Modulating the ground- and excited-state oxidation potentials of diaminonaphthalene by sequential N-methylation

Article abstract of DOI:10.1002/cphc.200900969

A series of 1,5-diaminonaphthalene derivatives were synthesized, and characterized to provide ground- and excited-state electron donors of similar structure but varying potential. Electrochemical and spectroscopic properties of the series are reported and together illustrate two opposing consequences of alkyl substitution on the aryl amines. Inductive effects of methylation are evident from the decrease in ground-state oxidation potential for derivatives containing monomethylamino substituents. In contrast, steric effects seem to dominate the increase in the ground-state oxidation potential of derivatives containing dimethylamino substituents since the conformational constraints created by dimethylation suppress delocalization of the nonbonding electrons. Absorption and emission properties also respond to increasing levels of N-methylation, and the excited-state oxidation potentials of the parent 1,5-diaminonaphthalene and its monomethylamine derivatives (ca.-3.2 V) are approximately 200 mV lower than the corresponding dimethylamino derivatives (-3.0 V).

Full text of DOI:10.1002/cphc.200900969

DOI: 10.1002/cphc.200900969
Modulating the Ground- and Excited-State Oxidation
Potentials of Diaminonaphthalene by Sequential
N-Methylation
Neil P. Campbell,[a] Amethist S. Finch,[b] and Steven E. Rokita*[a]
A series of 1,5-diaminonaphthalene derivatives were synthe-
sized and characterized to provide ground- and excited-state
electron donors of similar structure but varying potential. Elec-
trochemical and spectroscopic properties of the series are re-
ported and together illustrate two opposing consequences of
alkyl substitution on the aryl amines. Inductive effects of meth-
ylation are evident from the decrease in ground-state oxida-
tion potential for derivatives containing monomethylamino
substituents. In contrast, steric effects seem to dominate the
increase in the ground-state oxidation potential of derivatives
containing dimethylamino substituents since the conforma-
tional constraints created by dimethylation suppress delocali-
zation of the nonbonding electrons. Absorption and emission
properties also respond to increasing levels of N-methylation,
and the excited-state oxidation potentials of the parent 1,5-di-
aminonaphthalene and its monomethylamine derivatives (ca.
À3.2 V) are approximately 200 mV lower than the correspond-
ing dimethylamino derivatives (À3.0 V).
1. Introduction
Photoinduced electron transfer continues to receive significant
attention due to its application in a broad range of topics in-
cluding photolithography,[1] organic synthesis,[2] photocaging,[3]
photosynthesis[4] and photovoltaics.[5] Recent advances in
nanomaterials provide even greater opportunity for both fun-
damental investigation and application of electron transfer. For
example, DNA has proven to be a valuable material for con-
structing nanomaterials due to its ready availability and pre-
dictable assembly into helical structures.[6,7] The aromatic stack-
ing within these structures in particular has provided impetus
to investigate the ability of DNA to facilitate electron transfer
for use in electronic devices.[8,9]
structures of differing ground- and excited-state potentials.
This series should find application in a number of photoin-
duced and ground-state studies requiring an incremental pro-
gression of photochemical and redox properties.
2. Results and Discussion
2.1. Synthesis
The parent compound, 1,5-diaminonaphthalene (1), is available
commercially and was used to prepare N1,N1,N5,N5-tetrameth-
yl-1,5-diaminonapthalene (6) by treatment with dimethyl sul-
fate under basic conditions as described previously.[16,20] Syn-
thesis of the remaining derivatives containing an intermediate
number of N-methyl groups relied on Buchwald–Hartwig cou-
plings (Scheme 1). The naphthyl bromide 7 required for this
strategy was prepared in 43% yield from 1-nitronaphthalene
and Br2/FeCl3.[21] Subsequent coupling with methylamine and
dimethylamine alternatively yielded 8 (65% yield) and 9 (75%
yield). Standard use of the strong base sodium tert-butoxide in
these couplings was not compatible with the nitro group pres-
Electron transfer in DNA is additionally quite relevant to
human health since it mediates many of the therapeutic and
damaging effects of radiation.[10,11] Furthermore, electron trans-
fer plays a role in the repair of DNA in some organisms[12] and
perhaps even in the detection of DNA lesions as well.[13] Our
laboratory has focused on transfer of excess electrons through
duplex DNA, in part, because this process is less susceptible to
quenching by molecular oxygen than the complementary hole
transfer.[14–17] The intrinsic ability of DNA to sustain electron
transfer may also account for its apparent ability to promote
self-repair of its major photochemical lesion, a thymine–thy-
mine cyclobutane dimer.[18,19] Mechanistic investigation of
these electron transfer processes and especially their depend-
ence on driving force potential would greatly benefit from a
series of compounds offering a range of oxidation potentials
with minimal change of structure. Already, 1,5-diaminonaph-
thalene (1) demonstrated a much greater ability to initiate
excess electron transfer in DNA than its N1,N1,N5,N5-tetra-
methyl derivative (6), which is a weaker donor.[16] We have now
prepared and characterized the complete series of N-methylat-
ed derivatives of 1 to create a collection of closely related
[a] Dr. N. P. Campbell, Prof. S. E. Rokita
Department of Chemistry and Biochemistry
University of Maryland
College Park, MD 20742 (USA)
Fax: 1-301-405-9376
E-mail: Rokita@umd.edu
[b] Dr. A. S. Finch
US Army Research Laboratory
RDRL-SEE-O
2800 Powder Mill Road
Adelphi, MD 20783 (USA)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cphc.200900969.
