Quantum amplified isomerization in polymers based on triplet chain reactions

Article abstract of DOI:10.1021/jo8007786

(Graph Presented) Photoinitiated triplet quantum amplified isomerizations (QAI) of substituted Dewar benzene derivatives in polymeric media are reported. The quantum efficiencies and the ultimate extents of reactant-to-product conversions increase significantly with the incorporation of appropriate co-sensitizers; compounds whose triplet energies are similar to or lower than that of the sensitizer and close to that of the reactant. These co-sensitizers serve to promote chain-propagating energy transfer processes and thereby increase the action sphere of photosensitization. Isomerization quantum yields increase, as predicted, with increasing concentrations of the reactants and the co-sensitizers. Chain amplifications as large as ～16 and extents of conversion that approach 100% have been achieved. Mechanistic schemes are proposed to account for the dynamics of the inherent energy transfer processes and provide a predictively useful model for the design of a new class of photoresponsive polymers based on changes in the refractive index of the materials.

Full text of DOI:10.1021/jo8007786

Quantum Amplified Isomerization in Polymers Based on Triplet
Chain Reactions
Lorraine Ferrar,† Mark Mis,† Joseph P. Dinnocenzo,*,‡ Samir Farid,*,‡ Paul B. Merkel,*,‡
and Douglas R. Robello*,†
Department of Chemistry and the Center for Photoinduced Charge Transfer, UniVersity of Rochester,
Rochester, New York 14627-0216, and Research Laboratories, Eastman Kodak Company,
Rochester, New York 14650-2116
jpd@chem.rochester.edu; farid@chem.rochester.edu; pmerkel@rochester.rr.com;
douglas.robello@kodak.com
ReceiVed April 7, 2008
Photoinitiated triplet quantum amplified isomerizations (QAI) of substituted Dewar benzene derivatives
in polymeric media are reported. The quantum efficiencies and the ultimate extents of reactant-to-product
conversions increase significantly with the incorporation of appropriate co-sensitizers; compounds whose
triplet energies are similar to or lower than that of the sensitizer and close to that of the reactant. These
co-sensitizers serve to promote chain-propagating energy transfer processes and thereby increase the
action sphere of photosensitization. Isomerization quantum yields increase, as predicted, with increasing
concentrations of the reactants and the co-sensitizers. Chain amplifications as large as ∼16 and extents
of conversion that approach 100% have been achieved. Mechanistic schemes are proposed to account
for the dynamics of the inherent energy transfer processes and provide a predictively useful model for
the design of a new class of photoresponsive polymers based on changes in the refractive index of the
materials.
Introduction
can lead to large changes in refractive index that can be exploited
for optical recording applications.2 For example, the isomer-
ization of hexamethyl Dewar benzene (DB1) to the correspond-
ing benzene product (B1) is accompanied by a large change in
refractive index (∆n ∼ 0.04).2d Although this photoinduced
electron-transfer reaction was known to proceed with high
We recently described a new class of photoresponsive
polymeric materials based on a concept called quantum ampli-
fied isomerization (QAI).1 These QAI materials were based on
photoinitiated electron-transfer isomerizations that proceed via
chain reactions. When appropriately designed, the isomerizations
(1) Gillmore, J. G.; Neiser, J. D.; McManus, K. A.; Roh, Y.; Dombrowski,
G. W.; Brown, T. G.; Dinnocenzo, J. P.; Farid, S.; Robello, D. R. Macromolecules
2005, 38, 7684.
† Eastman Kodak.
‡ University of Rochester.
10.1021/jo8007786 CCC: $40.75
Published on Web 07/02/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 5683–5692 5683

Ferrar et al.
SCHEME 1. Key Reactions in Quantum Amplified
Isomerization of a Reactant, R, to a Product, P, via Triplet
Energy Transfer Induced by a Triplet Sensitizer, Sa
SCHEME 2. Schematic Representation of Triplet-Sensitized
Isomerization of Dewar Benzenes in Polymeric Matricesa
a The asterisks here and throughout the paper denote triplet excited states.
a The square represents a sensitizer molecule. At various stages in the
energy transfer/isomerization sequence the circles represent ground and
triplet states: R, R*, P*, and P. See text for details.
quantum yield in polar solvents,3 the reaction proceeded with
only limited amplification in polymeric matrices. The lower
quantum yield in polymers was attributed to the Coulombic
barrier for charge separation of the radical ion pair intermediates
that is required for efficient chain propagation.1 Thus, in
polymeric media, chain-terminating return electron transfer
strongly competes with chain propagation.
the reaction to quenching by impurities. The magnitude of the
drop in quantum yield, however, was dramatic. The detailed
kinetics we reported for the reaction in ethyl acetate offered an
explanation for the large difference in quantum yields and
potential ways to increase the efficiencies in polymers.
To circumvent the Coulombic restrictions for chain ampli-
fication of electron-transfer QAI processes in polymers we
considered the possibility of using QAI reactions based on
energy transfer instead of electron transfer. Toward that goal
we explored the triplet-sensitized, quantum chain isomerization
of Dewar benzene derivatives in fluid solution and found Dewar
benzene derivatives DB2 and DB3 to be excellent candidates.4
Chain amplifications for DB2 and DB3 in excess of 100 were
achieved via triplet, quantum chain reactions in solution.
Importantly, adiabatic isomerizations of triplet reactants (R*)
to the triplet products (P*) were found to occur with efficiencies
near unity (Scheme 1). Furthermore, because the triplet energy
of P is higher than that of R, the quantum chain is further
propagated by energy transfer from P* to another R. Extensive
kinetic studies of the quantum chain isomerizations of DB2 and
DB3 were conducted in fluid media to fully understand the
energetic and kinetic requirements for efficient reaction.4 The
insight gained from these studies was used to address new
challenges encountered when the reactions were carried out in
polymeric media. The mechanistic and kinetic aspects used in
the design of efficient systems are the subject of this paper.
We have shown that, following adiabatic isomerization of
an excited reactant molecule R* to an excited product molecule
P*, the rate for chain propagation involving energy transfer from
P* to another R is a slow process.4 For example, in the case of
DB2, the rate constant in ethyl acetate is only 2.3 × 107 M-1
s-1; nearly 50 times less than the rate constant for energy transfer
from P* to DETX (1.2 × 109 M-1 s-1). The small rate constant
for energy transfer from P* to R is due to large differences in
the nuclear configurations of R and R*, as well as smaller
differences between those of P and P*. Whenever energy transfer
between two molecules involves reorganization of both donor
and acceptor the rate constant is considerably reduced, even
with modest exothermicity.5 We now consider the consequences
of these kinetic processes in a polymeric matrix where diffusion
is highly restricted (Scheme 2).
