Tuning the optical properties of fluorinated indolylfulgimides

Article abstract of DOI:10.1021/jo026374n

Photochromic fluorinated indolylfulgides have been identified as potential candidates for a wide range of applications including optical switches, photoregulators of biological processes, and optical memory media. In humid environments or biological systems, hydrolytic stability is essential. In an effort to improve hydrolytic stability, a series of indolylfulgimides has been synthesized from a parent trifluoromethyl-substituted indolylfulgide. The nitrogen of the succinimide moiety is linked to either a dimethyl amino or one of seven substituted phenyl groups. The phenyl groups feature substituents with increasing electron-withdrawing ability. The spectral characteristics of each compound have been examined, revealing that the wavelength absorption maxima of each form increases with increasing electron-withdrawing ability of the substituted N-phenyl ring. The quantum yields of the photoreactions have been determined with the N-(phenyl)fulgimide showing a ring closure value of nearly 0.30 in toluene. In addition, the hydrolytic, thermal, and photochemical stabilities of each compound have been measured. The fulgimides exhibit at least a 200-fold enhancement of hydrolytic stability for the Z-form and over a 1000-fold enhancement for the C-form in comparison to the same form of the parent fulgide. The N-(2,3,5,6-tetrafluoro-4-trifluoromethylphenyl)fulgimide can undergo up to 3000 photochemical cycles (coloration followed by bleaching) before losing 20% of its initial absorbance at photostationary state.

Full text of DOI:10.1021/jo026374n

Tu n in g th e Op tica l P r op er ties of F lu or in a ted In d olylfu lgim id es
Mason A. Wolak, Craig J . Thomas, Nathan B. Gillespie, Robert R. Birge, and Watson J . Lees*
Department of Chemistry and W. M. Keck Center for Molecular Electronics, Syracuse University,
Syracuse, New York 13244
wjlees@syr.edu
Received August 30, 2002
Photochromic fluorinated indolylfulgides have been identified as potential candidates for a wide
range of applications including optical switches, photoregulators of biological processes, and optical
memory media. In humid environments or biological systems, hydrolytic stability is essential. In
an effort to improve hydrolytic stability, a series of indolylfulgimides has been synthesized from a
parent trifluoromethyl-substituted indolylfulgide. The nitrogen of the succinimide moiety is linked
to either a dimethyl amino or one of seven substituted phenyl groups. The phenyl groups feature
substituents with increasing electron-withdrawing ability. The spectral characteristics of each
compound have been examined, revealing that the wavelength absorption maxima of each form
increases with increasing electron-withdrawing ability of the substituted N-phenyl ring. The
quantum yields of the photoreactions have been determined with the N-(phenyl)fulgimide showing
a ring closure value of nearly 0.30 in toluene. In addition, the hydrolytic, thermal, and photochemical
stabilities of each compound have been measured. The fulgimides exhibit at least a 200-fold
enhancement of hydrolytic stability for the Z-form and over a 1000-fold enhancement for the C-form
in comparison to the same form of the parent fulgide. The N-(2,3,5,6-tetrafluoro-4-trifluorometh-
ylphenyl)fulgimide can undergo up to 3000 photochemical cycles (coloration followed by bleaching)
before losing 20% of its initial absorbance at photostationary state.
SCHEME 1. P h otor ea ction s of In d olylfu lgid esa
In tr od u ction
New alternatives to traditional data storage techniques
are currently under development to meet the ever-
increasing demands of today’s information-driven society.
One encouraging solution involves the use of photoactive
organic materials in high-density rewriteable optical
memory devices.1 In such a device, the organic media
would serve as the memory elements of a binary system.
Photochromic organic compounds are ideal candidates for
memory media because they can be interconverted be-
tween two key forms upon wavelength-specific illumina-
tion.2,3 Required attributes for optical memory media
include readily distinguishable absorption spectra for
each form, efficient photoreactions, nondestructive read-
out, and both thermal and photochemical stability. As
the availability of photons generally increases with
increasing wavelength, it is also desirable to utilize
materials that absorb light well into the visible region.
Among the many classes of photochromic compounds,
diarylethenes and fulgides have generated the greatest
interest, because they meet many of the aforementioned
requirements for optical memory. Within the fulgide
family, indolylfulgides are particularly attractive, as they
maintain the greatest resistance to photochemical and
thermal stress.4 Newly discovered fluorinated indolyl-
fulgides display enhanced photochemical stability relative
a
For fluorinated indolylfulgides, the cyclizable form is the
Z-form (due to IUPAC nomenclature). For virtually all other
fulgides the E- and Z- labels are switched.
to nonfluorinated analogues and also exhibit strong
bathochromic shifts in the cyclizable Z-form (Scheme 1).5,6
Although the thermal and photochemical stabilities of
these compounds have been studied, one requirement
that has been generally overlooked is hydrolytic stability.
The importance of hydrolytic stability is underscored
by the fact that optical memory devices would be expected
to maintain viability in humid environments. Previous
studies have demonstrated that fulgides are unstable in
hydrolytic solvents relative to the corresponding fulgi-
(1) Yokoyama, Y. Chem. Rev. 2000, 100, 1717-39.
(4) Kaneko, A.; Tomoda, A.; Ishizuka, M.; Suzuki, H.; Matsushima,
R. Bull. Chem. Soc. J pn. 1988, 61, 3569-73.
(2) Durr, H., Bousas-Laurent, H., Eds.; Photochromism, Molecules
and Systems; Elsevier: Amsterdam, 1990.
(5) Wolak, M. A.; Gillespie, N. B.; Thomas, C. J .; Birge, R. R.; Lees,
W. J . J . Photochem. Photobiol., A 2001, 144, 83-91.
(3) Crano, J . C., Guglielmetti, R. J ., Eds.; Organic Photochromic and
Thermochromic Compounds; Plenum Press: New York, 1999; Vol. 1.
(6) Yokoyama, Y.; Takahashi, K. Chem. Lett. 1996, 1037-8.