1768
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 2010, 11, 1768 – 1773

Oxidation Potential of Diaminonapthalene
methylation by dimethyl sulfate. Finally, the acetyl protecting
group of 13 was removed in high yield (90%) by treatment
with 2 N HCl.
2.2. Absorption and Emission Properties of the
Diaminonaphthalene Derivatives
All of the diaminonaphthalene derivatives exhibit low wave-
length absorption with a relatively invariant lmax of 231–
232 nm under the solvent conditions most relevant to future
studies with nucleic acids (Figure 1a). In contrast, the extinc-
tion coefficients at these wavelengths consistently decrease as
the extent of methylation increases beyond one (Table 1). Ad-
dition of four methyl groups collectively reduces the extinction
coefficient by approximately 50% as evident from comparison
of the values for 1 and 6. N1,N1-Dimethylation also suppresses
absorption in this region significantly more than N1,N5-dime-
thylation. This trend is just one consequence of the likely twist-
ing of the N1,N1-dimethylamino group out of conjugation
Scheme 1. Synthesis of compounds 2–6: a) Me2SO4, Na2CO3, MeOH/H2O/THF
(2:1:1); b) Æ-BINAP, Pd(OAc)2, Cs2CO3, R1R2NH, toluene, 808C; c) 10% Pd/C,
HCOOH, MeOH; d) Ac2O, reflux; e) 2 N HCl, reflux.
ent in 7,[22] and consequently the milder base Cs2CO3 was used
instead.[23,24] Attempts to reduce the nitro groups in 8 and 9
with either Zn/HCl or H2/Pd-C provided only incomplete con-
version even after extended reaction time (>14 h). In contrast,
reduction with formic acid/PdÀC yielded the desired products
2 and 4 in good yield (65% and 80%, respectively) within
0.5 h.
Generation of the symmetric bis-methylamine 3 was accom-
plished in two steps. A Sandmeyer-type reaction was used to
convert the diamine 1 to its diiodo derivative 10 in a 65%
yield (Scheme 1).[25] This derivative was then coupled with
methylamine in excellent yield (89%) under Buchwald–Hartwig
conditions as described above. Finally, synthesis of the unsym-
metric trimethyl derivative 5 required use of a protecting
group to prevent over methylation. The methylamino group of
8 was acetylated in 73% yield prior to reduction of its nitro
group (81% yield) under the same formic acid/PdÀC condi-
tions used above to reduce 7 (Scheme 1). Dimethylation to
form 13 was accomplished in 80% yield under the same condi-
tions used to convert 1 to 6 above. Reductive alkylation has
also been used for methylating a protected 1,5-diaminonaph-
thalene,[16] but this approach was not as robust herein as
Figure 1. a) Absorption spectra of compounds 1–6 (normalized to 10 mm)
and b) their relative fluorescence emission spectra in 100 mm NaCl and
10 mm sodium phosphate pH 7. Each emission spectrum is normalized to its
relative extinction coefficient at lex (See Table 1 for details). Compound 1 is
indicated in black, 2 in red, 3 in green, 4 in blue, 5 in purple and 6 in cyan.
The emission quantum yield of 6 (0.11) was determined previously.16
ChemPhysChem 2010, 11, 1768 – 1773
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemphyschem.org
1769

S. E. Rokita et al.
methylation (1 vs 2). Also, the
last methylation (5 vs 6) reverses
this trend toward lower ener-
gies.
