DMSO-d6,400 MHz) δ 28.61, 32.12,
2H).13CNMR (DMSO-d6,400 MHz)δ 47.03, 60.45, 34.65, 54.46, 60.76, 61.35, 67.29, 108.89, 110.91,
61.28, 63.58, 107.92, 110.61, 122.41, 125.68, 126.47, 126.57, 126.64, 126.77, 127.14, 130.68, 130.91,
126.59, 127.42, 129.41, 130.68, 130.85, 131.00, 131.07, 131.10, 131.28, 132.33, 132.47, 135.86,
131.82, 132.80, 135.71,136.36, 138.93, 151.75, 154.56, 136.41, 139.43, 152.54, 154.13, 168.53. ESI–MS: m/z
168.83. ESI–MS: m/z 479 [M+H]+.
521 [M+H]+.
2.7n 2-(3-(4((4-methoxynaphthalen-1-yloxy)methyl)-1H- 2.7q
2-(6-(4-((4-methoxynaphthalen-1-yloxy)methyl)-
1,2,3-triazol-1-yl)propyl)-1H-benzo[de]isoquinoline-1,3 1H-1,2,3-triazol-1-yl)hexyl)-1H-benzo[de]isoqunolene-
(2H)-dione (IV2−b): M.p. 58–60◦C;IR (KBr): 3076, 1,3(2H)-dione(IV2−e): M.p. 98–100◦C; IR (KBr):
2949, 2861, 2725, 2598, 2002, 1979, 1880, 1695, 3069, 2934, 2859, 2599, 2423, 2309, 1959, 1699,
1655, 1588, 1442, 1389, 1348, 1272, 1236, 1172, 1096, 1657, 1591, 1463, 1439, 1387, 1272, 1237, 1098, 1078,
1057 cm−1.1HNMR (DMSO-d6,400 MHz) δ 2.5 (m, 1023 cm−1.1HNMR (DMSO-d6,400 MHz) δ 1.3 (m,
2H), 3.5(t, J = 6.4 Hz, 2H), 3.9(s, 3H), 4.1 (t, J = 2H) 1.3 (m, 2H), 1.6 (m, 2H), 1.8 (m ,2H) 3.9 (s,3H),
7.6, 2H), 5.3 (s,2H), 7.1 (d, J = 7.2 Hz, 1H), 7.4 (d, 4.0 (t, J = 7.2 Hz, 2H), 4.4 (t, J = 6.8 Hz, 2H), 5.2
J = 7.2 Hz, 1H), 7.5(t, J = 2 Hz, 2H), 7.8 (t, J = (s,2H), 6.8 (d, J = 8.4 Hz, 1H), 7.0(d, J = 8.4 Hz, 1H),
7.6 Hz, 2H), 8.3 (d, J = 6 Hz, 2H), 8.3 (s, 1H), 8.4 7.4(t, J = 3.2 Hz, 2H), 7.8 (t, J = 7.2 Hz, 2H), 8.0
(d, J = 8.4 Hz, 2H), 8.5 (d, J = 7.2 Hz, 2H).13CNMR (d, J = 2.4 Hz, 2H), 8.3(s, 1H), 8.4 (d, J = 8.4 Hz, 2H),
(DMSO-d6, 400 MHz) δ 27.26, 39.58, 42.76, 54.55, 8.5 (d, J = 6.4 Hz, 2H).13CNMR (DMSO-d6,400 MHz)
64.22, 104.25, 104.38, 110.90, 111.15, 125.45, 126.60, δ 30.76, 31.12, 32.52, 34.77, 54.69, 60.56, 61.37,
129.60, 130.25, 131.27, 132.33, 132.45, 135.81, 67.40, 108.35, 108.47, 110.64, 110.96, 126.52, 126.69,
136.41, 139.39, 139.45, 147.90, 158.46, 168.55. 127.21, 129.52, 130.72, 130.78, 131.02, 132.01,
ESI–MS:m/z 493 [M+H]+.