10.1021/jo026374n CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/17/2002
J . Org. Chem. 2003, 68, 319-326
319

Wolak et al.
mides.7 In fulgimides, the anhydride moiety of the fulgide
is replaced with an imide moiety.8 Matsushima has
SCHEME 2 a
reported that the C-form of a thiazolylfulgide loses more
than 50% of its absorbance at λmax after 2 days in 1:2
toluene:ethanol. In comparison, the corresponding N-
phenyl-substituted thiazolylfulgimide did not show simi-
lar degradative loss. In addition, Matsushima has shown
that fulgimides maintain photochromic activity even in
aqueous mixtures (1:1 ethanol:H2O). Fulgimides have
also been utilized for photoswitchable energy transfer,9,10
photoregulation of binding to biomolecules,11,12 and as
precursors for photochromic copolymers.13,14 With limited
exceptions, photochemical attributes such as quantum
yields and photochemical fatigue have been largely
ignored.7,13,15
We have prepared a series of fluorinated indolylfulgim-
ides using the nitrogen atom as a linker to connect
substituted phenyl rings of increasing cumulative electron-
withdrawing ability. It was expected that altering the
electron-withdrawing ability of the phenyl ring would
lend insight into the impact of electronic considerations
on optical characteristics. Furthermore, we were inter-
ested in studying the hydrolytic stability of fulgimides
in aqueous solutions as prior reports featured limited
characterization. Herein, we report the photochemical
attributes of a series of fulgimides including predictive
trends in absorption spectra and the quantum yields of
the coloration (ring closing) and bleaching (ring opening)
photoreactions. In addition, each compound has been
analyzed for its thermal, photochemical, and hydrolytic
stability.
a
Reagents: (a) for 2 and 3, NH2R′, THF, 60 °C; for 4-7, NH2R′,
NaH, toluene, 50 °C; for 8 and 9, NH2R′, LDA, DMF.
TABLE 1. Extin ction Coefficien ts a t λm a x for F u lgid e 1
a n d F u lgim id es 2-9 in Tolu en e
λ
max/nm (ꢀmax/mol-1 L cm-1
)
compd
Z-form
E-form C-form
1
2
3
4
5
6
7
8
9
427 (5300)
399 (5500)
404 (5800)
406 (6400)
412 (6500)
418 (5500)
422 (5800)
417 (6600)
432 (6100)
441 (5600)
395 (5700)
419 (6000)
422 (6100)
432 (5600)
437 (4300)
438 (6000)
430 (5700)
449 (6400)
571 (6400)
545 (6500)
554 (6900)
557 (7400)
565 (7300)
573 (6500)
580 (6800)
573 (7700)
582 (7700)
addition of 1,1-dimethylhydrazine or substituted anilines
generated the corresponding N-substituted succinamic
acid.17 To enhance reactivity, anilines substituted with
electron-withdrawing groups were deprotonated with
NaH or LDA prior to the addition of 1Z. Subsequent
dehydration of the succinamic acid intermediates with
acetic anhydride in toluene yielded indolylfulgimides
2-9. All of the fulgimides were obtained as crystals in
the Z-form. However, on occasion, compounds 5 and 6
crystallized exclusively in the E-form.
Op tica l Ch a r a cter istics. The extinction coefficients
and absorption maxima of each form of fulgimides 2-9
are shown in Table 1. With the exception of compound
9, each fulgimide experienced a hypsochromic shift in its
Z-form absorption spectra relative to parent fulgide 1Z.
With regard to the C-form spectra, fulgimides 6-9
displayed moderate bathochromic shifts relative to fulgide
1C. With the exception of N-(dimethylamino)fulgimide
2, the noncyclizable E-form of each compound had a
longer wavelength maximum than the cyclizable Z-form.
Resu lts a n d Discu ssion
Syn th esis. Trifluoromethyl-substituted indolylfulgide
1Z was prepared as previously reported.16 Fulgide 1Z
then served as a precursor to fluorinated indolylfulgim-
ides 2-9 (Scheme 2). Anhydride ring opening of 1Z via
(7) Matsushima, R.; Sakaguchi, H. J . Photochem. Photobiol., A 1997,
108, 239-45.
(8) Hart, R. J .; Heller, H. G.; Salisbury, K. Chem. Commun. 1968,
1627-8.
(9) Walz, J .; Ulrich, K.; Port, H.; Wolf, H. C.; Wonner, J .; Effen-
berger, F. Chem. Phys. Lett. 1993, 213, 321-4.
(10) Port, H.; Hartschuh, A.; Hennrich, M.; Wolf, H. C.; Endtner, J .
M.; Effenberger, F. Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A 2000,
344, 145-50.
(11) Willner, I.; Rubin, S.; Wonner, J .; Effenberger, F.; Bauerle, P.
J . Am. Chem. Soc. 1992, 114, 3150-1.
(12) Willner, I.; Lion-Dagan, M.; Rubin, S.; Wonner, J .; Effenberger,
F.; Bauerle, P. Photochem. Photobiol. 1994, 59, 491-6.
(13) Liang, Y.; Dvornikov, A. S.; Rentzepis, P. M. J . Mater. Chem.
2000, 10, 2477-82.
(14) Liang, Y.; Dvornikov, A. S.; Rentzepis, P. M. Chem. Commun.
2000, 1641-2.
(15) Deblauwe, V.; Smets, G. Makromol. Chem. 1988, 189, 2503-
12.
(16) Thomas, C. J .; Wolak, M. A.; Birge, R. R.; Lees, W. J . J . Org.
Chem. 2001, 66, 1914-8.
(17) Darcy, P. J .; Heller, H. G.; Patharakorn, S.; Piggott, R. D.;
Whittall, J . J . Chem. Soc., Perkin Trans. 1 1986, 315-9.
320 J . Org. Chem., Vol. 68, No. 2, 2003

Optical Properties of Fluorinated Indolylfulgimides
TABLE 2. Qu a n tu m Yield s of P h otor ea ction s for
F u lgid e 1 a n d F u lgim id es 2-9 in Tolu en e
irradiation at 559 nm
irradiation at 427 nm
ΦZC ΦCZ ΦZE ΦEZ
C:Z:E at
PSS427nm
compd
ΦCZ
1
2
3
4
5
6
7
8
9
0.20 0.10 0.014 0.022
0.28 0.16
0.29 0.11
0.043
0.069
0.070
0.060
0.057
0.046
0.044
0.045
0.039
95:3:2
91:8:1
93:6:1
93:6:1
93:6:1
94:4:2
94:5:1
96:3:1
92:5:3
0.22 0.15
0.23 0.17 0.005 0.021
0.28 0.14 0.013 0.026
0.27 0.21
0.23 0.07
0.25 0.09
F IGURE 1. Absorption spectra of the Z-, E-, and C-forms of
dinitro-substituted indolylfulgimide 9 in toluene.
did not observe this trend when measuring absorption
spectra of furylfulgimides at the photostationary state
(PSS). However, due to the possible presence of other
forms, the wavelength absorption maxima measured at
PSS may not represent the true absorption maxima of
the pure compound. The ability to tailor the wavelength
absorption maxima of phenyl-substituted fluorinated
indolylfulgimides represents an advancement in the
field of photochromics. One could envision the prepara-
tion of new indolylfulgimides with predictable absorptive
characteristics designed and optimized for specific ap-
plications.
