Circularly Polarized Luminescence as a Probe for Long-Range Interactions in Molecular Aggregates

Abstract

The extreme sensitivity of circularly polarized luminescence (CPL) to long-range excitonic interactions inside a helical aggregate is investigated. It is found to persist even in the presence of strong energetic disorder and coupling of the exciton to molecular vibrations, when the emitting exciton is localized to only a few chromophores. The CPL dissymmetry, g(lum), is found to depend on a modulated sum over the excitonic couplings, ∑(n,s)J(n,n+s)s sin(φs), where J(n,n+s) is the coupling between molecules separated by s lattice spacings and φ is the pitch angle between adjacent chromophores. The validity of this relation is confirmed through full-scale numerical simulations of helical MPOV4 aggregates using the disordered Holstein Hamiltonian. In addition, an analytical expression for g(lum) is obtained for a helical chain containing a single, energetically detuned chromophore to represent strong disorder. Subsequently, the resulting expression is generalized to include full distributed disorder. Our results demonstrate that the spatial dependence of extended interactions can be extracted from experimental spectra, without having details on disorder or exciton-vibrational coupling.

Circularly Polarized Luminescence in Chiral Molecules and Supramolecular Assemblies

“…Later, the authors investigated the extreme sensitivity of CPL to long-range excitonic interactions inside a helical aggregate. 52 The CPL dissymmetry, was found to depend on a modulated sum over the excitonic couplings…”

Circularly Polarized Luminescence from Axially Chiral BODIPY DYEmers: An Experimental and Computational Study

“…On the contrary, there is much interest in CPL as a means for the detection and characterization of chiral supramolecular aggregates of chromophoric species, which are also exciton‐coupled. In this context, CPL has demonstrated an exceptional sensitivity to long‐range couplings and has therefore been used as a probe of supramolecular structure, mode of aggregation, degree of disorder, and other properties …”

Ultraviolet, Circular Dichroism, Fluorescence, and Circularly Polarized Luminescence Spectra of Regioregular Poly‐[3‐((S)‐2‐Methylbutyl)‐Thiophene] in Solution

“…To this scope, X has to be substituted regioregularly along the polythiophene chain, as first demonstrated by Langeveld-Voss et al 1,2 However, even though there is a general feeling and a large consensus on how optical activity is generated, both in absorption and emission, we have to admit that the understanding of the chiral phenomena in these systems is only qualitative. 3,4 In the past, in our group, we were able to synthesize and characterize a PAT polymer with a very short X substituent group ((S)-2-methylbutyl moiety) (PMBT) and a high degree of regioregularity: 5-8 chemicophysical methods for the structural characterization included, besides other spectroscopic methods, regular electronic CD 5-7 as well as Infrared or Vibrational CD. 3,4 In the past, in our group, we were able to synthesize and characterize a PAT polymer with a very short X substituent group ((S)-2-methylbutyl moiety) (PMBT) and a high degree of regioregularity: 5-8 chemicophysical methods for the structural characterization included, besides other spectroscopic methods, regular electronic CD 5-7 as well as Infrared or Vibrational CD.…”