132.60, 135.75, 136.41, 139.18, 152.59, 154.21,
168.47. ESI–MS:m/z 535 [M+H]+.
2.7o 2-(4-(4-((4-methoxynaphthalen-yloxy)methyl)-1H-
1,2,3-triazol-1-yl)butyl)-1H-benzo[de]isoqunolene-1,3
2.7r 2-(8-(4-((4-methoxynaphthalen-1-yloxy)methyl)-
(2H)-dione (IV2−c): M.p. 63–65◦C; IR (KBr): 3074, 1H-1,2,3-triazol-1-yl)octyl)-1H-benzo[de]isoqunolene-
2939, 2873, 2498, 2403, 2095, 1954, 1716, 1614, 1510, 1,3(2H)-dione(IV2−f ): M.p. 108–110◦C; IR (KBr):
1462, 1388, 1272, 1146, 1071 cm−1.1H NMR (DMSO- 2919, 2851, 1697, 1659, 1592, 1462, 1386, 1345,
d6, 400 MHz) δ 1.7(m, 2H), 2.0(m, 2H), 3.9(s 3H), 4.1 1271, 1237, 1156, 1096, 1024 cm−1.1HNMR (DMSO-
(t , J = 1.6 Hz, 2H) 4.4 (t, J = 1.6 Hz, 2H), 5.2 (s, 2H), d6,400 MHz) δ 1.2 (m, 8H) 1.6 (m, 2H), 1.8 (m, 2H),
6.1(s, 1H), 6.8 (d, J = 8.4 Hz, 1H), 6.9(m, 3H), 7.0 (d, 3.9 (s,3H), 4.0 (t, J = 7.6 Hz, 2H) 4.3 (t, J = 7.2 Hz,
J = 8.8 Hz, 1H), 7.5 (t, J = 3.6 Hz, 2H), 7.6 (d, J = 2H), 5.2 (s, 2H), 6.8 (d, J = 8.4 Hz, 1H), 7.0(d, J =
8.8 Hz, 2H), 8.1(d, J = 2 Hz, 2H), 8.3 (s, 1H), 8.3 (s, 8.4 Hz, 1H), 7.4(t, J = 0.8 Hz, 2H), 7.8 (t, J = 7.6 Hz,
1H).13CNMR (DMSO-d6,400 MHz) δ 23.32, 30.91, 2H), 8.0(d, J = 4.8 Hz, 2H), 8.3 (s, 1H), 8.4(d, J =
31.68, 54.29, 60.74, 67.30, 106.31, 108.83, 110.92, 8.0 Hz, 2 H), 8.4 (d, J = 6.8 Hz, 2H).13CNMR (DMSO-
116.31, 117.55, 118.26, 126.60, 126.75, 130.95, d6,400 MHz) δ 30.97, 31.62, 32.60, 33.41, 33.73,

1068
J Ramchander et al.
34.86, 54.57, 60.75, 67.29, 108.87, 110.95, 111.27, alkyl naphthimido-1,2,3-triazoles (IV1-2a-f) in excel-
126.56, 126.74, 127.20, 129.50, 130.67, 130.92, lent yields. The structures of all compounds were char-
1
131.04, 131.08, 131.29, 132.37, 132.49, 135.88, acterized by H, 13C NMR spectra and mass spectra.
136.45, 139.45, 152.51, 154.12, 168.54. ESI–MS:m/z Formation of triazole ring was unequivocally estab-
563 [M+H]+.
lished by the characteristic chemical shift value of the
triazolyl proton resonated at δ 8.07–8.54 ppm. Tri-
azole ring formation can also be confirmed by 13C-
spectra with the new signals of the olefinic C-atoms
of the 1,2,3-triazole moiety at δ 122.5–127 ppm and δ
139–148.
3. Results and discussion
The present investigation focuses on the development
of a few triazolonaphthalenes starting from 1-naphthol.
The synthetic chemistry employed to prepare the tar-
get compounds is outlined in scheme 1. Regioselective
synthesis of 1, 2, 3-triazole-substituted bisnaptholotria-
zoles involves three steps: (1) Propargylation of naph-
thol, (2) Synthesis of alkyl azides (scheme 2) and (3)
Click reaction of propargylated naphthols with azides
(scheme 1 and table 1).
