Download - Photoluminescent properties of fullerene derivatives

Transcript
Page 1: Photoluminescent properties of fullerene derivatives

''Photoluminescent properties of ''Photoluminescent properties of Fullerene Derivatives''Fullerene Derivatives''

Ümit TAYFUNÜmit TAYFUN

CHEM758 CHEM758 CHEMISTRY OF OPTOELECTRONIC SYSTEMS CHEMISTRY OF OPTOELECTRONIC SYSTEMS

Polymer Science & Technology M.E.T.U.Polymer Science & Technology M.E.T.U.

Page 2: Photoluminescent properties of fullerene derivatives

PhotoluminescencePhotoluminescence PhotoluminescencePhotoluminescence ( (PLPL) is a process ) is a process

in which a substance absorbs photons in which a substance absorbs photons (electromagnetic radiation) and then (electromagnetic radiation) and then re-radiates them.re-radiates them.

In photoluminescence,the electrons are promoted to excited states by absorption of photons of light energy. The emitted light is the result of those electrons which relax back to the ground state by emitting photons.

Sources of excitation of emission Sources of excitation of emission (fluorescence) of photoluminescent (fluorescence) of photoluminescent materials may be daylight, luminescent materials may be daylight, luminescent and incandescent lamps, UV-emitters.and incandescent lamps, UV-emitters.

They convert UV- and visible light into They convert UV- and visible light into

various coloured luminescent emission various coloured luminescent emission with afterglow duration from minutes to with afterglow duration from minutes to several hours. several hours.

Page 3: Photoluminescent properties of fullerene derivatives

Photoluminescent materialsPhotoluminescent materials ZnS:CuZnS:Cu

Rare Earth elements doped Alumina silicatesRare Earth elements doped Alumina silicates

ex. SrAlO4:Eu,Dy CaAlO4:Eu,Dyex. SrAlO4:Eu,Dy CaAlO4:Eu,Dy

Doped fluorescent polymers ex. Copolyfluorene-fluorenone (PFFO)

Fullerene-doped polymers

Fullerene-doped inorganic materials

Page 4: Photoluminescent properties of fullerene derivatives

Fullerene derivatives

Fullerenes and their derivatives show a strong absorption around 3.7 eV typical of a p-conjugated organic molecular system.

Due to the high molecular symmetry, the HOMO-LUMO transition of fullerenes is dipole forbidden, exhibiting only very weak luminescence at room temperature.

However, their PL increases as they are cooled to low temperature because of reduction of thermal quenching of excited states.

AAt very low temperature, as for instance the t very low temperature, as for instance the liquidliquid helium temperature, can helium temperature, can PLPL be be clearlyclearly detected. detected.

Page 5: Photoluminescent properties of fullerene derivatives

The highly conjugated nature of fullerene molecules leads tointeresting electronical properties. A close packed film of C60and many of its derivatives shows direct bandgap semiconductingbehaviour with a symmetry forbidden valence band–conductionband transition.

In the higher fullerenes like C70 and C84, this high degree of symmetry is broken and the low energy transitions become more prominent.

The chemical structures of some fullerene derivatives are depicted in Figure

Page 6: Photoluminescent properties of fullerene derivatives

Resonant energy transfer

Important factors are the distance between donor and acceptor, the overlap and strength of the donor emission and acceptor absorption as well as the orientation of the dipoles and the dielectric surrounding.

For a system of specific chromophores inside a matrix usually the leading dependency is in the distance.

Upon illumination, the excitation energy is transferred from the donor to the acceptor molecule. This leads to a quenching of the donor emission and—in contrast to the charge transfer.

Energy level diagram illustrating the resonance condition for energy transfer.

Page 7: Photoluminescent properties of fullerene derivatives

Fullerenes as energy transfer acceptors

Fullerene derivatives have an absorption range reaching to over 700 nm, as can be seen in Figure for the example of the fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester.

But the symmetry restrictions with the resulting low oscillator strength of absorption for energies below 2.5eV limits the characteristic radius of the energy transfer from even a highly luminescent donor.

Page 8: Photoluminescent properties of fullerene derivatives

Fullerenes as energy transfer donors

Compared with many photoactive organic substances, fullerenes have a relatively low energy gap of about 1.8 eV.

Additionally, they show only a weak luminescence due to the symmetry forbidden S1→S0 transition and a fast intersystem crossing to the triplet state.

Therefore, systems in which fullerenes can act as energy transfer donors with significant efficiency are very rare.

The triplet state of C60 can undergo a very efficient triplet energy transfer to a ground state triplet oxygen molecule transferring it into a very reactive singlet oxygen molecule.

Page 9: Photoluminescent properties of fullerene derivatives

Energy transfer from an organic molecule to a fullerene

Some combinations of fullerenes and organic molecules nevertheless clearly yield energy transfer instead of charge transfer upon excitation.

A near equal proportion of charge and energy

transfer of C60 linked to a perylene derivative via a pyrrolidine linker system, as can be seen from luminescence and ultrafast pump–probe measurements [Martini et al.].

A predominance of energy transfer in photoluminescence studies additionally claim that they see evidence for the presence of a weak charge transfer in photoconductivity studies on a similar system [Hua et al.].

These works underline the competing nature of the two processesthat are often simultaneously possible in a system of two organicchromophores in close contact.

