Highly phosphorescent supramolecular hydrogels based on platinum emitters

Article abstract of DOI:10.1002/chem.201403772

We have synthesised a neutral, water-soluble, PtII complex able to aggregate more efficiently in aqueous solutions than in organic solvents. The aggregates are luminescent and are not quenched by molecular oxygen. Further, we have prepared phosphorescent

Full text of DOI:10.1002/chem.201403772

DOI: 10.1002/chem.201403772
Communication
&
Supramolecular Hydrogels
Highly Phosphorescent Supramolecular Hydrogels Based on
Platinum Emitters
Naveen Kumar Allampally,[a] Michael Bredol,[b] Cristian A. Strassert,*[c] and Luisa De Cola*[d]
networks in different solvents and disassemble by various ex-
Abstract: We have synthesised a neutral, water-soluble,
ternal stimuli.[1a,c,3,4] Amongst the different type of gelators,
PtII complex able to aggregate more efficiently in aqueous
those able to entrap water are of particular interest, since the
solutions than in organic solvents. The aggregates are lu-
resulting hydrogel materials can find applications in biomed-
minescent and are not quenched by molecular oxygen.
icine,[5] and they can even lead to a 3D matrix for the encapsu-
Further, we have prepared phosphorescent hydrogels uti-
lation of living cells.[6] The gels can also be photoactive and
lising host–guest interactions between cyclodextrins and
emissive upon either incorporation of a luminescent species,
the tetraethylene glycol tails of the PtII complex. The soft
or by using emitters which act as gelators.[1c,7] Metal gelators,
assemblies feature host-dependent emission properties.
in particular those containing PtII chelates, are interesting due
to their luminescent properties.[8] In this respect, PtII complexes
and their assemblies have recently found applications in or-
ganic light emitting diodes (OLEDs),[8a,9] sensors,[10] vapochro-
Self-assembly of small molecules into new functional architec-
mic materials[11] and LMWGs.[8b,c,12] Indeed, organogels and hy-
tures has been object of intensive investigations in the past
few years.[1] Amongst the soft assemblies, gels play an impor-
tant role as materials for targeted drug delivery and tissue en-
gineering, particularly with polymer-based gels.[2] Unfortunate-
ly, the lack of biodegradability and issues related to chemical
composition come into picture as disadvantages.[3] Thus, low-
molecular-weight gelators (LMWGs) have been proposed as in-
teresting alternatives, as they can assemble forming intricate
drogels of PtII complexes have been reported in which electro-
static and/or p–p interactions played a fundamental role.[8f,13]
However, most of the hydrogels turned out to be non-lumines-
cent, most probably due to quenching of the long-lived phos-
phorescence by molecular dioxygen. Furthermore, luminescent
hydrogel matrices have been prepared by employing f-block
metal cations (3+) and sodium cholate, but without displaying
reversibility to sols.[14]
In many cases, the stability of the hydrogel is a problem and
a way to induce the formation of a strong gelating network is
to take advantage of host–guest interactions. Cyclodextrin
(CD) constitutes a water-soluble building block able to act as
a host. Indeed, the self-assembly of polyethylene glycol (PEG)
and a-CD was firstly reported by Harada et al.[15] They showed
that a-CD can assist the organisation by hosting PEG chains.
Following this approach, other hydrogels and self-assembled
structures that display reversible assembly and disassembly
upon external inputs have been described.[16] Therefore, an in-
teresting combination of luminescent and stable gels can be
obtained with phosphorescent PtII complexes possessing one
of these two components (PEG or CD) and adding the comple-
mentary guest or host in order to create phosphorescent hy-
drogels. However, PtII complexes can be quenched by the di-
oxygen present in the solvent, and therefore must be protect-
ed to avoid bimolecular interactions. In this respect, we have
recently reported the aggregation-induced emission (AIE) of
a PtII compound bearing a dianionic tridentate ligand[8a] and,
also shown that appropriate ancillary ligands facilitate the gela-
tion of solvents of different polarity, such as dichloromethane
(DCM) and dimethylformamide (DMF).[8i]
[a] Dr. N. K. Allampally
NRW Graduate School of Chemistry
Westfꢀlische Wilhelms-Universitꢀt Mꢁnster
Wilhelm-Klemm-Str.10, 48149 Mꢁnster (Germany)
and
Center for Nanotechnology (CeNTech) and Physikalisches Institut
Westfꢀlische Wilhelms-Universitꢀt Mꢁnster.
