Exciton Dephasing and Thermal Line Broadening in Molecular Aggregates

Using a model of Frenkel excitons coupled to a bath of acoustic phonons in the host medium, we study the temperature dependence of the dephasing rates and homogeneous line width in linear molecular aggregates. The model includes localization by disorder and predicts a power-law thermal scaling of the effective homogeneous line width. The theory gives excellent agreement with temperature dependent absorption and hole-burning experiments on aggregates of the dye pseudoisocyanine.Comment: 11 pages, 3 PostScript figure

Trapping time statistics and efficiency of transport of optical excitations in dendrimers

We theoretically study the trapping time distribution and the efficiency of the excitation energy transport in dendritic systems. Trapping of excitations, created at the periphery of the dendrimer, on a trap located at its core, is used as a probe of the efficiency of the energy transport across the dendrimer. The transport process is treated as incoherent hopping of excitations between nearest-neighbor dendrimer units and is described using a rate equation. We account for radiative and non-radiative decay of the excitations while diffusing across the dendrimer. We derive exact expressions for the Laplace transform of the trapping time distribution and the efficiency of trapping and analyze those for various realizations of the energy bias, number of dendrimer generations, and relative rates for decay and hopping. We show that the essential parameter that governs the trapping efficiency, is the product of the on-site excitation decay rate and the trapping time (mean first passage time) in the absence of decay.Comment: 26 pages, 6 figure

Difusión de los créditos del CDTI en las empresas innovadoras del País Vasco y Navarra

Se valora la transcendencia del CDTI (Centro para el Desarrollo Tecnologico Industrial) en las economías vasca y navarr

Do public policies that foster co-operation in innovation augment the cooperative attitude: the empirical facts

In this paper I offer a revision of the empirical literature on evaluation of policies fostering cooperation in innovation. Afterwads we analyse the case of the Spanish support on this topic. First I present a critical rewiew of the methods and findings of the existing empirical literature was made in an attempt to answer the question wether the policy of promotion of co-operation has been effective or not. Afterwards I analyse the impact of the public support for co-operative R&D in Spain

Justificación de la política de innovación desde un enfoque teórico y metodológico

Se ofrece una revisión de la literatura teórica que ofrece aportaciones respecto a la justificación de la política de innovación. La segunda sección revisa la literatura sobre el cambio tecnológico cuyos conceptos se utilizan como referencia en la terecera y cuarta sección, donde se analizan los argumentos teóricos reapecto a la justificación de la política tecnológica. Se analizan el enfoque neoclásico, la teoría del crecimiento endógeno y la perspectiva evolucionista. e ofrece un marco metodológico para estudios de evaluación

Local level statistics for optical and transport properties of disordered systems at finite temperature

It is argued that the (traditional) global level statistics which determines localization and coherent transport properties of disordered systems at zero temperature (e.g. the Anderson model) becomes inappropriate when it comes to incoherent transport. We define local level statistics which proves to be relevant for finite temperature incoherent transport and optics of one-dimensional systems (e.g. molecular aggregates, conjugated polymers, etc.).Comment: 4 pages, 2 figures, reported at EXCON'2006, to appear in the physica status solidi (c

Decoherence of Excitons in Multichromophore Systems: Thermal Line Broadening and Destruction of Superradiant Emission

We study the temperature-dependent dephasing rate of excitons in chains of chromophores, accounting for scattering on static disorder as well as acoustic phonons in the host matrix. From this we find a powerlaw temperature dependence of the absorption line width, in excellent quantitative agreement with experiments on dye aggregates. We also propose a relation between the line width and the exciton coherence length imposed by the phonons. The results indicate that the much debated steep rise of the fluorescence lifetime of pseudo-isocyanine aggregates above 40 K results from the fact that this coherence length drops below the localization length imposed by static disorder.Comment: 4 pages, 2 figure