F
K. G. Leslie et al.
R
O
R
O
1
MeCN, 85°C, 24 h
O
Cl–
+
N
H2N
O
H2N
O
2: R = CH3
3: R = CF3
NCR1: R = CH3
NCR2: R = CF3
Scheme 3 Synthesis of nicotinamide–coumarins NCR1 and NCR2.
128.7, 128.4, 126.8, 126.4, 125.4, 123.0, 30.0, 20.3, 14.2. m/z
(ESIMS) [M]þ 374; (HRMS þESI) 374.1498; calc. for
C22H20N3O3þ 374.1499 [M]þ.
1
O
N
O
O
N
O
MeCN, 85°C, 48 h
Cl–
NNpR2 (Scheme 5): orange solid (68 %). dH (500 MHz, [D6]
DMSO) 9.92 (s, 1H), 9.67 (d, J 6.0, 1H), 9.54 (s, 1H), 9.15 (d, J
8.4, 1H), 8.94–8.89 (m, 2H), 8.50–8.46 (dd, J 7.8, 6.5, 1H), 8.40
(d, J 8.6, 1H), 8.30–8.26 (m, 2H), 6.94 (d, J 8.65, 1H), 4.06 (t, J
7.6, 2H), 3.47–3.40 (m, 2H), 1.77–1.69 (m, 2H), 1.66–1.58 (m,
2H), 1.49–1.41 (m, 2H), 1.40–1.30 (m, 2H), 0.98–0.90 (m, 6H).
dC (125 MHz, [D6]DMSO) 163.3, 163.1, 163.0, 152.0, 147.4,
145.6, 145.1, 139.0, 136.7, 134.4, 130.4, 128.6, 126.8, 126.3,
124.0, 120.7, 107.6, 105.7, 43.2, 30.4, 30.2, 20.3, 20.2, 14.2. m/z
(ESIMS) [M]þ 445; (HRMS þESI) 445.2234; calc. for
C26H29N4O3þ 445.2234 [M]þ.
NH2
N+
NNpR1
4
NH2
O
Scheme 4. Synthesis of nicotinamide–naphthalimide NNpR1.
General Procedure for Nicotinamide–Coumarin
Synthesis (NCR1–2, Scheme 3)
Fluorescence Spectroscopy
A solution containing the corresponding coumarin (2 or 3,
All fluorescence spectra were recorded on a Varian Cary Eclipse
fluorometer in 1 cm pathlength quartz cuvettes. The emission
spectra of 10 mM solutions in 20: 80 MeCN/HEPES
(HEPES¼ 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid)
buffer (5mM) were recorded with 10 mL aliquots of freshly
prepared 1 M sodium dithionite in phosphate-buffered saline
(PBS) buffer until no further change in fluorescence was
observed.
1 equiv.) and 1 (1 equiv.) was heated under reflux conditions in
acetonitrile over 24 h and then left to cool. The resulting
precipitate was filtered and washed with cold acetonitrile, and
recrystallised from methanol to give the product as described
below.
NCR1: beige solid (69 %). dH (500 MHz, D2O) 9.63 (m, 1H),
9.40 (dt, J 6.2, 1.2, 1H), 9.17 (dt, J 8.2, 1.4, 1H), 9.45 (m, 1H),
8.19 (d, J 8.6, 1H), 7.9 (d, J 2.3, 1H), 7.85 (dd, J 8.6, 2.3, 1H),
6.62 (d, J 1.2, 1H), 2.62 (d, J 2.6, 3H). dC (125 MHz, D2O) 154.7,
153.1, 146.6, 145.6, 144.5, 143.9, 134.1, 128.6, 127.9, 122.7,
120.4, 116.0, 113.3, 18.0. m/z (high-resolution mass spectrome-
try (HRMS) positive electrospray ionisation (þESI)) 281.0920;
calc. for C16H13N2O3þ 281.0921 [M]þ.
NCR2: beige solid (55 %). dH (500 MHz, D2O) 9.71 (m, 1H),
9.42 (dt, J 6.2, 1.3, 1H), 9.19 (dt, J 8.2, 1.4, 1H), 8.47 (m, 1H),
8.25 (dd, J 8.8, 1.5, 1H), 8.06 (d, J 2.3, 1H), 7.92 (dd, J 8.7, 2.4,
1H), 7.25 (s, 1H). dC (125 MHz, D2O) 165.5, 160.8, 154.3,
146.8, 146.1, 144.7, 140.2 (q, JC–F 33.5), 134.3, 128.8, 128.1,
122.4, 121.1, 120.2, 119.0, 116.6, 114.2. m/z (HRMS þESI)
335.0637; calc. for C16H10F3N2O3þ 335.0638 [M]þ.
Cyclic Voltammetry
Electrochemical measurements were performed using a BAS
100B/W electrochemical analyser. A single-compartment cell
was used, consisting of a glassy carbon working electrode, a
platinum wire auxiliary electrode, and an electrolysed Ag/AgCl
wire reference electrode. Cyclic voltammograms (CVs) were
collected using a 1 mM solution of the analyte in MeCN, with
0.1 M tetrabutylammonium hexafluorophosphate as a support-
ing electrolyte. Prior to each experiment, the solution was
purged with Ar. Uncompensated resistance between the work-
ing and the reference electrodes was corrected by using iR
compensation. Measurements were converted to a standard
hydrogen electrode reference (versus SHE) for comparison with
the literature.
General Procedure for Nicotinamide–Naphthalimide
Synthesis (NNpR1–2)
A solution containing the corresponding naphthalimide (4 or
5;1.1 equiv.) and 1 (1 equiv.) was heated under reflux conditions
in acetonitrile over 48 h and then left to cool. The resulting
precipitate was filtered and washed with cold acetonitrile to give
the product as described below.
NNpR1 (Scheme 4): grey solid (75 %). dH (400 MHz, [D6]
DMSO) 9.92 (s, 1H), 9.55 (d, J 6.1, 1H), 9.37 (d, J 8.0, 1H), 8.92
(S, 1H), 8.76 (d, J 7.6, 1H), 8.67 (d, J 6.9, 1H), 8.59–8.53 (m,
1H), 8.40 (d, J 8.0, 1H), 8.25 (s, 1H), 8.06–7.97 (m, 2H), 4.10
(t, J 7.4, 2H), 1.71–1.62 (m, 2H), 1.43–1.32 (m, 2H), 0.98–0.92
(t, J 7.5, 3H). dC (125 MHz, [D6]DMSO) 163.5, 162.9, 162.8,
148.4, 146.8, 146.7, 143.1, 134.7, 132.4, 130.8, 130.1, 128.9,
Spectroelectrochemistry
The electrochemical characterisation of the molecules was
carried out in acetonitrile with 0.2 M tetrabutylammonium
hexafluorophosphate (TBAPF6). Oxygen was removed by
purging the MeCN solution with high-purity argon. A typical
three-electrode cell was employed, which was composed of a
glassy carbon (GC) working electrode (3-mm diameter, CH
Instruments, Austin, TX, USA), a platinum wire as counter, and
a silver wire as quasi-reference (QRE) electrode. A CHI620
electrochemical workstation (CH Instruments) was employed to
record the CVs. The potential of the reference electrode was