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

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

With the support of the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Professors Ellen M. Sletten and Justin R. Caram of the University of California-Los Angeles are developing new fluorescent chemical compounds that emit light in the shortwave infrared region of the electromagnetic spectrum. Shortwave infrared waves are invisible to the human eye but can be detected by special cameras. A major advantage of these waves is that they can pass through tissue and be used for imaging in complex organisms. Additional opportunities are also seen in improving long-haul telecommunications of fiber optical networks. In the first part of this research, small organic molecules will be prepared and structurally modified to achieve desired absorption and emission properties in the infrared region. These photophysical properties will then be amplified several orders of magnitude through self-assembly in solution yielding exceptionally red-shifted aggregates. To aid in experimental design and speed discovery, computational modelling will be used to correlate the structure of these aggregates with their electronic properties. The research activities associated with this award will increase broadening participation and enable training of high school, undergraduate, and graduate students in synthetic organic chemistry and spectroscopy. The creation of a PHOTONbooth and participation in “Illuminating the World of Molecules” events will provide attractive strategies to generate public interest in science and introduce STEM concepts to participants in the greater Los Angeles area. This research will focus on cyanine aggregation and self-assembly to access exceptionally red-shifted organic chromophores for the shortwave infrared region (SWIR) region of the electromagnetic spectrum. In the first objective, modified monomeric cyanine dyes will be synthesized through heteroatom substitution and lengthening of the polymethine chain. This structural modification will promote SWIR J-aggregates above 1300 nm and facilitate investigation of two of the current limitations of such aggregates, namely low quantum yield (objective 2) and their need to be stabilized in a matrix or nanoparticle for use in dilute/complex environments (objective 3). New structures will be investigated using circular and linear dichroism and modelled computationally to access excitonic structures and correlate them with photophysical properties. This work, if successful, will provide fundamental insight on the chromophore-chromophore coupling and long-range order necessary for emissive, band edge J-aggregate formation. The organic SWIR J-aggregates associated with this work have the potential to develop inexpensive, environmentally friendly and scalable nanotechnology in a wavelength regime deemed to be eye safe. 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.