1. Study of the Size-Reduction Effect on the
Photophysical Properties of [Ru(bpy)3][NaCr(ox)3]
Nano-Crystals and Functionalization of their Surface
Elia Previtera
November 24, 2016
Département de Chimie Physique, Université de Genève
Hauser Group

2. Nano-Size Materials
Applications: Medicine, Bio-imaging, IT, Solar-Energy Harvesting and
Conversion, Lasers, Catalysis, Displays …..
Quantum Dots: tunable emission
wavelength…...
Gold Nanoparticles: tunable absorption
wavelength…..
Size
1
SIZE DEPENDENT PROPERTIES
5
nm
10
nm
15
nm
20
nm
80
nm
90
nm
100
nm
Nano Today 2011.

3. Nano-Size Materials
2The New York Times article of February 22, 2005.

4. Nano-Size Materials
At least one dimensions between 1 and 100 nm
X
At least one physical or chemical size-
dependent property
M.L. Grieneisen, M. Zhang, Small 2011, 7, No. 20, 2836-2839.
What is What in the Nanoworld: A Handbook on Nanoscience and Nanotechnology
2012.
3

5. Energy Transfer and Migration
..
... .
..
Homo-Energy Transfer or Energy Migration
Hetero-Energy Transfer
..
..
. .
. .
..
. .
.
. .
.
..
... .
..
4

6. Radiative Energy Transfer and Migration
Acceptor or DonorDonor*
S0
S1
S0
S1
hν hν’
5

7. Non-radiative Energy Transfer and Migration
HOMO
LUMO
Förster
AcceptorDonor*
Dexter
AcceptorDonor*
kEET
F
∝
1
RDA
⎛
⎝
⎜⎜
⎞
⎠
⎟⎟
6
kEET
Ex
∝exp −
2RDA
RDA
0
⎛
⎝
⎜⎜
⎞
⎠
⎟⎟
HOMO
LUMO
10 Å < Rc
F < 80 Å 1 Å < Rc
Ex < 10 Å
6

8. Non-radiative Energy Transfer and Migration
ΩDA
= gD
(E)gA
(E)dE∫
Spectral overlap integral
ΩDA
λ
Emi(A)Emi(D)Abs(D) Abs(A)
I
gD gA
7

9. Energy Transfer and Migration in Natural Antennae
6 CO2 + 6 H2O C6H12O6 + 6 O2
Respiration
Photosynthesis
Sunlight Energy stored
Energy storedEnergy released
Nature, 1995, 374, 517. 8

10. Energy Transfer and Migration in Natural Antennae
Photosynthetic unit of Rhodopseudomonas acidophila
Nature, 1995, 374, 517. 9

11. Reference System: Microcrystals of [Ru(bpy)3][NaCr(ox)3]
Anionic Chiral 3D Polymeric Oxalate Networks
[NaCr(ox)3][Ru(bpy)3]
Na++
D3
[Cr(ox)3]3-
Crystal system
Cubic
Z = 4
Chiral Spacegroup
P213
Site symmetry of
all metal ions
C3
S. Decurtins et al., J. Amer. Chem. Soc. 116 (1994) 9521. 10

12. Reference System: Microcrystals of [Ru(bpy)3][NaCr(ox)3]
Anionic Chiral 3D Polymeric Oxalate Networks
[NaCr(ox)3][Ru(bpy)3]
Na++
D3
[Cr(ox)3]3-
Crystal system
Cubic
Z = 4
Chiral Spacegroup
P213
Site symmetry of
all metal ions
C3
S. Decurtins et al., J. Amer. Chem. Soc. 116 (1994) 9521. 11

13. Reference System: Microcrystals of [Ru(bpy)3][NaCr(ox)3]
Anionic Chiral 3D Polymeric Oxalate Networks
[NaCr(ox)3][Ru(bpy)3]
Na++
D3
[Cr(ox)3]3-
Crystal system
Cubic
Z = 4
Chiral Spacegroup
P213
Site symmetry of
all metal ions
C3
S. Decurtins et al., J. Amer. Chem. Soc. 116 (1994) 9521. 12

14. 3D oxalate network: [Ru(bpy)3][NaCr(ox)3]
[Ru(bpy)3]2+: antenna
Oxalate Networks to Study Photo-Induced Energy Transfer
Bulk: efficient energy migration in the 2E state of Cr(III)
[NaCr(ox)3]2- network: energy migration
Is there any influence of the crystal size on the energy migration
within the 2E state of the [Cr(ox)3]3- chromophores?
hν
Energy Transfer
Milos. M. et al., Coor. Chem. Rev., 252, 2000, 2540 13

