Nathan B. Gillespie

Optimization of bacteriorhodopsin for bioelectronic devices

Bacteriorhodopsin (BR) is the photoactive proton pump found in the purple membrane of the salt marsh archaeon Halobacterium salinarum. Evolution has optimized this protein for high photochemical efficiency, thermal stability and cyclicity, as the organism must be able to function in a hot, stagnant and resource-limited environment. Photonic materials generated via organic chemistry have yet to surpass the native protein in terms of quantum efficiency or cyclicity. However, the native protein still lacks the overall efficiency necessary for commercial viability and virtually all successful photonic devices using bacteriorhodopsin are based on chemical or genetic variants of the native protein. We show that genetic engineering can provide significant improvement in the device capabilities of proteins and, in the case of bacteriorhodopsin, a 700-fold improvement has been realized in volumetric data storage. We conclude that semi-random mutagenesis and directed evolution will play a prominent role in future efforts in bioelectronic optimization.

Optical properties of photochromic fluorinated indolylfulgides

Abstract Fluorinated indolylfulgides are a promising class of photochromic organic compounds for optical memory and switches. Absorption spectra, quantum yields, thermal stabilities, and photochemical fatigue resistances have been measured for a series of fluorinated indolylfulgides. The cyclizable form of the heptafluoropropyl-substituted 1,2-dimethylindolylfulgide displays the longest absorbance maxima yet reported for the cyclizable form of a fulgide. Photochemical durability was quantified in both solvent and polymer for the first time, with the trifluoromethyl derivative undergoing more than 2500 photochemical cycles before degrading by 20% in either environment. In addition, the thermal stability of the cyclizable form has been examined for the first time. Although each fulgide showed outstanding resistance to thermal stress in the C -form, the cyclizable form degraded rapidly at 80°C. These studies highlight the many advantageous properties associated with fluorination and identify areas for future improvements.

Thermolysis of fluorinated cycloalkylidene fulgides yields a new class of photochromic compoundsElectronic supplementary information (ESI) available: Synthetic procedures for 3–10. Optical and stability characterization methods. See http://www.rsc.org/suppdata/cc/b3/b300010a/

A series of fluorinated cycloalkylidene indolylfulgides has been designed, synthesized and characterized; most of the thermolysis products of these fulgides maintain photochromicity and display outstanding thermal and photochemical stability.