Novel naphthalimide–aminobenzamide dyads as OFF/ON fluorescent supramolecular receptors in metal ion binding

Article abstract of DOI:10.1080/10610278.2016.1149180

A series of novel naphthalimide–aminobenzamide (NAPIM-2ABZ) dyads 3 connected by different length polymethylene chains were synthesized and studied as fluorescent supramolecular receptors in metal ion binding. The photophysical properties were evaluated a

Full text of DOI:10.1080/10610278.2016.1149180

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20
Novel naphthalimide–aminobenzamide dyads as
OFF/ON fluorescent supramolecular receptors in
metal ion binding
Marco A. Landey-Álvarez, Adrián Ochoa-Terán, Georgina Pina-Luis, Marisela
Martínez-Quiroz, Milagros Aguilar-Martínez, José Elías-García, Valentín
Miranda-Soto, José-Zeferino Ramírez, Lorena Machi-Lara, Victoria Labastida-
Galván & Mario Ordoñez
To cite this article: Marco A. Landey-Álvarez, Adrián Ochoa-Terán, Georgina Pina-Luis, Marisela
Martínez-Quiroz, Milagros Aguilar-Martínez, José Elías-García, Valentín Miranda-Soto, José-
Zeferino Ramírez, Lorena Machi-Lara, Victoria Labastida-Galván & Mario Ordoñez (2016): Novel
naphthalimide–aminobenzamide dyads as OFF/ON fluorescent supramolecular receptors in
metal ion binding, Supramolecular Chemistry, DOI: 10.1080/10610278.2016.1149180
To link to this article: http://dx.doi.org/10.1080/10610278.2016.1149180
Published online: 09 Mar 2016.
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Date: 11 March 2016, At: 00:16

Supramolecular chemiStry, 2016
http://dx.doi.org/10.1080/10610278.2016.1149180
Novel naphthalimide–aminobenzamide dyads as OFF/ON fluorescent
supramolecular receptors in metal ion binding
Marco A. Landey-Álvareza , Adrián Ochoa-Terána , Georgina Pina-Luisa , Marisela Martínez-Quiroza,
Milagros Aguilar-Martíneza, José Elías-Garcíab, Valentín Miranda-Sotoa, José-Zeferino Ramírezc , Lorena Machi-
Larac, Victoria Labastida-Galvánd and Mario Ordoñezd
acentro de Graduados e investigación en Química, instituto tecnológico de tijuana, tijuana, mexico; bunidad académica de ciencias Químicas,
c
universidad autónoma de Zacatecas, Zacatecas, mexico; Departamento de investigación en polímeros y materiales, universidad de Sonora,
hermosillo, mexico; dcentro de investigaciones Químicas-(iicBa), universidad autónoma del estado de morelos, cuernavaca, mexico
ARTICLE HISTORY
ABSTRACT
received 9 September 2015
A series of novel naphthalimide–aminobenzamide (NAPIM-2ABZ) dyads 3 connected by different
accepted 28 January 2016
length polymethylene chains were synthesized and studied as fluorescent supramolecular
receptors in metal ion binding. The photophysical properties were evaluated and compared with
separated chromophores. The electronic absorption spectra of dyads 3 showed no interaction
between chromophores in the ground state. The fluorescence quantum yields were lower in dyads
3 in comparison with N-propyl-2-aminobenzamide (8). The fluorescence quenching is attributed
to a PET mechanism between fluorophores (from 2ABZ to NAPIM), which is dependent on the
polymethylene chain length. In metal binding study was found a response towards transition
metal ions such as Hg(II), Cu(II), Zn(II) and Ni(II). Dyad 3b presented selectivity towards Cu(II). The
UV-vis, IR and 1H-NMR studies demonstrated the interaction with 2ABZ moiety in the ground state,
and interestingly dyads with shorter polymethylene chains 3a (n = 0), 3b (n = 1) and 3c (n = 2)
exhibited an OFF/ON fluorescence behaviour due to the PET inhibition and the quenching of 2ABZ
fluorescence. Dyads 3d (n = 4) and 3e (n = 6) presented opposite response ON/OFF in the complex
with metal ions evidencing the absence of PET in these dyads.
KEYWORDS
pet; dyads; naphthalimide;
aminobenzamide; metal
binding
Introduction
reductive amination. The same strategy has been used
in the label of monosaccharides with N-aminoethyl-2-
aminobenzamide (2AEAB) (7), which has the advantage
of being a bifunctional molecule and allows to develop
microarrays to study the protein–carbohydrates interac-
tions (8). Fluorescent sensors for the detection of Zn(II)
with a 2ABZ moiety as fluorophore were reported (9, 10).
2-Aminobenzamide (2ABZ) has been extensively studied
as fluorescent label in order to improve the oligosaccha-
ride detection and sequencing by high-performance liquid
chromatography (1–6). The introduction of 2ABZ as fluo-
rescent probe into saccharides occurs through a two-step
CONTACT adrián ochoa-terán
© 2016 taylor & Francis
ochoa@tectijuana.mx

2
M. A. LANDEy-ÁLVAREZ ET AL.
Figure 1. Structure of Napim-DaNS 1, Napim-ptZ 2 and Napim-2aBZ 3 dyads, N-propyl-2-aminobenzamide (8) and N-propylnaphthali
mide (9).
electron donor–acceptor system with unique fluorescence
properties due to an internal charge transfer process (ICT).
Furthermore, several groups have investigated the coor-
dinating behaviour of 2ABZ and its derivatives. Lingaiah et
al. (11) reported the formation of a light green distorted
octahedral complex from N-phenyl-2ABZ to Cu(II) with
a 1:2 metal–ligand ratio. The molar conductance was 67
ohm−1cm2 mol−1 in DMF, which is in accordance to a 1:1
electrolyte. Recently, the mixed ligand complex synthesis
with 2ABZ, α-amino acids and transition cations such as
Cu(II) or Ni(II) was reported (12, 13). In these reports, the
coordination of the cation with the amino and carbonyl
groups of 2ABZ in an octahedral complex was proposed.
Recently, the immobilisation of N,N-alkyl-bis-2ABZs on
Merrifield’s resin and their labelling with a dansyl moiety
were reported (14). The fluorescent properties were stud-
ied as a function of the alkyl length chain and the labelling
with dansyl group. In the response with metal ions was
found a selective recognition to Mg(II) based on the inhi-
bition of PET when cation was combined with the ligand.
Additionally, bischromophoric dyads 1 containing
a 1,8-naphthalimide (NAPIM) and dansylamide (DANS)
Figure 2. (a) uV-vis spectra of 8, 9 and 3b. (b) uV-vis spectra of
fluorophores linked by a polymethylene chains were
reported by Pischel et al. (15). In their studies, they
3(a-e). Solvent: mecN. [8, 9 and 3(a-e)] = 1 × 10−5 m.
found singlet-singlet energy transfer (SSET) and pho-
toinduced electron transfer (PET) processes between
NAPIM and DANS, and both processes were affected by
the presence of protons quenching DANS and enhanc-
ing NAPIM fluorescence (Figure 1). Ramaiah et al. (16)
found that the presence of Cu(II) and Zn(II) has the same
Emission spectra appear in the visible region between
400 and 550 nm, and the detection is performed in
HEPES buffer at pH = 7.4. A fluorescence enhancement is
observed upon addition of Zn(II) to a ligand solution. The
structure of 2ABZ, with amino and amide groups, forms an