Qu an tu m Yields. Measurement of the quantum yields
for ring closure (φZC) and ring opening (φCZ) was carried
out as previously described.5 In keeping with former
studies, initiation of ring closure was accomplished via
irradiation with λ ) 427-nm light, while the ring opening
reactions were probed with λ ) 559-nm light.6
Few examples exist comparing the photochromic prop-
erties of fulgimides to their parent fulgides. Smets reports
little to no difference in quantum yield between the two
species for either ring closing or ring opening.15 Rentzepis
reports a moderate decrease in the quantum yield of ring
opening in a nonpolar solvent (hexane), while a much
larger loss in efficiency is seen for ring closing.13 In the
case of the fulgimides detailed herein, compounds 2-9
all displayed greater ring closing quantum yields in
toluene than the parent trifluoromethyl-substituted in-
dolylfulgide 1. Phenyl-substituted fulgimide 3 showed the
largest quantum yield with a value of 0.29, nearly 50%
higher than the fulgide precursor. The values obtained
for ΦZC for the series of fulgimides yielded no apparent
trend with increasing electron-withdrawing substituents
on the phenyl ring (Table 2).
F IGURE 2. Hammett plot of wavelength maxima vs σ value
for all three forms of fulgimides 3-9. In order of increasing σ
values: 3 (0.0), 4 (0.06), 5 (0.68), 8 (0.81), 6 (0.86), 7 (1.32), 9
(1.62).
As the cumulative electron-withdrawing power of the
phenyl-substituents increased, there was a corresponding
increase in the Z-form wavelength absorption maxima.
A similar trend was also observed for the E- and C-forms
of each compound. The trend culminates with the Z-form
of dinitro-substituted fulgimide 9 displaying the longest
wavelength maxima for any fulgimide reported to date
(Figure 1).
The electron-withdrawing ability of the substituted
phenyl ring of fulgimides 3-9 was quantified by sum-
mation of the known σ values for each substituent.18 In
the case of ortho substitution, the σ value corresponding
to para substitution was utilized. A plot of the sum of
the σ values vs the wavelength maxima of the Z-, E-, and
C-forms revealed correlation coefficients of >0.95 for each
form (Figure 2). The linear curve fits yielded the following
equations:
The ring-opening photoreactions did reveal a common
trend, as the quantum yield decreased with the increas-
ing additive electron-withdrawing nature of the substi-
tuted phenyl ring. As a result, the lowest ring opening
quantum yield exists for the dinitrophenyl-substituted
fulgimide 9. A Hammett plot of ΦCZ vs σ value for com-
pounds 3-9 showed reasonable correlation, with R ) 0.93
(Figure 3).
The excellent separation of the UV-vis spectra of the
cyclizable Z-form and the ring-closed C-form results in
outstanding control of the photoreactions of coloration
and bleaching. In all cases, the photostationary state
Z-form: Y ) 404 nm + 15.8Σ(σ) nm
E-form: Y ) 420 nm + 16.4Σ(σ) nm
C-form: Y ) 556 nm + 17.7Σ(σ) nm
It should be noted that the Rentzepis group has
synthesized19 and optically characterized a limited num-
ber of N-phenyl-substituted 2-indolylfulgimides that
reveal similar trends, thus suggesting that these cor-
relations may be somewhat general. Matsushmia et al.
(18) Exner, O. Correlation Analysis of Chemical Data, 1st ed.;
Plenum Publishing Corp.: New York, 1988.
(19) Liang, Y.; Dvornikov, A. S.; Rentzepis, P. M. Tetrahedron Lett.
1999, 40, 8067-9.
derived from irradiation with λ ) 427 nm (PSS427nm
)
contained at least 90% C-form (Table 2). Ring-opening
quantum yields at 427 nm (φCZ 427nm) have been deter-
J . Org. Chem, Vol. 68, No. 2, 2003 321

Wolak et al.
F IGURE 5. Hydrolytic decomposition of the Z-forms of
fulgimides 3 and 5-9 in 70:30 EtOH:H2O: open triangles (3),
open circles (5), open diamonds (6), filled circles (7), filled
squares (8), filled diamonds (9). The rates of decomposition
F IGURE 3. Hammett plot of ΦCZ vs σ value for fulgimides
3-9. The Y-axis format is identical to the one shown in
Figure 2.
were determined by fitting the curves to y ) (1 - A)e-kt
.
F IGURE 4. Loss of absorbance with time for indolylfulgide
1Z (triangles) and 1C diamonds) in 70:30 EtOH:H2O at room
temperature. Rate constants for hydrolysis were fitted to
exponential decay: kC ) 9.51 × 10-2 min-1, kZ ) 3.94 × 10-3
F IGURE 6. Hydrolytic decomposition of the C-form of fulgim-
ides 2-9 in 70:30 EtOH:H2O: open squares (2), open triangles
(3), crosses (4), open circles (5), open diamonds (6), filled circles
(7), filled squares (8), filled diamonds (9). The rates of
decomposition were determined by fitting the curves to y ) (1
min-1
.
mined from the photostationary state compositions
(Table 2). The C-form present in the PSS427nm can be
quantitatively converted to the Z-form with λ ) 559-nm
irradiation, as the Z-forms maintain no absorbance above
530 nm.
- A)e-kt
.
TABLE 3. Hyd r olytic Sta bility of F lu or in a ted
In d olylfu lgid es a fter 336 h a t 22 °C in 70:30 EtOH:H2O
a
a
A/A0
A/A0
Hyd r olytic Sta bility. A notable disadvantage of most
fulgides is their relative instability under humid or moist
conditions. It has been demonstrated that the anhydride
moiety is highly susceptible to hydrolysis.7 Both the Z-
and C-forms of fluorinated indolylfulgide 1 displayed
rapid loss of absorbance at room temperature when
dissolved in a 70:30 ethanol:H2O mixture (Figure 4). The
composition of the ethanol:H2O mixture was dictated by
solubility concerns; higher percentages of water resulted
in precipitation of the fulgimide from solution. Cyclic
fulgide 1C was fully consumed within 45 min, and
irradiation of the resulting solution with 430-nm light
yielded no changes in the UV-vis spectra. No evidence
existed to support C to Z isomerization under the given
reaction conditions. Although fulgide 1Z displayed greater
resistance to hydrolysis than its cyclic counterpart 1C,
it only took 12 h to fully degrade.
In contrast, fluorinated indolylfulgimides 2-9 dis-
played far superior resistance to hydrolysis (Figures 5
and 6). With the exception of N-(nitrophenyl)fulgimide
8, the Z-forms maintained at least 90% of their absor-
bance at λmax after 2 weeks at room temperature in 70:
30 ethanol:H2O (Table 3). Furthermore, fulgimides 2 and
4 showed no decomposition within experimental error.