Naphthols I1-2 on reaction with propargyl bromide
in presence of K2CO3 give propargylatednapthyl ethers
III1-2. The structure of naphthylether was confirmed by
appearance of propargylic and terminal alkyne protons
at δ 2.5 and 4.8 in the 1H NMR spectrum.The IR spectra
of these compounds exhibited a new weak absorption
maximum at around 2100 cm−1 characteristic of λc≡c
stretching indicating the formation of propargylated
naphthol ethers III 1-2.
N-(ω-bromo)alkyl)-1,8-naphthalimides (VIIIa−f) were
freshly generated by the reaction of naphthalimide with
appropriate alkyldibromides in acetonitrile and anhy-
drous potassium carbonate with good yields. Com-
pletion of the reaction was monitored by thin layer
chromatography.
N-(ω-Azido)alkyl)-1,8-naphthalimides (IXa-f) were
freshly prepared by the reaction of appropriate N-(ω-
bromo)alkyl)-1,8-naphthalimide (VIIIa-f) with sodium
azide in DMF with good yields.
3.1 Electronic spectral study of 1,4-disubstituted
naphthyloxy methyl N-alkyl
naphthimido-1,2,3-triazoles
Formation of 1,2,3-triazole moiety extended the aro-
matic conjugation between electron donor and elec-
tron acceptor molecules. It was demonstrated that 1,4-
disubstituted triazoles give enhanced spectral proper-
ties when triazole ring extends the aromatic delocal-
ization from the donor moiety to the acceptor through
intramolecular charge transfer phenomena 1,2,5. If
it is assumed that when the triazole is placed in
between two aromatic chromophores and prevent the
conjugation by introducing sp3-hybridized atoms then
the resulting molecule may yield no better spec-
tral properties. The 1,4-disubstituted naphthoxymethyl-
N-alkyl naphthalimide-1,2,3-triazoles reported in this
study possess no possibility for the electron delocaliza-
tion from naphthyl to naphthalimide or vice versa via
1,2,3-triazole ring due to the presence of sp3-hybridized
linker atoms such as oxygen, nitrogen and carbon. It is
therefore interesting to investigate the electronic
absorption and emission properties in order to eval-
uate aromatic conjugation from one end to another
(figure 1).
The final step of the synthesis was the click
reaction. Propargylic ethers of naphthalols (III1-2)
react with azidonaphthalimides (IXa-f) in presence
3.2 Electronic absorption spectral study
of aq. CuSO4. 5H2O and aq. sodium ascorbate in Electronic absorption spectra of IV 2c, IV 2d and IV
DMF to give 1,4-disubstituted naphthyloxy methyl-N- 2e in DMF are shown in figure 1. Similarly, electronic
N3
O
Br
H
N
O
N
O
O
O
O
N
O
O
O
Br
Br
n
NaN3
VII (a-f)
NH3, reflux,
12hr
DMF, 800C, 8hr
MeCN, K2CO3
Reflux, 12 hr
V
VI
VIII(a-f)
IX(a-f)
Where n = 2-a, 3-b, 4-c, 5-d, 6-e, 8-f.
Scheme 2. Synthesis of azidonapthalimides.

Synthesis of naphthlimide-based triazoles
1069
Table 1. Synthesis of 1,4-disubstituted naphthyloxymethyl-N-alkyl naphthimido-1,2,3-triazoles.
S. no.
Compound
R
N
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
IV 1a
IV 1b
IV 1c
IV 1d
IV 1e
IV 1f
IV 2a
IV 2b
IV 2c
IV 2d
IV 2e
IV 2f
H
H
H
H
H
2
3
4
5
6
8
2
3
4
5
6
8
12.0
12.0
12.0
12.0
12.0
12.0
12.0
12.0
12.0
12.0
12.0
12.0
82
86
92
89
74
88
90
79
82
94
90
79
H
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
9
10
11
12
absorption spectra of 2-(3-(4((4-methoxynaphthalen-1- ether in 1,4-disubstituted naphthoxymethyl-N-alkyl
yloxy)methyl)-1H-1,2,3-triazol-1-yl)propyl)-1H-benzo naphthalimide-1,2,3-triazoles. Similarly, covalent at-
[de]isoquinoline-1,3(2H)-dione, IV 2b in four dif- tachment of triazolyl unit to the alkoxy carbon of
ferent solvents are given in figure 2. Electronic naphthyl ether enhanced the absorptivity of 1,4-
absorption spectral data of all the 1,4-disubstituted disubstituted naphthoxymethyl-N-alkyl naphthalimide-
naphthoxymethyl-N-alkyl naphthalimide-1,2,3-triazoles 1,2,3-triazoles.
including the starting naphthols and their propargyl
ethers is shown in tables 2 to 6.