Table 1. Spectral data and redox properties of the diaminonaphthalene series 1–6.
[b]
lmax
e
lex
lem
l00
Eox [V][a]
E00 [kcal
molÀ1
Eox* [V]
[a]
[nm]
[mMÀ1 cmÀ1
]
[nm]
[nm]
[nm]
]
231
324
231
326
232
332
231
318
232
327
231
312
50.0Æ1.30
8.86Æ0.13
50.5Æ4.40
10.7Æ0.20
42.4Æ0.80
10.8Æ0.40
33.9Æ0.60
7.28Æ0.06
28.9Æ0.70
7.88Æ0.51
22.0Æ1.10
5.93Æ0.31
323
327
334
317
327
312
404
409
414
427
429
433
355
362
364
366
372
366
0.250Æ0.020 80.5
0.220Æ0.006 79.0
0.208Æ0.001 78.6
0.380Æ0.006 78.1
0.350Æ0.002 76.9
0.400Æ0.007 78.1
À3.24Æ0.02
À3.24Æ0.01
À3.18Æ0.01
À3.01Æ0.01
À2.98Æ0.01
À2.99Æ0.01
1
2
3
4
5
6
2.3. Redox Properties of the
Diaminonaphthalene
Derivatives
Electrochemistry
Our goal in preparing the vari-
ous diaminonaphthalene deriva-
tives was to create a closely re-
lated series of compounds with
complementary photochemical
and redox properties. The induc-
tive effect of the added methyl
[a] Average values of no less than three independent measurements. Uncertainty represents the standard devi-
ation. [b] See Figure S1 (Supporting Information).
from the aromatic system to relieve steric strain produced by a
peri interaction with H8. Such twisting is also predicted from
conformational analysis based on molecular mechanics calcula-
tions (Supporting Information, Figure S2).
groups was expected to lower the oxidation potential in this
series and yet these modifications could also raise this poten-
tial by suppressing delocalization of the nonbonding electrons
of the nitrogen due to peri interactions of the fused aromatic
rings (Figure S2). These competing effects were evident from
the spectroscopic characterization above and were also evi-
dent in the redox chemistry. Cyclic voltammetry was initially
considered for measuring the Eox values for 1–6, but all at-
tempts at this were thwarted by irreversible oxidation and
polymerization of the compounds that, for others, were used
successfully to generate electroactive films.[26] Replacing the
neutral aqueous solvent system used in these attempts might
have minimized the competing reactions, but would also have
diminished the significance of the results for electron transport
in DNA. Instead, the solvent conditions were retained and the
strategy for measuring oxidation potentials was changed. Al-
ternative use of AC voltammetry was successful as this ap-
proach detected only redox processes that were intrinsically re-
versible in our system.[27] Sample voltammograms are illustrat-
ed for diaminonaphthalene derivatives (Figure 2 and Support-
ing Information, Figure S3), and the resulting Eox values are
summarized in Table 1. Collectively, these compounds offer Eox
values ranging from almost 0.2 V to 0.4 V by only varying the
level of N-methylation. The inductive effect of single methyl
substitutions is evident from the decrease in Eox from 1 to 3,
but the steric effects of geminal N,N-dimethyl substitution
then dominate the remaining series from 4 to 6.
Each diaminonaphthalene derivative also exhibits a weak ab-
sorption in the range of 300–360 nm, and again, the extinction
coefficients vary by approximately 50% from a maximum for 2
and 3 to a minimum for 6 (Figure 1a, Table 1). For this absorp-
tion band, however, addition of a single methyl group to each
amine enhances the extinction coefficient whereas its further
conversion to a geminal N,N-dimethyl group suppresses this
coefficient relative to that of the unmethylated parent chromo-
phore. Competing effects of methylation are also evident in
the lmax values of this band. Whereas monomethylation indu-
ces a bathochromic shift, geminal dimethylation induces a
hypsochromic shift resulting in a range of lmax values centered
around that of the unmethylated parent 1 and delimited by
those of its tetramethylated 6 and the dimethylated 3 deriva-
tives.