Heisenbergstr. 11, 48149 Mꢁnster (Germany)
Current address:
Institut fꢁr Organische Chemie, Universitꢀt Wꢁrzburg
Am Hubland, 97074 Wꢁrzburg (Germany)
[b] Prof. Dr. M. Bredol
Department of Chemical Engineering
Mꢁnster University of Applied Sciences
Stegerwaldstr. 39, 48565 Steinfurt (Germany)
[c] Dr. C. A. Strassert
Center for Nanotechnology (CeNTech) and Physikalisches Institut
Westfꢀlische Wilhelms-Universitꢀt Mꢁnster
Heisenbergstr. 11, 48149 Mꢁnster (Germany)
E-mail: ca.s@wwu.de
[d] Prof. L. De Cola
Center for Nanotechnology (CeNTech) and Physikalisches Institut
Westfꢀlische Wilhelms-Universitꢀt Mꢁnster
Heisenbergstr. 11, 48149 Mꢁnster (Germany)
Current address:
Institut de Science et d’Ingꢂnierie Supramolꢂculaires
Universitꢂ de Strasbourg, 8 Allꢂe Gaspard Monge
67000 Strasbourg (France)
In the present work, we have tuned the structure in order to
make it water soluble by attaching two tetraethylene glycol
(TEG) chains on the ancillary ligand (Scheme 1, 1–4), while
keeping the chromophoric tridentate chelate unaffected. The
E-mail: decola@unistra.fr
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201403772.
Chem. Eur. J. 2014, 20, 1 – 7
1
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Communication
Scheme 1. Synthesis of complex Pt-TEG, a) NaH, dry THF, 3-chloro-2-(chloro-
methyl)prop-1-ene, from room temperature (RT) to 658C, overnight (90%
yield); b) BH3·THF stir at 08C for 3 h, NaOH-H2O2, stir at RT for 1.5 h (85%
yield); c) Ag2O, tosyl chloride, KI, DCM, RT, 2 h (75% yield), d) 4-hydroxypyri-
dine, K2CO3, CH3CN, reflux, 48 h (75% yield) and e) [Pt(dmso)2Cl2], 2,6-bis-
(tetrazole-5-yl)pyridine, DIPEA, CH3CN, reflux under N2 overnight (yield 60%).
Figure 1. Concentration-dependent absorption spectra of Pt-TEG in water at
RT (0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 05, 0.75 and 1 mm). Inset: Lambert–
Beer plot with nonlinear fit.
resulting complex, Pt-TEG (Scheme 1), can form hydrogels
upon interaction of the TEG chains with CDs. Interestingly, due
to the self-assembly of the complex, phosphorescence is ob-
served in water. Furthermore, we demonstrate that the lumi-
nescence of the resulting hydrogels can be tuned by changing
the size of the CD host (a- or b-CD). The synthesis, characteri-
sation, photophysical, rheological and morphological proper-
ties are described herein.
ance is plotted against the concentration (Figure 1 in water
and Figure S3 in DCM in the Supporting Information). Consis-
tently, only above 10À4 m, the emission of these aggregates
was observed at 590 nm in DCM and at 580 nm in water, and
3
can be assigned to a radiative transition from a MMLCT state.
The emission of the monomeric form was not observed at
room temperature. The excitation spectra obtained by moni-
toring the emission of the aggregates reproduce the band at
430 nm (Figure 2).