Examination of figure 2 reveals that absorption spec-
trum of the compound IV 2b in water is different from
From figure 1 it can be noticed that electronic tran- that of rest of the solvents. In water, compound IV 2b
sition that occurred are due to the naphthalene aro- exhibited a single broad absorption maximum, while in
matic ring. Further, these transitions occur due to the remaining solvents, it has given a doublet absorption
1
the naphthoxy moiety. The La transition of naph- maxima in the near visible region. Similar observation
1
thalene occurs at longer wavelength while the Lb was found in all the 1,4-disubstituted naphthoxymethyl-
transition occurred at shorter wavelength. However, N-alkyl naphthalimide-1,2,3-triazoles. On closer exam-
from molar extinction coefficients, it can be revealed ination of the absorption spectral data presented in
that the triazole ring contributed significantly to the tables 2 to 6, it can be observed that there is no exten-
spectral shifts. Attachment of triazole caused a little sive delocalization of aromatic π-elecrons in the 1,4-
bathochromic shift of naphthol or naphthoxypropargyl disubstituted naphthoxymethyl-N-alkyl naphthalimide-
1,2,3-triazoles.
IV 2d
IV 2c
0.4
IV 2e
IV 2d
1.Cyclohexane
2. Methanol
3. DMF
2
3
4
IV 2e
4. Water
0.6
0.3
0.0
1
IV 2c
0.2
0.0
300
350
Wavelength (nm)
400
450
300
400
Wavelength (nm)
Figure 1. Electronic absorption spectrum of IV 2c 1.32 ×
10−5 M, IV 2d 1.41 × 10−5 M and IV 2e 1.06 × 10−5 M in Figure 2. Electronic absorption spectrum of IV 2b 2.08 ×
DMF.
10−5 M in different solvents.

1070
J Ramchander et al.
Table 2. Electronic absorption and fluorescence data of α-naphthol, 4-methoxy naphthol, naphthylpropargylicethers, 1,4-
disubstituted naphthyloxymethyl-N-alkyl naphthimido-1,2,3-triazoles in cyclohexane.
Compound λabs max
.
(nm) (∈,dm2 mol−1
)
λex (nm) λflu.max (nm) Stokes shift (nm)
ꢀf
I -1
I -2
III -1
III -2
IV 1b
309(4.3 × 103), 323(3.53 × 103)
369
369
369
369
369
452
452
453
453
453
83
83
84
84
84
8 × 10−6
2.55 × 10−3
1.3 × 10−7
3.6 × 10−5
5.57 × 10−2
2.2 × 10−3
4.9 × 10−2
3.3 × 10−3
333(1.16 × 104), 369(1.93 × 103)
320(4.3 × 101), 379(4.2 × 102)
307(7.6 × 103), 315(7.6 × 103), 330(7.5 × 103)
283(4 × 104), 312(3.7 × 104), 320(3.72 × 104),
331(3.71 × 104), 342(3.74 × 104), 368(3.25 × 104)
290(2.43 × 104), 309(2.52 × 104), 320(2.51 × 104),
345(2.1 × 104)
IV 1c
IV 1d
IV 1e
368
368
369
453
453
453
85
85
84
231(15.7 × 104), 293(4.35 × 104), 312(4.13 × 104),
320(4.2 × 104), 330(4.3 × 104), 345(4.14 × 104)
232(3.4 × 104), 293(1.35 × 104), 306(1.14 × 104),
311(1.15 × 104), 320(1.2 × 104), 330(1.19 × 104),
345(1.12 × 104)
IV 1f
213(13.2 × 104), 232(13.7 × 104), 294(2.7 × 104),