The emission properties of this series also exhibit a depend-
ence on the level of N-methylation. The trend of fluorescence
efficiency is comparable to the trend of absorptivity at long
wavelength, and this correlation persists even after the emis-
sion spectra are normalized for differences in excitation effi-
ciency (Figure 1b). Moreover, fluorescence efficiency ranges
ten-fold from a maximum for N1,N5-dimethyldiamine 3 to a
minimum for the N1,N1,N5,N5-tetramethyldiamine 6. The com-
parable range in absorptivity is only two-fold. Emission lmax
also responds to N-methylation of the parent 1 but not in the
same manner as fluorescence efficiency. Each successive meth-
ylation shifts the emission maximum to lower energies, and
the greatest difference is observed between 3 containing one
methyl group on each amine and 4 containing two methyl
groups on a single amine (Table 1). The l00 values were also
determined in order to measure the E00 values that were used
below to estimate the excited-state potentials. The E00 values
conform to the same general trend exhibited by the lem
except that the biggest decrease is apparent after the first
Excited-State Oxidation Potential
The diaminonaphthalenes should find utility in two different
aspects of photoinduced electron transfer. They provide elec-
tron donors to photoexcited oxidants for which their Eox is cru-
cial, and additionally they may serve in their excited state as
strong reducing agents, an application our laboratory is cur-
rently investigating.[16,28,29] The Eox* can be estimated by the
Weller equation[30] based on the ground-state potential Eox, the
singlet excited-state energy represented as E00 (Table 1) and a
solvent correction term that is negligible for polar solvents.[31]
1770
www.chemphyschem.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 2010, 11, 1768 – 1773

Oxidation Potential of Diaminonapthalene
extent, but not position of the N-methylation, because the
electron-donating characteristic of the methyl groups appear
to dominate the excited state properties.
Experimental Section
General Methods and Materials: Solvents, starting materials, and re-
agents of the highest commercial grade were used without further
purification unless noted. All aqueous solutions were prepared
with water purified to a resistivity of 17.8–18.0 MW. Commercially
available 1,5-diaminonaphthalene was recrystallized in ethanol.
N1,N1,N5,N5-Tetramethyl-1,5-diaminonapthalene (6) [16,20], 1-bromo-
[21]
[25]
5-nitronapthalene (7)
and 1,5-diiodonaphthalene (10)
were
prepared as described previously. All UV/Vis measurements were
obtained with a Hewlett Packard 8453 UV/Vis spectrophotometer,
and all fluorescence spectra were obtained with a Hitachi F-4500
spectrophotometer. NMR spectra were recorded with a Bruker
AM400 spectrometer and referenced to residual protons in the sol-
vents. Chemical shifts (d) are reported in parts per million (ppm),
and coupling constants (J) are reported in hertz (Hz).
Figure 2. AC voltammograms of selected diaminonaphthalenes. The data
represents the average of three independent measurements for each com-
pound.
The E00 values in turn can be estimated from l00 as detected
by the overlay of the normalized fluorescence excitation and
emission spectra (Table 1 and Supporting Information, Fig-
ure S1).[32] These values are compensatory to the structural ef-
fects influencing the ground state Eox, and consequently a
broad variation in Eox* is suppressed. The excited-state donor
strength of the diaminonaphthalenes is most readily character-
ized by the degree of substitution on the amine groups. The
derivatives 1–3 containing no more than a single methyl
group on each amine are relatively strong electron donors,
and the remaining derivatives 4–6 containing one or more di-
methylamine groups are weaker excited-state electron donors
by ca. 200 mV. However, both groups are among the strongest
donors that have been used for study of excess electron trans-
fer in DNA and should have the power to reduce all of the nu-
cleobases including guanine with a potential of lower than
À2.76 V.[33,34]
Preparation of N1-Methylnaphthalene-1,5-diamine (2): A solution of
8 (300 mg, 1.48 mmol) and methanol (20 mL) was added to an
oven-dried round-bottom flask with a magnetic stir bar. This mix-
ture was stirred at room temperature until 8 was dissolved, at
which time 10% palladium on carbon (200 mg, 0.13 mmol) and
formic acid (2 mL) were added. The reaction was stirred under ni-
trogen atmosphere for 2 h at room temperature, and the resulting
mixture was filtered through a plug of Celite 545ꢁ. The filtrate was
diluted with CH2Cl2, and then washed with saturated NaHCO3,
water and brine. The organic layer was dried with anhydrous mag-
nesium sulfate, filtered and concentrated to dryness. The crude
material was purified by silica gel flash column chromatography
with 10% ethyl acetate:hexanes yielding the desired product as a
1
dark red solid (168 mg, 65%). H NMR (400 MHz, CDCl3): d=7.35 (t,
J=8.00, 1H), 7.23 (t, J=2.71 Hz, 1H), 7.18 (d, J=8.03 Hz, 1H), 6.77
(d, J=2.57 Hz, 1H), 6.75 (d, J=2.54 Hz, 1H), 6.62–6.56 (m, 1H), 4.41
(s, 1H), 4.11 (s, 2H), 2.99 (s, 3H). 13C NMR (101 MHz, CDCl3): d=
145.2, 143.1, 126.1, 125.5, 124.7, 124.5, 111.0, 110.3, 110.2, 104.3,
31.5.