In general, the Z-forms of fulgimides 7-9 featuring
trifluoromethyl or nitro substituents on the phenyl ring
compd
Z-form
C-form
compd
Z-form
C-form
1
2
3
4
5
b
6
7
8
9
0.986
0.923
0.845
0.901
0.833
0.641
0.591
0.547
c
0.909
0.946
0.913
0.753
0.979
c
0.945
a
Absorbance at λmax relative to initial absorbance after 336 h
b
at room temperature. Both forms of fulgide 1 decomposed fully
within 12 h. c No loss of absorbance within experimental error.
degraded faster than the fluoro-containing compounds.
No clear trend emerged for the hydrolytic stability of
fulgimides 3-6.
Concurrent C-to-Z isomerization complicated measure-
ment of the hydrolytic stability of the C-forms of fulgim-
ides 2-9. The values obtained for the C-forms represent
an upper limit to the rate of hydrolytic degradation,
because loss of absorbance occurred through both hy-
drolysis and isomerization to the Z-forms. Still, each com-
pound maintained at least 55% of its original absorbance
at the C-form λmax after 2 weeks at room temperature in
70:30 ethanol:H2O. The loss in absorbance increased with
increasing electron-withdrawing ability of the substitu-
ents on the phenyl ring. The only exception to this rule
was the N-(difluorophenyl)fulgimide 5, which degraded
faster than pentafluoro-substituted analogue 6.
322 J . Org. Chem., Vol. 68, No. 2, 2003

Optical Properties of Fluorinated Indolylfulgimides
TABLE 4. Th er m a l Sta bility of F lu or in a ted
In d olylfu lgid es in P MMA a t 80 °C
A/A0
C-formb
A/A0
C-formb
compd
Z-forma
compd
Z-forma
1
2
3
4
5
0.550
0.921
0.940
0.897
0.884
0.920
0.974
c
0.891
0.979
6
7
8
9
0.869
0.860
0.891
0.871
0.903
0.897
0.975
0.927
a
Absorbance at λmax relative to initial absorbance after 20 h at
b
80 °C. Absorbance at λmax relative to initial absorbance after 550
h at 80 °C. c No loss of absorbance within experimental error.
F IGURE 7. Thermal degradation of phenyl-substituted in-
dolylfulgimide 3 in PMMA.
The relative hydrolytic stability of the fulgides and
fulgimides will depend on the definition of stability, as
fulgides decompose exponentially and fulgimides do not.
However, the most conservative comparison, that of the
initial rates of hydrolysis, can be made. For fulgides, the
initial rate is k, while for fulgimides, it is (1 - A)k
(Figures 4-6). On the basis of initial rates, the C-forms
of the fulgimides are 3-4 orders of magnitude more
stable and the Z-forms are at least 200-fold more stable
than the corresponding fulgide form. For all compounds,
the C-form was less stable in aqueous environments than
the Z-form and thus likely to be the most vulnerable to
hydrolytic degradation in most applications.
Th er m a l Sta bility. Materials intended for use in
optical memory devices must maintain viability at el-
evated temperatures for extended periods of time. Cur-
rent industry standards such as CD and archival tapes
purport to maintain stability up to 50 °C. The thermal
stability of both the Z- and C-forms of fulgimides 2-9
was measured in poly(methyl methacrylate) (PMMA)
films held at 80 °C (Table 4). The temperature of 80 °C
was chosen to allow direct comparison to previously
studied fulgides, including compound 1Z. Previous stud-
ies have demonstrated the relative instability of indolyl-
fulgide 1 toward thermal stress.5 Indeed, the Z-form of
1 lost nearly half of its absorbance at λmax after only 20
h at 80 °C. Each of the derivatives examined herein
displayed greater thermal stability in the Z-form, high-
lighted by phenyl-substituted fulgimide 2, which lost only
6.0% of its absorbance under identical conditions. It
should be noted that despite the slower degradation
exhibited by the fulgimides, a similar pattern emerged
in the time-dependent UV-vis scans. For each compound,
an initial drop in absorbance is followed by a bathochro-
mic shift and subsequent increase in absorbance (Figure
7). J udging by the similarities between the shifts in the
UV-vis spectra, it can be postulated that the Z-forms of
the fulgimides undergo the same degradative pathway
that has been established for fulgide 1Z, albeit at a slower
rate.20
F IGUR E 8. Thermal degradation of pentafluorophenyl-
substituted indolylfulgimide 6 in PMMA.
F IGURE 9. Photochemical decomposition of 2-5 in toluene,
giving decreasing absorbance with repeated coloration and
bleaching cycles: open squares (2), open triangles (3), crosses
(4), open circles (5). The decomposition of compounds 2, 4, and
5 was fit to an exponential decay.
spectra of indolylfulgimide 6 in PMMA with prolonged
exposure to 80 °C.
P h ot och em ica l St a b ilit y. The repeatability of the
photochemical coloration and bleaching of fluorinated
fulgimides 2-9 was measured in toluene using a method
similar to one previously detailed.5 Ring closure was
initiated with λ ) 410-nm light, while ring opening was
achieved with λ > 530-nm light. Samples were irradiated
to 90% of the photostationary state (PSS410nm) attained
for ring closure, followed by quantitative bleaching as
described by Irie.21 Data were fit to an exponential decay
to determine percent decomposition per photochemical
cycle (Figures 9 and 10). No photodecomposition products
were isolated in the study.
Table 4 also shows the outstanding thermal stability
of the C-forms of fulgimides 2-9. After 1 week at 80 °C,
each compound maintained at least 94% of its initial
absorbance. Fulgimides 3 and 5 showed no loss of
absorption within experimental error after 1 week. The
C-forms of each fulgimide retained at least 89% of its
initial absorbance even after 3 weeks at elevated tem-
perature. Figure 8 shows the change in the absorption
(20) Wolak, M. A.; Sullivan, J . M.; Thomas, C. J .; Finn, R. C.; Birge,
R. R.; Lees, W. J . J . Org. Chem. 2001, 66, 4739-41.
(21) Irie, M. Chem. Rev. (Washington, D. C.) 2000, 100, 1685-1716.
J . Org. Chem, Vol. 68, No. 2, 2003 323

Wolak et al.
A curious anomaly to the exponential-like photochemi-
cal decay was provided by phenyl-substituted fulgimide
3 (Figure 9). For the first 500 cycles, the compound
reproducibly displayed no loss of absorbance at PSS410nm
within experimental error. As the number of cycles
increased, the rate of degradation increased rapidly,
suggesting an autocatalytic mechanism. At this point, the
pathway of photochemical degradation remains unclear.