SUPRAMOLECULAR CHEMISTRy
3
Figure 3. (a) Fluorescence spectra of 8, 9 and 3b, λex(8) = 324 nm,
λem(8) = 394 nm, λex(9) = 332 nm, λem(9) = 378 nm, λex(3b) =
328 nm, λem(3b) = 398 nm. [8] = [9] = 1 × 10−5 m (b) emission
spectra of dyads 3(a-e). Solvent: mecN. [3(a-e)] = 1 × 10−5 m.
λex(3a) = 340 nm, λex(3b-3c) = 328 nm.
Figure 4. (a) uV-vis spectra obtained by titration of 8 with
hg(clo4)2 in mecN. (b) absorbance profiles at 326 nm obtained
by titration of 8 with different metal ions in acetonitrile. [8] =
1 × 10−5 m.
Experimental
effect in dyads with shorter spacing length due to the
SSET and PET processes, instead a Förster resonance
energy transfer (FRET) process occurs between NAPIM
and DANS fluorophores in dyads with longer polyme-
thylene chain (six and eight methylenes) (17). The radi-
ometric response was influenced by the length of the
polymethylene chain in both works.
It is well known that NAPIM derivatives have excellent
electron–acceptor properties and have been used in many
studies of PET involving the interaction with different donors
(18–24). In addition, other NAPIM derivatives such as naph-
thalimide–phenothiazine (NAPIM-PTZ) dyads 2 capable to
form intramolecular exciplex and intermolecular excimer in
non-polar solvents have been described (25). Nevertheless,
2ABZ acts as energy donor in fluorescence energy-transfer
probes containing nitrotyrosine as energy acceptor in con-
formation studies of medium size peptides (26).
General
All reagents were purchased in the highest quality avail-
able and were used without further purification. Nuclear
magnetic resonance (NMR) spectra of H and 13C were
1
recorded in a Varian 200 MHz and in a Bruker 400 MHz
Spectrometer in DMSO-d6, CDCl3 or CD3CN with TMS
as internal standard. Chemical ionisation mass spectra
and HRMS were recorded on a MStation JMS-700 JEOL.
Electronic impact mass spectra were obtained by direct
insertion in an Agilent 5975C mass spectrometer, and the
intensities were reported as a relative percentage to the
base peak after the corresponding m/z value. Infrared
spectra were recorded on a Spectrum 400 FTIR-ATR spec-
trophotometer. Melting points were obtained on aThermo
Scientific apparatus model Mel-Temp, and the value is
reported as an average of three separated experiments.
Fluorescence spectra were measured on a Cary Eclipse
spectrofluorometer, and the absorbance spectra were
measured on a Cary 100 Conc UV-Visible spectrophotom-
eter. The measurements were taken at room temperature
in 1-cm quartz cuvettes.
In this work were synthesised a series of novel naph-
thalimide–aminobenzamide (NAPIM-2ABZ) dyads 3 linked
with different length polymethylene chains in order to
evaluate their optical properties and the complex forma-
tion with transition metal ions in solution, as well as their
effect on PET process between NAPIM and 2ABZ.

4
M. A. LANDEy-ÁLVAREZ ET AL.
General procedure for the synthesis of
1,8-naphthalimide alkylamines 6
In a round-bottom flask, the corresponding alkyldiamine
(7 equiv. 17.64 mmol) was dissolved in 50 mL of dis-
tiled water, and the solution was stirred and heated at
80 °C. 1,8-naphthalenetetracarboxylic acid anhydride (4)
(500 mg, 2.52 mmol) was added portion wise, and the
mixture was heated for 20 min. The suspended solid was
filtered and was cooled into an ice bath until a yellow
solid was formed. The solid was separated by filtration
and dry at room temperature.
2-(3-Aminoethyl)-1H-benzo[de]isoquinoline-1,3(2H)-
dione (6a)
yellow solid, 304 mg, 1.27 mmol, 50% yield. Mp 129–130 °C.
FTIR (KBr): 3340, 3450, 3063, 2929, 1693, 1609, 1388 cm−1.
1H-NMR (DMSO-d6, 400 MHz): δ 8.48 (dd, J = 7.3, 1.0 Hz, 2H),
8.44 (dd, J = 8.3, 1.0 Hz, 2H), 7.86 (dd, J = 8.3, 7.3 Hz, 2H), 4.1
(t, J = 7.0 Hz, 2H), 2.81 (t, J = 7.0 Hz, 2H). 13C-NMR (DMSO-d6,
50 MHz): δ 163.5, 134.0, 131.1, 130.4, 127.3, 127.0, 122.1,
42.7, 39.6.
Figure 5. (a) emission spectra obtained by titration of 8 with
hg(clo4)2 in acetonitrile. (b) Fi/Fi0 profiles at 394 nm obtained
by titration of 8 with different metal ions in acetonitrile.
[8] = 1 × 10−5 m.
2-(3-Aminopropyl)-1H-benzo[de]isoquinoline-
1,3(2H)-dione (6b)
yellow solid, 237 mg, 0.93 mmol, 37% yield. Mp 141–142 °C.
FTIR (KBr): 3340, 3450, 3063, 2929, 1693, 1609, 1388 cm−1.
1H-NMR (CDCl3, 200 MHz): δ 8.59 (d, J = 7.2 Hz, 2H), 8.21
(d, J = 8.0 Hz, 2H), 7.75 (t, J = 8.0 Hz, 2H), 4.19 (t, J = 7.3 Hz,
2H), 2.76 (t, J = 6.9 Hz, 2H), 1.8 (m, 2H). 13C-NMR (DMSO-d6,
50 MHz): δ 164.1, 133.7, 131.5, 131.3, 126.9, 122.7, 41.8,
39.5, 28.5.
2-(4-Aminobutyl)-1H-benzo[de]isoquinoline-1,3(2H)-
dione (6c)
yellow solid, 223 mg, 0.83 mmol, 33% yield. Mp
129–130 °C. FTIR (KBr): 3343, 3448, 3058, 2931, 1690,
1
1615, 1373 cm−1. H-NMR (CDCl3, 200 MHz): δ 8.59 (dd,
J = 7.3, 1.1 Hz, 2H), 8.21 (dd, J = 7.3, 1.1 Hz, 2H), 7.75 (t,
J = 7.9 Hz, 2H), 4.21 (t, J = 7.5 Hz, 2H), 2.76 (t, J = 6.9 Hz,
2H), 1.77 (m, 2H), 1.57 (m, 2H). 13C-NMR (DMSO-d6,
50 MHz): δ 164.2, 133.9, 131.5, 131.2, 126.9, 122.5, 41.9,
40.1, 25.4, 31.2.
2-(6-Aminohexyl)-1H-benzo[de]isoquinoline-1,3(2H)-
dione (6d)
yellow solid, 313 mg, 1.06 mmol, 42% yield. Mp 101–102 °C.
FTIR (ATR): 3340, 3452, 3062, 2929, 1690, 1612, 1379 cm−1.
1H-NMR (CDCl3, 200 MHz): δ 8.59 (d, J = 7.1 Hz, 2H), 8.2 (d,
J = 7.9 Hz, 2H), 7.75 (t, J = 7.9 Hz, 2H), 4.2 (t, J = 7.4 Hz, 2H), 2.78
(t, J = 6.6 Hz, 2H), 1.69 (m, 2H), 1.59 (m, 2H), 1.39 (m, 2H), 1.31
(m, 2H). 13C-NMR (DMSO-d6, 50 MHz): δ 164.1, 133.8, 131.5,
131.2, 126.9, 122.6, 42.0, 32.2, 26.4, 26.4, 32.7, 40.4
Figure 6. (a) uV-vis spectra obtained by titration of dyad 3b
with hg(clo4)2 in acetonitrile. (b) uV-vis absorbance profiles at
328 nm obtained by titration of 3b with different metal ions in
acetonitrile. [3b] = 1 × 10−5 m.

