Bridging the gap between H- and J-aggregates: Classification and supramolecular tunability for excitonic band structures in two-dimensional molecular aggregates

Author:

Deshmukh Arundhati P.1ORCID,Geue Niklas12ORCID,Bradbury Nadine C.1ORCID,Atallah Timothy L.13ORCID,Chuang Chern4ORCID,Pengshung Monica1ORCID,Cao Jianshu5ORCID,Sletten Ellen M.1ORCID,Neuhauser Daniel1ORCID,Caram Justin R.1ORCID

Affiliation:

1. Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Dr. East, Los Angeles, California 90095, USA

2. The Michael Barber Centre for Collaborative Mass Spectrometry, Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom

3. Department of Chemistry and Biochemistry, Denison University, 500 West Loop, Granville, Ohio 43023, USA

4. Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada

5. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

Abstract

Molecular aggregates with long-range excitonic couplings have drastically different photophysical properties compared to their monomer counterparts. From Kasha's model for one-dimensional systems, positive or negative excitonic couplings lead to blue or red-shifted optical spectra with respect to the monomers, labeled H-and J-aggregates, respectively. The overall excitonic couplings in higher dimensional systems are much more complicated and cannot be simply classified from their spectral shifts alone. Here, we provide a unified classification for extended 2D aggregates using temperature dependent peak shifts, thermal broadening, and quantum yields. We discuss the examples of six 2D aggregates with J-like absorption spectra but quite drastic changes in quantum yields and superradiance. We find the origin of the differences is, in fact, a different excitonic band structure where the bright state is lower energy than the monomer but still away from the band edge. We call this an “I-aggregate.” Our results provide a description of the complex excitonic behaviors that cannot be explained solely on Kasha's model. Furthermore, such properties can be tuned with the packing geometries within the aggregates providing supramolecular pathways for controlling them. This will allow for precise optimizations of aggregate properties in their applications across the areas of optoelectronics, photonics, excitonic energy transfer, and shortwave infrared technologies.

Funder

National Science Foundation

Publisher

AIP Publishing

Subject

General Earth and Planetary Sciences,General Engineering,General Environmental Science

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