The arrows in Scheme 2 denote the direction of triplet energy
transfer. Following energy transfer from an excited sensitizer,
S*, to an adjacent R (reaction 1) and adiabatic R* f P*
isomerization, chain propagation through energy transfer from
P* to an adjacent R is expected to be much slower than the
back energy transfer to the sensitizer (P* + S f P + S*,
(2) (a) Robello, D. R.; Dinnocenzo, J. P.; Farid, S.; Gillmore, J. G.; Thomas,
S. W., III Polym. Prepr. 2001, 42, 717. (b) Robello, D. R.; Farid, S.; Dinnocenzo,
J. P.; Gillmore, J. G. Polym. Prepr. 2002, 43, 163. (c) Robello, D. R.; Dinnocenzo,
J. P.; Farid, S.; Gillmore, J. G.; Thomas, S. W., III. Quantum Amplified
Isomerization: A New Chemically Amplified Imaging System in Solid Polymers.
In Chromogenic Phenomena in Polymers; Jenekhe, S. A., ; Kiserow, D. J., Eds.;
American Chemical Society: Washington, DC; 2004; pp 135-146. (d) Robello,
D. R.; Farid, S. Y.; Dinnocenzo, J. P.; Brown, T. G. Proc. SPIE (Org. Photon.
Mater. DeV. VIII) 2006, 61170F/1. (e) Robello, D. R.; Ferrar, L.; Mis, M.; Brown,
T. G.; Li, Y. Polym. Prepr. 2007, 48, 155. (f) Dinnocenzo, J. P; Farid, S. Y.;
Robello, D. R.; Erdogan, T. Optical Recording Material. U.S. Patent 6,569,600,
2003. (g) Robello, D. R.; Farid, S. Y.; Dinnocenzo, J. P.; Gillmore, J. G. Optical
Recording Material. US Patent 6,969,578, 2005.
Results and Discussion
Molecularly-Doped Polymers. We began our investigation
of the triplet-sensitized isomerization of Dewar benzenes DB2
and DB3 in polymeric matrices by molecularly doping the
reactant, sensitizer, and other additives in a binder of poly-
(methyl methacrylate), PMMA. Irradiation of a 20 µm film of
DB2 (10 wt %) in PMMA sensitized with 2,4-diethylthioxan-
thone (DETX) showed an isomerization quantum yield of 2.2
at low conversion, in contrast to the quantum yield of ∼100
for DB2 in ethyl acetate.4 The markedly lower quantum yield
in polymer solution was not entirely surprising given the
restricted mobility in polymers and the greater susceptibility of
(3) Evans, T. R.; Wake, R. W.; Sifain, M. M. Tetrahedron Lett. 1973, 701.
(4) Merkel, P. B.; Roh, Y.; Dinnocenzo, J. P.; Robello, D. R.; Farid, S. J.
Phys. Chem. A 2007, 111, 1188. For triplet sensitized isomerization of
unsubstituted Dewar benzene, see: Turro, N. J.; Ramamurthy, V.; Katz, T. J.
NouV. J. Chem. 1977, 1, 363.
(5) Saltiel, J.; Wang, S.; Ko, D.-H.; Gormin, D. A. J. Phys. Chem. A 1998,
102, 5383.
5684 J. Org. Chem. Vol. 73, No. 15, 2008

Quantum Amplified Isomerization in Polymers
energies similar to that of DB2 (ET ) 60 kcal/mol).4 These co-
sensitizers led to an increase in quantum yield by a factor of
∼2, to 5.3, at the modest level of 5 wt % of co-sensitizer. Similar
behavior was observed in a limited set of data for DB3 with
DETX as sensitizer (Figure 2). In both cases, quantum yield
enhancement occurs only when the triplet energy of C is <60
kcal/mol, i.e., when the energy transfer from P* (ET ∼ 69 kcal/
mol)4 to C (reaction 7, Scheme 3) starts to compete favorably
with the back energy transfer from P* to S (reaction 4). As
shown in Figure 1, the effect of the co-sensitizer decreased when
its triplet energy became lower than that of the reactant, where
it begins to act as a triplet quencher.
SCHEME 3. Schematic Representation of Triplet-Sensitized
Isomerization of Dewar Benzenes in the Presence of a
Co-sensitizer (C)a
a As in Scheme 2, at various stages in the energy transfer/isomerization
sequence the circles represent R, R*, P* and P. See text for explanation of
the different reactions.
Interestingly, when photoisomerization of DB3 was sensitized
with the ketocoumarin derivative, KC, a slight increase in
quantum yield was observed even with co-sensitizers with triplet
energies higher than that of the sensitizer (Figure 3). This
behavior can be explained in terms of energy transfer from P*
to C (reaction 7 in Scheme 3) and the follow-up reactions 8-10,
discussed above.7
reaction 2), as mentioned above. In fluid solution this process
is a relatively minor contributor due to rapid diffusional
separation of S and P*. Diffusion in the rigid polymer medium
is highly restricted and, therefore, return energy transfer from
P* to S is expected to predominate. Thus, further chain
propagation will proceed by subsequent energy transfer from
S* to another adjacent R, followed by similar steps as before
(reactions 3 and 4). Importantly, after the R molecules in the
immediate vicinity of the sensitizer have been converted to P
molecules, the chain is likely to terminate because energy
transfer from S* to P is highly endothermic and energy transfer
from S* to more remote R molecules will be slow. Thus, in
this situation, the excited sensitizer will simply undergo
deactivation back to the ground state. We describe next a
materials strategy that mitigates this limitation.
Co-sensitization. Promotion of energy transfer beyond the
immediate vicinity of the sensitizer was achieved through use
of a co-sensitizer (C). As shown in Scheme 3, the function of
the co-sensitizer is to act as a chemically unreactive species
that facilitates energy transfer from the sensitizer to reactants,
first by energy transfer from S* to C (reaction 5) and,
subsequently, by energy transfer from C* to an R that is further
removed from S (reaction 6). This alternate route for energy
transfer to R can extend the chain and expand the “action
sphere” of the sensitizer. Similarly, energy transfer from P* to
C (reaction 7) can compete with return energy transfer to S
(reaction 4) and extend the chain through energy transfer from
C* to a more remote R (reaction 8), followed by return energy
transfer from P* to C (reaction 9) and, potentially, additional
energy transfer to another R (reaction 10). To function according
to the design of Scheme 3, the co-sensitizer (C) must have a
triplet energy similar to or lower than that of the sensitizer and
close to that of the reactant to facilitate energy transfer from
C* to R. In addition, the co-sensitizer should be a fairly rigid
molecule with minimal structural differences between its ground
and triplet states; otherwise, its reorganization energy will slow
the energy transfer rates to and from C (e.g., reactions 5-7).