3. Conclusions
Preparation of N1,N5-Dimethylnaphthalene-1,5-diamine (3): Anhy-
drous toluene (2 mL) and Æ-BINAP (66 mg, 0.11 mmol) were com-
bined and sealed in an oven-dried round-bottom flask with a mag-
netic stir bar. The mixture was heated to 808C until the Æ-BINAP
dissolved. The resulting solution was then cooled to approximately
308C before addition of palladium acetate (47.5% palladium,
12 mg). The resulting dark orange solution was further cooled to
room temperature while stirring for 5 min. Next, 10 (125 mg,
0.329 mmol) was added, and after another 10 min, Cs2CO3 (203 mg,
1.05 mmol) was added. The mixture was stirred for an additional
20 min and then methylamine (2m solution in THF, 0.5 mL) was
added. The reaction vessel was quickly sealed and heated to 808C
for 48 h. The resulting reaction mixture was filtered through a plug
of Celite 545ꢁ, and the plug was rinsed with several portions of
CH2Cl2. The filtrate was concentrated to dryness. The resulting solid
was purified by silica gel flash chromatography using a gradient of
5–30% ethyl acetate in hexanes yielding the desired product as a
A new series of electron donors has been constructed and
characterized to support mechanistic investigation of photoin-
duced electron transfer. In particular, these diaminonaphtha-
lene derivatives will help in the future to identify the parame-
ters controlling electron injection and transfer in DNA. This
series also has the potential for application in numerous other
systems for which an incremental variation in potential is
needed. The derivatives 1–6 illustrate the opposing effects of
the inductive and steric properties of N-methylation in naph-
thyl amines. Influence of this methylation is evident in the
photochemical excitation and emission as well as ground- and
excited-state oxidation of diaminonaphthalenes. Both lex and
Eox respond similarly to 1) the stabilization provided by the
electron donating ability of a methyl substituent and 2) the de-
stabilization caused by a diminished conjugation of the nitro-
gen lone pair into the aromatic system that results from a
steric clash between the N-methyl and its proximal aryl hydro-
gen. In contrast, the lem and l00 are primarily influenced by the
1
dark red, viscous oil (55 mg, 89% yield). H NMR (400 MHz, CDCl3):
d=7.33 (t, J=7.96 Hz, 2H), 7.15 (d, J=8.50 Hz, 2H), 6.60 (d, J=
7.56 Hz, 2H), 4.42 (s, 2H), 2.99 (s, 6H). 13C NMR (101 MHz, CDCl3):
d=145.1, 125.5, 123.8, 108.7, 103.9, 31.1.
ChemPhysChem 2010, 11, 1768 – 1773
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemphyschem.org
1771

S. E. Rokita et al.
Preparation of N1,N1-Dimethylnaphthalene-1,5-diamine (4): Reduc-
tion of 9 (761 mg, 3.45 mmol) in methanol (100 mL) was performed
equivalently to that described in preparation of 2 above using
10% palladium on carbon (370 mg, 0.350 mmol) and formic acid
(2 mL) to yield the desired product (523 mg, 80%). 1H NMR
(400 MHz, CDCl3): d=7.69 (d, J=8.52 Hz, 1H), 7.49 (d, J=8.44 Hz,
1H), 7.36 (t, J=7.94 Hz, 1H), 7.27 (t, J=7.94 Hz, 1H), 7.06 (d, J=
7.37 Hz, 1H), 6.76 (d, J=7.35 Hz, 1H), 4.09 (s, 2H), 2.87 (s, 6H).
13C NMR (101 MHz, CDCl3): d=151.2, 142.4, 140.3, 130.1, 125.5,
124.7, 115.5, 115.1, 114.0, 100.8, 45.2.
was performed equivalently to that described for preparation of 2
above using 10% palladium on carbon (105 mg, 0.0989 mmol) and
formic acid (2 mL) to yield the desired product (175 mg, 81%).
