Interplay between Intra- and Intermolecular Charge Transfer in the Optical Excitations of J-Aggregates

TL;DR

This study uses first-principles calculations to analyze how intra- and intermolecular interactions influence optical excitations in J-aggregates of organic dyes, revealing mixed charge transfer characteristics and a pure intermolecular excitation.

Contribution

It provides a detailed microscopic understanding of optical excitations in J-aggregates, highlighting the interplay of intra- and intermolecular charge transfer effects.

Findings

The J-band excitation involves both intra- and intermolecular charge transfer.

A pure intermolecular charge-transfer excitation exists within the J-band.

These insights improve understanding of collective excitations in organic semiconductors.

Abstract

In a first-principles study based on density functional theory and many-body perturbation theory, we address the interplay between intra- and intermolecular interactions in a J-aggregate formed by push-pull organic dyes by investigating its electronic and optical properties. We find that the most intense excitation dominating the spectral onset of the aggregate, i.e., the J-band, exhibits a combination of intramolecular charge transfer, coming from the push-pull character of the constituting dyes, and intermolecular charge transfer, due to the dense molecular packing. We also show the presence of a pure intermolecular charge-transfer excitation within the J-band, which is expected to play a relevant role in the emission properties of the J-aggregate. Our results shed light on the microscopic character of optical excitations of J-aggregates and offer new perspectives to further understand the nature of collective excitations in organic semiconductors.