Finally, the co-sensitizer should have a long triplet lifetime to
minimize chain-terminating deactivation to the ground state.
Quantum Yields. The effects of a variety of co-sensitizers
with different triplet energies (ET) on the quantum yields for
isomerization of DB2 and DB3 in PMMA were determined
where the reactant concentration (10 wt %) and co-sensitizer
concentration (5 wt %) were held constant. The results are listed
in Table 1 and graphically illustrated in Figures 1-3.
Attainable Conversion. In addition to increasing the isomer-
ization quantum yields, the co-sensitizers can also increase the
attainable levels of reactant-to-product conversion. This effect
is illustrated in Figure 4 for the DETX- and KC-sensitized
reactions of DB3 at 10 wt % of reactant and 5 wt % of co-
sensitizer in PMMA (see also Table 1). Cosensitizers with ET
> 60 kcal/mol have a relatively small effect on the extent of
conversion. As noted above, co-sensitizers in this energy range
also have only a small effect on the isomerization quantum yield
for DB3. Thus, not surprisingly, the effect on attainable
conversion is also limited in this range of co-sensitizer energies.
As also noted earlier, with high-energy co-sensitizers energy
transfer to C is only possible from P* (reaction 7, Scheme 3)
and, therefore, only partially promotes an increase in quantum
yield and extent of conversion. As a result, the conversion of
DB3 sensitized by KC only increases modestly from ∼32%
without co-sensitizer to ∼55% for co-sensitizers with ET > 60
kcal/mol. With decreasing ET of the co-sensitizer, however, the
conversions increase significantly. In this energy range, energy
transfer can also occur from S* to C (reaction 5, Scheme 3),
thus further increasing the quantum yield and the extent of
conversion. We note that the higher attainable conversion with
DETX vs KC is simply due to the higher concentration of the
former (0.14 vs 0.013 mol/kg, respectively), which was neces-
sitated by the lower extinction coefficient of DETX at the
excitation wavelength.
Concentration Effects. The efficiencies of the quantum chain
reactions described above are expected to increase with increas-
ing concentration of both the reactants and the co-sensitizers.
The effect of reactant concentration was tested using DB3 with
KC as sensitizer. The concentration of DB3 was varied, while
keeping the sum of DB3 plus di-n-butyl phthalate constant at
15 wt % to minimize potential effects of plasticization of the
polymer and variations in the glass transition temperatures (Tg)
of the molecularly doped polymers. At DB3 concentrations of
5, 10, and 15 wt %, the quantum yields increased from 0.8 to
1.7 to 2.6, respectively.
(6) Merkel, P. B.; Dinnocenzo, J. P. J. Photochem. Photobiol. A: Chem. 2008,
193, 110.
As predicted based on the proposed co-sensitization mech-
anism in Scheme 3, the maximum enhancement on the isomer-
ization quantum yield for DB2 with DETX as a sensitizer
(Figure 1) was achieved with co-sensitizers that have triplet
(7) The lack of this effect for the DETX-sensitized reactions is likely due to
the higher concentration of DETX (∼4 wt %) which will tend to favor energy
transfer to nearby sensitizers (P* + S f P + S*) over energy transfer to nearby
co-sensitizers (P* + C f P + C*) when ET(C) > ET(S) and [S] ≈ [C].
J. Org. Chem. Vol. 73, No. 15, 2008 5685

Ferrar et al.
TABLE 1. Isomerization Quantum Yields (Φisom) and Maximum Attainable Conversions of Dewar Benzenes DB2 and DB3 Doped in PMMA
at 10 wt % and Sensitized with DETX or KC as a Function Triplet Energies (ET) of Co-sensitizers, Added at 5 wt %
b
a Reference 6. Measured at 10-15% conversion and corrected for incomplete light absorption, error limits <0.2. Excitation at 405 nm (6 × 10-8
Einstein/min per cm2). c Attainable conversion upon prolonged exposure. Average values from several measurements ((3%). d When the triplet energy
of C is much lower than that of R, C acts as a quencher instead of a co-sensitizer.
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Quantum Amplified Isomerization in Polymers
FIGURE 1. Isomerization quantum yield of DB2 (10 wt %) in PMMA
sensitized with DETX (0.14 mol/kg) as a function of the triplet energy
(ET, Table 1) of added co-sensitizer (5 wt %) measured at ∼10%
conversion (data from Table 1).
FIGURE 4. Attainable conversion of DB3 (molecularly doped in
PMMA at 10 wt %) as a function of the triplet energy of the
co-sensitizer (5 wt %) using DETX (0.14 mol/ kg), unfilled circles, or
KC (0.013 mol/kg), filled circles.
FIGURE 2. Isomerization quantum yield of DB3 (10 wt %) in PMMA
sensitized with DETX (0.14 mol/kg) as a function of the triplet energy
(ET, Table 1) of added co-sensitizer (5 wt %) measured at ∼10%
conversion.
FIGURE 5. Conversion of DB3 (molecularly doped in PMMA at 10
wt %), sensitized with KC, as a function of time at varying concentra-
tions (0-8 wt %) of ethyl 1-naphthoate as co-sensitizer.
FIGURE 6. Isomerization quantum yield of DB3 (molecularly doped
in PMMA at 10 wt %), sensitized with KC, as a function of co-sensitizer
(ethyl 1-naphthoate) concentration.
FIGURE 3. Isomerization quantum yield of DB3 (10 wt %) in PMMA
sensitized with KC (0.013 mol/kg) as a function of the triplet energy
of added co-sensitizers (Table 1, 5 wt %) measured at ∼10%
conversion.
absence of co-sensitizer to ∼92% in the presence of 8 wt % of
ethyl 1-naphthoate. The significant effect of the co-sensitizer
concentration on the initial quantum yield (at ∼10% conversion)
is evident from the change in initial slope in Figure 5 and is
plotted in Figure 6. The quantum yield increased more than 4
fold, from ∼1.5 without co-sensitizer to ∼6.8 with 8 wt % co-
sensitizer.
The effect of co-sensitizer concentration on the quantum yield
was evaluated in the KC-sensitized reactions of DB3 in the
presence of various amounts of ethyl 1-naphthoate. Figure 5
shows the dramatic effect of co-sensitizer concentration on the
attainable conversion, which increased from ∼32% in the
J. Org. Chem. Vol. 73, No. 15, 2008 5687

Ferrar et al.