SUPRAMOLECULAR CHEMISTRy
5
2-(8-Aminooctyl)-1H-benzo[de]isoquinoline-1,3(2H)-
dione (6e)
yellow solid, 261 mg, 0.81 mmol, 32% yield. Mp 71–72 °C.
FTIR (ATR): 3342, 3452, 3062, 2930, 1682, 1610, 1382 cm−1.
1H-NMR (CDCl3, 200 MHz): δ 8.58 (dd, J = 7.2, 0.9 Hz, 2H),
8.21 (dd, J = 8.3, 0.9 Hz, 2H), 7.74 (dd, J = 8.3, 7.2 Hz, 2H),
4.16 (t, J = 7,3 Hz, 2H), 2.63 (t, J = 6.6 Hz), 1.84–1.69 (m, 4H),
1.50–1.41 (m, 4H), 1.37–1.25 (m, 4H). 13C-NMR (DMSO-d6,
50 MHz): δ 164.1, 133.8, 131.5, 131.2, 126.9, 122.7, 42.2,
40.5, 33.7, 29.3, 28.1, 27.1, 26.8.
General procedure for the synthesis of dyads 3
In a round-bottom flask, a naphthalimide derivative 6 (1
equiv.) was dissolved in 20 mL of dry THF or DMF depend-
ing on the solubility under argon atmosphere. Then, isatoic
anhydride (44 mg, 0.27 mmol) was added portion wise,
and the mixture was refluxed for 2 h. Finally, the solvent
was removed under vacuum pressure, and the solid was
washed with acetonitrile.
2-amino-N-(2-(1,3-dioxo-1H-benzo[de]isoquinolin-
2(3H)-yl)ethyl)benzamide (3a)
Figure 7. emission spectra obtained by titration of 3b with
hg(clo4)2 in acetonitrile (a), and its emission profiles obtained by
titration with different metal ions. [3b] = 1 × 10−5 m. λex(3b) =
328 nm.
yellow solid, 36 mg, 0.10 mmol, 24% yield based on 100 mg
(0.41 mmol) of 6a. Mp 189–190 °C. FTIR (KBr): 3465, 3377,
3362, 3062, 2964, 1692, 1643, 1635, 1610, 1585, 1334,
1233 cm−1. 1H-NMR (DMSO-d6, 400 MHz): δ 8.48 (dd, J = 7.2,
1.1 Hz, 2H), 8.45 (dd, J = 8.3, 1.0 Hz, 2H), 8.27 (t, J = 6.0 Hz,
2H), 7.86 (dd, J = 8.3, 7.2 Hz, 2H), 7.28 (dd, J = 7.9, 1.4 Hz,
2H), 7.07 (ddd, J = 8.3, 7.2, 1.5 Hz, 1H), 6.62 (dd, J = 8.2,
1.0 Hz, 1H), 6.42 (ddd, J = 8.3, 7.2, 1.1 Hz, 1H), 6.17 (br,
2H), 4.26 (t, J = 5.8 Hz, 2H), 3.57 (dt, J = 6.0, 5.8 Hz, 2H).
13C-NMR (DMSO-d6, 50 MHz): δ169.5, 164.2, 149.8, 134.6,
131.9, 131.8, 131.1, 128.5, 127.7, 122.9, 116.6, 115.7, 115.0,
40.1, 37.3. MS(EI) m/z (rel. int.): 359 (5) [M]+, 342 (2), 223
(100), 162 (9), 136 (3), 70 (45). HRMS (CI+): calculated for
C21H18N3O3 [M + H]+, m/z = 360.1348, found for [M + H]+,
m/z 360.1336.
2-amino-N-(3-(1,3-dioxo-1H-benzo[de]isoquinolin-
2(3H)-yl)propyl)benzamide (3b)
yellow solid, 106 mg, 0.28 mmol, 72% yield based on
100 mg (0.39 mmol) of 6b. Mp 177–178 °C. FTIR (KBr): 3340,
3261, 3063, 2929, 1693, 1609, 1338 cm−1. 1H-NMR (CDCl3,
200 MHz): δ 8.62 (d, J = 7.3 Hz, 2H), 8.23 (d, J = 8.4 Hz, 2H),
7.77 (dd, J = 8.4, 7.3 Hz, 2H), 7.60 (d, J = 7.7 Hz, 1H), 7.26
(br, 1H), 7.20 (d, J = 7.7 Hz, 1H), 6.76–6.65 (m, 2H), 5.62 (br,
2H), 4.34 (t, J = 6.1 Hz, 2H), 3.41 (dt, J = 6.1, 5.8 Hz, 2H), 2.05
(qnt, J = 6.1 Hz, 2H). 13C-NMR (DMSO-d6, 50 MHz): δ 169.2,
164.8, 149.0, 134.3, 132.1, 131.6, 128.2, 127.4, 122.3, 117.3,
116.7, 116.1, 37.4, 35.7, 27.8. MS(EI) m/z (rel. int.): 373 (12)
[M]+, 253 (2), 236 (100), 198 (9), 137 (8), 120 (76). HRMS (CI+):
Figure 8. (a) emission spectra obtained in the titration of 3b-
hg(ii) complex with cu(ii). (b) Batch competitive assay with 3b,
hg(ii) and cu(ii).

6
M. A. LANDEy-ÁLVAREZ ET AL.
Figure 9. reversibility study of the ion recognition using eDta as competitive ligand with 3b-Hg(II). inset: Fluorescence profile upon
addition of eDta.
Figure 10. 1h-Nmr spectra obtained in the titration of 3b with Zn(clo4)2 in cD3cN. [3b] = 5 mm.
calculated for C22H20N3O3 [M + H]+, m/z = 374.1505, found
for [M + H]+, m/z 374.1501.
J = 7.4, 1.0 Hz, 1H), 7.18 (ddd, J = 7.8, 7.4, 1.6 Hz, 1H), 6.65
(dd, J = 7.6, 1.6 Hz, 1H), 6.63 (ddd, J = 7.8, 7.6, 1.0 Hz, 1H),
6.45 (s, 1H), 5.51 (br, 2H), 4.23 (t, J = 7.1 Hz, 2H), 3.52 (dt,
J = 6.5, 6.0 Hz, 2H), 1.93–1.66 (m, 4H). 13C-NMR (DMSO-d6,
50 MHz): δ 169.3, 164.3, 148.7, 134.0, 132.1, 131.5, 131.3,
128.1, 127.3, 127.0, 122.5, 117.2, 116.5, 114.6, 39.6, 39.4,
26.8, 25.5. MS(EI): m/z (rel. int.): 387 (88) [M]+, 267 (46), 222
(18), 197 (16), 136 (19), 120 (100). HRMS (CI+): calculated for
C23H22N3O3 [M + H]+, m/z = 388.1661, found for [M + H]+,
m/z 388.1682.
2-amino-N-(4-(1,3-dioxo-1H-benzo[de]isoquinolin-
2(3H)-yl)butyl)benzamide (3c)
yellow solid, 62 mg, 0.16 mmol, 43% yield based in
100 mg (0.37 mmol) of 6c. Mp 165–166 °C. FTIR (KBr):
1
3348, 3277, 3059, 2931, 1690, 1615, 1373 cm−1. H-NMR
(CDCl3, 200 MHz): δ 8.60 (dd, J = 6.0, 1.0 Hz, 2H), 8.21 (dd,
J = 8.0, 1.0 Hz, 2H), 7.75 (dd, J = 8.0, 6.0 Hz, 2H), 7.38 (dd,

