14 research outputs found
Theory of excited state absorptions in phenylene-based -conjugated polymers
Within a rigid-band correlated electron model for oligomers of
poly-(paraphenylene) (PPP) and poly-(paraphenylenevinylene) (PPV), we show that
there exist two fundamentally different classes of two-photon A states in
these systems to which photoinduced absorption (PA) can occur. At relatively
lower energies there occur A states which are superpositions of one
electron - one hole (1e--1h) and two electron -- two hole (2e--2h) excitations,
that are both comprised of the highest delocalized valence band and the lowest
delocalized conduction band states only. The dominant PA is to one specific
member of this class of states (the mA). In addition to the above class of
A states, PA can also occur to a higher energy kA state whose 2e--2h
component is {\em different} and has significant contributions from excitations
involving both delocalized and localized bands. Our calculated scaled energies
of the mA and the kA agree reasonably well to the experimentally
observed low and high energy PAs in PPV. The calculated relative intensities of
the two PAs are also in qualitative agreement with experiment. In the case of
ladder-type PPP and its oligomers, we predict from our theoretical work a new
intense PA at an energy considerably lower than the region where PA have been
observed currently. Based on earlier work that showed that efficient
charge--carrier generation occurs upon excitation to odd--parity states that
involve both delocalized and localized bands, we speculate that it is the
characteristic electronic nature of the kA that leads to charge generation
subsequent to excitation to this state, as found experimentally.Comment: Revtex4 style, 2 figures inserted in the text, three tables, 10 page
Effect of growth stoichiometry on the electrical activity of screw dislocations in GaN films grown by molecular-beam epitaxy
Molecular Orientation in Octanedithiol and Hexadecanethiol Monolayers on GaAs and Au Measured by Infrared Spectroscopic Ellipsometry
En memòria de Miquel Porter, historiador, divulgador, crític i professor de cinema.
El doctor Miquel Porter i Moix (Barcelona, 1930 - Altafulla,Tarragonès, 2004), catedràtic d'història del cinema al Departament d'Història de l'Art de la Universitat de Barcelona, ha estat una de les persones que més han contribuït al coneixement i estima del cinema a Catalunya