SCHEME 4. Schematic Representation of Triplet-Sensitized
Isomerization of Dewar Benzenes from a Long-Lived Triplet
Sensitizer (S) That Can Lead to Energy Transfer over a
Long Distance (Reaction 11, at the Inner Dashed Circle),
Followed by Further Energy Propagation to Reactants at
Even Longer Distance from the Sensitizer (Reaction 12, at
the Outer Dashed Circle)a
Effective Action Sphere. The attainable conversion can be
used to evaluate the “action sphere” of the sensitizer, i.e., the
average, maximum distance from the center of a sensitizer
molecule at which isomerization occurs. The size of the action
sphere and the effect of co-sensitizers on increasing the
attainable conversion will be discussed in terms of its mecha-
nistic implications.
In the photoisomerization of DB3 in PMMA with KC as
sensitizer, the average volume per sensitizer can be readily
calculated from its concentration (0.013 mol/kg) to be ∼106000
Å3. Thus, a conversion level of ∼32% for KC in the absence
of co-sensitizer corresponds to an action sphere of ∼34000 Å3
with a radius ∼20 Å. This large action sphere is partially reflective
of the long lifetime of triplet KC* in PMMA (τ ∼0.13 s). The
Dexter model8 can be used to estimate the KC/DB3 distance at
which the rate constant for triplet energy transfer is equal to 1/ τ
of ∼8 s-1. According to this model, the rate constant for triplet
energy transfer, k(r), as a function of donor/acceptor separation
distance, r, may be expressed by eq 1, where k0 is the rate constant
for triplet energy transfer from a donor to an acceptor in physical
contact, r0 is the contact distance between donor and acceptor
centers, and L is an orbital size factor.
a As in Scheme 1, at various stages in the energy transfer/isomerization
sequence the circles represent R, R*, P*, and P. See text for detailed
explanation.
k(r) ) k0 exp[-2(r - r0) ⁄ L]
(1)
in the presence of 5 wt % of co-sensitizers that have triplet
energies >60 kcal/mol. A 55% conversion corresponds to an
action sphere radius of ∼24 Å, i.e. ∼4 Å longer than that in
the absence of a co-sensitizer.12 The increase in the action sphere
for co-sensitizers in this energy range can be explained by a
process similar to reaction 11 in Scheme 4, except where energy
transfer occurs from P* to a nearby co-sensitizer, which is
followed by energy transfer from C* to a nearby reactant
molecule at further distance from the sensitizer.
As is shown in Figure 4, the attainable conversion increases
substantially with decreasing co-sensitizer triplet energy from
60 to 58 kcal/mol and levels off at lower ET. The increase in
attainable conversion is also accompanied by a substantial
increase in the initial quantum yield (Figure 3). As explained
above (Scheme 3), the incremental increase in both conversion
and quantum yield within this narrow range of co-sensitizer
triplet energies is attributable to the added contribution of energy
transfer from S* to C, which can lead to further chain
propagation.
Thus, overall, the net effect of co-sensitizers is to enhance
the migration of energy away from the sensitizer, thereby,
increasing the action sphere and the isomerization quantum
yield. As shown in Figure 5, nearly complete conversion
(∼92%) of DB3 can be achieved with 8 wt % co-sensitizer,
which corresponds to an action sphere with a radius of ∼29 Å.
The effects of co-sensitization on the reaction efficiencies and
conversion can also be observed when the co-sensitizer is
covalently attached to the polymer backbone, as described
below.
Functionalized Polymers. Attempts to continue increasing
the quantum yields for QAI materials by further increases in
co-sensitizer concentration have practical limits with molecularly
doped polymers due to the effects of plasticization that lower
the glass transition temperature and lead to tacky films. Several
functionalized polymers were synthesized (see the Experimental
From our solution energy transfer measurements k0 is
estimated to be ∼109 s-1 for energy transfer from KC* to DB3.9
A value of 7 Å may be used for r0 and L is typically ∼1 Å.10
Upon substitution of these values, a k(r) of 8 s-1 is obtained at
radius of 16.3 Å, which is less than the measured KC action
sphere radius of ∼20 Å. This difference is too large to be
accounted for by Dexter energy transfer because a ∼200 s triplet
lifetime for KC* would be required to transfer energy directly
to a DB3 molecule at ∼20 Å, which is clearly unreasonable and
inconsistent with the measured lifetime in PMMA (∼0.13 s). A
reasonable explanation for the larger, effective action sphere is
provided by Scheme 4. As explained earlier (cf. Scheme 2), the
reactant molecules in close proximity to the sensitizer are
the ones that would react first with a modest quantum
amplification. Because of the long lifetime of KC*, energy
transfer from KC* to a reactant molecule within ∼16 Å
(reaction 11) can take place (inner dashed circle in Scheme
4). However, unlike the situation at near contact distances,
back energy transfer from P* to S at such a long distance
can be slower than energy transfer from P* to another nearby
R molecule that lies outside the 16 Å radius (reaction 12),
which would lead to the larger action sphere (outer circle in
Scheme 4).11
As noted above, the attainable conversion with KC and DB3
increases from ∼32% in the absence of co-sensitizer to ∼55%
(8) Dexter, D. L. J. Chem. Phys. 1953, 21, 836.
(9) The measured rate constant for energy transfer, kq, from KC* to DB3 in
ethyl acetate is 2 × 108 M-1 s-1. According to eq 9 in ref 4, kq ) kd ket/(ket
+
k-d), where ket is the first-order rate constant for triplet energy transfer in an
encounter of KC* and DB3, kd is the rate constant for diffusional formation of
the encounter/cage complex, and k-d is the rate constant for dissociation of the
encounter/cage pair. Taking kd as 1.5 × 1010 M-1 s-1 and k-d as 3 × 1010 s-1
in ethyl acetate4 yields a value for ket of 4 × 108 s-1. This value corresponds to
the rate constant for triplet energy transfer within a solvent cage where KC*
and DB3 are nominally an aVerage of ∼0.5 Å apart. From the Dexter expression
with L ) 1 Å, the energy transfer rate constant, k0, for KC* and DB3 in physical
contact (i.e., ∼ 0.5 Å closer) would be ∼1 × 109 s-1
.
(10) (a) Strambini, G. B.; Galley, W. C. J. Chem. Phys. 1975, 63, 3467. (b)
Strambini, G. B.; Galley, W. C. Chem. Phys. Lett. 1976, 39, 257.
