Diaryl-substituted norbornadienes with red-shifted absorption for molecular solar thermal energy storage

Article abstract of DOI:10.1039/c3cc47517d

Red-shifting the absorption of norbornadienes (NBDs), into the visible region, enables the photo-isomerization of NBDs to quadricyclanes (QCs) to be driven by sunlight. This is necessary in order to utilize the NBD-QC system for molecular solar thermal (MOST) energy storage. Reported here is a study on five diaryl-substituted norbornadienes. The introduced aryl-groups induce a significant red-shift of the UV/vis absorption spectrum of the norbornadienes, and device experiments using a solar-simulator set-up demonstrate the potential use of these compounds for MOST energy storage. the Partner Organisations 2014.

Full text of DOI:10.1039/c3cc47517d

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DOI: 10.1039/C3CC47517D
Diaryl-Substituted Norbornadienes with Red-Shifted Absorption for
Molecular Solar Thermal Energy Storage†
Victor Gray,a Anders Lennartson,a Phasin Ratanalert,a Karl Bo¨rjessona,b‡ and Kasper Moth-
Poulsen∗a
Received Xth XXXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
First published on the web Xth XXXXXXXXXX 200X
DOI: 10.1039/b000000x
Red-shifting the absorption of norbornadiene (NBD), into
the visible, enables the photo-isomerization of NBD to
quadricyclane (QC) to be driven by sunlight. This is neces-
sary in order to utilize the NBD-QC system for molecular
solar thermal (MOST) energy storage. Reported here is a
study on five diaryl-substituted norbornadienes. The in-
troduced aryl-groups induce a significant red-shift on the
UV/Vis absorption spectrum of the norbornadienes, and
device experiments with a solar-simulator set-up demon-
strates the potential use of these compounds in MOST en-
ergy storage.
ergy diagram of a MOST system describing these parameters
is displayed in figure 1.
The world wide energy consumption is predicted to double
within the next 40 years.1 It is probable that solar power will
play an important role in meeting future energy demands,
considering that the sun provides earth with vast amounts
of energy; each hour more energy is provided than is con-
sumed by mankind during a whole year.1 However, sunlight,
as most other renewable energy resources, is intermittent and
this put higher demands on the power-grid and requires effi-
cient means of energy storing.1–3
One potential way of storing solar energy is in the form
of chemical bonds in molecules that undergo photo-induced,
reversible and endothermic, isomerizations.4 The maximum
efficiency of such a molecular solar thermal energy storage
(MOST) system has recently been estimated to 10.6 %,5 at an
absorption threshold of 590 nm and an isomerization quantum
yield (φiso) of unity. Other important parameters for a MOST
system is the storage life-time, determined by the activation
barrier (∆H‡) for the reversed isomerization reaction, and the
energy stored by the photoisomer (∆Hstorage). A schematic en-
Fig. 1 Schematic energy diagram of a MOST system. The parent
molecule absorbs a photon, and while in its electronically excited
state it undergoes an isomerization, forming the photoisomer. With a
suitable activation barrier (∆H‡) the photoisomer is stable over an
extended period of time (months-years). The energy difference
between parent and photoisomer is the amount of energy stored in
the system and is regained as heat when the reversed isomerization
is activated, either by a catalyst or thermally.
There has been many different molecular candidates for
MOST systems over the years. Recently an organo-metalic
ruthenium complex has been investigated6,7 and demonstrated
in devices, with8 and without,9 photon-upconversion. Other
possible types of compounds are azobenzene derivatives10
where Grossman et al. has suggested a number of ways to
increase the storage-density and storage-times by using car-
bon nanostructured-scaffolds11,12 or by connecting the ac-
tive molecules in circular structures.13 The most studied sys-
tem for MOST energy storage is probably the norbornadiene-
quadricyclane (NBD-QC) system4,14 (for recent reviews see
ref. 4 and 14.) Norbornadiene and its derivatives have many
promising properties for this application, e.g. high isomeriza-
tion quantum yields and low molecular weight15–18. The main
weakness of norbornadiene is its absorption onset (<300 nm),
† Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See DOI:
10.1039/b000000x/
a
Department of Chemical and Biological Engineering, Chalmers
Technical University, Gothenburg, Sweden.
