# NOCI‑F Electronic Couplings in Assemblies of Indolonaphthyridine Molecules: From Dimers to the Full Stack

## TL;DR

This paper uses a new computational method to study electronic interactions in stacks of indolonaphthyridine molecules, revealing how structure affects processes like energy transfer.

## Contribution

The study introduces an advanced postanalysis tool for NOCI-F data, enabling full-stack Hamiltonian analysis and providing new insights into excitonic processes.

## Key findings

- Electronic couplings in indolonaphthyridine stacks were quantified for processes like singlet fission and charge diffusion.
- Structural disorder significantly impacts intermolecular electronic couplings in molecular stacks.
- A new postanalysis tool was developed to analyze full stacks, offering additional physical insights beyond dimer/trimer models.

## Abstract

Key electronic processes
related to molecular excitonic states
of finite stacks of indolonaphthyridine molecules are analyzed via
the non-orthogonal configuration interaction with fragments (NOCI-F)
method. Indolonaphthyridine is an organic chromophore that can undergo
several electronic photoexcitation-related intermolecular processes,
such as exciton and electron transfer. The structures studied here
are noncrystalline arrangements built as either ordered stacks of
indolonaphthyridine or stacks extracted from molecular dynamics simulations
including thermal disorder. Taking dimers or trimers from either model,
we performed CASSCF and NOCI-F calculations to quantify the intermolecular
electronic couplings governing singlet fission, excited singlet and
triplet diffusion, and hole and electron diffusion processes. Also,
comparing the results for the different models, we studied the effect
of structural disorder and distortion on these couplings. Finally,
we present a newly developed, advanced postanalysis tool. It takes
the NOCI-F data as input to carry out a multifragment full Hamiltonian
procedure that involves the complete stack, providing physical information
not available from the dimer/trimer models, hence giving access to
additional insight into the material’s properties.