(11) A small amount of long-range resonance energy transfer allowed by
the long KC* lifetime may also contribute to the larger action sphere: Anderson,
R. W.; Hochstrasser, R. M.; Lutz, H.; Scott, G. W J. Chem. Phys. 1974, 61,
2500.
(12) In contrast, the 80% conversion of DB3 obtained with DETX and higher
energy co-sensitizers leads to an apparent action sphere radius of only 12.4 Å.
This is largely reflective of the higher concentration of DETX. At 0.168 M, the
average volume/molecule of DETX is 9900 Å3, which corresponds to a maximum
action sphere radius of ∼13 Å.
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Quantum Amplified Isomerization in Polymers
TABLE 2. Isomerization Quantum Yields (Φisom) and Percent of
Attainable Conversions for 10 wt % DB2 and DB3, Sensitized with
DETX and KC, Respectively, in Polymers with Covalently Attached
Co-sensitizers
DB2/DETX
DB3/KC
a
a
polymer Tg (°C) Φisom
% conversionb Φisom
% conversionb
P1
P2
P3
P4
P5
82
89
88
85
54
7.3
8.6
99
100
11.4
85
99
99
∼16
∼16
a Measured at 10-15% conversion and corrected for incomplete
absorption; error limits <0.2. Excitation at 405 nm (6 × 10-8 Einstein/
min per cm2). b Attainable conversion with prolonged exposure (30
min).
FIGURE 7. Conversion as a function of time of DB3, molecularly
doped at 10 wt % in P3 (filled circles) and in PMMA (unfilled circles)
sensitized with KC. The dashed lines represent the initial slopes, which
provide the quantum yields at low conversion. The solid lines are fittings
to % conversion ) R{1 - exp(-ꢀ × time)}. The parameter R gives
the maximum conversion, and the product R·ꢀ is proportional to the
initial quantum yield.
Section) with covalently attached co-sensitizers (P1-P5) to
explore higher levels of co-sensitizer concentration. These
materials can be thought of as energy-conducting polymers.
Polymers P1, P2, P4, and P5 were prepared by conventional
free radical polymerization of the corresponding monomers,
which were synthesized by esterification of the commercially
available alcohols with methacryloyl chloride. P3 was prepared
by esterification of poly(vinyl alcohol) with naphthoyl chloride.
The quantum yield ratio is 7.6, which shows that the quantum
yield increased from 1.5 in PMMA to 11.4 in P3. The maximum
conversion, derived from the fitting equations given in the
caption of Figure 7, also shows an increase from PMMA to
P3, from ∼32% to ∼95%.
We next sought to prepare copolymers that were function-
alized with both reactant and co-sensitizer to evaluate their
performance. A polymerizable monomer (4) containing the
Dewar benzene monoester reactant was synthesized from DB2
as shown in Scheme 5. Interestingly, initial attempts to hydrolyze
DB2 under a variety of conventional conditions led to a mixture
of conjugated (1) and deconjugated (2) acids that were difficult
to separate. Control experiments showed that deconjugation
occurs through ester DB2 not acid 1. Ultimately, clean conver-
sion of DB2 to 1 was achieved under enzymatic hydrolysis
conditions with pig liver esterase as the catalyst. Preparation
of a diester Dewar benzene monomer (5) began with the
selective monohydrolysis of DB3 under heterogeneous condi-
tions using the method of Niwayama13 to give monoacid 3
(Scheme 5). Esterification of acids 1 and 3 with hydroxyethyl
methacryate under dicyclohexylcarbodiimide coupling condi-
tions proceeded uneventfully to give Dewar benzene monomers
4 and 5, which were successfully copolymerized to give
polymers P6 and P7, respectively, under the standard free radical
conditions described previously.1
The quantum yields for photoisomerization of P6 and P7 with
DETX as sensitizer were found to be comparable, ∼11 and 10
( 1, respectively. The quantum yield for P6 is most ap-
propriately compared to the isomerization quantum yield of 8.6
for 10 wt % DB2 in P2. P6 contains nearly the same
co-sensitizer concentration as P2 (28 vs 25 wt %), however,
P6 contains a greater loading of the reactant (22 vs 10 wt %).14
Thus, the greater reactant concentration in P6 leads to a greater
quantum yield, as found for molecularly doped polymers. The
quantum yield with P7, which contains ∼13 wt % co-sensitizer,
is most appropriately compared to that for DB3 in PMMA
containing a comparable amount of methyl 1-naphthyl acetate
The quantum yields and attainable conversions for 10 wt %
DB2 and DB3 in P1-P5 are summarized in Table 2. The
quantum yield for isomerization of DB2 sensitized with DETX
in copolymer P2 containing a 1-alkyl-substituted naphthalene
co-sensitizer (∼25 wt % co-sensitizer) was 8.6. This compares
with a lower quantum yield of 5.3 when the structurally similar
co-sensitizer 1-naphthyl acetate was molecularly doped in
PMMA at 5 wt % (Table 1). Similarly, the isomerization
quantum yield of DB3 sensitized with KC was 11.4 in
polyvinylnaphthoate (P3) and ∼16 in copolymers P4 and P5.
These compare to a quantum yield of only 4.3 when ethyl
1-naphthoate is molecularly doped in PMMA at 5 wt % (Table
1). The reason for the lower quantum yield in P3 than in P4
and P5 is, as yet, unclear. It may be due to the lower flexibility
of the naphthoate moiety in P3, although trace impurities in P3
that terminate the triplet chain cannot be excluded.
Shown in Figure 7 is a comparison of the quantum yield and
the maximum attainable conversion for DB3 in P3 with that in
PMMA without added co-sensitizer. The initial slopes are
proportional to the quantum yields at low conversion (<10%).
(13) Niwayama, S. J. Org. Chem. 2000, 65, 5834.
(14) Calculations of the weight percentages of reactants and co-sensitizers
in the functionalized polymers are based on the fractional weight equivalent of
the corresponding molecularly doped materials.
J. Org. Chem. Vol. 73, No. 15, 2008 5689

Ferrar et al.
SCHEME 5. Synthesis of Monomers 4 and 5
144.26, 166.35. Exact mass, C22H27O4 (M + H): calcd 355.1909,
found m/z 355.1915 (PIES-HRMS).
(10 wt %) as a co-sensitizer (Table 1). The greater quantum
yield for P7 vs the molecularly doped polymer (4.8) reflects
the greater concentration of reactant in the functionalized
polymer (57 vs 10 wt %).