312(2.64 × 104), 320(2.78 × 104), 330(2.89 × 104),
345(2.8 × 104)
368
454
86
2.3 × 10−1
IV 2b
IV 2c
IV 2d
235(10.7 × 104), 331(3.13 × 104), 344(2.87 × 104)
241(1.83 × 104), 317(1.54 × 104), 373(4.16 × 103)
317(2.66 × 104), 330(3 × 104), 345(1.98 × 104),
381(3 × 103)
369
369
369
454
452
453
85
83
84
2.6 × 10−2
9.1 × 10−2
8 × 10−2
IV 2e
IV 2f
317(7.95 × 104), 330(8.3 × 104), 334(7 × 104)
318(3.28 × 104), 330(3.76 × 104), 344(2.78 × 104)
368
369
453
453
85
84
2.4 × 10−2
6.2 × 10−2
Absorption maxima of the title compounds lie in the end to the other naphthyl ring at the other end via 1,2,
range of absorption maxima of naphthol and alkylated 3-triazoles. To identify the light absorbing chromophore
napthimide. It is therefore difficult to assign the light in the 1,4-disubstituted naphthoxymethyl-N-alkyl naph-
absorbing chromophore in the absence of delocaliza- thalimide-1,2,3-triazoles, excitation and emission studies
tion aromatic π-electrons from one naphthyl ring at one have been undertaken with spectrofluorophotometer.
Table 3. Electronic absorption and fluorescence data of α-naphthol, 4-methoxy naphthol, naphthylpropargylicethers, 1,4-
disubstituted naphthyloxymethyl-N-alkylnaphthimido-1,2,3-triazoles in chloroform.
Compound λabs max
.
(nm)(∈,dm2 mol-1)
λex (nm) λflu.max(nm) Stokes shift (nm)
ꢀf
I -1
I -2
III -1
III -2
IV 1b
323(2.8 × 103)
373
373
372
373
372
458
460
458
459
459
85
87
86
86
87
1.74 × 10−3
1.8 × 10−3
4.6 × 10−6
7.2 × 10−5
1.3 × 10−2
333(1.12 × 104), 374(1.75 × 103)
320(4.11 × 102), 352(4.33 × 101)
244(4.7 × 103), 316(1.29 × 103), 361(2.96 × 102)
295(9 × 103), 307(8.57 × 103), 322(9.69 × 103),
336(1.12 × 104), 351(1.19 × 104), 373(6.63 × 103)
294(2.68 × 104), 312(3.07 × 104), 321(1.35 × 104)
283(2 × 104), 294(2.13 × 104), 307(1.86 × 104),
321(2.1 × 104), 334(2.17 × 104), 349(1.93 × 104)
294(1.64 × 104), 307(1.37 × 104), 321(1.47 × 104),
335(1.49 × 104), 350(1.35 × 104)
IV 1c
IV 1d
395
372
434
433
39
61
2.4 × 10−4
5.7 × 10−3
IV 1e
IV 1f
372
370
457
459
85
89
2.8 × 10−3
9.5 × 10−2
2.2 × 10−1
4.5 × 10−2
5.2 × 10−2
4.7 × 10−2
1.8 × 10−2
295(2.52 × 104), 307(2.29 × 104), 321(2.65 × 104),
334(2.84 × 104), 349(2.55 × 104)
IV 2b
IV 2c
IV 2d
IV 2e
IV 2f
241(6.29 × 104), 283(1.6 × 104), 336(3.85 × 104)
244(3.26 × 104), 320(2.66 × 104)
372
372
372
372
372
457
458
459
458
457
85
86
87
86
82
241(10 × 104), 332(4.3 × 104)
284(2.1 × 104), 332(3.59 × 104)
242(6.7 × 104), 333(3.83 × 104)

Synthesis of naphthlimide-based triazoles
1071
Table 4. Electronic absorption and fluorescence data of α-naphthol, 4-methoxy naphthol, naphthylpropargylicethers, 1,4-
disubstituted naphthyloxy methyl-N-alkylnaphthimido-1,2,3-triazoles in methanol.
Compound λabs max
.
