Luminescence of metal complexes
Jablonski diagram
Differences between transition metal complexes and organic molecules
• The ground state of the transition metal complexes often not singlet: there are many different ground and excited states with different multiplicity.
• Generally transition metals have higher atomic
numbers („heavy atoms”) therefore the probability of the forbidden transitions increases via the spin-orbit coupling.
Electronic transitions of metal complexes
CT: charge transfer
MLCT: metal-to-ligand CT LMCT: ligand-to-metal CT MC: metal-centered
LC: ligand-centered
Absorption and luminescence spectra of
[Ru(bpy)
3]
2+Excited states of Ru complexes
Tuning the luminescence of Ir complexes
by changing the ligands
Heavy atom effect
• Mixing of the spin states due to spin-orbit coupling:
there are not pure singlet, triplet states
• The probability of the forbidden transitions increases
• Accelaration of the radiative and nonradiative transitions
• The effect depend mainly on the atomic number (~Z4)
• Relativistic effect
• Significant in case of platinum group metals and Au (Br, I)
Heavy atom effect
F F / ns k ISC / s-1 P P / ms H2TPP 0,11 13 6 x 107 4 x 10 -5 6
MgTPP 0,15 9,2 9 x 107 0,015 45
ZnTPP 0,03 2,7 4 x 108 0,012 26
CdTPP 4 x 10 -4 0,065 2 x 1010 0,04 2,4 PdTPP 2 x 10 -4 0,02 5 x 1010 0,17 2,8
F k ISC / s-1 P P / ms
naphthalene 0,55 1,6 x 106 0,051 2300
1-fluoronaphthalene 0,84 5,7 x 105 0,056 1500 1-chloronaphthalene 0,058 4,9 x 107 0,30 290 1-bromonaphthalene 0,0016 1,9 x 109 0,27 20 1-iodonaphthalene < 5 x 10 -4 > 6 x 109 0,38 2
Investigation of luminescence
• Sample: solution, solid
• Spectra: emission, excitation
• Quantumyield (
L)
• Lifetime measurement:
timecorrelated singlephoton counting (TCSPC), gating method
Strong quenching effect of O
2→ deoxygenation
Interpretation → quantum chemistry
Luminescence of lanthanides
• Lanthanides: Ln - Lu
• Application of lanthanides:
lasers: Nd, Y, Er magnets: Nd, Sm
MRI contrast materials: Gd optical lenses: Ln
• Luminescence:
UV: Gd
3+VIS: Sm
3+, Eu
3+, Tb
3+, Dy
3+NIR: Nd
3+, Er
3+, Yb
3+Transitions of lanthanide ions
• Electron configuration: [Xe]4f 0-145d16s2
• Charge of metal ions: 3+, electrons in 4f orbit are shielded by the external closed 5s2 5p6 shells
• Ionic interaction dominates in coordination compounds
• Removing of the degeneration of 4f orbit (spin-orbit coupling)
• Absorption and luminescence spectra:
f→f transitions are slightly influenced by surrounding environment → narrow bands
• Forbidden electronic transitions → small (<10 M-1cm-1), : s - ms
Antenna-metal ion complexes
• Lantanide chelate complexes containing strong chromofor ligands
• Ligands: large (103-104 M-1cm-1)
• Efficient energy transfer to the metal ion (exoterm)
• The luminescence is specific to the lantanide (spectrum, lifetime)
• Increase of L
Antenna complex
Immunoassay
(Detection of antigen-antibody interaction)
The autofluorescence of the sample can be excluded by gating technic.
Measurement of an antibiotics
(competitive immunoassay)
Luminescence of Au(I) complexes
• Electron structure of Au(I) ion: [Xe] 4f
145d
10• Very high (Z=79) atomic number → strong heavy atom effect → phosphorescence
• Inter or intramolecular aurophilic interaction
Aurophilic (metalophilic) interaction
• Attractive interaction between two Au (Ag, Cu) atoms
• Similar to the van der Waals interaction but stronger
• Typical range of action: 2,75-3,40 Å
• Appearance of luminescence
Mechanochromic luminescence
(JACS, 2008,130, 10044)
Interpretation of the mechanochromic luminescence
Application of luminescence of the metal complexes
• Analitical chemistry
• Sensors based on metal complexes (O
2, pH, ion)
• Biological application, microscopic imaging
• Electroluminescencent displays (OLED)
Photoinduced electrontransfer (PET)
PET metal ion sensor based on acridone
(Tetrahedron, 2010, 66, 2953)
K
+sensor Au(I) complex
Complexation → aurophilic interaction (emission at 720 nm)
Oxygen sensors
• The excited (singlet, triplet) states are quenched by molecular oxygen very efficiently.
• Stern-Volmer equation:
• Intensity measurement
• Lifetime measurement
Oxygen sensor
(Relative intensity measurement)
• Fluorescence intensity independent of [O2] (F = 0,5 ns)
• Phosphorescence intensity dependent on [O2] (P = 14 s)
Oxygen sensor film
(Relative intensity measurement)
B: CdTe quantum dot A:
A B
Oxygen sensor
(Intensity and lifetime measurement)
Microscopic imaging of oxygen distribution
(Relative intensity measurement)
Ru(dpp)3
The luminescence lifetime measurement is independent of [O2].
Microscopic imaging of oxygen distribution
(Lifetime measurement)