The complex Pt-TEG was prepared by reacting the ancillary
ligand 4 and 2,6-bis(tetrazole-5-yl)pyridine with [Pt(dmso)2Cl2]
(Scheme 1). The compound was purified by column chroma-
1
tography and characterised by H and 13C NMR spectroscopy,
The emission of Pt-TEG is red-shifted from 550 nm in neat
films to 590 nm in fluid DCM (Figure 2 and Figure S4 in the
Supporting Information), due to the stabilisation of the emis-
sive CT state by the solvent. However, we observe a subtle yet
clear blue-shift of the luminescence when going from DCM to
HR-MS and elemental analysis. Solvent-dependent 1H NMR
studies confirmed the aggregation phenomena evidenced by
the photophysical properties (vide infra). Indeed, the aromatic
signals (doublets in CD2Cl2) collapse into broad bands in D2O
(Figure S1 in the Supporting Information). Furthermore, the ar-
omatic signals are broadened and shifted to higher fields
when compared to CD2Cl2, which indicates that the aromatic
(hydrophobic) part is mainly responsible for the aggregation
process induced by p–p interactions. Thus, the aromatic pro-
tons are shifted up-field upon aggregation, whereas the signals
of the TEG chains are barely displaced and remain essentially
unaffected in terms of multiplicity (Figure S1 in the Supporting
Information).
The room-temperature absorption spectra of Pt-TEG in DCM
(Figure S2 in the Supporting Information) and in water
(Figure 1) display an ancillary pyridine- and a tridentate-ligand-
centred (1LC) p–p* transition (310 and 340 nm, respectively), as
well as the characteristic, lower energy, metal-to-ligand charge-
transfer (1MLCT) bands (360–400 nm).[8a,i] Comparing solutions
of increasing concentration (between 10À5 and 10À3 m), the rise
of a new absorption band at 430 nm can be observed above
10À4 m, and can be assigned to a metal-to-metal-to-ligand
charge-transfer (1MMLCT) absorption band, which clearly
points towards ground state aggregation equilibria. This is sup-
ported by the clear deviations from linearity when the absorb-
Figure 2. Excitation (left, lem =580 or 590 nm) and emission (right,
lex =430 nm) of 10À4 m Pt-TEG at RT in aerated DCM (—) and water (···).
&
&
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
2
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communication
3
water. A slightly increased Pt–Pt distance due to an enhanced
solvation of the hydrophilic TEG tails in the periphery of the
aggregates accounts for this observation. As water solvates the
hydrophilic TEG tails more efficiently than DCM, it increases
the separation between the PtII centres, causing a concomitant
blue-shift. Bredas et al.[17] have recently shown that the proper-
ties of triplet excimers of PtII complexes strongly depend on
their relative orientation, and the resulting Pt–Pt distances and
p–p stacking. Thus, we cannot exclude a different packing in
the two solvents, leading in DCM to a syn-orientation between
two adjacent complexes (both tridentate ligands on top of
each other), and an anti-configuration in water (with the tri-
dentate ligand on top of the pyridine). Indeed, the observed
augmentation of the radiative rate constant (Table 1) also
points towards a higher transition dipole moment. Thus, a four-
fold enhancement of the luminescence quantum yield is ob-
tained in water, as compared to DCM. Such enhancement of
the radiative process indicates that the above-mentioned dif-
ferent relative orientations and their effect on the excited state
are mostly responsible for the variation of the transition dipole
moments.
emission at 420 or 450 nm, the long LC decay (ca. 13 ms) is ob-
served. At 570 nm, the emission decay shows a shorter-lived
3MMLCT component (ca. 4 ms) (Table 1).
The Pt-TEG complex self-assembles into discrete aggregates
at higher concentrations in water, rather than forming a gelat-
ing network. Indeed, dynamic light scattering (DLS) measure-
ments (Figure S5a in the Supporting Information) and trans-
mission electron microscopy (TEM) (Figure S5b–d in the Sup-
porting Information) revealed that above 1 mm, Pt-TEG assem-
bles into amorphous structures of variable size. The DLS meas-
urements showed two distributions, one below 6 nm that can
be assigned to the smaller aggregates observed in the TEM
(Figure S5b–d), and one between 30 and 300 nm related to
the larger assemblies.