Con clu sion
Fluorinated indolylfulgimides 2-9 display several at-
tractive characteristics in comparison to parent indolyl-
fulgide 1. Areas of particular interest include enhanced
hydrolytic stability, improvement of the ring-closing
quantum yields, and tunable absorption spectra. For the
most part, the thermal and photochemical stability of the
fluorinated indolylfulgimides remains comparable to the
parent fulgide. Fulgimide 7 loses only 0.006% of its
absorbance per photochemical cycle, making it the most
photochemically robust fulgide derivative reported to
date.
We have demonstrated that the Z- and C-forms of
fulgimides 2-9 are at least 200- to 1000-fold more stable
respectively in aqueous environments than the same form
of fulgide 1. The Z-forms of fulgimides 2 and 4 showed
no loss in absorbance within experimental error after 2
weeks in 70:30 ethanol:H2O. With the augmented hy-
drolytic stability, fulgimides display potential for utiliza-
tion in a variety of environments. Hydrolytic stability is
vital for addressing biological concerns such as photo-
regulation of enzymatic activity.11,23,24 In addition, fulgim-
ides used in optical memory devices are not expected to
show degradative loss under humid conditions.
F IGURE 10. Photochemical decomposition of 6-9 in toluene,
giving decreasing absorbance with repeated coloration and
bleaching cycles: open diamonds (6), filled circles (7), filled
squares (8), filled diamonds (9). Decomposition of compounds
6-9 was fit to an exponential decay.
TABLE 5. P h otoch em ica l F a tigu e Resista n ce of F u lgid e
1 a n d F u lgim id es 2-9 in Tolu en e
no. of
no. of
compd cyclesa A/A0 %/cycle compd cyclesa A/A0 %/cycle
1
2
3
4
5
3000b 0.791 0.007
6
7
8
9
750 0.791 0.031
3000 0.802 0.006
750 0.828 0.025
2000 0.788 0.011
750
2250
1500
1500
0.801 0.028
0.786
0.805 0.014
0.801 0.013
c
a
Number of photochemical cycles attained at 20% loss of
b
absorbance of the PSS. Photochemical fatigue of fulgide 1 was
measured with 436-nm light. c Photochemical decomposition of
N-(phenyl)fulgimide 3 could not be fitted to exponential decay.
Furthermore, the use of substituted phenyl groups
linked to the nitrogen of the succinimide functionality
affords materials with finely tuned spectral character-
istics. Increasing the cumulative electron-withdrawing
ability of the phenyl ring results in predictive bathochro-
mic shifts for the Z-, E-, and C-form spectra. Accordingly,
dinitro-substituted fulgimide 9 has the longest Z-form
absorption maxima of any fulgimide reported to date.
Future compounds can be rationally designed making use
of the predictive model presented herein.
F IGURE 11. Photostationary state absorbances of fulgimide
4 in toluene after the indicated number of cycles.
In general, indolyl-substituted fulgides are more pho-
tochemically robust than fulgides containing other aro-
matic groups.4,22 Additionally, fluorination of the methyl
group attached to the bridging alkene of indolylfulgides
has been shown to provide an enhancement in photo-
chemical fatigue resistance relative to the nonfluorinated
analogue.6 Although the fulgimide derivatives maintain
strong resistance to photochemical degradation, a major-
ity of the compounds failed to match the stability of
parent trifluoromethyl fulgide 1 (Table 5).5 The single
exception was fulgimide 7, highlighted by a degradation
rate of only 0.006% per cycle. No correlation could be
drawn between the percentage decomposition per cycle
and the electronic structure of the substituted phenyl
rings of 3-9. Figure 11 shows the absorption spectrum
of fulgimide 4 as a function of photoconversion in
intervals of 500 photocycles.
Exp er im en ta l Section
Gen er a l P r oced u r es a n d Ma ter ia ls. All commercially
available materials were used without further purification.
NMR spectra were recorded on a 300 MHz NMR spectrometer.
1H and 13C NMR samples were internally referenced to TMS
(0.00 ppm). Flash chromatography was performed with 230-
400 mesh silica gel. E&R Microanalytical Laboratory Inc.
performed all elemental analysis.
The C-forms of compounds 2-9 were obtained by irradiating
Z-form solutions with 427-nm light followed by purification
via flash column chromatography (silica gel:toluene). The
resulting pure C-form solutions were utilized directly for
spectra determination. Fulgimides 2-9 were initially prepared
in the Z-form. The E-forms of compounds 5 and 6 were also
isolated upon separate crystallization.
P r ep a r a tion of F u lgim id es 2 a n d 3 (2 Given a s Rep -
r esen ta tive). To a stirred solution of 1Z (151 mg, 0.42 mmol)
(23) Willner, I.; Rubin, S. React. Polym. 1993, 21, 177-86.
(24) Willner, I.; Rubin, S.; Riklin, A. J . Am. Chem. Soc. 1991, 113,
3321-5.
(22) Liang, Y. C.; Dvornikov, A. S.; Rentzepis, P. M. J . Photochem.
Photobiol., A 1999, 125, 79-84.
324 J . Org. Chem., Vol. 68, No. 2, 2003

Optical Properties of Fluorinated Indolylfulgimides
in THF (40 mL) was added 1,1-dimethylhydrazine (500 µL,
6.6 mmol). The solution was heated to 60 °C and stirred until
the color was lost (approximately 5 min). Solvent was removed
in vacuo and the resulting solid was suspended in toluene (40
mL). Upon addition of 5 mL of acetic anhydride, the solid
immediately dissolved and the solution was tinted orange. The
solution was allowed to stir at 70 °C for 10 min and solvent
was removed in vacuo to yield an orange oil. Purification via
column chromatography (2:1 hexane:ethyl acetate) and crys-
tallization from 4:1 hexane:dichloromethane yielded N-(dim-
ethylamino)fulgimide as a yellow solid (33.5 mg, 20% yield).
3H), 2.30 (q, J ) 1.5 Hz, 3H). C-Form: 1H NMR (CDCl3) δ
7.76 (d, J ) 6.9 Hz, 1H), 7.38 (t, J ) 8.4 Hz, 1H), 7.12-7.04
(m, 2H), 6.83-6.76 (m, 2H), 6.66 (d, J ) 8.4 Hz, 1H), 2.95 (s,
3H), 1.83 (s, 3H), 1.38 (s, 3H), 1.29 (s, 3H).
