Charge delocalization characteristics of regioregular high mobility polymers.

Controlling the regioregularity among the structural units of narrow bandgap conjugated polymer backbones has led to improvements in optoelectronic properties, for example in the mobilities observed in field effect transistor devices. To investigate how the regioregularity affects quantities relevant to hole transport, regioregular and regiorandom oligomers representative of polymeric structures were studied using density functional theory. Several structural and electronic characteristics of the oligomers were compared, including chain planarity, cation spin density, excess charges on molecular units and internal reorganizational energy. The main difference between the regioregular and regiorandom oligomers is found to be the conjugated backbone planarity, while the reorganizational energies calculated are quite similar across the molecular family. This work constitutes the first step on understanding the complex interplay of atomistic changes and an oligomer backbone structure toward modeling the charge transport properties

METHOD OF ESTIMATION OF ENVIRONMENTAL HAZARD OF URBAN LAND USING FOR VITAL ACTIVITY OF POPULATION

It is noted that the global updating of the ecological problems at the end of the XX - the beginning of the XXI centuries, the undeniable importance of the ecological component of human existence, causes the urgent need for a balanced, holistic, integrated approach to the analysis and solution of issues of ensuring the ecological safety of the vital activities of the population, including the city. At the same time, at the legislative level, environmental safety is identified as one of the priority tasks in the state policy of Ukraine in order to achieve sustainable development. It is proved that the provision of environmental safety remains the main way of solving ecological problems, which guarantees citizens the development and living in harmony with the environment and opens up new opportunities for other forms of activity in the field of nature management, in particular, political, economic, social, etc. The methodical approach to an estimation of ecological danger of urban land use for vital activity of the population and typification of land use of green plantings is grounded. An assessment of the state of ecological danger for the city of Kiev is given. On the basis of the proposed methodical approach, it is justified that today there are threats to the ecological stability of land use, and accordingly, environmental insecurity of land use, which indicates a lack of change in the structure of land use for many years

METHODOLOGICAL PRINCIPLES OF THE INTEGRAL ASSESSMENT OF LAND EFFICIENCY AND LAND ORGANIZATION WITHIN THE TERRITORIES OF THE VILLAGE COUNCILS

In the context of reforming land relations and land system usage individual methodological approaches and systems of natural and economic indicators of land use efficiency assessment require improvement. The current research covers various views and approaches of native scientists to the evaluation of land resource usage with taking into account factorial and result indicators, which differentially influence the formation of elements of land tenure system and land management efficiency. The efficiency of land tenure system and land management is substantiated to be determined by a set of its priority types: environmental, technological, legal, social, economic, and budgetary efficiency and their varieties. A system of criteria and indicators for integrated assessment of land tenure system and land management efficiency level at the local level has been proposed. It includes assessment of environmental, social and economic efficiency, which are interrelated and interdependent. It has been confirmed that the development of sustainable and effective methodological bases for land tenure system and land management evaluation is gaining great importance in the context of land market introduction in Ukraine and the abolition of moratorium on agricultural land sale

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Contains research objectives and reports on one research projects.Lincoln Laboratory, Purchase Order DDL B-00368U. S. ArmyU. S. NavyU. S. Air Force under Air Force Contract AF19(604)-7400National Institutes of Health (Grant MH-04737-02

Excitonic Funneling in Extended Dendrimers with Non-Linear and Random Potentials

The mean first passage time (MFPT) for photoexcitations diffusion in a funneling potential of artificial tree-like light-harvesting antennae (phenylacetylene dendrimers with generation-dependent segment lengths) is computed. Effects of the non-linearity of the realistic funneling potential and slow random solvent fluctuations considerably slow down the center-bound diffusion beyond a temperature-dependent optimal size. Diffusion on a disordered Cayley tree with a linear potential is investigated analytically. At low temperatures we predict a phase in which the MFPT is dominated by a few paths.Comment: 4 pages, 4 figures, To be published in Phys. Rev. Let

Morphology Effectively Controls Singlet-Triplet Exciton Relaxation and Charge Transport in Organic Semiconductors

We present a comparative study of ultrafast photo-conversion dynamics in tetracene (Tc) and pentacene (Pc) single crystals and Pc films using optical pump-probe spectroscopy. Photo-induced absorption in Tc and Pc crystals is activated and temperature-independent respectively, demonstrating dominant singlet-triplet exciton fission. In Pc films (as well as C$_{60}$-doped films) this decay channel is suppressed by electron trapping. These results demonstrate the central role of crystallinity and purity in photogeneration processes and will constrain the design of future photovoltaic devices.Comment:

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Contains reports on six research projects split into two sections.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 36-039-AMC-03200(E)National Science Foundation (Grant GK-835)National Institutes of Health (Grant 2 P01 MH-04737-06)National Aeronautics and Space Administration (Grant NsG-496

Theory of nonlinear optical properties of phenyl-substituted polyacetylenes

In this paper we present a theoretical study of the third-order nonlinear optical properties of poly(diphenyl)polyacetylene (PDPA) pertaining to the third-harmonic-generation (THG) process. We study the aforesaid process in PDPA's using both the independent electron Hueckel model, as well as correlated-electron Pariser-Parr-Pople (P-P-P) model. The P-P-P model based calculations were performed using various configuration interaction (CI) methods such as the the multi-reference-singles-doubles CI (MRSDCI), and the quadruples-CI (QCI) methods, and the both longitudinal and the transverse components of third-order susceptibilities were computed. The Hueckel model calculations were performed on oligo-PDPA's containing up to fifty repeat units, while correlated calculations were performed for oligomers containing up to ten unit cells. At all levels of theory, the material exhibits highly anisotropic nonlinear optical response, in keeping with its structural anisotropy. We argue that the aforesaid anisotropy can be divided over two natural energy scales: (a) the low-energy response is predominantly longitudinal and is qualitatively similar to that of polyenes, while (b) the high-energy response is mainly transverse, and is qualitatively similar to that of trans-stilbene.Comment: 13 pages, 7 figures (included), to appear in Physical Review B (April 15, 2004

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Contains reports on six research projects.National Institutes of Health (Grant 5 PO1 GM14940-04)National Institutes of Health (Grant 5 PO1 GM15006-03)Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E