1H NMR (400 MHz, CDCl3): d=7.88 (d, J=8.53 Hz, 1H), 7.49–7.43
(m, 1H), 7.40–7.32 (m, 2H), 7.23 (d, J=8.42 Hz, 1H), 6.85 (d, J=
7.38 Hz, 1H), 4.33 (s, 2H), 3.34 (s, 3H), 1.77 (s, 3H).
Preparation of N-[5-(Dimethylamino)naphthalen-1-yl]-N-methylace-
tamide (13): Methanol (6 mL), water (3 mL) and THF (3 mL) were
combined and used to suspend 12 (100 mg, 0.467 mmol) and
Na2CO3 (198 mg, 1.87 mmol). Dimethyl sulfate (0.176 mL,
1.87 mmol) was added to the mixture, and together stirred at
room temperature overnight under N2. The reaction was quenched
with 1m NaOH to a pH>11 and extracted with ethyl acetate. The
organic layer was dried over MgSO4, filtered and concentrated to
dryness to yield the desired material (94 mg, 80%). 1H NMR
(400 MHz, CDCl3): d=8.30 (d, J=8.53 Hz, 1H), 7.50 (m, 3H), 7.36 (d,
J=7.16 Hz, 1H), 7.16 (dd, J=6.36 Hz, 1H), 3.37 (s, 3H), 2.94 (s, 6H),
1.80 (s, 3H). 13C NMR (101 mHz, CDCl3): d=171.2, 152.3, 141.0,
132.3, 130.7, 127.1, 126.9, 125.3, 124.2, 117.1, 115.1, 45.9, 37.2, 22.2.
Preparation of N1,N1,N5-Trimethylnaphthalene-1,5-diamine (5): A
mixture of 13 (100 mg, 0.413 mmol), 25 mL THF and 5 mL 2 N HCl
was heated to reflux overnight, cooled to room temperature, and
diluted with ethyl acetate. The resulting organic layer was then
neutralized with saturated NaHCO3, washed with brine, dried over
MgSO4, filtered and concentrated to dryness to yield 5 (74 mg,
1
90%). H NMR (400 MHz, CDCl3): d=7.68 (d, J=8.54 Hz, 1H), 7.51
(d, J=8.48 Hz, 1H), 7.45 (m, 2H), 7.11 (d, J=7.41 Hz, 1H), 6.64 (d,
J=7.51 Hz, 1H), 4.45 (s, 1H), 3.04 (s, 3H), 2.92 (s, 6H). 13C NMR
(101 MHz, CDCl3): d=151, 145, 129, 126, 125, 124, 115, 114, 113,
104, 45, 31
AC Voltammetry and Excited-State Oxidation Potential: Measure-
ments were carried out using a CH Instruments 660 A electrochem-
ical workstation (Austin, TX) courtesy of the Army Research Labs,
Adelphi, MD. Experiments were run in a three component elec-
trode cell with a platinum working electrode, platinum wire coun-
ter and saturated calomel reference electrode. Phosphate buffered
saline (PBS, 10 mm potassium phosphate, 137 mm NaCl and
2.7 mm KCl, pH 7.4) was used as the electrolyte. Stock solutions of
diaminonaphthalenes (500 mm) were prepared with HPLC-grade
acetonitrile and added (10 mL) to a final concentration of 500 mm in
10 mL PBS and less than 5% acetonitrile. AC voltammetry [incr
E(V)=0.004, amplitude (V)=0.025, frequency (Hz)=10] was per-
formed a minimum of three times for each compound. Eox values
were identified by the apex of the average of these scans, and Eox*
values were then calculated from the relationship: Eox*(V)=
Eox(V)ÀE00 (kcalmolÀ1)/23.06.[30]
Preparation of N-Methyl-5-nitronaphthalen-1-amine (8): The desired
compound was produced using analogous conditions to those de-
scribed for 3 with Æ-BINAP (247 mg, 0.397 mmol), palladium ace-
tate (47.5% palladium, 71 mg, 0.32 mmol), 7 (1.0 g, 0.40 mmol),
Cs2CO3 (160 mg, 0.48 mmol) and methylamine (2m in THF,
2.40 mL). The crude material was purified by silica gel flash column
chromatography using a 5–10% gradient of ethyl acetate in
hexane to yield the desired solid (523 mg, 65% yield). 1H NMR
(400 MHz, CDCl3): d=8.05 (t, J=8.50 Hz, 1H), 7.76 (d, J=8.69 Hz,
1H), 7.53 (t, J=8.22 Hz, 1H), 7.39 (t, J=8.05 Hz, 1H), 6.67 (d, J=
7.72 Hz, 1H), 4.62 (s, 1H), 3.00 (s, 3H). 13C NMR (101 MHz, CDCl3):
d=147.5, 144.8, 130.4, 126.0, 125.9, 124.6, 123.3, 122.5, 111.3,
105.5, 31.0. m.p.: 135–1378C.
