Harding University Course Catalog 1988-1989

Catalog of Harding University 1988-1989https://scholarworks.harding.edu/catalogs/1050/thumbnail.jp

Photovoltaic effect in self-assembled molecular monolayers on gold: influence of orbital energy level alignment on short-circuit current generation

Photoinduced current generation at metal–organic monolayer interfaces is observed upon photoexcitation of a monolayer of hemicyanine molecules chemically adsorbed onto a gold electrode. A series of hemicyanines is investigated that bind to the gold via a thiol moiety, in an orientation such that the acceptor moiety of the hemicyanine is closer to the metal than its donor part. The quantum yield of short-circuit photocurrent generation in a diode using a liquid electrolyte as second contact, correlates with the strength of the donor moiety of the dyes. Modeling of the photocurrent generation using Marcus theory indicates that the net photocurrent results from asymmetry in the electron transfer rates of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) with the electrodes. The quantum efficiency of short-circuit photocurrent generation decreases for the HOMO levels of the hemicyanine going deeper below the Fermi-level of the metal. The deeper HOMO level provides a larger driving force for back electron transfer from the metal to the photo-oxidized molecule and suppresses current generation in favor of quenching of the excited state

Reflection and extinction of light by self-assembled monolayers of a quinque-thiophene derivative: A coherent scattering approach

Scattering matrix theory is used to describe resonant optical properties of molecular monolayers. Three types of coupling are included: exciton-exciton, exciton-photon, and exciton-phonon coupling. We use the K-matrix formalism, developed originally to describe neutron scattering spectra in nuclear physics to compute the scattering of polaritons by phonons. This perturbation approach takes into account the three couplings and allows one to go beyond molecular exciton theory without the need of introducing additional boundary conditions for the polariton. We demonstrate that reflection, absorption, and extinction of light by 2D self-assembled monolayers of molecules containing quinque-thiophene chromophoric groups can be calculated. The extracted coherence length of the Frenkel exciton is discussed

Photovoltaic action in a self-assembled monolayer of hemicyanine dyes on gold from dissociation of surface plasmons

Hemicyanine dye molecules, containing a thiol functionality, form a self-assembled monolayer (SAM) on thin films of gold. The combined SAM-gold layer system supports surface plasmons and can be converted into a diode using a liquid electrolyte top contact. Diodes fabricated on a quartz prism allow for incoupling of incident light to surface plasmons and show a spontaneous photocurrent under short-circuit conditions. Measurement of the short-circuit photocurrent as function of incident angle of the light shows that the photocurrent arises from dissociation of surface plasmons into pairs of charge carriers

Synthesis and properties of small band gap thienoisoindigo based conjugated polymers

Using Stille and Suzuki polymerization reactions we incorporate thienoisoindigo (TII) as an acceptor co-monomer into a series of alternating p-conjugated copolymers with combinations of benzene, thiophene and carbazole as donor co-monomers. By changing the nature and length of the donor segments, the optical band gap of these soluble TII copolymers can be varied over a large range from 1.52 eV down to 0.87 eV. The semiconducting properties of the TII copolymers were established in bottom-gate bottom-contact field-effect transistors that provide hole mobilities for these materials in the range of 10-3 to 10-2 cm2 V-1 s-1

Reflection and extinction of light by self-assembled monolayers of a quinque-thiophene derivative: A coherent scattering approach

Scattering matrix theory is used to describe resonant optical properties of molecular monolayers. Three types of coupling are included: exciton-exciton, exciton-photon, and exciton-phonon coupling. We use the K-matrix formalism, developed originally to describe neutron scattering spectra in nuclear physics to compute the scattering of polaritons by phonons. This perturbation approach takes into account the three couplings and allows one to go beyond molecular exciton theory without the need of introducing additional boundary conditions for the polariton. We demonstrate that reflection, absorption, and extinction of light by 2D self-assembled monolayers of molecules containing quinque-thiophene chromophoric groups can be calculated. The extracted coherence length of the Frenkel exciton is discussed

Photovoltaic action in a self-assembled monolayer of hemicyanine dyes on gold from dissociation of surface plasmons

Hemicyanine dye molecules, containing a thiol functionality, form a self-assembled monolayer (SAM) on thin films of gold. The combined SAM-gold layer system supports surface plasmons and can be converted into a diode using a liquid electrolyte top contact. Diodes fabricated on a quartz prism allow for incoupling of incident light to surface plasmons and show a spontaneous photocurrent under short-circuit conditions. Measurement of the short-circuit photocurrent as function of incident angle of the light shows that the photocurrent arises from dissociation of surface plasmons into pairs of charge carriers

Synthesis and properties of small band gap thienoisoindigo based conjugated polymers

Using Stille and Suzuki polymerization reactions we incorporate thienoisoindigo (TII) as an acceptor co-monomer into a series of alternating p-conjugated copolymers with combinations of benzene, thiophene and carbazole as donor co-monomers. By changing the nature and length of the donor segments, the optical band gap of these soluble TII copolymers can be varied over a large range from 1.52 eV down to 0.87 eV. The semiconducting properties of the TII copolymers were established in bottom-gate bottom-contact field-effect transistors that provide hole mobilities for these materials in the range of 10-3 to 10-2 cm2 V-1 s-1