SUPRAMOLECULAR CHEMISTRy
7
Figure 11. (colour online) infrared spectra of 3b and 3b-Zn(ii) complex.
200 MHz): δ 8.57 (dd, J = 7.3, 0.8 Hz, 2H), 8.20 (dd, J = 7.9,
0.8 Hz, 2H), 7.74 (dd, J = 7.9, 7.3 Hz, 2H), 7.37 (dd, J = 7.4,
1.3 Hz, 1H), 7.18 (ddd, J = 8.3, 7.9, 1.5 Hz, 1H), 6.69–6.59 (m,
2H), 6.29 (br, 1H), 5.15 (br, 2H), 4.19 (t, J = 7.3 Hz, 2H), 3.40
(dt, J = 6.6, 6.1 Hz, 2H), 1.77 (qnt, J = 6.9 Hz, 2H), 1.66–1.56
(m, 2H), 1.50–1.46 (m, 4H). 13C-NMR (DMSO-d6, 50 MHz): δ
169.4, 164.3, 148.6, 133.9, 132.1, 131.6, 131.2, 127.2, 127.0,
122.7, 117.2, 116.6, 40.1, 39.4, 29.4, 27.9, 26.4, 26.4. MS(EI)
m/z (rel. int.): 415 (84) [M]+, 295 (61), 198 (25), 150 (34),
120 (100). HRMS (CI+): calculated for C25H26N3O3 [M + H]+,
m/z = 416.1974, found for [M + H]+, m/z 416.1963.
2-amino-N-(8-(1,3-dioxo-1H-benzo[de]isoquinolin-
2(3H)-yl)octyl)benzamide (3e)
yellow solid, 58 mg, 0.131 mmol, 42% yield based in
100 mg (0.31 mmol) of 6e. Mp 197–198 °C. FTIR: 3452,
3342, 3062, 2930, 1682, 1610, 1282 cm−1. 1H-NMR (CDCl3,
200 MHz): δ 8.56 (d, J = 6.3 Hz, 2H), 8.18 (d, J = 7.0 Hz, 2H),
7.73 (dd, J = 7.0, 6.3 Hz, 2H), 7.30 (dd, J = 7.9, 1.3 Hz, 1H),
7.17 (ddd, J = 8.3, 7.9, 1.3 Hz, 1H), 6.67 (d, J = 8.2 Hz, 1H),
6.63 (ddd, J = 7.8, 7.4, 1.0 Hz, 1H), 6.13 (s, 1H), 5.46 (br,
2H), 4.16 (t, J = 7.5 Hz, 2H), 3.38 (dt, J = 6.8, 6.1 Hz, 2H),
1.76–1.66 (m, 2H), 1.62–1.52 (m, 2H), 1.43–1.25 (m, 8H).
13C-NMR (DMSO-d6, 50 MHz) δ: 169.0, 164.2, 148.5, 133.9,
132.1, 131.5, 131.2, 127.1, 127.0, 122.6, 117.2, 116.6, 40.4,
39.7, 29.6, 29.2, 29.1, 28.0, 27.0, 27.0. MS(EI) m/z (rel. int.):
443 (8) [M]+, 323 (6), 295 (4), 198 (39), 120 (100). HRMS (CI+):
Figure 12. (colour online) optimised geometries by DFt for dyad
3a (a) and 3b (b).
2-amino-N-(6-(1,3-dioxo-1H-benzo[de]isoquinolin-
2(3H)-yl)hexyl)benzamide (3d)
Brown solid, 48 mg, 0.116 mmol, 43% yield based in
80 mg (0.27 mmol) of 6d. Mp 161–162 °C. FTIR (KBr): 3351,
3281, 3058, 2931, 1696, 1614, 1377 cm−1. 1H-NMR (CDCl3,

8
M. A. LANDEy-ÁLVAREZ ET AL.
Figure 13. (colour online) optimised mos for dyad 3a.
[M]+, 120 (100), 92 (48), 65 (80). MS(CI+): 179 [M + H]+. HRMS
(CI+): calculated for C10H15N2O [M + H]+, m/z = 179.1184,
found for [M + H]+, m/z 179.1184.
N-propyl 1,8-naphthalimide (9)
In a round-bottom flask, propylamine (4 equiv. 10.08 mmol)
was dissolved in 50 mL of toluene, and 1,8-naphthalenetet-
racarboxylic acid anhydride (4) (200 mg, 1.01 mmol) was
added portion wise; the mixture was stirred for 30 min at
room temperature. Then, the reaction mixture was stirred
and refluxed for 4 h. The solvent was evaporated, and the
solid was successively washed and filtered with CH2Cl2,
Et2O and petroleum ether.
Pale yellow solid, 130 mg, 0.54 mmol, 54% yield. Mp
151–152 °C. FTIR (ATR): 3077, 2950, 1691, 1654, 1624,
1
1588, 1346, 1237 cm−1. H-NMR (CDCl3, 400 MHz): δ 8.59
(d, J = 7.3 Hz, 2H), 8.19 (d, J = 8.2 Hz, 2H), 7.73 (dd, J = 8.2,
7.3 Hz), 4.15 (t, J = 7.5 Hz, 2H), 1.77 (sext, J = 7.5 Hz, 2H),
1.02 (t, J = 7.5 Hz, 3H). 13C-NMR (DMSO-d6, 50 MHz) δ:
164.2, 133.8, 131.6, 131.1, 128.2, 126.9, 122.8, 41.9, 21.4,
11.5. MS(EI) m/z (rel. int.): 239 (80) [M]+, 197 (100), 180 (50),
126 (40). MS(CI+): 240 [M + H]+. HRMS(CI+): calculated for
C15H14NO2 [M + H]+, m/z = 240.1025, found for [M + H]+,
m/z 240.1021.
Figure 14. (colour online) optimised geometries of 3b-Hg(II) (a)
and 3b-Zn(II) (b) complexes with the pm7 semiempirical method.
calculated for C27H30N3O3 [M + H]+, m/z = 444.2287, found
for [M + H]+, m/z 444.2287.
N-propyl 2-aminobenzamide (8)
Determination of quantum yields
In a round-bottom flask, propylamine (1.1 equiv.) was
dissolved in 20 mL of dry THF under argon atmosphere.
Then, isatoic anhydride (200 mg, 1.23 mmol) was added
portion wise, and the mixture was refluxed for 2 h. Finally,
the solvent was removed under vacuum pressure, and the
solid was washed with acetonitrile.
Pale brown solid, 110 mg, 0.617 mmol, 50% yield.
Mp 83–84 °C. FTIR (ATR): 3420, 3296, 3189, 3063, 2960,
1633, 1617, 1532, 1309, 1258, 1152 cm−1. 1H-NMR (CDCl3,
200 MHz): δ 7.30 (dd, J = 7.7, 1.5 Hz, 1H), 7.20 (ddd, J = 8.2,
7.2, 1.5 Hz, 1H), 6.67 (d, J = 8.2 Hz, 1H), 6.64 (ddd, J = 7.9,
7.2, 1.2 Hz, 1H), 6.11 (s, 1H), 5.21 (br, 2H), 3.37 (dt, J = 7.2,
5.8 Hz, 2H), 1.62 (sext, J = 7.2 Hz, 2H), 0.98 (t, J = 7.2 Hz, 3H).
13C-NMR (DMSO-d6, 50 MHz) δ: 169.4, 148.5, 132.1, 127.0,
117.2, 116.6, 41.4, 22.9, 11.5. MS(EI) m/z (rel. int.): 178 (50)
Fluorescence quantum yields was measured using
anthracene in toluene as standard with a known ϕF of
0.30. Solutions of dyads 3(a-e), 8 and 9 were prepared at
1 × 10−6 M in spectroscopic grade acetonitrile. Absorbance
and fluorescence spectra were measured, and the data
required for Equation (1) were obtained from these spectra.
Procedure for spectroscopic titrations
The effect of metal cations upon the absorbance and flu-
orescence intensities was examined by adding 10 μL of a
1 × 10−3 M metal ion stock solution to a known volume
(3 mL) of 1 × 10−5 M ligand solution. The addition was lim-
ited to 0.09 mL, so that dilution remained insignificant.

