The design, synthesis, and characterization of polymethine dyes for all-optical signal processing applications

Material development is necessary before all-optical signal processing (AOSP) can be realized. Traditional AOSP will require materials with a large magnitude of the real part of the third-order polarizability, while having a small imaginary magnitude of third-order polarizability. The aim of this thesis is to investigate the potential for polymethine dyes to be used for AOSP applications. The basic structure of a polymethine dye was synthetically modified in a variety of positions to observe the effects upon the linear and nonlinear optical properties. The modifications included variation in the terminal group, substituents in the polymethine bridge, and exchange of the counterion. The dyes were generally synthesized using the Vilsmeyer-Haack reaction to form simple polymethine precursors, and then complexity was added by performing the Knoevenagel condensation with various acceptors and the polymethine precursor. Ion metathesis was often employed to exchange the initial counterion for a counterion that provided increased solubility in common organic solvents. The third-order nonlinear optical polarizabilities were characterized by Dr. Joel Hales who used the open- and closed-aperture Z-scan technique at 1300 nm and non-degenerate two-photon absorption experiments to identify the position of the two-photon absorption bands.Ph.D.Committee Chair: Seth Marder; Committee Member: Anselm Griffin; Committee Member: Jean-Luc Bredas; Committee Member: Joseph Perry; Committee Member: Laren Tolber

Ultrafast energy transfer in biomimetic multistrand nanorings

We report the synthesis of LH2-like supramolecular double- and triple-stranded complexes based upon porphyrin nanorings. Energy transfer from the antenna dimers to the π-conjugated nanoring occurs on a subpicosecond time scale, rivaling transfer rates in natural light-harvesting systems. The presence of a second nanoring acceptor doubles the transfer rate, providing strong evidence for multidirectional energy funneling. The behavior of these systems is particularly intriguing because the local nature of the interaction may allow energy transfer into states that are, for cyclic nanorings, symmetry-forbidden in the far field. These complexes are versatile synthetic models for natural light-harvesting systems

Effects of Dendronization on the Linear and Third-Order Nonlinear Optical Properties of Bis(thiopyrylium) Polymethine Dyes in Solution and the Solid State

Effects of the size and attachment position of benzyl aryl ether dendrons covalently attached to bis­(thiopyrylium) penta- and heptamethines on the optical properties of these dyes in solution and in solid films have been investigated. In dilute solution the low-energy absorption bands of some of the dendronized species differ from those of the parent compounds in having much smaller transition dipole moments, this effect possibly due to differences in ion pairing, while at higher concentrations, dye–dye interactions lead to a decrease in the transition dipole moments of the nondendronized species, but not of the dendronized ones. Consequently, in the high concentration range, dendronized and nondendronized species exhibit similar values of the real part of the microscopic third-order polarizability at 1550 nm. Solid-state film absorption spectra suggest that the dendrons significantly disrupt the chromophore–chromophore interactions seen for the nondendronized species, reducing, but not eliminating, linear absorption losses in the near-IR, and suppressing absorption peaks that are hypsochromically shifted from the solution spectra maximum: centrally placed dendrons have a larger effect than terminal dendronization, so that the corresponding thin-film spectra more closely resemble those seen in solution with increasing generations of dendronization. Z-scan measurements at 1550 nm indicate that the third-order susceptibility of dendronized heptamethine guest–host films depend approximately linearly on doping ratio of dyes and are in reasonable agreement with values extrapolated from solution-derived third-order polarizabilities; in contrast, the susceptibilities of films highly doped with an undendronized analogue fall short of values expected from solution polarizabilities

Ultrafast energy transfer in biomimetic multistrand nanorings.

We report the synthesis of LH2-like supramolecular double- and triple-stranded complexes based upon porphyrin nanorings. Energy transfer from the antenna dimers to the π-conjugated nanoring occurs on a subpicosecond time scale, rivaling transfer rates in natural light-harvesting systems. The presence of a second nanoring acceptor doubles the transfer rate, providing strong evidence for multidirectional energy funneling. The behavior of these systems is particularly intriguing because the local nature of the interaction may allow energy transfer into states that are, for cyclic nanorings, symmetry-forbidden in the far field. These complexes are versatile synthetic models for natural light-harvesting systems