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Luminescence of metal complexes

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.

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Luminescence of metal complexes

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  1. Luminescence of metal complexes

  2. Jablonski diagram

  3. 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.

  4. Electronic transitions of metal complexes CT: charge transfer MLCT: metal-to-ligand CT LMCT: ligand-to-metal CT MC: metal-centered LC: ligand-centered

  5. Absorption and luminescence spectra of [Ru(bpy)3]2+

  6. Excited states of Ru complexes The energy and the order of the excited states depend on the charge of the metal ion and the redox properties of the ligand.

  7. Tuning the luminescence of Ir complexes by changing the ligands

  8. 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)

  9. Heavy atom effect

  10. Investigation of luminescence • Sample: solution, solid • Spectra: emission, excitation • Quantumyield (L) • Lifetime measurement: timecorrelated singlephoton counting (TCSPC), gating method Strong quenching effect of O2 → deoxygenation Interpretation → quantum chemistry

  11. 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: Gd3+ VIS: Sm3+, Eu3+, Tb3+, Dy3+ NIR: Nd3+, Er3+, Yb3+

  12. 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

  13. 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

  14. Antenna complex

  15. Immunoassay(Detection of antigen-antibody interaction) The autofluorescence of the sample can be excluded by gating technic.

  16. Measurement of an antibiotics(competitive immunoassay)

  17. Luminescence of Au(I) complexes • Electron structure of Au(I) ion: [Xe] 4f14 5d10 • Very high (Z=79) atomic number → strong heavy atom effect → phosphorescence • Inter or intramolecular aurophilic interaction

  18. 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

  19. Mechanochromic luminescence(JACS, 2008,130, 10044)

  20. Interpretation of the mechanochromic luminescence

  21. Application of luminescence of the metal complexes • Analitical chemistry • Sensors based on metal complexes (O2, pH, ion) • Biological application, microscopic imaging • Electroluminescencent displays (OLED)

  22. Photoinduced electrontransfer (PET)

  23. PET metal ion sensor based on acridone (Tetrahedron, 2010, 66, 2953)

  24. K+ sensor Au(I) complex Complexation → aurophilic interaction (emission at 720 nm)

  25. Oxygen sensors • The excited (singlet, triplet) states are quenched by molecular oxygen very efficiently. • Stern-Volmer equation: • Intensity measurement • Lifetime measurement

  26. Oxygen sensor(Relative intensity measurement) • Fluorescence intensity independent of [O2] (F = 0,5 ns) • Phosphorescence intensity dependent on [O2] (P = 14 s)

  27. Oxygen sensor film(Relative intensity measurement) A: A B B: CdTe quantum dot

  28. Oxygen sensor(Intensity and lifetime measurement)

  29. Microscopic imaging of oxygen distribution(Relative intensity measurement) Ru(dpp)3 Oregon Green 488

  30. Microscopic imaging of oxygen distribution (Lifetime measurement) The luminescence lifetime measurement is independent of [O2]. [Ru(bpy)3]Cl2

  31. Pressure imaging in wind tunnel Visualization by oxygen pressure sensitive dye

  32. pH sensor

  33. Cyanid ion sensor

  34. Phosphorescent Ir complexes (OLED)

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