15. Reference System: Microcrystals of [Ru(bpy)3][NaCr(ox)3]
Tetrahedral microcrystalline particles with side length 4 µm
S. Decurtins et al., J. Amer. Chem. Soc. 116 (1994) 9521.
5 µm
14

16. How to Synthesize Nanocrystals?
Ø Synthesis by the Reverse Micelles technique
Aqueous phase: Solubilization of
[Ru(bpy)3]Cl2
.6H2O and K3[Cr(ox)3].3H2O
Surfactant: Sodium bis(2-ethylhexyl)
Sulfosuccinate (AOT)
Solvent: n-Heptane
TEM à Tetrahedral Shape of Nanocrystals
Centrifugation and
washing in EtOH
15

17. Size Controlled Micro- and Nanocrystals
Tetrahedral Shape of Nanoparticles
ImageJ
Large Size Distribution
16
1000 nm

18. Size & Volume Weighted Distribution
Iluminescence ≈ a3
a
17Previtera E. et al., Eur. J. Inorg. Chem. 2016, 1972-1979
< Size > =
Σa
Number of NPs < Size Signal > =
Σ(a x a3)
Total a3

19. Size Controlled Micro- and Nano-crystals
Ø Modification of the water-to-surfactant ratio (Wo)
Wo =
[H2O]
[Surfactant]
Size Control of final product!
Wo= 2 Wo= 5 Wo= 8
2.5 µm MPs changing Wo and lowering the
concentration of reactants inside micelles
(Wo= 8 and 0.025 M)
Previtera E. et al., Adv. Mater. 2015, 27, 1832. 18

20. Size Controlled Micro- and Nanocrystals
2θ = 5.8°
140 nm
220 nm
360 nm
450 nm
670 nm
2.5 µm
4 µm
Previtera E. et al., Adv. Mater. 2015, 27, 1832.
19

21. Chromium (III): d3 in C3 Symmetry
Ligand field states
4A2(t2g
3)
4T2(t2g
2eg
1)
4A2
2E
Oh C3 + Hso
R1 R2
D (2E) = 13.7 cm-1
D (4A2) = 1.3 cm-1
hν hν
Spin-flip
Δr ≈ 0
t2g → eg
Δr ≈ 0.1 Å2E(t2g
3)
ISC
t2g
eg
t2g
eg
t2g
eg
E
RCr-O
Ms = ± 3/2
Ms = ± 1/2
20

22. Solid State Spectroscopy Background
Homogeneous line width and inhomogeneous band broadening
Lorentzian with the
homogeneous linewidth
Γhom
2E
4A2
R1
D
A perfect crystal
Electronic origin of Chromium (III)
Andreas Hauser, Lecture Notes. 21

23. Solid State Spectroscopy Background
Homogeneous line width and inhomogeneous band broadening
Lorentzian with the
homogeneous linewidth
Γhom
2E
4A2
R1
D
A perfect crystalA real crystal
Electronic origin of Chromium (III)
Gaussian profile with the
i n h o m o g e n e o u s b a n d
broadening
Γinh
Andreas Hauser, Lecture Notes. 22

24. Excitation Spectra of Cr3+ R-Lines
Previtera E. et al., Adv. Mater. 2015, 27, 1832. 23

25. Excitation Spectra of Cr3+ R-Lines
Previtera E. et al., Adv. Mater. 2015, 27, 1832. 24

26. Luminescence Spectra
Previtera E. et al., Adv. Mater. 2015, 27, 1832. 25

27. Solid State Spectroscopy Background
Laser selective
excitation
non-resonant
fluorescence
2E
4A2
R1
D
resonant fluorescence
In the absence of any other
processes only the excited subset
emits.
The principle of Fluorescence Line Narrowing Spectroscopy (FLN)
Andreas Hauser, Lecture Notes. 26

28. Solid State Spectroscopy Background
Fluorescence Line Narrowing Spectroscopy Setup
27

29. FLN Spectra
Previtera E. et al., Eur. J. Inorg. Chem. 2016, 1972-1979
Ø Energy Transfer Core à Surface
28

30. FLN Spectra across the R1 Absorption
Previtera E. et al., Eur. J. Inorg. Chem. 2016, 1972-1979
Size: 140 nm
Ø Smaller numbers of members in the FLN multiline pattern at lower energy
29