Synthesis of Methyl 9,9-Diethylfluorene-2-carboxylate. A
mixture of 10.0 g (41 mmol) of 2-bromofluorene, 5.7 g (100 mmol)
of potassium hydroxide, and 50 mL of dimethyl sulfoxide was
stirred with slight cooling until a uniform solution was obtained.
Ethyl iodide (19.1 g, 122 mmol) was added dropwise at room
temperature, and the mixture was stirred for 1 h. An additional
charge of ethyl iodide (6 g, 38 mmol) was added, and stirring was
continued for 18 h. The reaction mixture was poured into 200 mL
of water and extracted with ether (3 × 100 mL). The combined
ethereal extracts were dried (MgSO4) and concentrated to deposit
a gold oil that partially crystallized after trituration with cold
methanol. The intermediate product, 2-bromo-9,9-diethylfluorene,
was recrystallized from methanol with decolorizing carbon, produc-
ing 5.64 g (46%) of a white solid in two crops.
A heavy-walled glass bottle was charged with 2-bromo-9,9-
diethylfluorene (2.78 g, 9.2 mmol), methanol (7.4 g, 230 mmol),
1,8-diazabicyclo[5.4.0]undec-7-ene (3.19 g, 23 mmol), triph-
enylphosphine (0.1 g, 0.4 mmol), dichlorobis(triphenylphos-
phine)palladium(II) (0.13 g, 0.2 mmol), and 40 mL of N,N-
dimethylacetamide. The stirred mixture was deaerated by sparging
with nitrogen, and then the bottle was closed and pressurized to 60
psi with carbon monoxide. The stirred reaction mixture was heated
at 120 °C for 2 h, cooled to room temperature, filtered, and poured
into 300 mL of water. The resulting milky suspension was extracted
with ether (3 × 100 mL), and the combined extracts were
successively washed with 5% aq HCl, three times with water, and
with brine. The solution was dried (MgSO4) and concentrated to
deposit a gold oil. The product was purified by column chroma-
tography (elution with a mixture of heptane and dichloromethane)
and then distilled at reduced pressure to provide 1.91 g (74%) of
a viscous colorless oil that gradually crystallized (mp 52-54 °C).
1H NMR (CDCl3): δ 0.29 (t, 6 H), 2.07 (m, 4 H), 3.95 (s, 3 H),
7.36 (m, 3 H), 7.76 (d, 2 H), 8.01 (m, 2 H). 13C NMR (CDCl3): δ
8.40. 32.58. 52.05, 56.27, 119.34, 120.55, 123.05, 124.05, 127.03,
128.27, 128.52, 128.88, 140.30, 146.25, 149.92, 150.94, 167.54.
Exact mass, C19H20O2 (M): calcd 280.1463, found m/z 280.1458
(APPI-HRMS).
Conclusions
A second, improved generation of QAI polymers has been
successfully developed that is based on the triplet quantum chain
isomerization of substituted Dewar benzene derivatives. Efficient
chain propagation in polymeric media was achieved by incor-
poration of triplet energy co-sensitizers that facilitate long
distance energy migration and, thereby, markedly increase the
isomerization quantum yields and the extents of reactant-to-
product conversion that can ultimately be achieved. In the best
systems examined thus far, quantum amplifications of ∼16 and
conversions approaching 100% have been achieved. The
combined results, coupled with the large refractive index
changes (∆n ∼ 0.02) for the materials,2d demonstrate that triplet
QAI polymers may be promising optical materials for a variety
of applications.15 Experiments that demonstrate applications will
be reported separately.
Experimental Section
Synthesis of Di-n-butyl 4,4′-Biphenyldicarboxylate. A mixture
of biphenyl-4,4′-dicarboxylic acid (15.2 g, 63 mmol), 100 mL of
n-butanol, 200 mL of toluene, and a catalytic amount of p-
toluenesulfonic acid was heated at reflux with continuous separation
of evolved water for 7 d. The reaction mixture was cooled to room
temperature, diluted with dichloromethane, filtered, washed with
10% aqueous NaHCO3 and then with brine, dried (MgSO4), and
concentrated. The crude product was purified by recrystallization
from heptane to obtain 13.4 g (60%) of colorless crystals (mp
1
45-48 °C). H NMR (CDCl3): δ 0.97 (t, 6 H), 1.5 (m, 4 H), 1.8
(m, 4 H), 4.35 (q, 4 H), 7.68 (d, 4 H), 8.13 (d, 4 H). 13C NMR
(CDCl3): δ 13.77, 19.27, 30.76, 64.96, 127.18, 130.00, 130.13,
Synthesis of 2-(1-Naphthyl)ethyl Methacrylate. A solution of
2-(1-naphthyl)ethanol (30.0 g, 174 mmol), triethylamine (24.2 g,
(15) Farid, S. Y.; Robello, D. R.; Dinnocenzo, J. P.; Merkel, P. B.; Ferrar,
L. S.; Roh, Y. U.S. Patent Application 2005136357 A1, June 23, 2005.
5690 J. Org. Chem. Vol. 73, No. 15, 2008

Quantum Amplified Isomerization in Polymers
TABLE 3. Number Average (Mn) and Weight Average (Mw)
Molecular Weights of Polymers P1-P7 and Their Glass Transition
Temperatures (Tg)
was added via a FMI laboratory pump at a rate to maintain the pH
at 7.8 ( 0.1. After 8 h, the reaction mixture was filtered, insoluble
material was washed with pH 7.8 buffer, and the filtrate was
acidified with 10% HCl. The resulting tan precipitate was collected
and dissolved in warm (60 °C) ethyl acetate. The solution was
filtered to remove residual enzyme, dried (MgSO4), and concen-
a
a
b
polymer
Mn
Mw
Tg (°C)
P1
P2
P3
P4
P5
P6
P7
13800
12200
47000
41700
82
89
88
85
54
84
77
1
trated to give 38 g (76%) of 1. H NMR (CDCl3): δ 1.15 (s, 3H),
1.25 (s, 3H) 1.58 (s, 3H), 1.64 (s, 3H), 2.05 (s, 3H). 13C NMR
(CDCl3): δ 9.3, 10.6, 11.0, 11.3, 14.4, 54.6, 57.1, 137.7, 141.5,
145.5, 169.8, 172.6. Exact mass, C12H15O2 (M - H): calcd
191.1072, found m/z 191.1052 (NIES-HRMS).