Page 10: Photoluminescent properties of fullerene derivatives

ExamplesExamplesFullerene-doped polymer films:Due to the special optical and electrical properties of fullerenes,

fullerene-doped polymer films have attracted much interest in the past few years.

PL of C60 doped polyvinylcarbazole PVK films showed that the efective charge and energy transfer processes happened in these films.

Page 11: Photoluminescent properties of fullerene derivatives

ExamplesExamples

Fullerene C60 or C70-doped PMMA films display intense visible PL.

Normally, C60 HOMO–LUMO transition is forbidden due to the high symmetry of its structure. Under laser irradiation in air, C60 undergoes some photochemical reactions with molecular oxygen and polymer to form oxidized C60-polymer adducts, with oxygen atoms attached to the fullerene cage.

The low symmetry of C60-polymer or oxidized C60-polymer adducts strengthens the HOMO–LUMO transition.

So, PL of fullerene-doped polymer could be increased largely by laser irradiation in air.

Page 12: Photoluminescent properties of fullerene derivatives

PL behavior of the solution looks like that of the blends of PS and C60.

Although C60 is well known as a strong quencher, it is not a predominant factor for the observed PL quenching of the PS segments because the PL of pure PS is also strongly quenched in chlorobenzene.

ExamplesExamples

Page 13: Photoluminescent properties of fullerene derivatives

ExamplesExamples HHighly photoluminescent fullerene-ighly photoluminescent fullerene-

silicasilica nanoparticles(FSNPnanoparticles(FSNP):):

Monodisperse, spherical nanoparticles Monodisperse, spherical nanoparticles showed showed an excellent PLan excellent PL intensity and it was intensity and it was successfully employed as bioimaging successfully employed as bioimaging materialmaterial increased photoluminescence, increased photoluminescence, compared to both Ccompared to both C6060 and silica and silica nanoparticles, arnanoparticles, ariise from the C-O-Si linkages se from the C-O-Si linkages that seems to be formed in the sol-gel that seems to be formed in the sol-gel processprocess..

C60 in Zeolites:C60 in Zeolites:

The incorporation into the zeolites of isolated The incorporation into the zeolites of isolated C60C60 results in a clear modification of the results in a clear modification of the fullerene electronicfullerene electronic structure. structure.

The C60-matrix interaction gives novel The C60-matrix interaction gives novel characteristics in particular PL emission of characteristics in particular PL emission of white light at room temperature and shifts white light at room temperature and shifts in the opticalin the optical absorption peaks. absorption peaks.

Page 14: Photoluminescent properties of fullerene derivatives

ReferencesReferences

Increase of photoluminescence from fullerenes-doped poly (alkyl methacrylate) under laser irradiation, G.Z. Li, N. Minami / Journal of Luminescence 104 (2003) 210 207–213

Photoinduced charge and energy transfer involving fullerene derivatives, R. Koeppe and N. S. Sariciftci/Photochemical & Photobiological Sciences, (2006)

Photoluminescence from fullerene-doped polyvinylcarbazole (PVK) prepared by solution casting under laser irradiation, G.Z. Li, N. Minami / Chemical Physics Letters 331 (2000) 26-30

Photoluminescence Characteristics of a Highly Soluble Fullerene-Containing Polymer, Jungahn Kim, Young Chul Kim, Macromol. Res., Vol. 10, No. 5, 2002

Photoluminescence of fullerene-doped copolymers of methyl methacrylate during laser irradiation G. Z. Li, C. U. Pitmann Jr., Journal of Mat. Sci. (2003) 3741 – 3746

Photoconductivity of fullerene-doped polymers, Y. Wang, Nature, 1992, 356, 585–587 Ultrafast competition between energy and charge transfer in a functionalized electron

donor/fullerene derivative, I. B. Martini, B. Ma, T. Da Ros, R. Helgeson, F. Wudl and B. J. Schwartz, Chem. Phys. Lett., 2000, 327(5–6), 253–262

Resonance energy transfer from organic chromophores to fullerene molecules, J. Appl. Phys., Y. Liu, M. A. Summers, S. R. Scully and M. D. McGehee, 2006, 99, 093521

Ultrafast competition between energy and charge transfer in a functionalized electron donor/fullerene derivative, I. B. Martini, B. Ma, T. Da Ros, R. Helgeson, F. Wudl and B. J. Schwartz, Chem. Phys.Lett., 2000, 327(5–6), 253–262

Novel soluble and thermally-stable fullerene dyad containing perylene, J. L. Hua, F. S.Meng, F. Ding, F. Y. Li and H. Tian, J. Mater. Chem., 2004, 14(12), 1849–1853

White Light Emission from C,, MoleculesWhite Light Emission from C,, Molecules Confined in Molecular Cage MaterialsConfined in Molecular Cage Materials, Hamilton, B.; , Hamilton, B.; Rimmer, J. S.; Anderson, M.; Leigh, D. Rimmer, J. S.; Anderson, M.; Leigh, D. Adv. Mater. Adv. Mater. 1993, 1993, 5, 583.5, 583.

Fullerene-Based Organic-Inorganic Nanocomposites and Their Applications, Fullerene-Based Organic-Inorganic Nanocomposites and Their Applications, Plinio Innocenzi* Plinio Innocenzi* and Giovanna Brusatinand Giovanna Brusatin, , Chem. Mater. 2001, 13, 3126-3139Chem. Mater. 2001, 13, 3126-3139