E-mail: kasper.moth-
poulsen@chalmers.com
b
Institut de Science et d’Ingee´nierie Supramole´culaires, Universite´ de Stras-
bourg, Strasbourg, France.
‡ Present address
1–4 | 1

ChemComm
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DOI: 10.1039/C3CC47517D
consequently the sun can not drive this isomerization. There-
fore the need to shift the norbornadiene absorption spectrum
closer to the optimal 590 nm absorption edge.
Numerous substituted norbornadienes have been synthe-
sized over the years, mainly relying on the Diels-Alder reac-
tion between substituted cyclopentadienes and alkynes.17,19,20
A recurring problem is the decrease in thermal stability to-
wards reversed isomerization of the photo-isomer when red-
shifting auxochromes are introduced.17,21 As the Diels-Alder
reaction poses a number of restrictions on what types of sub-
stituted norbornadienes that can be made, one can understand
that Maruyama et al. claimed in the early 80’s that, in a
practical sense, the most efficient system amongst norborna-
diene derivatives had been found.22 However, lately Tranmer
et al. and Yoo et al. presented a new way of synthesiz-
ing aryl-substituted norbornadienes through Suzuki-Miyaura
cross couplings.23,24 To the best of our knowledge, none of
these norbornadienes have been characterized fully for the use
in MOST energy storage systems. We also believe that, fol-
lowing the procedure developed by Tranmer and Yoo, new
norbornadienes better optimized for MOST energy storage
can be synthesized. A great advantage with this Suzuki-
coupling based method is that one can address the two sp2-
carbons in the same double-bond individually. We therefore
synthesized five diaryl-substituted norbornadienes with one
electron donating aryl and one electron accepting aryl group,
creating a novel push-pull conjugated system over one double
bond in norbornadiene (Fig 2). For experimental procedures
see ESI†. Two of these norbornadienes 3a and 3b have been
synthesized previously,24,25 but full characterization for the
use in MOST energy storage has not been reported before.
Fig. 3 Absorption spectra of unsubstituted norbornadiene, 1 (- -),
and substituted norbornadienes; 3a(ꢀ), 3b( ), 3c(N) 3d(ꢁ) and
3e(+). 1 in acetonitrile and 3a-e in toluene.
out degradation, when irradiated at respective absorption max-
imum.
Isomerization quantum yields were determined at 366 nm in
toluene (Table 1) by potassium ferrioxalate actionometry.26,27
Samples were not degassed as previous work has indicated
that the presence of oxygen does not affect the isomerization
quantum yields.17,25 We note that the obtained φiso values for
our push-pull aryl-substituted norbornadienes 3a-e are 6-37
times higher than those reported for norbornadienes with sim-
ilar absorption characteristics¶.22
Aryl-substituents are known to reduce the thermal stability
of quadricyclane.17,20,21 Analogous to this quadricyclanes 4a-
e are readily converted to corresponding norbornadienes above
80◦C. However, Eyring parameters, in table 1, for 4a, 4b and
4d indicate that the stability is sufficient for these compounds,
corresponding to half-lives of weeks to months at 25◦C. Both
4c and 4e, with trifluoromethyl as the electron withdrawing
group, display significantly lower thermal stability, with half-
lives of 2.9 days and 1.9 h at 25◦C, respectively.
The cyclability of the isomerizations were studied and fig-
ure S3† shows the normalized norbornadiene concentration as
a function of isomerization cycles. Contrary to the photo-
isomerization, that is almost quantitative, the thermal reversed
isomerization of 4a-e to 3a-e occurs with some degradation.