(nm)(∈,dm2 mol−1
)
λex (nm) λflu.max(nm) Stokes shift (nm)
ꢀf
I -1
I -2
III -1
III -2
IV 1b
232(2.4 × 104), 295(4.3 × 103), 323(2.4 × 103)
368
368
367
369
371
429
429
429
429
429
61
61
62
60
58
4.7 × 10−4
6 × 10−5
244(4.3 × 103), 321(1.1 × 103), 332(1 × 103)
227(5 × 103), 289(1 × 103), 319(3.23 × 102)
242(6.2 × 103), 315(1.6 × 103), 328(1.4 × 103)
207(1.2 × 105), 230(4.55 × 104), 292(6.63 × 103),
306(8.57 × 103), 320(6.22 × 103), 343(6.33 × 103)
222(7.76 × 104), 292(2.75 × 104), 312(3.13 × 104),
320(3.3 × 104)
4.3 × 10−7
2.4 × 10−4
2.6 × 10−3
IV 1c
IV 1d
368
369
428
429
60
60
5.3 × 10−4
6.6 × 10−2
210(14.3 × 104), 231(12.6 × 104), 291(1.96 × 104),
306(1.6 × 104), 320(1.89 × 104),
334(2 × 104), 343(1.95 × 104)
IV 1e
IV 1f
IV 2b
227(3.69 × 104), 292(1.6 × 104), 306(1.29 × 104),
350
367
347
429
435
401
79
68
54
1.8 × 10−3
6.5 × 10−2
2.6 × 10−2
312(1.23 × 104), 320(1.42 × 104),
333(1.44 × 104), 343(1.38 × 104)
214(13.2 × 104), 231(13.5 × 104), 293(2 × 104),
306(1.78 × 104), 320(2.18 × 104),
333(2.38 × 104), 343(2.27 × 104)
209(9.3 × 104), 233(11.8 × 104), 333(3.44 × 104),
343(3.27 × 104)
IV 2c
IV 2d
209(12.3 × 104), 242(2 × 104), 318(2.12 × 104)
210(14.4 × 104), 234(9.93 × 104), 330(2.97 × 104),
343(2.2 × 104)
369
369
429
428
60
59
2.2 × 10−2
4.3 × 10−2
IV 2e
IV 2f
209(15.2 × 104), 234(10 × 104), 331(3 × 104),
343(2.1 × 104)
368
369
429
429
61
60
2.3 × 10−2
2.2 × 10−2
212(9.69 × 104), 234(10 × 104), 331(3 × 104),
343(1.2 × 104)
Table 5. Electronic absorption and fluorescence data of α-naphthol, 4-methoxy naphthol , naphthylpropargylicethers,1,4-
disubstituted naphthyloxymethyl-N-alkyl naphthimido-1,2,3-triazoles in dimethylformamide.
Compound λabs max
.
(nm)(∈,dm2 mol−1
)
λex (nm) λflu.max(nm) Stokes shift (nm)
ꢀf
I -1
I -2
III -1
III -2
IV 1b
298(5 × 103), 310(4.27 × 103), 324(3.43 × 103)
373
373
374
374
372
434
434
434
434
433
61
61
60
60
61
7.3 × 10−6
2 × 10−3
278(7.3 × 103), 322(1.4 × 104), 355(1.36 × 104)
260(6.68 × 102), 292(1.1 × 103), 321(3.9 × 102)
227(1.18 × 103),317(1.79 × 103), 330(1.69 × 103)
295(6.53 × 103), 307(6.5 × 103) 321(6.94 × 103),
334(6.73 × 103)
6.2 × 10−7
2.7 × 10−4
3.4 × 10−2
IV 1c
IV 1d
295(2.49 × 104), 312(2.9 × 104), 320(2.92 × 104)
295(1.87 × 104), 295(1.7 × 104),
373
372
434
433
61
61
1.5 × 10−3
3.6 × 10−2
321(1.95 × 104), 334(1.98 × 104)
IV 1e
IV 1f
295(1.63 × 104), 295(1.42 × 104),
373
372
433
434
60
62
3.5 × 10−2
6.98 × 10−2
7.5 × 10−2
4.6 × 10−2
4.8 × 10−2
3.43 × 10−2
9.4 × 10−2
313(1.4 × 104), 321(1.49 × 104), 334(1.42 × 104)
295(2 × 104), 307(2 × 104), 322(2.28 × 104),
334(2.39 × 104), 343(2.2 × 104)
IV 2b
IV 2c
IV 2d
IV 2e
IV 2f
333(3.31 × 104), 342(2 × 104)
372
373
373
373
373
434
433
434
433
434
62
60
61
60
61
320(2.09 × 104), 342(5.9 × 103)
322(3.14 × 104), 344(2 × 104)
332(3.2 × 104), 344(2.1 × 104)
332(3.24 × 104), 344(8.8 × 103)

1072
J Ramchander et al.