To favour the gelation process in water, CDs were added to
induce host–guest interactions between the TEG chains of the
complex and the hydrophobic cavity of the CDs. In order to
obtain stable gels, the minimum molar concentration ratio be-
tween Pt-TEG and CDs is 1:7 (Table 2). Interestingly, a- and b-
CDs gave stable gels (Figure 3a, b, e and f), whereas no gela-
tion was observed with g-CD (Figure S7 in the Supporting In-
formation), most likely due to the size mismatch between the
TEG tails and the cavity.[15b] In the case of a- or b-CD, one CD
unit forms a host–guest complex with one ethylene oxide seg-
ment.[15] As the Pt-TEG complex bears two tetraethylene glycol
moieties, up to four CD molecules can be bound to one mole-
cule of Pt-TEG. The excess of three CD molecules is probably
required for hydrogen bonding between the host–guest com-
The emission and excitation spectra of Pt-TEG at 77 K were
measured in 2-methyltetrahydrofuran (2-MeTHF) (Figure S4 in
the Supporting Information). The emission of the monomer
and the aggregates were both observed, depending on the ex-
citation wavelength. Upon excitation in the UV (lex =330 nm),
we observed predominant deep-blue emission (lem =420 nm)
with a clear vibrational progression that can be assigned to
the phosphorescence from the metal-perturbed ligand-centred
excited triplet state (3LC) of the monomeric species, and
a weaker unstructured luminescence (lem =570 nm) similar to
the room-temperature emission of the aggregated species,
Table 2. Composition of hydrogels.
Hydrogel
Guest (Pt-TEG)
[mg]
Host (CD)
[mg]
Volume of
water [mL]
3
which is attributed to a MMLCT state. As expected, due to the
CT character, the emission of the aggregates in a rigid matrix
at 77 K is blue-shifted as compared to fluid solution. Excited
state lifetimes confirm these assignments.[8i] Monitoring the
a-hydrogel
b-hydrogel
16.5
16.6
117
120
250
250
Table 1. Photophysical data of Pt-TEG.
t [ms][c]
lem [nm]
F (ꢁ100)
kr [106 sÀ1
]
knr [10À6 sÀ1
]
DCM[a]
0.040 (74%), 0.154 (26%)
0.038 (74%), 0.145 (26%)
0.017 (81%), 0.058 (19%)
0.513
0.219 (62%), 0.382 (38%)
0.126 (67%), 0.384 (33%)
0.285 (39%), 0.567 (61%)
0.511
3.89 (90%), 11.58 (10%)
3.99 (91%), 12.90(9%)
4.07(87%), 12.85(13%)
12.96
590
590
580
550
558
580
555
555
570
570
570
0.07[d]
0.01
0.01
0.105
0.385
0.237
0.22
0.39
0.525
–
–
–
–
–
14.48
15.4
40.25
1.56
3.32
4.53
1.8
1.43
–
–
–
–
–
DCM[b]
0.07[d]
water
neat film
a-hydrogel
b-hydrogel
a-xerogel
b-xerogel
2-MeTHF, 77 K (lex =435 nm, lem =570 nm)
2-MeTHF, 77 K (lex =365 nm, lem =570 nm)
2-MeTHF, 77 K (lex =330 nm, lem =570 nm)
2-MeTHF, 77 K (lex =365 nm, lem =450 nm)
2-MeTHF, 77 K (lex =365 nm, lem =420 nm)
2-MeTHF, 77 K (lex =330 nm, lem =450 nm)
2-MeTHF, 77 K (lex =330 nm, lem =420 nm)
0.26[d]
19.73[f]
6.65[e]
4.60[e]
18.05[e]
26.85[e]
–
–
–
–
–
–
–
570, 420, 450
13.05
12.65
12.88
570, 420, 450
570, 420, 450
570, 420, 450
–
–
–
–
[a] Deaerated. [b] Aerated. [c] Relative amplitudes are given in brackets. [d] Quantum yields determined using [Ru(bpy)3Cl2]·xH2O as a reference (lex
=
390 nm).[18] [e] Quantum yields measured using an integrating sphere (lex =445 nm). [f] Quantum yields measured using an integrating sphere, averaging
between lex =330 nm and lex =430 nm.
