AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
A Collision-Based Model for the Kinetics of Bacteriochlorophyll c Self-Assembly in Methanol-Water Solution
GERARD LAKIN, Vivek Shah, Gregory Orf, Robert Blankenship, Pratim Biswas, Washington University in St. Louis
Abstract Number: 433 Working Group: Aerosol Physics
Abstract Dye-sensitized solar cells (DSSCs) have received a great amount of attention in recent years as a potential low-cost alternative to single crystal silicon solar cells. To improve the efficiency of DSSCs it is necessary to develop dyes that are capable of absorbing a wide spectrum of incident wavelengths with a large extinction coefficient while maintaining effective charge transfer to the oxide substrate. Naturally occurring photosynthetic light-harvesting complexes (LHCs) have generated interest as models for highly efficient light absorption and transfer. The chlorosome LHC is capable of photosynthesis at low and diffuse illumination levels due to the high order of the bacteriochlorophyll (BChl) c pigment structures, which are assembled with almost negligible influence from proteins. It is possible to self-assemble light-harvesting antennae from BChl c for use in a DSSC. We propose to utilize electrospray to simultaneously self-assemble and deposit pigment antennae, making use of the monodispersity of electrospray droplets to control the size of deposited structures. In order to fully make use of electrospray deposition technique we must understand the kinetics of self-assembly.
In this study we have performed kinetic self-assembly experiments for BChl c in bulk methanol-water solutions and developed a collision-based empirical model that successfully describes the rate of monomer integration into self-assembled aggregates. Various methods were tested: modification of the Brownian collision rate by various interaction forces, the modification of the rate for slower growth, and others will be described in the presentation. We have performed experiments showing the time dependence of the full UV-visible absorbance spectra as well as the time dependence of the peaks at 670 nm and 740 nm which represent the monomer and self-assembled aggregate concentrations, respectively. The model fits our data to determine the time-dependent collision frequency, fraction of collisions that result in assembly, and the equilibrium monomer concentration.