The maximum average yield of each cycle, of the aerated
samples, was obtained for norbornadiene 3b and was 98.9
%. For norbornadiene 3e the average cycle yield was the
lowest, namely 87.7 %. Removing oxygen prior to cycling
minimized degradation of 3e and the average yield of cycling
Entry
3a
3b
X2
-H
-OMe
-CF3 -OMe
-CN -OMe
-NMe2
X2
X1
-H
-H
X2
4a-e
3a-e
1
hv
heat
3c
3d
3e
-CF3
X1
X1
Fig. 2 Synthezised diaryl-substituted norbornadienes and
corresponding quadricyclanes
Absorption spectra of 3a-e are compared to unsubstituted
norbornadiene (1) in figure 3. All substituted norbornadienes
showed a bathochromic shift compared to 1 which has an on-
set at ∼ 267 nm (onset defined as lg(ε)=2). The most signif-
icant shifts were observed for norbornadiene 3e with an ab-
sorption onset of 462 nm, corresponding to a redshift of ap-
proximately 195 nm. Aryl-substituted norbornadienes were
isomerized, to the corresponding qadricyclanes, by exposure
to an Osram Powerstar HQ-IR 150 W, metal halide lamp.
Isomerization was followed by NMR and UV/Vis absorption
spectroscopy (see figure S2 in ESI†). Isobestic points indi-
cated that the isomerization from NBD to QC proceeded with-
¶ λmax ∼ 325 nm, ε ∼ 8000
2 |
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Table 1 Photochemical data, Eyring parameters for substituted norbornadienes 3a-f determined in toluene.
Entry
εmax [M−1cm−1
]
Aaonset [nm]
∆H‡ [kJ/mol]
∆S‡ [J/mol]
tb1/2
φc [%]
3a
3b
3c
3d
3e
8.0×103 (308 nm)
9.0×103 (309 nm)
7.2×103 (318 nm)
9.5×103 (350 nm)
10.1×103 (365 nm)
389
402
414
431
462
108.8 ± 2.3
106.7 ± 1.8
97.1 ± 8.9
106.5 ± 2.9
43.1 ± 13.7
−8.8 ± 6.5
42.9 days
31.3 days
2.9 days
8.7 days
1.9 h
60.2 ± 1.5
72.0 ± 3.7
75. ± 2.2
61.6 ± 0.1
45.8 ± 0.2
−13.1 ± 5.0
−25.18 ± 25.2
−2.9 ± 8.0
−176.9 ± 39.0
a) Absorption onset defined as log(ε) = 2. b) determined from Eyring parameters at 25◦C. c) Measured in toluene at 366 nm (FWHM = 10
nm), yielding a photon flux of 2.16 nE/s.
was increased to 99.6 %. Preferably a catalyst that activates
the back-isomerization and simultaneously minimizes degra-
dation should be optimized. As there already exists many
known catalysts for the quadricyclane-norbornadiene isomer-
ization17,22,28,29 we believe that this is possible.
References
1 N. Lewis and D. Nocera, Proc. Natl. Acad. Sci. U. S. A., 2006, 103,
15729–15735.
2 T. R. Cook, D. K. Dogutan, S. Y. Reece, Y. Surendranath, T. S. Teets and
D. G. Nocera, Chem. Rev., 2010, 110, 6474–6502.
To demonstrate the MOST energy storage concept, at a
larger scale, a parabolic solar-collector (26×32 cm) was con-
structed and fitted with a glass pipe as a continuous flow re-
actor (isometric drawing in figure S5 in ESI†). Molecule 3c
was dissolved in toluene (0.1 % w/v) and the solution was
pumped through the glass pipe while the set-up was irradiated
by a large area solar-simulator lamp (EYE Lighting Interna-
tional). Quantitative conversion was achieved at 60 min resi-
dence time (described in figure S6 in ESI†). This experiment
demonstrates the potential use of aryl-substituted norbornadi-
enes for MOST energy storage under natural irradiation con-
ditions.
3 S. M. Amin and A. M. Giacomoni, Fundamentals of Materials for En-
ergy and Environmental Sustainability, Cambridge University Press, New
York, 1st edn, 2012, ch. 42, pp. 578–593.
4 T. J. Kucharski, Y. Tian, S. Akbulatov and R. Boulatov, Energy Environ.
Sci., 2011, 4, 4449–4472.
5 K. Bo¨rjesson, A. Lennartson and K. Moth-Poulsen, ACS Sustainable
Chem. Eng., 2013, ASAP, 585–590.
6 R. Boese, J. K. Cammack, A. J. Matzger, K. Pflug, W. B. Tolman, K. P. C.
Vollhardt and T. W. Weidman, J. Am. Chem. Soc., 1997, 119, 6757–6773.