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
3
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Communication
sulting solvation of the emissive aggregates is less efficient in
the a-hydrogel than in the b-hydrogel, thus shifting the lumi-
nescence to higher energies at which the xerogels also emit
(lmax =550 nm). Indeed, the emission wavelengths of both xe-
rogels (Figure 3c, d, g and h) are similar to the neat films of
pure Pt-TEG, due to the complete lack of solvent stabilisation
of the emissive excited state (Table 1 and Figure S6 in the Sup-
porting Information). The excited state lifetime of the b-xerogel
and the neat film are the same, whereas those of the a-xerogel
are of the same order of magnitude, but bi-exponential in
nature (Table 1). The b-xerogel reaches the highest photolumi-
nescence quantum yield (PLQY), namely 27%, whereas the a-
xerogel is somewhat less luminescent (PLQY=18%).
Both hydrogels are stable at room temperature for several
days, and display reversible sol–gel transitions for several times
upon heating to 70–808C and leaving at room temperature for
10–15 min. A rheological characterisation was carried out for
the a-hydrogel, whereas the b-hydrogel appears too grainy for
reliable measurements. A stress amplitude sweep at
258C under oscillating deformation at 1 Hz showed
that the elastic part of the shear modulus (G’) re-
mains dominant by about two orders of magnitude
over the viscous part (G’’), up to very high stress am-
plitudes (ca. 200 Pa), thus pointing to a quite rigid
underlying three-dimensional structure (Figure 5a). In
measurements in which the gap between cone and
plate of the rheometer was filled only in the region
around the cone tip (in order to avoid problems with
sample slip at high stress amplitudes), G’ and G’’ are
demonstrated to be clearly correlated with each
other (as expected by the Kramers–Kronig relations),
showing the consistency of the rheological data (Fig-
ure S9 in the Supporting Information).
Figure 3. a-hydrogel a) under day light and b) UV-light; c) and d) are SEM
images of the a-xerogel. b-hydrogel under e) day light and f) UV-light; g)
and h) are SEM images of the b-xerogel.
For stationary flow, conditions for mechanical
breakdown of the gel can be interpreted as yield
stress. In systems with strong interaction, flow
beyond yield stress often follows a power law (Ost-
wald–de Waele equation). In Figure S10 in the Sup-
porting Information, the absolute value of the com-
plex viscosity of the a-hydrogel (as measured in Fig-
ure S9 in the Supporting Information) is plotted over
Figure 4. Left: Excitation spectra (lem =555 nm or lem =580 nm for a- and b-hydrogels,
respectively); right: emission spectra (lex =445 nm) of a-hydrogel (···) and b-hydrogel
(—).
plexes and with water, which ultimately stabilises the hydro-
gels (Figure S8 in the Supporting Information). The hydrogels
showed emissions in the visible part of the electromagnetic
spectrum (Figure 4) that depend on the CD employed for the
gelation. The a-hydrogel emission (lmax =558 nm) is strongly
blue-shifted as compared to the b-hydrogel (lmax =580 nm),
whereas the radiative rate constant remains essentially unaf-
fected (Table 1). The fact that the radiative process is not influ-
enced indicates that the nature of the emissive state is essen-
tially the same in both cases. Thus, a comparable relative ori-
entation of the aggregated complexes is expected. Indeed, in
the absence of water, the radiative rate constants of the xero-
gels are comparable with the ones of the hydrogels, whereas
the non-radiative deactivation is significantly prevented due to
the higher rigidity of the environment in the absence of sol-
vent. Thus, it is clear that the accessibility to water and the re-
the stress amplitude in that region only, that is, the part domi-
nated by the viscous part of the modulus, G’’. The data can be
fitted to a power law with an exponent typical for shear-thin-
ning behaviour. This demonstrates again that the structure of
the a-hydrogel is dominated by strong local interactions. How-
ever, once the a-hydrogel is destroyed by mechanical stress, it
recovers from its fluid state only slowly, but not to the previ-
ous strength; this can be restored only through thermal cy-
cling via the sol state. Amplitude sweeps after mechanical
breakdown showed gel-like elastic behaviour (G’ is much
larger then G’’), but not with the same high values of G’ as pre-
viously observed, and without being resistant against high
stress levels as before (Figure 5b). The gels obtained by recov-
ery after breakdown at room temperature are evidently weaker
than the freshly prepared ones by cooling from the sol state. It
thus appears that the mobility of the constituents at room
&
&
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
4
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communication
d) C. A. Palma, M. Cecchini, P. Samori, Chem. Soc. Rev. 2012, 41, 3713–
3730; e) G. M. Whitesides, B. Grzybowski, Science 2002, 295, 2418–2421;