11300
14200
24300
37700
23600
28000
57900
77300
Synthesis of 3. DB3 (5.0 g, 20 mmol) was dissolved in 80 mL
of tetrahydrofuran, cooled to 0 °C, and treated with 80 mL of 0.375
M aqueous NaOH (30 mmol). The resulting mixture was stirred at
0 °C for 2 h and then warmed to room temperature. The mixture
was washed three times with diethyl ether, and the aqueous phase
was separated and acidified. The resulting precipitate was extracted
into ethyl acetate and dried over sodium sulfate. The solvent was
removed at reduced pressure to deposit a yellow solid which was
purified by column chromatography to give 3.2 g (68%) of 3 (mp
a Absolute molar mass averages by SEC using viscometric detection
and universal calibration. b Glass transition temperature measured by
DSC.
239 mmol), 4-(dimethylamino)pyridine (1.1 g, 9.1 mmol), and
dichloromethane (500 mL) was treated dropwise under nitrogen
with methacryloyl chloride (18.9 g, 181 mmol) and then heated at
reflux for 4 h. The reaction mixture was cooled to room temperature
and diluted with diethyl ether. The solution was filtered and the
filtrate washed twice with water, once with NaHCO3, and once with
brine. The solution was dried (Na2SO4), concentrated to a yellow
oil, and distilled at reduced pressure (bp 120-125 °C, 0.08 mm)
1
108-110 °C). H NMR (CDCl3): δ 1.30 (s, 3 H), 1.35 (s, 3 H),
1.60 (s, 3 H), 1.64 (s, 3 H), 3.90 (s, 3 H), 12.10 (s, 1 H). 13C NMR
(CDCl3): δ 9.51, 9.91, 11.09, 11.20, 53.17, 55.45, 57.09, 142.52,
143.67, 150.42, 159.43, 161.07, 166.52. Exact mass, C13H15O2 (M
- H): calcd 235.0970, found m/z 235.0970 (NIES-HRMS).
Syntheses of 4 and 5. A mixture of 1 (3.8 g, 19.8 mmol),
2-hydroxyethyl methacrylate (7.7 g, 59.3 mmol), 4-(dimethylami-
no)pyridininium p-toluenesulfonate (2.3 g, 7.8 mmol), and anhy-
drous dichloromethane (31 mL) was cooled to 0 °C under nitrogen,
and 1,3-dicyclohexylcarbodiimide (5.3 g, 25.7 mmol) was added.
After 15 min, the reaction mixture was warmed to room temperature
and stirred for 12 h. The precipitate that formed was filtered, and
the filtrate was washed successively with 10% aqueous HCl, 10%
aqueous NaHCO3, water, and brine. The organic layer was dried
(Na2SO4) and concentrated to give a yellow oil. The product (4)
was vacuum distilled (bp 85-90 °C, 0.05 mm) to give 3.0 g (50%)
of a colorless oil. 1H NMR (CDCl3): δ 1.15 (s, 3 H), 1.23 (s, 3 H),
1.57 (s, 3H), 1.60 (s, 3 H), 1.95 (s, 3 H), 2.00 (s, 3 H), 4.35 (m, 4
H), 5.6 (s, 1 H), 6.25 (s, 1 H). 13C NMR (CDCl3): δ 9.30, 10.62,
10.98, 11.19, 14.24, 18.23, 54.61, 56.98, 61.01, 62.62, 125.88,
135.99, 137.64, 141.73, 145.32, 163.88, 167.08, 169.98. Exact mass,
C18H24O4 (M + Na): calcd 327.15722, found m/z 327.15702 (ES-
HRMS). The synthesis of 5 was analogous to 4 except that the
1
to give 36.0 g (86%) of a colorless oil. H (CDCl3): δ 2.00 (s, 3
H), 3.50 (t, 2 H), 4.55 (t, 2 H), 5.60 (s, 1 H), 6.15 (s, 1 H), 7.50
(m, 4 H), 7.8 (d, 1 H), 7.9 (d, 1 H), 8.2 (d, 1 H). 13C NMR (CDCl3):
δ 18.28, 32.18, 64.69, 123.61, 125.42, 125.54, 125.61, 126.13,
127.02, 127.39, 128.75, 132.02, 133.76, 133.82, 136.28, 167.39.
Exact mass, C16H16O2 (M + NH4): calcd 258.14940, found m/z
258.14772 (ES-HRMS).
Synthesis of 2-(1-Naphthoyloxy)ethyl Methacrylate. A mixture
of 1-naphthoic acid (8.0 g, 46 mmol), 2-hydroxyethyl methacrylate
(18.1 g, 139 mmol), 4-(dimethylamino)pyridininium p-toluene-
sulfonate (5.5 g, 19 mmol), and anhydrous dichloromethane (45
mL) was cooled to 0 °C under nitrogen, and 1,3-dicyclohexylcar-
bodiimide (12.5 g, 60 mmol) was added. After 15 min, the reaction
mixture was warmed to room temperature and stirred for 3 h. The
precipitate that formed was filtered, and the filtrate was washed
successively with 10% aqueous HCl, 10% aqueous NaHCO3, water,
and brine. The organic layer was dried (Na2SO4) and concentrated
to a gold oil that was purified by column chromatography to provide
1
8.2 g (62%) of a pale yellow oil. H NMR (CDCl3): δ 1.90 (s, 3
1
product was purified by column chromatography (60% yield). H
H), 1.55 (m, 2 H), 1.70 (m, 2 H), 5.60 (s, 1 H), 6.20 (s, 1 H),
7.55(m, 3 H), 7.90 (d, 1 H), 8.05 (d, 1 H), 8.20 (d, 1 H), 8.90(d, 1
H). 13C NMR (CDCl3): δ 18.29, 62.49, 62.67, 124.48, 125.70,
126.12, 126.22, 126.71, 127.79, 128.56, 130.41, 131.30, 133.58,
133.81, 135.92, 167.14, 167.23. Exact mass, C17H16O4 (M + NH4):
calcd 302.13923, found m/z 302.13876 (ES-HRMS).
NMR (CDCl3): δ 1.20 (s, 3 H), 1.23 (s, 3 H), 1.55 (s, 3 H), 1.58
(s, 3 H), 1.90 (s, 3 H), 3.72 (s, 3 H), 4.35 (m, 4 H), 5.5 (s, 1 H),
6.1 (s, 1 H). 13C NMR (CDCl3): δ 9.90(2C), 10.91, 10.99, 18.20,
51.65, 56.12, 56.33, 62.15, 62.32, 126.03, 135.86, 143.17, 143.26,
150.70, 152.28, 161.73, 162.69, 166.99. Exact mass, C19H24O6
(M + H): calcd 349.16511, found m/z 349.16417 (ES-HRMS).