31. FLN Spectra across the R1 Absorption
Previtera E. et al., Eur. J. Inorg. Chem. 2016, 1972-1979
Size: 670 nm Size: 2.5 µm
Ø Smaller numbers of members in the FLN multiline pattern at lower energy
30

32. ZFS as Function of FLN Excitation Wavelength
Previtera E. et al., Eur. J. Inorg. Chem. 2016, 1972-1979
Ø Crystalline environment of the [Cr(ox)3]3- chromophores at the
surface is slightly different to that of the complexes in the bulk
31

33. Time Resolved FLN Spectra
Previtera E. et al., Eur. J. Inorg. Chem. 2016, 1972-1979
hν’
Energy migration inside 2E of Cr(III)
Cr3+
2E
4A2
hν
4A2
2E
Cr3+ Cr3+ Cr3+
4T2
Core Surface
32

34. Luminescence Decay Kinetics
Ø Directional Energy Transfer from the Core to the Surface
Previtera E. et al., Adv. Mater. 2015, 27, 1832.
Previtera E. et al., Eur. J. Inorg. Chem. 2016, 1972-1979
Multi line pattern
decay
(at 14394 cm-1)
τ4 µm = 1.3 ms
τ2.5 µm = 155 µs
τ670 nm = 132 µs
τ140 nm = 57 µs
Broad band rise to
maximum intensity
(at 14371 cm-1)
220 µs for 2.5 mm
180 µs for 670 nm
60 µs for 140 nm
Broad band rise to
maximum intensity
(at 14351 cm-1)
400 µs for 2.5 mm
360 µs for 670 nm
180 µs for 140 nm
33
l

35. How far does the energy travel?
Ø Average distance travelled by the energy is of the order of a few hundreds nm
RC resonant process à up to 30 Å
Ø l = 140 nm à d = 30 nm
10 steps for energy migration
Core à Surface
Ø l = 670 nm à d = 138 nm
46 steps for energy migration
Core à Surface
Ø l = 2.5 µm à d = 510 nm
170 steps for energy migration
Core à Surface
Previtera E. et al., Adv. Mater. 2015, 27, 1832.
Previtera E. et al., Eur. J. Inorg. Chem. 2016, 1972-1979
34

36. Energy Transfer Mechanism
Previtera E. et al., Eur. J. Inorg. Chem. 2016, 1972-1979
1A1
[Ru(bpy)3]2+
35
<< 1 µs
< 1 ns

37. Conclusions
• Size-controlled micro- and nano-crystals of [Ru(bpy)3][NaCr(ox)3]
• Directional Energy Transfer from the Core to the Surface
• Average distance travelled by the energy is of the order of few hundreds nm
Previtera E. et al., Adv. Mater. 2015, 27, 1832.
Previtera E. et al., Eur. J. Inorg. Chem. 2016, 1972-1979
36
l

38. Control of the surface state
$ Growth of oxalate network shell with
cavities filled with energy acceptor
[Cr(bpy)3]3+
$ Direct chemical grafting of Ln3+ complexes
(Ln3+ = Er3+, Eu3+, Yb3+)
37

39. Growing an Oxalate network shell
• Core: 670 nm NPs
[Ru(bpy)3][NaCr(ox)3] and [Ru(bpy)3][NaAl(ox)3] = RuCr, RuAl
• Core-Shell:
[Ru(bpy)3][NaAl(ox)3]@[Ru(bpy)3][NaCr(ox)3] = RuAl@RuCr
[Ru(bpy)3][NaCr(ox)3]@[NaCr(ox)3][Cr(bpy)3]ClO4 = RuCr@CrCr
[Ru(bpy)3][NaAl(ox)3]@[NaCr(ox)3][Cr(bpy)3]ClO4 = RuAl@CrCr
38

40. Growing an Oxalate network shell
PUMP
Reactants Size
nm
[Ru(bpy)3][NaMIII(ox)3]
MIII = Cr3+, Al3+
670
(NH4)3[Cr(ox)3] -
[Ru(bpy)3]Cl2
.6H2O -
[Cr(bpy)3]ClO4 -
NaCl -
39