Table 6. Electronic absorption and fluorescence data of α-naphthol, 4-methoxy naphthol , naphthylpropargylicethers,1,4-
disubstituted naphthyloxymethyl-N-alkyl naphthimido-1,2,3-triazoles in water.
Compound
λabs.max
(nm)(∈,dm2 mol−1
)
λex (nm)
λflu.max(nm)
Stokes shift (nm)
ꢀf
I -1
I -2
291(4 × 103), 321(2 × 103), 361(2.3 × 102)
241(3.78 × 104),
362
374
451
431
89
57
1.2 × 10−4
1.45 × 10−4
318(9.3 × 103), 329(8.77 × 103)
287(9.17 × 102), 319(2.95 × 102),
361(1.17 × 101)
III -1
III -2
362
360
462
413
100
53
6.3 × 10−6
1.39 × 10−4
240(4.92 × 103), 304(1.29 × 103),
313(1.3 × 103)
IV 1b
IV 1c
IV 1d
IV 1e
IV 1f
IV 2b
IV 2c
IV 2d
IV 2e
IV 2f
350(9.8 × 104)
346
321
343
344
343
344
322
341
355
345
395
384
384
390
395
384
384
386
406
392
49
63
41
46
52
40
62
45
51
47
2 × 10−3
1.5 × 10−4
2.5 × 10−4
5.93 × 10−3
1 × 10−5
320(1.95 × 103)
358(1.43 × 104)
320(7.3 × 102), 344(7 × 102)
348(5.3 × 101)
293(7.8 × 103), 344(3.2 × 104)
321(2.5 × 103)
1.92 × 10−4
1.32 × 10−4
8.6 × 10−5
1.99 × 10−3
2.96 × 10−4
332(2.13 × 102), 343(1.42 × 102)
354(6.23 × 103)
234(3.68 × 103), 343(1.23 × 103)
3.3 Fluorescence study
by absorption spectroscopy as both the naphthalene
rings at 1,4-position of the triazole absorb in the
same region. However, from the excitation and emis-
sion maxima, napthol is the assigned light absorb-
ing and emitting chromophore but not naphthalim-
ide. The excitation and emission wavelength maxima
in the disubstituted triazole compounds are close to
that of naphthol rather than naphthalimide. The excita-
tion and emission wavelength maxima of naphthimides
are <340 and 400 nm, respectively. However, in
the present 1,4-disubstituted naphthoxymethyl-N-alkyl
naphthalimide-1,2,3-triazoles, the excitation and emis-
sion maxima are in the region 365 to 370 nm and 400 to
460 nm, respectively. Therefore, the light absorbing
Fluorescence spectra of IV 1d, IV 1e, IV 1f, IV 2d and
IV 2f in cyclohexane are given in figure 3. Similarly,
fluorescence spectra of IV 1f in cyclohexane, chloro-
form, methanol, DMF and water are shown in figure 4.
From the figure 3 it can be observed that emission
spectra of IV 1f appear similar to a mirror image of its
absorption spectrum.
Similar observation was made with the other com-
pounds in all the investigated solvents. Emission data
obtained in the present study is tabulated in tables 2 to 6.
The light absorbing chromophore was not established
IV 2f
400
IV 1f
600
4
IV 2d
IV 1d
IV 1e
1. Water
2. cyclohexane
3. Chloroform
4. DMF
300
1
IV 2f
400
5. Methanol
3
IV 1d
200
IV 2d
IV 1e
200
2
5
IV 1f
100
0
400
500
0
Wavelength (nm)
350
400
450
500
550
Wavelength (nm)
Figure 3. Fluorescence spectra of IV 2f 2.6 × 10−5 M, IV
1e 1 × 10−4 M, IV 1d 9.8 × 10−6 M, IV 2d 1.41 × 10−5
and IV 1f 1.88 × 10−5 M in cyclohexane.