N-(2,3,4,5,6-P en ta flu or op h en yl)fu lgim id e (6). Z-Form:
53% yield; 1H NMR (CDCl3) δ 7.35-7.13 (m, 4H), 3.72 (s, 3H),
2.28 (s, 3H), 2.16 (s, 3H), 1.04 (s, 3H); 13C NMR (CDCl3) δ
164.2, 162.0, 157.3, 145.7 (m), 143.9 (dm, J CF ) 259 Hz), 142.1
(dm, J CF ) 257 Hz), 138.0 (dm, J CF ) 253 Hz), 137.4, 136.9,
131.3 (q, J CCF ) 36 Hz), 131.0, 125.1, 122.2, 122.2 (q, J CF
)
278 Hz), 122.0, 121.2, 119.5, 109.3, 107.4, 30.1, 26.9, 22.7, 12.0.
Anal. Calcd for C25H16F8N2O2: C, 56.83; H, 3.05; F, 28.76; N,
5.30. Found: C, 56.96; H, 3.06; F, 29.04; N, 5.25. E-Form: 1H
NMR (CDCl3) δ 7.44 (d, J ) 7.8 Hz, 1H), 7.29 (d, J ) 7.8 Hz,
1H), 7.19 (m, 1H) 7.12 (m, 1H), 3.73 (s, 3H), 2.52 (s, 3H), 2.37
(s, 3H), 2.32 (q, J ) 1.5 Hz, 3H). C-Form: 1H NMR (CDCl3) δ
7.76 (d, J ) 7.8 Hz, 1H), 7.39 (t, J ) 7.8 Hz, 1H), 6.81 (t, J )
8.1 Hz, 1H), 6.66 (d, J ) 8.1 Hz, 1H), 2.96 (s, 3H), 1.82 (s,
3H), 1.40 (s, 3H), 1.31 (s, 3H).
N-(Dim eth yla m in o)fu lgim id e (2). Z-Form: 20% yield; 1H
NMR (CDCl3) δ 7.30-7.09 (m, 4H), 3.70 (s, 3H), 3.02 (s, 6H),
2.21 (s, 3H), 2.11 (s, 3H), 0.92 (s, 3H); 13C NMR (CDCl3) δ
165.8, 164.2, 153.7, 136.9, 136.7, 131.8, 125.4, 122.4 (q, J CF
)
278 Hz), 121.9, 121.5, 121.3, 120.9, 119.5, 109.1, 107.2, 44.4,
30.0, 26.4, 22.2, 11.9. Anal.Calcd for C21H22F3N3O2: C, 62.21;
H, 5.47; F, 14.06; N, 10.36. Found: C, 62.08; H, 5.54; F, 14.42;
N, 10.35. C-Form: 1H NMR (CDCl3) δ 7.73 (d, J ) 8.4 Hz,
1H), 7.35 (t, J ) 8.4 Hz, 1H), 6.78 (t, J ) 8.4 Hz, 1H), 6.62 (d,
J ) 8.4 Hz, 1H), 2.93 (s, 6H), 2.91 (s, 3H), 1.78 (s, 3H), 1.32 (s,
3H), 1.23 (s, 3H).
N-(2,3,5,6-Tetr a flu or o-4-tr iflu or om eth ylph en yl)fu lgim -
id e (7). Z-Form: 64% yield; 1H NMR (CDCl3) δ 7.34-7.14 (m,
4H), 3.73 (s, 3H), 2.29 (s, 3H), 2.17 (s, 3H), 1.06 (s, 3H); 13C
NMR (CDCl3) δ 163.6, 161.4, 157.8, 145.1 (m), 144.8 (dm, J CF
) 245 Hz), 143.8 (dm, J CF ) 254 Hz), 137.5, 136.9, 131.7 (q,
J CCF ) 36 Hz), 130.6, 125.0, 122.3, 122.1 (q, J CF ) 278 Hz),
121.5, 121.3, 120.5 (q, J CF ) 266 Hz), 119.5, 115.5, 109.4, 107.3,
30.1, 26.9, 22.8, 12.0. Anal. Calcd for C26H16F10N2O2: C, 53.99;
H, 2.79; F, 32.85; N, 4.84. Found: C, 54.29; H, 3.00; F, 32.85;
N, 4.64. C-Form: 1H NMR (CDCl3) δ 7.76 (d, J ) 8.4 Hz, 1H),
7.40 (t, J ) 8.4 Hz, 1H), 6.81 (t, J ) 8.4 Hz, 1H), 6.67 (d, J )
8.4 Hz, 1H), 2.97 (s, 3H), 1.83 (s, 3H), 1.42 (s, 3H), 1.31 (s,
3H).
N-(P h en yl)fu lgim id e (3). Z-Form: 27% yield; 1H NMR
(CDCl3) δ 7.54-7.37 (m, 5H), 7.34-7.13 (m, 4H), 3.72 (s, 3H),
2.28 (s, 3H), 2.16 (s, 3H), 1.00 (s, 3H); 13C NMR (CDCl3) δ
166.3, 164.1, 154.5, 137.1, 136.8, 132.7, 131.6, 129.3 (q, J CCF
) 36 Hz), 128.9, 128.3, 126.8, 125.4, 122.6, 122.5 (J CF ) 277
Hz), 121.9, 120.9, 119.6, 109.2, 107.6, 29.9, 26.6, 22.4, 12.0.
Anal. Calcd for C25H21F3N2O2: C, 68.49; H, 4.83; F, 13.00; N,
6.39. Found: C, 68.17; H, 4.67; F, 12.71; N, 6.06. C-Form: 1H
NMR (CDCl3) δ 7.76 (d, J ) 8.1 Hz, 1H), 7.49-7.43 (m, 2H),
7.39-7.32 (m, 4H), 6.79 (t, J ) 7.2 Hz, 1H), 6.65 (d, J ) 8.1
Hz, 1H), 2.95 (s, 3H), 1.84 (s, 3H), 1.39 (s, 3H), 1.30 (s, 3H).
P r ep a r a tion of F u lgim id es 4-7 (4 Given a s Rep r esen -
ta tive). To a solution of 1Z (147 mg, 0.40 mmol) with
suspended magnesium sulfate (250 mg) in toluene (40 mL) was
added 4-fluoroaniline (230 mg, 2.1 mmol). The solution was
allowed to stir for 10 min at 50 °C. Sodium hydride (75 mg,
1.9 mmol; 60% dispersion in oil) was added and the solution
allowed to stir for 4 h at 50 °C. To the now colorless solution
was added 25 mL of acetic anhydride. The solution im-
mediately turned orange and was allowed to stir for an
additional 30 min at 50 °C. Precipitates were then filtered off,
and the solvent was removed in vacuo to yield an orange solid.
