Linking molecular structure with excited-state photochemical dynamics is crucial for developing photochemical applications and engineering efficient molecular electronics. Undergraduate students have played a critical role in helping to develop and explore two ongoing molecular materials projects in the Walter Research Group at UNC Charlotte: studying the singlet exciton diffusion lengths in carboalkoxyphenylporphyrin thin films and the development of a new family of highly fluorescent thiazolothiazole viologen dyes. The effects of molecular orientation on the singlet exciton diffusion lengths in solution-cast porphyrin thin films with various alkyl chain lengths have been determined. The photoluminescent singlet decay lifetime of pristine porphyrin films and films lightly doped with [6,6]-phenyl-C61-butryic acid methyl ester (PCBM) were used in a 3D exciton diffusion Monte Carlo simulation to extract the exciton diffusion parameters and the nanocomposition.<sup> </sup>Longer alkyl chain derivatives yielded increased PL decay lifetimes and lengthened exciton diffusion lengths (L<sub>D</sub>). Nematic molecular organization resulted in an increase in the exciton diffusion length. Our findings are an important step toward a deeper understanding of the exciton diffusivity and molecular packing relationship. We have also synthesized a class of extended viologen dye structures that incorporate a thiazolo[5,4-d]thiazole backbone. The dyes exhibit both reversible yellow to dark blue electrochromism and high fluorescence quantum efficiency that is deactivated upon electrochemical reduction. The fused bicyclic thiazolothiazole heterocycle allows the alkylated pyridinium groups to remain planar, strongly affecting their electrochemical properties. The electrochromic and strongly fluorescent properties make these materials attractive for molecular electronics, biomolecular sensing, and other photochemical applications. Both projects involve significant undergraduate efforts and leadership. Synthesis is an important aspect of this work, however, many undergraduate students also take on active roles in device development, photochemical analyses, and they have been encouraged to explore new ideas and platforms. This strategy has helped laid the foundation for new materials discoveries and continues to enrich our research program.

Undergraduate photochemistry research: The photophysical properties of porphyrin thin films and thiazolothiazole viologens

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.