SUPRAMOLECULAR CHEMISTRy
9
Scheme 1. Synthesis of dyads 3(a-e).
for amide groups. The carbonyl vibrations in NAPIM moiety
were at 1693 and 1653 cm−1 for symmetric and asymmetric
stretching, and at 1638 cm−1 was identified as the stretch-
ing vibration for amide carbonyl (Figure S1). The rest of
dyads presented the same vibration pattern.
Reversibility analysis
The reversibility analysis was examined by adding 6 μL of
1 × 10−3 M EDTA stock solution to a known volume (3 mL)
of 1 × 10−5 M ligand and 1.5 × 10−5 M Hg(ClO4)2 solutions.
The dilution remained insignificant, as the addition was
limited to 0.06 mL.
1
In H-NMR spectra obtained in CDCl3, the typical pat-
terns of signal for NIPAM and 2ABZ moieties were found
(Table S1). It is noteworthy that there are significant dif-
ferences in chemical shift for amide hydrogens Hf, and
the signals appear at 6.93, 7.28, 6.45, 6.29 and 6.15 ppm,
respectively. In dyads with shorter alkyl chains, 3a and 3b,
the amide hydrogens are unprotected, and as the polyme-
thylene chain becomes longer, the signal shifts to up-field.
In fact, in dyad 3e, the signal almost has the same chem-
ical shift than in compound 8. In accordance with these
results is convincing that the presence and proximity of
NAPIM moiety affect the chemical environment of the
amide hydrogens. Also, an interesting solvent influence
over the chemical shift of 3a signals was found when it was
analysed in CD3CN and DMSO-d6. The signal for Hf shifted
to 7.05 ppm in CD3CN and 8.27 ppm in DMSO-d6. Another
significant change as function of solvent was the chemical
shift of hydrogens Hg, Hh and Hi. These hydrogen signals
are in 8.59, 7.72 and 8.18 ppm in CDCl3, but in DMSO-d6, Hg
shifted to up-field (8.48 ppm) and Hi and Hh shifted down-
field (8.45 and 7.86 ppm, respectively). Additionally, all the
aromatic hydrogens of 2ABZ moiety appear at slightly high
field compared with the same signals in CDCl3. These dif-
ferences may be attributed to an interaction with the sol-
vent, which increases with the polarity and viscosity.
Dyads 3(a-e) were analysed by MS(EI), and the
molecular ions M+ at 359, 373, 387, 415 and 443 amu
were, respectively, detected. MS(CI+) analysis pro-
vided the corresponding [M + H]+ ions at 360, 374,
388, 416 and 444 amu, respectively; and HRMS con-
firmed the chemical composition for all compounds.
Voltamperometric analysis
Voltamograms were obtained in potentiostat–galvanostat
station using Ag/AgCl as reference electrode, Pt as counter
electrode and Pt as working electrode. The solutions of 8
(3.4 × 10−3 M), 9 (6.4 × 10−5 M) and 3b were prepared in an
electrolytic solution of KBF4 (0.07 M).
Results and discussion
Synthesis and characterisation
The synthesis of dyads 3(a-e) started with the reaction of
1,8-naphthalenetetracarboxylic acid anhydride (4) with a
series of dialkylamines (with n = 0, 1, 2, 4 and 6) at 80 °C
in aqueous media. 1,8-naphthalimide alkylamines 6(a-
e) were obtained in good yields and purity; these prod-
ucts reacted with isatoic anhydride (7) in THF at reflux
providing the dyads 3 in moderate yields (Scheme 1)
(27). In addition, N-propyl-2-aminobenzamide (8) and
N-propylnaphthalimide (9) were synthesised under the
same conditions, in order to compare the spectroscopic
and photophysical properties of the individual chromo-
phores with those for dyads 3(a-e).
Dyads 3(a-e) were characterised by infrared spectros-
copy (IR), NMR and electronic impact mass spectrome-
try MS(EI), and their chemical composition was verified
by high-resolution mass spectrometry (HRMS). Dyad 3b
IR spectra showed the vibrations corresponding to N-H
stretching at 3460 and 3400 cm−1 for amine and 3345 cm−1

10
M. A. LANDEy-ÁLVAREZ ET AL.
Table 1. Fluorescence quantum yields (ϕF) of 8, 9 and dyads 3(a-e) in mecN.
Compound
MeCN
λA/nm
λF/nm
λA−λF/nm
ϕF
8
330
343
350
339
340
336
331
390
376
432
397
398
390
388
60
33
82
58
58
54
57
0.189
0.097
0.030
0.090
0.100
0.126
0.123
9
3a
3b
3c
3d
3e
As was expected, compound 8 has higher quantum
Photophysical properties of NAPIM-2ABZ dyads
yield than 9, which is in accordance with the fluorescent
intensity in Figure 3(a). In dyads 3(b-e), quantum yields
are lower than 8 and comparable with 9, although the
quantum yield dyad 3a is even lower. These results indi-
cate that a fluorescence quenching of NAPIM and 2ABZ
occurs by a PET process as in NAPIM-DANS dyads (15,16).
According to these quenching mechanisms, irradiating
at 328 nm, both fluorophores may be excited to form
1(NAPIM)*-2ABZ and NAPIM-1(2ABZ)*; if PET mechanism
occurs from 2ABZ to NAPIM forms NAPIM⊝-2ABZ⊕, but
if it occurs from NAPIM to 2ABZ forms NAPIM⊕−2ABZ⊝;
in either case, the energy emission is inactivated and
the quantum yields are lower. Voltamperometric anal-
ysis of 8, 9 and 3b was performed in order to establish
the direction of the electronic transfer. Compound 8
showed a reduction peak at −0.713 V and a quasi-re-
versible oxidation peak at −0.569 V, and 9 presented
reduction and oxidation peaks at −1.250 V and −1.200 V,
respectively. The dyad 3b shows one reduction and oxi-
dation peak at −1.230 and −1.180 V associated with the
NAPIM moiety, and a quasi-reversible oxidation peak
at −0.690 V corresponding to the 2ABZ (see Figure
S2). These results indicate that 2ABZ moiety is easier
to reduce than NAPIM when they are separated, but
if they are linked 2ABZ, only oxidizes while the NAPIM
behave a redox process. This is a clear evidence that the
electronic transfer from 2ABZ to NAPIM is possible. The
quenching of fluorescence by PET is more effective in
dyads with shorter spacer as 3a, but with the longest
polymethylene chain the effect of PET is not so strong.
In addition, the red shift (40 nm) and broadening emis-
sion of 3a may suggest an intermolecular interaction
between both fluorophores in the excited state.
In order to determine whether there is an interaction
between the two chromophores in the ground state, the
absorption spectra of 8, 9 and 3b were compared. The
Figure 2(a) shows that the spectrum of dyad 3b corre-
sponds to the addition spectra of 8 and 9. It has the absorp-
tion band at 230 nm and the structured band at 332 nm
belonging to NAPIM chromophore and the absorption
bands at 214 (π–π*), 255 (n–π*) and 326 nm (auxocrome
n–π*) belonging to aminobenzamide 8. The same pattern
in the rest of dyads was observed (Figure 2(b)). Based on
these results, no ground state interaction between the two
chromophores in dyads 3(a-e) was observed.
As well as the absorbance, the fluorescence spectra
of 8, 9 and 3b were obtained and are compared in Figure
3(a). Compound 8 exhibits a high-intensity broad emis-
sion band with a maximum peak at 394 nm, whereas 9
presents a less intense typical structured emission band
with a maximum peak at 378 nm. Dyad 3b has a broad
emission band with a maximum peak at 398 nm, but
it is twenty times less intensive than 8. Dyads 3(c-e)
have the same shape emission band, and the quenching
of fluorescence intensity for all of them was observed.
Although it is interesting that the fluorescence intensity
increases as the polymethylene chain becomes greater.
Again, dyad 3a presents singular fluorescent properties,
and a low-intensity broad emission band with a maxi-
mum peak at 430 nm was detected.
The fluorescence efficiency of dyads 3(a-e) was esti-
mated by measuring the fluorescent quantum yield ϕF
using Equation (1).
ꢀ = ꢀ × IntARn2∕IntRA nR2
(1)
F
R
where ϕF is the sample quantum yield, Int is the area under
the emission peak (at a given wavelength scale), A is the
absorbance at the excitation wavelength and n is the
refractive index of the sample. The subscript R denotes the
respective values of the reference substance. The quantum
yields for 8, 9 and dyads 3(a-e) measured in acetonitrile
at 1 × 10−6 using anthracene as reference substance are
presented in Table 1.
Metal ion binding properties
Evaluation of binding properties, coordination of com-
pound 8 with a different alkaline, alkaline earth and tran-
sition metallic ions was studied by electronic absorption
(UV-vis) and fluorescence in acetonitrile. Nevertheless,