Purification via flash chromatography (CH2Cl2) and crystal-
lization from ligroin and dichloromethane provided N-(4-
fluorophenyl)fulgimide as bright orange crystals (65.8 mg, 36%
yield).
P r ep a r a tion of F u lgim id es 8 a n d 9 (8 Given a s Rep -
r esen ta tive). To a stirred solution of 1Z (175 mg, 0.48 mmol)
in DMF (30 mL) at 0 °C was added 4-nitroaniline (80 mg, 0.58
mmol). LDA (0.5 mL, 2.0 M solution) was added and the
solution immediately turned red. After 14 h at room temper-
ature the solvent was removed in vacuo and the resulting solid
was suspended in toluene (10 mL). Acetic anhydride (5 mL)
was then added and the resulting orange solution was allowed
to stir at room temperature for 1 h before the solvent was
removed in vacuo. Purification via flash chromatography (2:1
hexane:ethyl acetate) and crystallization from 2-propanol
provided N-(4-nitrophenyl)fulgimide as bright orange crystals
(89 mg, 38% yield).
1
N-(4-Nitr op h en yl)fu lgim id e (8). Z-Form: 38% yield; H
NMR (CDCl3) δ 8.39-8.32 (m, 2H), 7.79-7.72 (m, 2H), 7.34-
7.14 (m, 4H), 3.72 (s, 3H), 2.30 (s, 3H), 2.16 (s, 3H), 1.02 (s,
3H); 13C NMR (CDCl3) δ 165.4, 163.4, 156.3, 146.6, 137.4,
137.3, 136.8, 131.3, 130.3 (q, J CCF ) 32 Hz), 127.2, 125.1, 124.1,
122.1, 122.3 (q, J CF ) 276 Hz), 122.0, 121.1, 119.5, 109.3, 107.4,
30.1, 26.8, 22.7, 12.2. Anal. Calcd for C25H20F3N3O4: C, 62.11;
H, 4.17; F, 11.79; N, 8.69. Found: C, 61.88; H, 4.27; F, 11.94;
N, 8.51. C-Form: 1H NMR (CDCl3) δ 8.15 (d, J ) 9.0 Hz, 2H),
7.77 (d, J ) 8.4 Hz, 1H), 7.71 (d, J ) 9.0 Hz, 2H), 7.39 (t, J )
7.8 Hz, 1H), 6.82 (t, J ) 7.8 Hz, 1H), 6.67 (d, J ) 8.4 Hz, 1H),
2.97 (s, 3H), 1.85 (s, 3H), 1.40 (s, 3H), 1.30 (s, 3H).
N-(2,4-Din itr op h en yl)fu lgim id e (9). Z-Form: 17% yield;
1H NMR (CDCl3) δ 9.00 (d, J ) 2.3 Hz, 1H), 8.59 (dd, J ) 8.7,
2.3 Hz, 1H), 7.85 (d, J ) 8.7 Hz, 1H), 7.80-7.48 (m, 4H), 3.72
(s, 3H), 2.32 (s, 3H), 2.17 (s, 3H), 1.06 (s, 3H); 13C NMR (CDCl3)
δ 164.6, 162.3, 157.7, 147.1, 145.4, 137.7, 136.9, 131.8, 131.4,
130.8, 127.9, 125.5, 122.2 (q, J CF ) 278 Hz), 122.1, 121.8, 121.3,
119.7, 109.3, 107.5, 30.1, 27.2, 22.8, 11.7. Anal. Calcd for
N-(4-F lu or op h en yl)fu lgim id e (4). Z-Form: 36% yield; 1H
NMR (CDCl3) δ 7.49-7.37 (m, 2H), 7.35-7.13 (m, 6H), 3.72
(s, 3H), 2.28 (s, 3H), 2.15 (s, 3H), 1.00 (s, 3H); 13C NMR (CDCl3)
δ 166.2, 164.0, 162.0 (d, J CF ) 249 Hz), 154.7, 137.0, 136.8,
132.3, 129.8, 128.7, 128.6, 127.5, 125.3, 122.5, 122.4 (q, J CF
)
278 Hz), 120.9, 119.6, 115.9 (d, J CCF ) 24 Hz), 109.2, 107.8,
30.0, 26.7, 22.4, 12.0. Anal. Calcd for C25H20F4N2O2: C, 65.79;
H, 4.42; F, 16.65; N, 6.14. Found: C, 66.01; H, 4.38; F, 16.98;
N, 5.93. C-Form: 1H NMR (CDCl3) δ 7.75 (d, J ) 8.4 Hz, 1H),
7.40-7.33 (m, 3H), 7.17-7.11 (m, 2H), 6.80 (t, J ) 7.5 Hz, 1H),
6.65 (d, J ) 8.4 Hz, 1H), 2.95 (s, 3H), 1.83 (s, 3H), 1.38 (s,
3H), 1.29 (s, 3H).
N-(3,5-Diflu or op h en yl)fu lgim id e (5). Z-Form: 11% yield;
1H NMR (CDCl3) δ 7.35-7.11 (m, 6H), 6.92-6.82 (m, 1H), 3.71
(s, 3H), 2.28 (s, 3H), 2.16 (s, 3H), 1.01 (s, 3H); 13C NMR (CDCl3)
δ 165.5, 163.4, 162.7 (dd, J CF ) 249 Hz, J CCCF ) 14 Hz), 155.8,
C
25H19F3N4O6: C, 56.82; H, 3.62; F, 10.79; N, 10.60. Found:
137.3, 136.8, 133.4 (t, J CCCF ) 14 Hz), 131.5, 130.4 (q, J CCF
35 Hz), 125.2, 122.4 (q, J CF ) 278 Hz), 122.1, 121.0, 119.5,
110.3, 110.2 (d, J CCF ) 27 Hz), 110.1, 109.3, 103.8 (t, J CCF
)
C, 56.58; H, 3.57; F, 10.67; N, 10.43. C-Form: 1H NMR (CDCl3)
δ 8.98 (d, J ) 2.4 Hz, 1H), 8.59 (dd, J ) 9.0, 2.4 Hz, 1H), 7.76
(d, J ) 9.0 Hz, 2H), 7.40 (t, J ) 8.1 Hz, 1H), 6.82 (t, J ) 8.1
Hz, 1H), 6.67 (d, J ) 8.1 Hz, 1H), 2.97 (s, 3H), 1.81 (s, 3H),
1.45 (s, 3H), 1.31 (s, 3H).