Preparation of Polymer Films. Solutions were prepared with
DB2 or DB3 (100 mg), co-sensitizer (50 mg), sensitizer (40 mg of
DETX or 5 mg of KC), and PMMA (810 or 845 mg, so that the
total weight of solids was 1 g) in 4 mL of dichloromethane and
filtered by using a Whatman syringeless PTFE membrane (0.45
µm).
The solutions were hand coated using a 10 cm × 127 µm knife
on a 100 µm transparent poly(ethylene terephthalate) support with
a thin (<0.5 µm) adhesion layer (15/79/6 copolymer of acrylonitrile,
vinylidene chloride, and acrylic acid), maintained at 23-25 °C,
and the samples were air-dried for 15 min. The films were cut into
∼4 × 4 cm square pieces and mounted between two black-anodized
aluminum plates with a 25 mm circular aperture, clamped, and dried
in a vacuum oven at 40 °C for 16-17 h. The thickness of the dried
films was ∼22 ( 2 µm, and the optical densities at 405 nm were
0.4 ( 0.05.
Representative Polymer Synthesis Procedure: Synthesis of
P2. A solution of 2.50 g (10.4 mmol) of 2-(1-naphthyl)ethyl
methacrylate, 10.1 g (101 mmol) of methyl methacrylate, and 0.28 g
(1.11 mmoles) of 2,2′-azobis(2,4-dimethylvaleronitrile) in benzene
was deaerated by sparging for 10 min with nitrogen. The reaction
mixture was then heated to 52 °C for 24 h. The resulting polymer
was precipitated into cold ligroin twice and dried in a vacuum oven
at 60 °C (Table 3).
Synthesis of Poly(vinyl 1-naphthoate), P3. A suspension of
2.2 g of poly(vinyl alcohol) in 100 mL of dry pyridine was stirred
overnight at 55-70 °C protected from air. 1-Naphthoyl chloride
(9.5 g) was added, and the mixture was heated for 18 h at 60 °C.
After being cooled to room temperature, the amber reaction mixture
was filtered and the polymer precipitated in 1.5 L of cold water.
The product was collected, washed with water, air-dried, and then
dried in vacuo to give 7.6 g of a flaky white solid. Tg (DSC) )
88 °C.
Synthesis of 1. Crude porcine liver esterase (25 g) was dissolved
in 500 mL of pH 7.8 buffer and warmed to 40 °C. To this solution
was added 53.0 g (257 mmol) of DB2. NaOH solution (0.1 M)
Quantum Yield Measurements and Conversion Experiments.
The samples were irradiated (usually in duplicates for 0.5, 1, 2, 4,
and 30 min) using the strongly defocused output of a high-pressure
J. Org. Chem. Vol. 73, No. 15, 2008 5691

Ferrar et al.
Hg lamp (200 W), filtered through Corning 5-58 broadband filter,
a 3-75 cutoff filter, and a 404.7 nm interference filter. The photon
flux of the lamp at 405 nm (∼5-6 × 10-8 Einstein/min/cm2) was
measured using the reaction of 9,10-phenanthrenequinone (0.001
M) with trans-stilbene (0.1 M) in benzene as an actinometer.16
In the case of DB2 as reactant, the center of the exposed films
was cut out using a 12.3 × 12.3 mm arch punch and extracted
with 0.4 mL dichloromethane to which was added 50 µL of a
cyclohexane solution containing tetradecane (6.04 mg/mL, 1.53 ×
10-6 M) as an internal standard. The samples were sonicated for
15 min, cyclohexane (1.8 mL) was added to precipitate the polymer,
and the solutions were filtered through a cotton-plugged pipet. The
solutions were analyzed by GC using an RTX-5 Crossbond 5%
diphenyl-95% dimethyl polysiloxane column (15 m × 0.32 mm ×
0.25 µm) with an oven temperature that was ramped from 45 to
235 °C over 17 min. In an independent experiment, a GC calibration
was performed to determine the ratio of area counts/mol for several
concentrations (from 6 × 10-8 to 1.5 × 10-6 M) of the product
(P2) and the reactant (DB2) to that of 1.5 × 10-6 M of tetradecane.
In general, the mass balance of product plus reactant of the irradiated
samples against the amount of reactant from unirradiated samples
was quantitative within experimental error ((3%).
In the case of DB3, the polymer films were prepared as for DB2
but were analyzed by HPLC (see Instrumentation, Supporting
Information). Peak areas were standardized vs those of unirradiated
samples and were response factor corrected.
For polymers P6 and P7, the isomerization quantum yields were
obtained by comparing the diffraction efficiency response after
holographic exposure of the irradiated film relative to that of a
sample in which DB2 was molecularly doped in PMMA.17,18
Details of this experiment will be described in a separate paper.
Acknowledgment. Research support was provided by the
National Science Foundation (DMR-0071302), Eastman Kodak,
and the Center for Electronic Imaging Systems (CEIS), a
NYSTAR-designated Center for Advanced Technology. We
thank Jonathan Dordick (Rensselear Polytechnic Institute) for
advice on the selection and use of enzymes, Thomas C. Jackson
(Eastman Kodak) for GC-MS analysis, Thomas Mourey and
Kim Lee (Eastman Kodak) for SEC analysis, Roger Moody
(Eastman Kodak) for DSC analysis, J. Michael Hewitt (Eastman
Kodak) for NMR assistance, and Samuel Thomas and Robert
Daly (Eastman Kodak) for synthetic assistance. We are also
pleased to acknowledge valuable advice and encouragement
from Jack C. Chang (Eastman Kodak).
Supporting Information Available: Experimental methods,
materials, and 1H NMR spectra of Dewar benzene derivatives,
co-sensitizers, monomers, and functionalized polymers. This
material is available free of charge via the Internet at
http://pubs.acs.org.
JO8007786
(16) (a) Bohning, J. J.; Weiss, K. J. Am. Chem. Soc. 1966, 88, 2893. (b)
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4162.
(17) (a) Burland, D. M.; Bjorklund, G. C.; Alvarez, D. C. J. Am. Chem. Soc.
1980, 102, 7117. (b) Bra¨uchle, C.; Burland, D. M. Angew. Chem., Int. Ed. Engl.
1983, 22, 582. (c) Burland, D. M. Acc. Chem. Res. 1983, 16, 218. (d) Burland,
D. M. IEEE J. Quantum Electron. 1986, QE-22, 1469.
(18) Peer, A. S. Volume Holography in Optically Isomerized Polymer Media.
Ph.D. Thesis, University of Rochester, Rochester, NY, 2003.
5692 J. Org. Chem. Vol. 73, No. 15, 2008