SUPRAMOLECULAR CHEMISTRy
11
Table 2. Binding constants (log Kf) for some complexes in mecN.
Dyad
Metal ion
Log Kf
ΜL2
Μ3L2
3a
hg(ii)
cu(ii)
Zn(ii)
Ni(ii)
hg(ii)
cu(ii)
Zn(ii)
Ni(ii)
hg(ii)
cu(ii)
Zn(ii)
Ni(ii)
hg(ii)
cu(ii)
Zn(ii)
Ni(ii)
hg(ii)
cu(ii)
Zn(ii)
Ni(ii)
5.950 0.240
8.381 0.044
8.446 0.029
7.625 0.132
10.048 1.660
3b
3c
3d
3e
9.378 1.520
10.689 0.050
9.428 0.026
7.748 0.132
9.003 0.043
9.188 0.029
9.427 0.026
7.748 0.132
9.004 0.042
9.188 0.029
8.997 0.049
8.229 0.235
7.974 2.828
6.357 0.088
3.282 0.174
9.188 0.028
9.428 0.025
8.230 0.026
12.184 1.848
transition metal ions such as Cu(II), Hg(II) and Zn(II), as
perchlorate salts, gave important spectroscopic changes.
The absorption bands were most affected with Cu(II) and
Hg(II). Several isosbestic points indicating the interaction
of the ligand with the metal ions were observed. It is note-
worthy that the corresponding n–π* transition absorption
band at 326 nm due to the electron delocalisation from the
amino group to the benzamide and other transitions in the
carbonyl group at 255 (n–π*) and 214 (π–π*) nm were con-
siderably diminished (Figure 4(a)). This behaviour indicates
coordination of the metal ions with amino and carbonyl
groups. The absorbance profile at 326 nm showed at least
two different complexes, one with a 1:2 and other with a
3:2 metal–ligand ratio (Figure 4(b)).
The fluorescence of 8 was completely quenched by
Cu(II) and Hg(II) in acetonitrile. The FI/FI0 profile at 394 nm
confirmed the formation of two complexes with a 1:2 and
3:2 metal–ligand ratio (Figure 5). The fluorescence of 8 is
quenched in the complex due to the suppression of the ICT
process of the 2ABZ. In other words, the excitation band
at 326 nm (So → S1) in the fluorescence spectra of 8 corre-
sponds to the auxocrome n–π* absorption band in UV-vis.
This transition disappears when the metal ion coordinates
with the ligand; there is not excitation in the complex at
important for interpreting the results obtained with
dyads 3(a-e).
The binding of dyads 3(a-e) with different alkaline,
alkaline earth and transition metallic ions was studied by
UV-vis and fluorescence in acetonitrile. Again, only tran-
sition metal ions such as Cu(II), Hg(II), Zn(II) and Ni(II), as
perchlorate salts, gave important spectroscopic changes.
Interestingly in the titration of 3b with Hg(II) in acetoni-
trile, the absorbance at 214, 253 and 334 nm decreases
(Figure 6). These bands, belonging to the 2ABZ moiety,
disappear during the titration. The final spectrum becomes
equal to the spectrum of naphthalimide 9. This result indi-
cates that the binding site is the 2ABZ and that the NAPIM
moiety does not participate in the complexation in the
ground state. The absorbance profile showed two succes-
sive complex formations with 1:2 and 2:3 metal–ligand
stoichiometric ratio, as observed for compound 8. Similar
results with the rest of dyad were observed.
The dyads with shorter oligomethylene chain 3a, 3b
and 3c presented a strong inhibition of PET process by
the addition of metallic ions in the order Hg(II) >> Cu(II) >
Zn(II) >> Ni(II). A semi-structured emission band at 388 nm
increases in dyad 3a as the amount of Hg(II) increases
beyond 0.5 equivalents (Figure S4), and the emission
turns from yellow to blue color. The fluorescence profiles
showed higher sensibility for Hg(II) (FI/FI0 = 13.5), and is
evident the formation of two different complexes with 1:2
and 3:2 metal–ligand stoichiometric ratio, respectively.
In dyad 3b with Hg(II) and Cu(II) increases, the flores-
cence intensity and a band shift from 398 nm to 408 nm
were observed upon the addition of 0.5 equivalents,
evidencing the formation of a 1:2 metal:ligand complex.
Continuing with the addition of metallic ion increases
the intensity of a structured band at 380 nm (Figure 7
this wavelength, and therefore, there is no emission of flu
-
orescence (Figure S3).
The study of binding properties of 8 gives important
information regarding this type of ligands: (a) the com-
plexation with metal ions occurs in the ground state,
(b) amino and carbonyl groups participate as coordina-
tion sites, (c) coordination with metal ion decreases the
absorbance and quenches the fluorescence of 2ABZ and
(d) there is selectivity towards Cu(II) and Hg(II) ions in a
well-defined metal–ligand ratio. This information was