)
25 Hz), 30.0, 26.8, 22.6, 12.1. Anal. Calcd for C25H19F5N2O2:
C, 63.29; H, 4.04; F, 20.02; N, 5.90. Found: C, 63.36; H, 3.94;
F, 20.39; N, 5.78. E-Form: 1H NMR (CDCl3) δ 7.44 (d, J ) 7.8
Hz, 1H), 7.30 (d, J ) 7.8 Hz, 1H), 7.20 (m, 1H), 7.12 (m, 1H),
6.91 (m, 2H), 6.75 (m, 1H), 3.74 (s, 3H), 2.52 (s, 3H), 2.38 (s,
P r ep a r a tion of Th in F ilm s. An initial solution was
prepared by adding 2-4 mg of fulgimide to a solution of 10%
J . Org. Chem, Vol. 68, No. 2, 2003 325

Wolak et al.
poly(methyl methacrylate) (PMMA, low molecular weight,
average Mw ca. 120 000) in CH2Cl2 (5 mL). The polymer
solution (1.5 mL) was then deposited via pipet onto circular 1
The isomers were separated using a Waters Spherisorb S5 W
column with 85:15 hexane:dioxane as the eluent at a flow rate
of 2.7 mL/min. A 1:1:1 mixture of the three isomers in toluene
was analyzed via HPLC to ascertain their relative extinction
coefficients in the HPLC solvent. Where applicable, quantum
yields for ΦZE and ΦCZ at 427 nm were determined from the
photostationary state measurements.
P h otoch em ica l Sta bility. Air-saturated solutions of the
Z-form of fulgimides 2-9 were prepared in toluene with an
initial absorbance of 0.6 at the absorption maxima. Samples
were irradiated to the photostationary state with light supplied
from an Oriel 200 W Hg(Xe) lamp utilizing a 410-nm narrow
band-pass filter. After measuring the UV-vis spectra of the
PSS410nm mixture, a pure Z-form solution was irradiated to 90%
of the PSS and the reaction was timed. The 90% PSS mixture
was then bleached with >530-nm light using a separate filter
and again the reaction was timed. Absorbance at the C-form
λmax was <0.01 upon bleaching.
1
in. × /16 in. BK-7 glass slides (escoproducts) and allowed to
spread over the surface of the slide. The sample was allowed
to dry overnight at room temperature. The resulting films
varied in thickness from 100 to 200 µm and were utilized in
the thermal stability studies.
Spectr a Deter m in ation . Concentrated, air-saturated stock
solutions of the Z-form of fulgimides 2-9 and the E-form of
fulgimides 5 and 6 in toluene were prepared in duplicate or
triplicate. From each stock solution, five samples ranging in
concentration from 0.20 to 0.05 mM were then prepared by
dilution with toluene. Absorption coefficients and λmax were
determined. E-form spectra for compounds 2-4 and 7-9 were
obtained via spectral subtraction of an E/Z mixture in toluene-
d8 generated by irradiation with 350-nm light and bleached
with 580-nm light to eliminate C-form. The relative concentra-
tions of the E- and Z-forms were determined via 1H NMR.
Stock solutions containing freshly purified C-form in toluene
(see General Procedures and Materials) were diluted to four
or five different concentrations and their UV-vis spectra
obtained. Each C-form solution was then quantitatively con-
verted to Z-form with 580-nm light and the concentration of
fulgimide present was ascertained using the predetermined
Z-form extinction coefficients. Absorption coefficients and λmax
for the C-forms were then determined from the initial spectra.
Once the duration of irradiation was established for both
the 90% PSS coloration and <1% C-form bleaching reactions,
the system was automated through use of a filter switch. All
solutions were capped and stirred. Control experiments were
performed to correct for evaporation. After
a designated
number of irradiation cycles, the samples were fully converted
to PSS410nm and their UV-vis spectra scanned. The photo-
chemical fatigue was then determined by comparison with the
initial PSS410nm absorption spectrum.
Qu a n tu m Yield s. Quantum yields for ring closing (ΦZC
)
Th er m a l Sta bility. Thin films containing either the Z- or
C-form of fulgimides 2-9 were wrapped in aluminum foil and
placed in an oven maintained at 80 °C. The films were removed
at prescribed intervals and their UV-vis spectra measured.
The films were monitored for the shorter of 10 d or until no
further changes occurred in the UV-vis spectra.
Hyd r olytic Sta bility. Solutions of approximately 0.1 mM
concentration of both the Z- and C-forms of fulgide 1 and
fulgimides 2-9 were prepared in a 70:30 ethanol:H2O mixture.
Samples were transferred to 3.0 mL stoppered cuvettes and
wrapped in Teflon tape and Parafilm to prevent evaporative
loss. Initial UV-vis spectra were obtained and solutions were
then placed in the dark. At prescribed intervals, the solutions
were removed and their UV-vis spectra scanned. Samples
were monitored for loss of absorbance for the shorter of 450 h
or until fully decomposed.
and E-to-Z photoisomerization reactions (ΦEZ) were deter-
mined with monochromatic light of wavelength 427 nm.
Quantum yields for ring-opening reactions (ΦCZ) were deter-
mined with monochromatic light of wavelength 559 nm.
Determination of quantum yields for the Z-to-E photoreaction
(φZE) is detailed in the following section. A Coherent Infinity
XPO laser served as the radiation source for all quantum yield
experiments.
Air-saturated solutions of fulgimides 2-9 were prepared in
toluene with an approximate concentration of 0.1 mM. Samples
were irradiated to between 5 and 10% conversion as deter-
mined by HPLC and UV-vis. Coherent LMP-2 energy detec-
tors measured the amount of light absorbed by the fulgimide
solution in comparison to a toluene blank. Separation of
isomers for the coloration and bleaching reactions was achieved
using a Waters Spherisorb S5 W column with toluene as the
eluent at a flow rate of 4.0 mL/min. Separation of isomers for
the E-to-Z photoisomerization reaction was achieved using the
same column with 85:15 hexane:dioxane as the eluent at a
flow rate of 2.7 mL/min. The apparatus was calibrated with
the chemical actinometer trioxalatoferrate(III) and Aber-
chrome 540, a furylfulgide.
Ack n ow led gm en t. Financial support from the Na-
tional Science Foundation (NSF CHE9975076 to W.J.L.),
the Army Research Office (MURI program, DAAD19-
99-1-0198 to R.R.B.), and the NSF Qubic program (NSF
EIA0129731 to R.R.B.) is gratefully acknowledged. We
would also like to thank Dr. Michael Sponsler for his
insightful comments.
P h otosta tion a r y Sta te Mea su r em en ts. Fulgimides 2-9
were irradiated with 427-nm light supplied by a Coherent
Infinity XPO laser and their isomeric ratios monitored via
HPLC until a photostationary state (PSS427nm) was attained.
J O026374N
326 J . Org. Chem., Vol. 68, No. 2, 2003