f) J. M. Lehn, Proc. Natl. Acad. Sci. USA 2002, 99, 4763–4768; g) D. Philp,
J. F. Stoddart, Angew. Chem. Int. Ed. Engl. 1996, 35, 1154–1196; Angew.
Chem. 1996, 108, 1242–1286; h) G. V. Oshovsky, D. N. Reinhoudt, W. Ver-
boom, Angew. Chem. Int. Ed. 2007, 46, 2366–2393; Angew. Chem. 2007,
119, 2418–2445; i) W. Li, Y. Kim, M. Lee, Nanoscale 2013, 5, 7711–7723;
j) E. Busseron, Y. Ruff, E. Moulin, N. Giuseppone, Nanoscale 2013, 5,
7098–7140; k) A. R. Hirst, B. Escuder, J. F. Miravet, D. K. Smith, Angew.
Chem. Int. Ed. 2008, 47, 8002–8018; Angew. Chem. 2008, 120, 8122–
8139.
[2] a) Y. Q. Liang, Y. Qiao, S. T. Guo, L. Wang, C. P. Xie, Y. L. Zhai, L. D. Deng,
A. J. E. Dong, Soft Matter 2010, 6, 1915–1922; b) J. K. Oh, Soft Matter
2011, 7, 5096–5108; c) M. H. Park, M. K. Joo, B. G. Choi, B. Jeong, Acc.
Chem. Res. 2012, 45, 424–433; d) I. Tomatsu, K. Peng, A. Kros, Adv. Drug
Delivery Rev. 2011, 63, 1257–1266.
[3] W. T. Truong, Y. Su, J. T. Meijer, P. Thordarson, F. Braet, Chem. Asian J.
2011, 6, 30–42.
[4] a) X. Y. Yang, G. X. Zhang, D. Q. Zhang, J. Mater. Chem. 2012, 22, 38–50;
b) H. Maeda, Chem. Eur. J. 2008, 14, 11274–11282; c) J. H. van Esch,
Langmuir 2009, 25, 8392–8394; d) S. S. Babu, V. K. Praveen, A. Ajaya-
ghosh, Chem. Rev. 2014, 114, 1973–2129; e) G. Yu, X. Yan, C. Han, F.
Huang, Chem. Soc. Rev. 2013, 42, 6697–6722; f) N. M. Sangeetha, U.
Maitra, Chem. Soc. Rev. 2005, 34, 821–836.
[5] Z. Yang, G. Liang, B. Xu, Acc. Chem. Res. 2008, 41, 315–326.
[6] a) Z. Huang, H. Lee, E. Lee, S. K. Kang, J. M. Nam, M. Lee, Nat. Commun.
2011, 2, 459; b) C. Yang, D. Li, Z. Liu, G. Hong, J. Zhang, D. Kong, Z.
Yang, J. Phys. Chem. B 2012, 116, 633–638; c) S. Zhang, M. A. Greenfield,
A. Mata, L. C. Palmer, R. Bitton, J. R. Mantei, C. Aparicio, M. O. de La Cruz,
S. I. Stupp, Nat. Mater. 2010, 9, 594–601; d) E. C. Wu, S. Zhang, C. A. E.
Hauser, Adv. Funct. Mater. 2012, 22, 456–468.
[7] a) J. W. Steed, Chem. Commun. 2011, 47, 1379–1383; b) G. De Paoli, Z.
ˇ
ˇ
Dzolic, F. Rizzo, L. De Cola, F. Vçgtle, W. M. Mꢂller, G. Richardt, M. Zinic,
Adv. Funct. Mater. 2007, 17, 821–828; c) Y. Qiao, Y. Lin, S. Zhang, J.
Huang, Chem. Eur. J. 2011, 17, 5180–5187; d) P. K. Sukul, D. Asthana, P.
Mukhopadhyay, D. Summa, L. Muccioli, C. Zannoni, D. Beljonne, A. E.