12
M. A. LANDEy-ÁLVAREZ ET AL.
and S5) characteristic of NAPIM fluorophore. Dyads 3b
and 3c were more sensitive towards Hg(II) (FI/FI0 = 10 and
4.6, respectively), followed by Cu(II) (FI/FI0 = 6.05 and 2.6,
respectively), and the stoichiometric ratio of these ligands
is the same that of dyad 3a. However, in dyads 3a, 3b and
3c, the fluorescence increases to a maximum value upon
the addition of 1.5 equivalents of Cu(II), and beyond this
point the fluorescence decreases again. It is believed that
Cu(II) quenches fluorescence by collisions with NAPIM
fluorophore, and the paramagnetic nature of this ion may
promote charge transfer from the ligand to metal centre
or another energy deactivating mechanism. Additionally,
in dyad 3b is interesting the response profile with Zn(II),
fluorescence increases two times when 0.5 equivalents
of Zn(II) were added, and it remains constant until three
equivalents. The Job’s plot indicates a 1:2 metal–ligand
ratio in the complex 3b-Zn(II), and 1:2 and 3:2 in 3b-Hg(II)
(Figure S6).
Dyads 3d and 3e present an opposite fluorescent
response with the addition of metallic ions. Interestingly,
the intensity of the broad emission band at 395 nm
decrease and a structured band of NAPIM appears at
380 nm. In the titration of 3d with Hg(II), a minor fluo-
rescence quenching occurs until the NAPIM structured
emission band appears, and its intensity increases slightly
upon the addition of more equivalents of Hg(II) (Figure
S7). However, in the titration with Cu(II), the quenching
of fluorescence is predominant due to the quenching of
Cu(II) to the NAPIM fluorescence, as occurs in the other
dyads. In dyad 3e occurs a fluorescence quenching with
both cations, but Cu(II) induces a strongest effect. Once the
NAPIM emission band appears in the titration with Hg(II), it
remains almost constant upon the addition of more Hg(II),
while Cu(II) quenches the NAPIM fluorescence (Figure S8).
This peculiar ON–OFF fluorescence response indicates that
the distance of six and eight methylene groups between
NAPIM and 2ABZ in 3d and 3e does not favour PET pro-
cess (Figure S9). The fluorescence of 2ABZ is quenched by
suppression of the ICT process in coordination with the
metallic ion as occurs in the ligand 8, and there is no flu-
orescence enhancement of NAPIM.
combining dyad 3b with 1.5 M equivalents of each cation
and with both Cu(II) and Hg(II) was done. Fluorescence of
free ligand and complexes were measured, and the relative
intensities with respect to the free ligand are presented
in Figure 8. The relative fluorescence in the mixture with
both cations is more comparable to the observed for the
complex with Cu(II). In a second experiment, a solution
of complex 3b-Hg(II) was titrated with Cu(II) from 0.0 to
3.0 M equivalents (Figure 8(b)). The quenching of the fluo
-
rescence was found as result from a FI/FI0 = 9.5 to 3.8 indi-
cating the displacement of Hg(II) by Cu(II). Interestingly,
the emission band in the final addition of the titration is
exactly the same as observed for the 1:2 metal–ligand
complex obtained in the direct titration of 3b with Cu(II).
This demonstrates the complex 1:2 is more stable than 3:2.
The results show that 3b has binding preferences towards
Cu(II) over Hg(II) ion. Competitive assays for the rest of
dyads showed no selective response to any of these two
cations (Figures S11 to S14). Therefore, selectivity of 3b
towards Cu(II) ions can be explained based on the hard–
soft acid base theory (28). Considering that Cu(II) ion and
the coordination binding site of 3b have been classified
as borderline species (28–30), the formation of the adduct
3b-Cu(II) will be favoured rather than the adduct 3b-Hg(II),
which can be described as a borderline–soft interaction.
In addition, the reversibility of the ion recognition using
EDTA as competitive ligand was studied. In Figure 9, the
emission spectra of 3b (λem = 398 nm, full line) and the
spectra obtained in the titration of complex 3b-Hg(II) with
0.0 eq (dashed line) to 2.0 eq (dotted lines) of EDTA in ace-
tonitrile are compared. The structured fluorescence emis-
sion band at λem = 386 nm decreased as the EDTA solution
was gradually added, but it remained constant from 1.0
to 2.0 equivalents. Nevertheless, the free ligand emission
band was not recovered, and the shape and position of
the emission corresponded to the NAPIM fluorophore.
These results mean that EDTA competes by the Hg(II) in the
3:2 metal–ligand complex, but the complex 1:2 remains
even in the presence of an excess of EDTA. In other words,
1.0 eq. of Hg(II) was combined with EDTA and the other
0.5 eq. with 3b. The same experiment with 3b-Cu(II) was
performed, and in this case the emission band of 3b was
recovered, and with the excess of EDTA the fluorescence
was quenched (see Figure S15).
Comparing the response profile with Hg(II) and Cu(II),
dyads 3a-3c exhibit an OFF–ON fluorescence behaviour
due to the suppression of PET when the metallic ion coor-
dinates to 2ABZ moiety (see Figure S10).It is noteworthy
that dyad 3a presents the highest enhancement of flu-
orescence for Hg(II) and 3b for Cu(II) indicating that an
alkyl spacer with two and three methylene groups give the
optimal distance between NAPIM and 2ABZ fluorophores
to inhibit the PET process upon coordination.
The formation of complex 3b-Zn(II) was analysed by an
NMR titration of a 3b solution in CD3CN with Zn(ClO4)2. A
stacked 1H NMR spectra is shown in Figure 10, which allows
to compare how the signals of 3b behave in the presence
of 0.0, 0.2, 0.4, 0.6 and 1.0 M equivalents of Zn(II). The sig-
nals g, h and i correspond to the NAPIM hydrogens and
after the addition of Zn(II) shift to up-field (0.11, 0.10 and
0.16 ppm, respectively, at 0.6 eq), probably due to a pro-
tecting effect over the NAPIM in the complex. The signals
Based on the previous results, competitive assays
were performed in order to establish the selectivity of
dyad 3b towards Cu(II) or Hg(II). First, a batch experiment