M
Figure 4. Fluorescence spectra of IV 1f 1.88 × 10−5 M in
different solvents.

Synthesis of naphthlimide-based triazoles
1073
chromophore is the naphthol moiety rather than the 4. Conclusions
naphthimide part of 1,2,3-triazole. The absorption
Synthesis of a few 1,4-disubstituted naphthoxymethyl-
N-alkylnaphthalimide-1,2,3-triazols is reported. The
structure of these triazoles was established by spectral
studies. It is proved that electronic excitation and emis-
sion techniques are superior techniques over the elec-
tronic absorption spectral technique to identify the light
absorbing chromophore. Sp3-hybridized linker atoms
such as nitrogen, oxygen and carbon in between the tri-
azole ring and the naphthalene moieties at 1,4-position
prevent extensive delocalization of π-electrons lead-
ing to little change in the absorption and emission
properties of 1,4-disubstituted naphthoxymethyl-N-
alkylnaphthalimide-1,2,3-triazols when compared with
1-naphthol.
maxima and the emission maxima of the methoxy-
substituted naphthoxytriazoles (IV 2) are similar to
that of the simple naphthoxy-substituted triazole (IV
1) derivatives. This is possibly due to the absence
of delocalization of π-electrons of the positive
mesomerism of methoxy group to an extent of influenc-
ing the absorption of light. Both the substituted naph-
thalene rings at 1,4-position of 1,2,3-triazoles are nei-
ther in conjugation with one another, nor with the tria-
zole ring as the naphthoxy part is insulated by –OCH3
and the naphthalimide group by alkyl chain. There-
fore, it can be concluded that in the absence of con-
jugation between the three absorbing chromophores,
i.e., 1-naphthyloxy, 1,2,3-triazole and naphthalimide,
the light absorbing chromophore is the naphthyloxy-
chromophore.
The naphthoxymethylalkylimido-1,2,3-triazoles are
moderately fluorescent compounds, exhibiting little sol-
vent and substituent effects on the quantum yield and
emission maxima. A closer look at tables 2 to 6 reveals
that the order of quantum yield is IV>I 2> I 1> III
2> III 1. A triazole ring added on to naphtholpro-
porgyl ether improved the light emission; the methoxy
substituent in naphthol also enhances the radiative
emission. However, proporgylation on the oxygen of
1-naphthol quenched the fluorescence. The length of
the alkyl chain between the triazole and naphthimide
did not bring any considerable changes in spectral
properties of the 1,4-disubstituted naphthoxymethyl-N-
alkyl naphthalimide-1,2,3-triazoles. Aprotic polar sol-
vent, DMF enhanced the quantum yield while the protic
polar solvents quenched the fluorescence. The effect of
the solvent on the quantum yield of a given compound
follows the order: DMF > cyclohexane > chloroform
> methanol > water. Aqueous medium is the more
quenching medium. Similarly, the effect of solvent on
fluorescence emission maximum and excitation max-
ima is not the same for all the compounds. However, a
broad generalization can be made based on the spectral
data presented in the tables 2 to 6. The effect of sol-
vent on the emission maxima varies in the order: chloro-
form > cyclohexane > methanol > DMF > water. The
water is unique in the sense that it is the most quenching
and hypsochromic medium than the remaining media.
This may be due to the fact that absorption and emis-
sion maxima in water are attributed to the naphthalim-
ide part rather than naphthol chromophore, unlike in the
remaining solvents.28 The Stokes shift exhibits linearity
neither with the solvent polarity nor to the length of the
alkyl chain, indicating that the absorbing and emitting
chromophore is the naphthoyloxy moiety.
Supplementary information
1H, 13C spectra, mass spectra, spectral data, fluores-
cence spectra and tables are submitted as supplemen-
tary information.
Acknowledgements
One of the authors J Ramchander thanks Osmania
University, Hyderabad for providing financial support
under faculty development programme.
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