41. Growing an Oxalate network shell
Surface change
• Roughness
• Round corners
Bigger average size
RuAl RuAl@RuCr
RuCr RuCr@CrCr
RuAl RuAl@CrCr
40

42. Growing an Oxalate network shell
41

43. Growing an Oxalate network shell
Ø Energy Transfer Core à Shell?
42

44. Growing an Oxalate network shell
43

45. Growing an Oxalate network shell
44

46. Conclusions
• It is possible to grow an Oxalate network shell of good crystalline quality
containing in its cavities the energy acceptor [Cr(bpy)3]3+.
• No evidence of energy transfer towards the shell in RuCr@CrCr was found.
45

47. Direct chemical grafting of Ln3+ complexes
Up-Conversion Nanoparticles
Nature Materials 2011. 46

48. Direct chemical grafting of Ln3+ complexes
365 nm
a) b)
[Rh(bpy)3][NaAl(ox)3]ClO4 + [Eu(hfac)3dig] [Rh(bpy)3][NaAl(ox)3]ClO4@[Eu(hfac)3] + dig
Preliminary Test
47
hfac = hexafluoroacetylacetonate
dig = diglyme or bis(2-methoxyethyl)ether

49. Direct chemical grafting of Ln3+ complexes
[Rh(bpy)3][NaAl(ox)3]ClO4 + [Eu(hfac)3dig] [Rh(bpy)3][NaAl(ox)3]ClO4@[Eu(hfac)3] + dig
48

50. Direct chemical grafting of Ln3+ complexes
Reactants Size
nm
[Ru(bpy)3][NaCr(ox)3]
RuCr
220
[Eu(hfac)3dig]
Eu
-
[Er(hfac)3dig]
Er
-
[Yb(hfac)3dig]
Yb
-
RuCr + [Ln(hfac)3dig] RuCr@[Ln(hfac)3] + dig
49
hfac = hexafluoroacetylacetonate
dig = diglyme or bis(2-methoxyethyl)ether

51. Excitation Spectra of Cr3+ R-Lines
50

52. ZFS as Function of FLN Excitation Wavelength
51

53. Direct chemical grafting of Ln3+ complexes
Ø Energy Transfer Core à [Ln(hfac)3]
52

54. Down-Converted Luminescence
53

55. Down-Converted Luminescence
54

56. Down-Converted Luminescence
55

57. Down-Converted Luminescence
56

58. • Improving of the NPs’ surface.
• Quenching of the broad band luminescence.
• Efficient excitation energy transfer from the 2E excited states of
the [Cr(ox)3]3- ions located at the surface towards the
lanthanides complexes grafted at the NPs’ surface.
• Good indication of down conversion luminescence related to
the lanthanides transitions 4I9/2à4I15/2 and 2F5/2à2F7/2 for
Erbium and Ytterbium.
• No up-conversion luminescence.
Conclusions
57

59. Outlook
• Direct chemical grafting of [Gd(hfac)3dig]
6P3/2
5/2
7/2
8S7/2
32200cm-1
• Enhancing of the lifetime of the surface [Cr(ox)3]3- chromophores?
• Would direct excitation of [Gd(hfac)3] complexes grafted at the surface give
directional energy transfer towards the chromophores located at the surface or
further into the core? 58

60. • This work contributes to the expansion of the basic
knowledge about nano-size materials.
• The energy can travel few hundreds of nanometers in
NCs. This important basic knowledge can be useful for
future applications in solar energy harvesting and
conversion.
• This work demonstrates that also particles with sizes
bigger than 100 nm can show size-dependent properties.
General Conclusions
59

61. Acknowledgements
Prof. Hauser
Dr. Lawson Daku
Dr. Chakraborty
Dr. Suffren
Dr. Sun
Teresa Delgado Perez
Andrea Missana
Catherine Ludy
Nahid Jeddi
Patrick Barman
Dominique Lovy
Laurent Devenoge
Hauser’ Group:
Prof. Decurtins
Prof. Hagemann
Dr. Tissot
Jury members:
Dr. Moury
Dr. Olchowka
Dr. Bierwagen
Manish Sharma
Daniel Sethio
Angelina Gigante
Hagemann’ Group:
Prof. Piguet
Dr. Nozary
Piguet’ Group:
Dr. Varnholt
Dr. Lawson Daku
Dr. Chakraborty
Dr. Moury
Andrea Missana
Manish Sharma
Corrections:
60

62. Thank you for your
attention!
61