Preparation of N1,N1-Dimethyl-5-nitronaphthalen-1-amine (9): The
desired compound was produced using analogous conditions to
those described for 3 with Æ-BINAP (25 mg, 0.040 mmol), palladi-
um acetate (47.5% palladium, 9.4 mg, 0.020 mmol), 7 (100 mg,
0.40 mmol) Cs2CO3 (160 mg, 0.48 mmol) and dimethylamine (2m in
THF, 0.30 mL). The crude material was purified by silica gel flash
column chromatography with 5% ethyl acetate:95% hexanes to
Acknowledgements
This work was supported in part by the National Science Founda-
tion (CHE-0517498), the Donors of the American Chemical Society
Petroleum Research Fund (PRF 41514-AC4) and a SMART Fellow-
ship from the Department of Defense (A.S.F.). We also thank Dr.
James Sumner for his invaluable assistance with the AC voltam-
metry, and Dr. Lyle Isaacs for help with molecular mechanics.
1
provide 9 in 75% yield (64 mg) as a dark red oil. H NMR (400 MHz,
CDCl3): d=8.53 (d, J=8.49 Hz, 1H), 8.13–8.07 (m, 2H), 7.54 (t, J=
8.14 Hz, 1H), 7.46 (t, J=8.04 Hz, 1H), 7.14 (d, J=7.48 Hz, 1H), 2.85
(s, 6H). 13C NMR (101 MHz, CDCl3): d=151.6, 147.3, 130.7, 130.1,
129.4, 126.5, 123.6, 123.1, 117.2, 115.5, 45.3.
Preparation of N-Methyl-N-(5-nitronaphthalen-1-yl)-acetamide (11):
Acetic anhydride (3 mL) and 8 (52 mg, 0.26 mmol) were refluxed
overnight, cooled to room temperature and diluted with 25 mL
water. The resulting solution was adjusted to pH 7 using saturated
aqueous NaHCO3. The solution was extracted 3ꢂ50 mL with
CH2Cl2. The organic layers were combined, washed (100 mL water
and 100 mL brine), dried over magnesium sulfate, and concentrat-
ed to dryness. The resulting yellow-orange solid was purified by
silica gel flash chromatography using 5–20% ethyl acetate in
hexane to yield the desired product (46 mg, 73% yield). 1H NMR
(400 MHz, CDCl3): d=8.30 (d, J=8.53 Hz, 1H), 7.50 (m, 3H), 7.36 (d,
J=7.16 Hz, 1H), 7.16 (dd, J=6.36 Hz, 1H), 3.37 (s, 3H), 2.94 (s, 6H),
1.80 (s, 3H).
Keywords: diaminonaphthalenes · electron transfer · excited-
state electron donor · fluorescence · voltammetry
[1] N. A. O’Connor, A. J. Berro, J. R. Lancaster, X. Gu, S. Jockusch, T. Nagai, T.
Ogata, S. Lee, P. Zimmerman, C. G. Willson, N. J. Turro, Chem. Mater.
2008, 20, 7374–7376.
[2] A. G. Griesbeck, N. Hoffmann, K.-D. Warzecha, Acc. Chem. Res. 2007, 40,
128–140.
[3] J. B. Borak, S. Lꢃpez-Sola, D. E. Falvey, Org. Lett. 2008, 10, 457–460.
[4] S. Fukuzumi, Phys. Chem. Chem. Phys. 2008, 10, 2283–2297.
[5] M. T. Lloyd, J. E. Anthony, G. G. Malliaras, Mater. Today 2007, 10, 34–41.
[6] M. Endo, H. Sugiyama, ChemBioChem 2009, 10, 2420–2423.
[7] N. C. Seeman, P. S. Lukeman, Rep. Prog. Phys. 2005, 68, 237–270.
[8] A. K. Feldman, M. L. Steigerwald, X. Guo, C. Nuckolls, Acc. Chem. Res.
