Electronic Excitations in Organic Based Nanostructures

The possibility of growing tailor-made systems incorporating in different ways organic crystalline materials , eventually joined to inorganic heterostructures, has opened a new field of research in fundamental and applied physics. This is the first book devoted to a systematic study of electronic excitations and energy transfers in such materials. The book can be useful to physicists interested in material science and to chemists and biologists as well.

After three initial Chapters which contain a tutorial and updated introduction to the physics of electronic excitations in organic and inorganic solids, multilayer organic structures and organics based heterostructures are considered.

In the first class of materials the role of quasi two-dimensional effects at surfaces and interfaces is described. "The Fermi Resonance Interface modes", and the related bistability and multistability in the energy transmission through the interface are investigated, as well as Frenkel excitons and charge-transfer excitons in organic multilayers and at donor-acceptor interfaces. Phase transition to the conducting state (cold photoconductivity) and exciton-polaritons in organic microcavities with crystalline and disordered organics are also discussed..

In the materials which result from the combination of organic and inorganic matter in a single hybrid nanostructure (quantum wells, quantum wires, quantum dots and microcavities) new peculiar excitations which share properties of Frenkel excitons(large oscillator strength) and of Wannier excitons (large radius) are shown to arise for strong coupling and to give rise to large enhansments in the nonlinear optical effects . Such hybrid excitons are also discussed in the case when the organic-inorganic layers are inbedded in a microcavity and hybridization is produced by the cavity electromagnetic field instead of Coulombic dipole-dipole interaction.

The performance of opto-electronic devices in planar microcavity structures are described in the book, in connection with experiments which demonstraite a giant Rabi splitting in organic microcavities and polariton relaxation strongly affecting absorption , transmission and luminescence.

In the case of weak resonance coupling between Wannier excitons in inorganic nanostructure and Frenkel excitons in the organic overlayer a fast energy transfer from the first to the second is shown to occur, with subsequent strong luminescence. As a consequence new concepts for light emitting devices can be developed and are described in the book. The energy transfer is also considered when the organic and inorganic nanostructures are imbedded in one microcavity or in two interacting microcavities, in which case the energy transfer between the donor and the acceptor nanostructures is greatly enhanced by the cavity electromagnetic interaction. The role of the acceptor absorber and of different dissipative processes is analyzed in detail, in connection with recent experiments.