7 M. R. Harpham, et. al, Angew. Chem. Int. Ed. Engl., 2012, 51, 7692–7696.
8 K. Bo¨rjesson, D. Dzebo, B. Albinsson and K. Moth-Poulsen, J. Mater.
Chem. A, 2013, 1, 8521–8524.
9 K. Moth-Poulsen, D. Coso, K. B
o¨rjesson, N. Vinokurov, S. K. Meier,
A. Majundar, K. P. C. Vollhardt and R. A. Sealman, Energy Environ. Sci.,
2012, 5, 8534–8537.
10 I. John Olmsted, J. Lawrence and G. G. Yee, Solar Energy, 1983, 30,
In summary, five diaryl-substituted norbornadienes have
been scrutinized for molecular solar thermal (MOST) energy
storage. The new push-pull conjugated system in these nor-
bornadienes resulted in a maximum red-shift of the absorption
onset of 195 nm, to 462 nm and enables the isomerization
to be driven by sunlight. We also constructed a continuous
flow solar-collector, utilizing norbornadiene 3c as the active
specimen, to demonstrate a large scale, solar-collecting part,
of a MOST energy storage system. Future work in this
regard will be devoted to further demonstrate the concepts
of closed-cycle energy storage. Further optimization of
the norbornadiene system is also necessary, especially the
thermal stability and cyclability must be improved in order
to demonstrate a fully working, closed-cycle, MOST energy
storage system.
271–274.
11 A. M. Kolpak and J. C. Grossman, Nano Lett., 2011, 11, 3156–3162.
12 A. M. Kolpak and J. C. Grossman, J. Chem. Phys., 2013, 138, 034303–
(1–6).
13 E. Durgun and J. C. Grossman, J. Phys. Chem. Lett., 2013, 4, 854–860.
14 A. D. Dubonosov, V. A. Bren and V. A. Chernoivanov, Russ. Chem. Rev.,
2002, 71, 917–927.
15 R. R. Hautala, J. Little and E. Sweet, Solar Energy, 1977, 19, 503–508.
16 L. R. Canas and D. B. greenberg, Solar Energy, 1985, 34, 93–99.
17 Z.-I. Yoshida, J. Photochem., 1985, 29, 27–40.
18 Y. Harel, A. W. Adamson, C. Kutal, P. A. Grutsch and K. Yasufuku, J.
Phys. Chem., 1987, 91, 901–904.
19 H. Ikezawa, C. Kutal, K. Yasufuku and H. Yamazaki, J. Am. Chem. Soc.,
1986, 108, 1589–1594.
20 T. Nagai, K. Fujii, I. Takahashi and M. Shimada, Bull. Chem. Soc. Jpn.,
2001, 74, 1637–1678.
21 S. Miki, Y. Asako and Z.-I. Yoshida, Chem. Lett., 1987, 16, 195–198.
22 K. Maruyama, K. Terada and Y. Yamamoto, Chem. Lett., 1981, 10, 839–
842.
23 G. K. Tranmer, C. Yip, S. Handerson, R. W. Jordan and W. Tam, Can. J.
Chem., 2000, 78, 527–535.
The authors would like to acknowledge funding from
Chalmers Materials Area of Advance, the Swedish Energy
Agency and Swedish Research Council (B0361301). The
authors would like to thank prof. Nina Kann for the support in
purification of compound 3d and Gustave Holmqvist, Reine
Nohlborg and Jan Bragee for their valuable comments on the
design and production of the solar concentrator.
24 W.-J. Yoo, G. C. Tsui and W. Tam, New J. Chem., 2005, 2005, 1044–1051.
25 G. Kaupp and H. Prinzbach, Chem. Ber., 1971, 104, 182–204.
26 C. A. Parker, Proc. R. Soc. A, 1953, 220, 104–116.
27 C. G. Hatchard and C. A. Parker, Proc. R. Soc. A, 1956, 235, 518–536.
28 K. Maruyama, H. Tamiaki and S. Kawabata, J. Org. Chem., 1985, 50,
1–4 | 3

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4742–4749.
29 K. Maruyama, H. Tamiaki and S. Kawabata, J. Chem. Soc., Perkin Trans.
II, 1986, 2, 543–549.
4 |
1–4