2008, 41, 1731–1741.
Preparation of N-(5-Aminonaphthalen-1-yl)-N-methyl-acetamide
(12): Reduction of 11 (200 mg, 0.989 mmol) in methanol (20 mL)
1772
www.chemphyschem.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 2010, 11, 1768 – 1773

Oxidation Potential of Diaminonapthalene
[9] A. A. Gorodetsky, M. C. Buzzeo, J. K. Barton, Bioconjugate Chem. 2008,
19, 2285–2296.
[26] M. Abdel-Azzem, U. S. Yousef, G. Pierre, Eur. Polym. J. 1998, 34, 819–
826.
[10] Z. Cai, M. D. Sevilla, Top. Curr. Chem. 2004, 237, 103–128.
[11] C. von Sonntag, Adv. Quantum Chem. 2007, 52, 5–20.
[12] A. Sancar, Chem. Rev. 2003, 103, 2203–2238.
[27] S. E. Creager, T. T. Wooster, Anal. Chem. 1998, 70, 4257–4263.
[28] T. Ito, S. E. Rokita, Angew. Chem. 2004, 116, 1875–1878; Angew. Chem.
Int. Ed. 2004, 43, 1839–1842.
[13] A. K. Boala, J. C. Genereuxa, P. A. Sontza, J. A. Gralnick, D. K. Newmanc,
J. K. Barton, Proc. Natl. Acad. Sci. USA 2009, 106, 15237–15242.
[14] G. B. Schuster, Acc. Chem. Res. 2000, 33, 253–260.
[15] A. Okamoto, K. Tanaka, I. Saito, J. Am. Chem. Soc. 2003, 125, 5066–
5071.
[16] T. Ito, S. E. Rokita, J. Am. Chem. Soc. 2004, 126, 15552–15559.
[17] C. L. Cleveland, R. N. Barnett, A. Bongiomo, J. Joseph, C. Liu, G. B. Schus-
ter, U. Landman, J. Am. Chem. Soc. 2007, 129, 8408–8409.
[18] M. R. Holman, T. Ito, S. E. Rokita, J. Am. Chem. Soc. 2007, 129, 6–7.
[19] F. Masson, T. Laino, I. Tavernelli, U. Rothlisberger, J. Hutter, J. Am. Chem.
Soc. 2008, 130, 3443–3450.
[29] S. E. Rokita, T. Ito, in Charge Transfer in DNA: From Mechanism to Appli-
cation (Ed.: H.-A. Wagenknecht), Wiley-VCH, Weinheim, 2005, pp. 133–
151.
[30] D. Rehm, A. Weller, Isr. J. Chem. 1970, 8, 259–271.
[31] P. Daublain, A. K. Thazhathveetil, V. Shafirovich, Q. Wang, A. Trifonov, T.
Fiebig, F. D. Lewis, J. Phys. Chem B, DOI: 10.1021/jp9107393.
[32] J. B. Birks, Photophysics of Aromatic Molecules, Wiley-Interscience, New
York, 1970, Ch. 4, p. 84–141.
[33] C. A. M. Seidel, A. Schulz, M. H. M. Sauer, J. Phys. Chem. 1996, 100,
5541–5553.
[34] H.-A. Wagenknecht, in Charge Transfer in DNA: From Mechanism to Ap-
plication (Ed.: H.-A. Wagenknecht), Wiley-VCH, Weinheim, 2005, pp. 1–
26.
[20] Y. Chung, B. F. Duerr, T. A. McKelvey, P. Najappan, A. W. Czarnik, J. Org.
Chem. 1989, 54, 1018–1032.
[21] X. Gao, Y. Zhang, B. Wang, New J. Chem. 2005, 29, 579–586.
[22] J. P. Wolfe, S. L. Buchwald, J. Org. Chem. 2000, 65, 1144–1157.
[23] J. F. Hartwig, Acc. Chem. Res. 1998, 31, 852–860.
[24] D. S. Surry, S. L. Buchwald, Angew. Chem. 2008, 120, 6438–6461; Angew.
Chem. Int. Ed. 2008, 47, 6338–6361.
Received: December 9, 2009
Revised: March 2, 2010
[25] J. G. Rodrꢄguez, J. L. Tejedor, J. Org. Chem. 2002, 67, 7631–7640.
Published online on April 7, 2010
ChemPhysChem 2010, 11, 1768 – 1773
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemphyschem.org
1773