Ronald R. Chance

Bio: Ronald R. Chance is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Polyacetylene & Polymerization. The author has an hindex of 64, co-authored 185 publications receiving 14135 citations. Previous affiliations of Ronald R. Chance include Algenol & Dartmouth College.

Chain-length dependence of electronic and electrochemical properties of conjugated systems: polyacetylene, polyphenylene, polythiophene, and polypyrrole

Abstract: The valence effective Hamiltonian (VEH) technique is used to compute ionization potentials, optical transition energies, and electron affinities of oligomers and polymers in four conjugated systems: polyacetylene, poly@-phenylene), polythiophene, and polypyrrole. The theoretical results compare very favorably with experimental data on gas-phase ionization potentials, optical absorption, and electrochemical redox potentials. The latter case is especially important, and the calculated oxidation and reduction potentials are in remarkably good agreement with experiment. For polyacetylene the predicted oxidation potential is 0.4 V vs. SCE, and the predicted reduction potential is -1.1 V, both of which are in good agreement with experimentally observed oxidation and reduction onsets. In these systems, the electronic and electrochemical properties predicted by VEH theory for the oligomers extrapolate to those of the polymer with an inverse chain-length dependence.

Molecular Fluorescence and Energy Transfer Near Interfaces

Abstract: Summary This chapter contains sections titled: Introduction Dipole Emission Near Interfaces Dyadic Green's Function Method Energy Transfer and Surface Plasmons Summary

Highly conducting polyparaphenylene, polypyrrole, and polythiophene chains: An ab initio study of the geometry and electronic-structure modifications upon doping

Abstract: The effect of charge-transfer doping on the geometric and electronic structures of conjugated polymers has been investigated at the ab initio level with explicit consideration of the doping agents. Three systems were chosen for study as prototypical examples of conjugated polymers with nondegenerate ground states: polyparaphenylene, polypyrrole, and polythiophene. As a result of charge transfer with electron-donating dopants, extra charges appear on the polymer chains and induce strong geometry modifications. The lattice evolves from an aromatic structure towards a quinoid-like structure. Charged defects associated with lattice deformations such as spinless bipolarons are formed. The influence on the electronic structure of the polymer chains is such that with respect to the undoped case, new states appear within the gap. For the maximum doping levels experimentally achieved, band-structure calculations demonstrate that the states in the gap overlap to form bipolaron bands, a few tenths of an electron volt wide. The presence of these bipolaron bands is consistent with optical data as well as with magnetic data which suggest that the charge carriers in the highly conducting regime are spinless.

Optical Nonlinearities in One-Dimensional-Conjugated Polymer Crystals.

Abstract: The one-dimensional electronic delocalization that results from the solid-state polymerization of diacetylenes produces a dramatic enhancement of the optical nonlinearities of these compounds. The third-order susceptibilities of the polymerized crystals reach very high values comparable to those of inorganic semiconductors.

Comparative theoretical study of the doping of conjugated polymers: Polarons in polyacetylene and polyparaphenylene

Abstract: Defect-state calculations on all-trans polyacetylene and polyparaphenylene have been performed in the framework of the adiabatic H\"uckel Hamiltonian with $\ensuremath{\sigma}$-bond compressibility. In polyacetylene, the study of the energetics of the separation of the radical (neutral defect) -ion (charged defect) pair induced upon doping indicates that the two defects tend to remain in close proximity, resulting in the formation of a polaron. The binding energy of the polaron is estimated to be about 0.05 eV with this model. Absorption spectra at low doping levels are shown to be compatible with polaron formation, thus demonstrating the nonuniqueness of the previously proposed soliton model in explaining these absorption data. At higher doping levels, interaction between polarons leads to the formation of charged solitons carrying no spin. In polyparaphenylene, defects are always correlated in pairs due to the absence of a degenerate ground state. At low doping, polarons with a binding energy estimated at 0.03 eV are formed on ionization of polyparaphenylene. The related deformation of the lattice is relatively sof, in agreement with crystallographic data on biphenyl anions, and extends over about five rings. Increasing the doping level leads to the formation of bipolarons (doubly charged defects) that require a stronger deformation of the lattice and carry no spin. The possibility of a conduction mechanism in polyparaphenylene involving motion of bipolarons is consistent with magnetic data indicative of very low Pauli susceptibility in the metallic regime of Sb${\mathrm{F}}_{5}$-doped polyparaphenylene.