SUPRAMOLECULAR CHEMISTRy
13
Table 3. energy data of mos and distance between fluorophores in dyads 3(a-e).
Dyad
ΔE[(HOMO-n)-HOMO] (eV)
ΔE(HOMO-LUMO) (eV)
ΔE[(HOMO-n)-LUMO)] (eV)
Distance (Å)
3a
3b
3c
3d
3e
1.52
1.20
1.19
1.12
1.10
2.44
2.79
2.80
2.88
2.89
3.96
3.99
3.99
4.00
4.00
7.72
8.96
10.80
14.94
17.42
a, b, c, d, e and f correspond to the 2ABZ hydrogens and to
all those shifted to downfield except signal e, which shifts
to up-field. The most affected signals in the complex are
the hydrogens e (0.51 ppm) and f (−0.84 ppm), which are
located in the binding site with the metallic ion. The first
one shifts to up-field probably because of a retro donating
effect of the metallic ion in the complex. The second one
shifts to downfield due to an increase in its acidity when
carbonyl coordinates with metallic ion. The hydrogens
located in orto (d) and para positions (b) also were signif-
icantly affected by the coordination of the amine group
with Zn(II) because of the absence of electronic density in
this positions, and the chemical shifts were −0.5 ppm and
−0.66 ppm, respectively. In the graphs of chemical shift
versus molar equivalents of Zn(II), there is an inflexion at
0.5 equivalents, corresponding to a 1:2 metal–ligand stoi-
chiometry, which is in accordance with the data obtained
by spectroscopic techniques (Figure S16).
3b-Hg(II) were found, indicating the coordination of per-
chlorate with the metallic ion in a monodentate fash-
ion (Figures S19 and S20) (31). These results indicate a
different coordination number of Zn(II) with respect to
Cu(II) and Hg(II) in the complexes; Zn(II) may be forming
a tetrahedral complex with no vacancy for more ligands,
whereas Cu(II) and Hg(II) may be octahedral including
perchlorate ligands.
The binding constants Kf of the complexes were deter-
mined on the basis of fluorescence responses using the
Hyperquad program considering the formation of 1:2 (ML2)
and 3:2 (M3L2) complexes (32,33). In Table 2 are reported
the Kf values for several complexes. In general, the values
are in agreement with the analytical responses, and the
values of log Kf vary between 8 and 10 because the exper-
iments were performed using acetonitrile as a non-com-
petitive solvent.
The formation of complex with Hg(ClO4)2 was also ana-
lysed by 1H-NMR, and similar changes were observed upon
the addition of the metallic ion. However, the chemical
shifts of the signals were higher with Hg(II) compared with
Zn(II). Besides, the signal for amine hydrogens becomes
broad since the first addition of the metal solution (Figure
S17). Interestingly, in the graphs of chemical shifts versus
molar equivalents, there is an inflexion at 0.5 equivalents
indicating a metal–ligand ratio of 1:2 (Figure S18).
In Figure 11, the infrared spectra of 3b and 3b-Zn(II)
complex obtained by ATR are compared. There are sig-
nificant changes in the vibrations corresponding to
the amino N-H (3461 and 3401 cm−1) and amide C=O
(1638 cm−1) groups, the N-H stretching vibrations
for amino group shifted lower frequencies 3326 and
3260 cm−1, indicating coordination of this group with the
metal ion. The amide N-H vibration at 3345 cm−1 was not
significantly affected, as well as the carbonyls of NAPIM,
indicating these groups do not coordinate with metal-
lic ion. The amide carbonyl shifted from 1638 cm−1 to
1619 cm−1 (~19 cm−1). This result is in accordance with
the data reported in the literature (11–13). The band at
1515 cm−1 related with N–H bending vibration shifted to
1544 cm−1. A strong broad vibration at 1059 cm−1 corre-
sponds to the perchlorate acting as counter ion in the
complex. Interestingly, two well-defined bands at 1082
and 1043 cm−1 in 3b-Cu(II) and 1067 and 1034 cm−1 in
Theoretical analysis
The geometries of dyads 3(a-e) were optimised with the
PM6 semiempirical method and then by DFT using a non
local correlation B3LyP and a 6–31G+(d,p) basis set in
the gas phase with Gaussian 09 computational package
(34). First, the structure of dyads 3 were optimised at
semiempirical level, and then from these geometries, a
scan calculation was performed by rotation of a carbon–
carbon bond in the oligomethylene chain. The relative
minimum energy geometries found for each dyad were
fully optimised using DFT and after their frequencies
were calculated. Figure 12 shows the minimum energy
geometries for dyads 3a and 3b. Interestingly, an intra-
molecular hydrogen bond between the amide N-H and
a carbonyl group of NAPIM is present in both structures.
The distance between the hydrogen and oxygen atoms
is 2.154 and 2.140 Å, respectively. The hydrogen bond
maintains closer the two fluorophores in the geometry
of 3a (7.72 Å centre to centre) in almost perpendicu-
lar position. In the 3b optimised geometry, the cen-
tre-to-centre distance of both fluorophores is 8.96 Å,
but they are almost in the same plane. For dyads 3c-e,
any hydrogen bond is present in their minimal energy
geometries, and the fluorophores should be as far apart
as possible in order to minimise the repulsive interac-
tions (Figure S21).

14
M. A. LANDEy-ÁLVAREZ ET AL.
These theoretical results explain the unexpected chem-
Conclusions
ical shifts in dyads 3a and 3b for amide hydrogens in 1H-
NMR; the presence of an intramolecular hydrogen bond
shifts the signals and as shorter is the distance more the
signal shifts to downfield. Furthermore, the proximity and
position of both fluorophores in dyad 3a favors an interac-
tion between both fluorophores in the excited state. The
latter may explain the unique broad emission band shifted
to a higher wavelength in this dyad.
In this work, the binding ability of dyads 3 towards metal-
lic ions, of clinical and environmental importance, such as
Hg(II), Cu(II) and Zn(II) was demonstrated. Moreover, the
ligand design with NAPIM and 2ABZ fluorophores sepa-
rated by different length polymethylene chains induced
versatility in the analytical response. The inhibition of PET in
dyads with shorter spacing chain gave an OFF/ON response
when 2ABZ moiety coordinates the metallic ion. Analytic
studies by UV-vis, IR and 1H-NMR showed that NAPIM does
not participate in the complex. On the contrary, in dyads
with longer spacing chains there is ON/OFF fluorescence
response due to the absence of PET and the quenching of
2ABZ fluorescence. In addition, the energy of MOs calcu-
lated theoretically confirms the existence of PET as well as
the optimisation of geometries, and the suitable distance
between both fluorophores that favours this process.
Moreover, important information comparing the molec-
ular orbitals (MOs) in these geometries was found (Figure
13). The highest occupied molecular orbital (HOMO) in
the dyad 3a is mainly located in 2ABZ fluorophore and
the lowest unoccupied molecular orbital (LUMO) is in the
NAPIM fluorophore. Comparing the energies of the MOs
were observed that the HOMO is located between the
HOMO-3 and the LUMO, and these MOs are involved in
the excitation and emission of fluorescence in NAPIM. This
electronic condition is determinant in the PET process as
well as in the distance between the donor and the accep-
tor. Additionally, the HOMO-3 is located in both moieties
and may be an evidence of the interaction of both fluoro-
phores due to their proximity promoted by the intramo-
lecular hydrogen bond. These characteristics are useful to
explain the unique photophysical properties of dyad 3a.
InTable3arelistedtheΔE[(HOMO-n)-LUMO], ΔE[(HOMO-
n)-HOMO] and ΔE(HOMO-LUMO) energies and centre–cen-
tre distance between the two fluorophores obtained in the
optimisation of these molecules under the same calcula-
tion procedures and theory level. The HOMO is located
between the [(HOMO-n)-LUMO)], and technically PET pro-
cess would be allowed in all dyads, but also depends on the
distance between the donor and the acceptor. For these
dyads, the maximum calculated distance in which the PET
process is effective was around 10.8 Å.
Supplemental material
Supplemental data for this article can be accessed online here:
http://dx.doi.org/10.1080/10610278.2016.1149180.
Acknowledgements
Authors thank to Tecnológico Nacional de México (TecNM) for
their financial support [grant number 5151.13-P]. Marco A. Land-
ey-Álvarez thanks to Consejo Nacional de Ciencia y Tecnología
(CONACyT) for the scholarship received for postgraduate studies.
Disclosure statement
No potential conflict of interest was reported by the authors.
ORCID
Marco A. Landey-Álvarez
http://orcid.org/0000-0002-9737-
Considering all the spectroscopic data of the complexes
formed with dyads 3 and metallic ions, the geometries of
complexes 3a-Hg(II), 3a-Zn(II), 3b-Hg(II) and 3b-Zn(II) were
optimised with the PM7 semiempirical method (Figure 14
and S22). Figure 14a shows the plausible structure of com-
plex 3b-Hg(II) where two Hg(II) ions are coordinated with
two ligands through the amino and carbonyl groups of
2ABZ, and another Hg(II) ion coordinates with a carbonyl
group of NAPIM moiety. An octahedral configuration for
Hg(II) and the six perchlorate units which are coordinated
in a monodentade fashion were considered in the opti-
misation, and this represents a 3:2 metal–ligand ratio. In
the structure of complex 3b-Zn(II) (Figure 14(b)), one tet-
rahedral Zn(II) ion coordinates with two ligands through
the amine and the carbonyl groups, the hydrogen bond
between the amide N–H and a NAPIM carbonyl remains
in the complex, and the coordination of perchlorate units
to the Zn(II) was not considered.
7781
Adrián Ochoa-Terán
Georgina Pina-Luis
José-Zeferino Ramírez
Victoria Labastida-Galván
9462
http://orcid.org/0000-0002-3746-3960
http://orcid.org/0000-0001-6823-0943
http://orcid.org/0000-0002-3616-9137
http://orcid.org/0000-0003-0676-
Mario Ordoñez
http://orcid.org/0000-0001-9395-7079
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