Rowan, S. Malik, Chem. Commun. 2011, 47, 11858–11860; e) A. Kishi-
mura, T. Yamashita, T. Aida, J. Am. Chem. Soc. 2005, 127, 179–183.
[8] a) C. A. Strassert, C. H. Chien, M. D. Galvez Lopez, D. Kourkoulos, D.
Hertel, K. Meerholz, L. De Cola, Angew. Chem. Int. Ed. 2011, 50, 946–
950; Angew. Chem. 2011, 123, 976–980; b) A. Y. Tam, K. M. Wong, V. W.
Yam, J. Am. Chem. Soc. 2009, 131, 6253–6260; c) K. C. Chang, J. L. Lin,
Y. T. Shen, C. Y. Hung, C. Y. Che, S. S. Sun, Chem. Eur. J. 2012, 18, 1312–
1321; d) W. Lu, Y. C. Law, J. Han, S. S. Chui, D. L. Ma, N. Zhu, C. M. Che,
Chem. Asian J. 2008, 3, 59–69; e) J. Zhang, X.-D. Xu, L.-J. Chen, Q. Luo,
N.-W. Wu, D.-X. Wang, X.-L. Zhao, H.-B. Yang, Organometallics 2011, 30,
4032–4038; f) J. Wang, Y. Chen, Y. C. Law, M. Li, M. X. Zhu, W. Lu, S. S.
Chui, N. Zhu, C. M. Che, Chem. Asian J. 2011, 6, 3011–3019; g) M.
Mydlak, M. Mauro, F. Polo, M. Felicetti, J. Leonhardt, G. Diener, L.
De Cola, C. A. Strassert, Chem. Mater. 2011, 23, 3659–3667; h) C.
Cebriꢃn, M. Mauro, D. Kourkoulos, P. Mercandelli, D. Hertel, K. Meerholz,
C. A. Strassert, L. De Cola, Adv. Mater. 2013, 25, 437–442; i) N. K. Allam-
pally, C. A. Strassert, L. De Cola, Dalton Trans. 2012, 41, 13132–13137.
[9] A. Y. Tam, D. P. Tsang, M. Y. Chan, N. Zhu, V. W. Yam, Chem. Commun.
2011, 47, 3383–3385.
Figure 5. a) Amplitude sweep of the a-hydrogel, and b) amplitude sweeps
of the a-hydrogel after mechanical breakdown (loss of elastic nature by me-
chanical stress); time elapsed after breakdown according to the legend.
temperature is too small to enable the complete self-reassem-
bly of the a-hydrogel.
In summary, our strategy combines the versatility of supra-
molecular self-assemblies with the tuneable multi-centred
phosphorescence of PtII complexes within a soft architecture.
The sensitivity of the luminescence towards structural varia-
tions paves a new way for the design of water-processable
functional materials with optical and sensing properties for
technological and biomedical applications.
[10] a) V. W. Yam, K. H. Chan, K. M. Wong, N. Zhu, Chem. Eur. J. 2005, 11,
4535–4543; b) K. M. Wong, V. W. Yam, Acc. Chem. Res. 2011, 44, 424–
434.
Acknowledgements
[11] J. R. Kumpfer, S. D. Taylor, W. B. Connick, S. J. Rowan, J. Mater. Chem.
2012, 22, 14196.
N. K. Allampally acknowledges the NRW Graduate School of
Chemistry (NRW GSC-MS) for doctoral fellowship. We acknowl-
edge Dr. Henning Lꢂlf for the SEM images.
[12] a) N. Komiya, T. Muraoka, M. Iida, M. Miyanaga, K. Takahashi, T. Naota, J.
Am. Chem. Soc. 2011, 133, 16054–16061; b) A. Y. Tam, K. M. Wong, N.
Zhu, G. Wang, V. W. Yam, Langmuir 2009, 25, 8685–8695; c) Y. Li, A. Y.
Tam, K. M. Wong, W. Li, L. Wu, V. W. Yam, Chem. Eur. J. 2011, 17, 8048–
8059; d) T. Cardolaccia, Y. Li, K. S. Schanze, J. Am. Chem. Soc. 2008, 130,
2535–2545; e) C. A. Strassert, M. Mauro, L. De Cola in Photophysics of
soft and hard molecular assemblies based on luminescent complexes, Vol.