Fingerprints of global warming on wild animals and plants

Abstract: Over the past 100 years, the global average temperature has increased by approximately 0.6 °C and is projected to continue to rise at a rapid rate1. Although species have responded to climatic changes throughout their evolutionary history2, a primary concern for wild species and their ecosystems is this rapid rate of change3. We gathered information on species and global warming from 143 studies for our meta-analyses. These analyses reveal a consistent temperature-related shift, or ‘fingerprint’, in species ranging from molluscs to mammals and from grasses to trees. Indeed, more than 80% of the species that show changes are shifting in the direction expected on the basis of known physiological constraints of species. Consequently, the balance of evidence from these studies strongly suggests that a significant impact of global warming is already discernible in animal and plant populations. The synergism of rapid temperature rise and other stresses, in particular habitat destruction, could easily disrupt the connectedness among species and lead to a reformulation of species communities, reflecting differential changes in species, and to numerous extirpations and possibly extinctions.

Photoinduced electron transfer from a conducting polymer to buckminsterfullerene.

Abstract: Evidence for photoinduced electron transfer from the excited state of a conducting polymer onto buckminsterfullerene, C(60), is reported. After photo-excitation of the conjugated polymer with light of energy greater than the pi-pi* gap, an electron transfer to the C(60) molecule is initiated. Photoinduced optical absorption studies demonstrate a different excitation spectrum for the composite as compared to the separate components, consistent with photo-excited charge transfer. A photoinduced electron spin resonance signal exhibits signatures of both the conducting polymer cation and the C(60) anion. Because the photoluminescence in the conducting polymer is quenched by interaction with C(60), the data imply that charge transfer from the excited state occurs on a picosecond time scale. The charge-separated state in composite films is metastable at low temperatures.

Principles of nano-optics

Abstract: 1. Introduction 2. Theoretical foundations 3. Propagation and focusing of optical fields 4. Spatial resolution and position accuracy 5. Nanoscale optical microscopy 6. Near-field optical probes 7. Probe-sample distance control 8. Light emission and optical interaction in nanoscale environments 9. Quantum emitters 10. Dipole emission near planar interfaces 11. Photonic crystals and resonators 12. Surface plasmons 13. Forces in confined fields 14. Fluctuation-induced phenomena 15. Theoretical methods in nano-optics Appendices Index.

Charge transport in organic semiconductors.

Abstract: 2.2. Materials 929 2.3. Factors Influencing Charge Mobility 931 2.3.1. Molecular Packing 931 2.3.2. Disorder 932 2.3.3. Temperature 933 2.3.4. Electric Field 934 2.3.5. Impurities 934 2.3.6. Pressure 934 2.3.7. Charge-Carrier Density 934 2.3.8. Size/molecular Weight 935 3. The Charge-Transport Parameters 935 3.1. Electronic Coupling 936 3.1.1. The Energy-Splitting-in-Dimer Method 936 3.1.2. The Orthogonality Issue 937 3.1.3. Impact of the Site Energy 937 3.1.4. Electronic Coupling in Oligoacene Derivatives 938

Conjugated polymer-based chemical sensors.

Abstract: When considering new sensory technologies one should look to nature for guidance. Indeed, living organisms have developed the ultimate chemical sensors. Many insects can detect chemical signals with perfect specificity and incredible sensitivity. Mammalian olfaction is based on an array of less discriminating sensors and a memorized response pattern to identify a unique odor. It is important to recognize that the extraordinary sensory performance of biological systems does not originate from a single element. In actuality, their performance is derived from a completely interactive system wherein the receptor is served by analyte delivery and removal mechanisms, selectivity is derived from receptors, and sensitivity is the result of analyte-triggered biochemical cascades. Clearly, optimal artificial sensory sys-