Designing Bright and Fast Fluorophores with Large Stokes' Shifts Based on Superradiant Molecular J-Aggregates

With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the NSF division of Chemistry, Professor Moungi G. Bawendi and his team at the Massachusetts Institute of Technology will study and harness fundamental properties of molecular interactions to develop materials that generate efficient bursts of light in short timescales that are on the order of a few hundred picoseconds.

Materials that can emit light quickly and efficiently have a wide range of applications, including deep-space optical communication, high-speed smart light-emitting diodes (LEDs), and quantum information technologies. Inspired by the complexity and exquisite efficiency of natural light harvesting systems, the team will explore how the optical properties of molecules can be improved by arranging them in nano- and microscale clusters called J-aggregates.

In addition to this research, the team will work to make science more inclusive by providing opportunities to under-represented minorities and women in order to help develop their scientific potential and empower disadvantaged communities. In particular, the team will take part in the MIT ACCESS program that provides classes and research opportunities to students to help bridge the gap in transitioning from undergraduate to graduate school.

The team will also utilize complementary programs aimed at K-12 students to convey the excitement of conducting scientific research.

This project aims to gain understanding of fundamental properties that underlie excitonic behavior, stability, and coupling in interacting molecular J-aggregates to develop materials with short lifetimes that are on the order of hundreds of picoseconds and that feature large Stokes shifts and high quantum yields. Traditional fluorophores are used in a variety of fields and have been optimized for high quantum yield, large Stokes shift, and favorable absorption cross-section.

However, their application in systems that require a short response time have been limited due to their inherently long lifetimes that are typically in the nanosecond range. Coupled molecular J-aggregates have the potential to fill the need for fast, bright chromophores. The team will investigate how structural changes and environmental effects alter the excitonic behavior of molecular aggregates, and what dynamics play a role in interactions between aggregates.

First, the team will study matrix effects and structural changes in nanotubular light harvesting aggregates, as well as the impact of rigidification through encapsulation in a silica shell. Second, the team will investigate origins of non-radiative loss pathways in molecular aggregates and potential ways to mitigate them. Third, the team will look at the coupling between stabilized nanotubular aggregates to understand the key dynamics involved in energy transfer between supramolecular fluorophores.

This research has the potential to lead to a fundamental understanding of the properties that limit excitonic behavior and interactions of J-aggregates.

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.