Engineering cyanine aggregation and self-assembly to access exceptionally red-shifted organic chromophores

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In this project funded by the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professors Ellen M. Sletten and Justin R. Caram of the Department of Chemistry at the University of California-Los Angeles are developing new fluorescent chemical compounds that re-emit light in the infrared region of the electromagnetic spectrum. Infrared waves are generally invisible to the human eye, but can be felt or detected as heat. Similar to x-rays, this light can penetrate through many objects, including skin and tissue. The compounds used in this research are very complex, yet easily made with unique properties that enable them to be highly colored. Additionally, they are several orders of magnitude brighter when assembled through molecular interactions in solution. The light intensity is particularly important for biomedical imaging applications such as early detection of cancer cells in human body. Additionally, the research is of relevance to the development of new and exciting devices in telecom-relevant optical fields in which information is communicated through long distances using infrared light. This work provides training and education to undergraduate and graduate students in synthetic organic chemistry and analytical characterization techniques. Several outreach activities are also developed that include educating the broader community about fluorescence and electromagnetic radiation. The research is an excellent avenue for engaging underrepresented minority and community college students in science.This research is focused on J-aggregates of cyanine fluorophores which emit in the shortwave infrared region of the electromagnetic spectrum (SWIR, 1000 to 2000 nm). To create SWIR J-aggregates, a systematic study of the factors that promote the self-assembly of chromophores into J-aggregates is conducted. Cyanine dyes are ideal complexes because they are easily synthetically accessible and are known to form J-aggregates with significant redshifts. In the first part of the project, four phenomena that are hypothesized to control J-aggregation (amphiphilicity, counterions, polymethine chain modification, and heterocycle polarizability) are explored through systematic chemical modifications and environmental control. In the second aim, these strategies are extended to a known SWIR cyanine dye. This research has the potential to generate transformative novel nanomaterials for applications in bioimaging and telecommunications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.