63 Academic Press, 2011, pp. 47–103.
Keywords: aggregation · host–guest systems · hydrogels ·
phosphorescence · platinum
[1] a) L. A. Estroff, A. D. Hamilton, Chem. Rev. 2004, 104, 1201–1218; b) S. S.
Babu, S. Prasanthkumar, A. Ajayaghosh, Angew. Chem. Int. Ed. 2012, 51,
1766–1776; Angew. Chem. 2012, 124, 1800–1810; c) M. O. Piepenbrock,
G. O. Lloyd, N. Clarke, J. W. Steed, Chem. Rev. 2010, 110, 1960–2004;
[13] a) W. Lu, Y. Chen, V. A. Roy, S. S. Chui, C. M. Che, Angew. Chem. Int. Ed.
2009, 48, 7621–7625; Angew. Chem. 2009, 121, 7757–7761; b) X.-S.
Xiao, W. Lu, C.-M. Che, Chem. Sci. 2014, 5, 2482–2488; c) C. Rest, M. J.
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Communication
Mayoral, K. Fucke, J. Schellheimer, V. Stepanenko, G. Fernandez, Angew.
Chem. Int. Ed. 2014, 53, 700–705; Angew. Chem. 2014, 126, 716–722.
[14] S. Banerjee, R. Kandanelli, S. Bhowmik, U. Maitra, Soft Matter 2011, 7,
8207–8215.
[15] a) A. Harada, J. Li, M. Kamachi, Nature 1992, 356, 325–327; b) A. Harada,
J. Li, M. Kamachi, Nature 1994, 370, 126–128; c) A. Harada, M. Okada, J.
Li, M. Kamachi, Macromolecules 1995, 28, 8406–8411; d) A. Harada, M.
Kamachi, Macromolecules 1990, 23, 2821–2823.
[16] a) S. Tamesue, Y. Takashima, H. Yamaguchi, S. Shinkai, A. Harada, Angew.
Chem. Int. Ed. 2010, 49, 7461–7464; Angew. Chem. 2010, 122, 7623–
7626; b) Y. Yan, H. Wang, B. Li, G. Hou, Z. Yin, L. Wu, V. W. Yam, Angew.
Chem. Int. Ed. 2010, 49, 9233–9236; Angew. Chem. 2010, 122, 9419–
9422; c) T. Ogoshi, Y. Takashima, H. Yamaguchi, A. Harada, J. Am. Chem.
Soc. 2007, 129, 4878–4879; d) Y. Takashima, T. Nakayama, M. Miyauchi,
Y. Kawaguchi, H. Yamaguchi, A. Harada, Chem. Lett. 2004, 33, 890–891;
e) W. Deng, H. Yamaguchi, Y. Takashima, A. Harada, Angew. Chem. Int.
Ed. 2007, 46, 5144–5147; Angew. Chem. 2007, 119, 5236–5239; f) Y.
Wang, N. Ma, Z. Wang, X. Zhang, Angew. Chem. Int. Ed. 2007, 46, 2823–
2826; Angew. Chem. 2007, 119, 2881–2884; g) Y. Wang, H. Xu, X. Zhang,
Adv. Mater. 2009, 21, 2849–2864.
[17] D. Kim, J. L. Bredas, J. Am. Chem. Soc. 2009, 131, 11371–11380.
[18] H. Ishida, S. Tobita, Y. Hasegawa, R. Katoh, K. Nozaki, Coord. Chem. Rev.
2010, 254, 2449–2458.
Received: June 1, 2014
Published online on && &&, 0000
&
&
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communication
COMMUNICATION
&
Supramolecular Hydrogels
N. K. Allampally, M. Bredol,
C. A. Strassert,* L. De Cola*
&& – &&
Highly Phosphorescent
Supramolecular Hydrogels Based on
Platinum Emitters
Light and sweet! Phosphorescent hy-
drogels based on a PtII emitter (guest)
and cyclodextrins (a- and b-CD; host)
are presented. The resulting soft assem-
blies feature host-dependent emission
properties.
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
7
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