# Quasi-periodic and fractal polymers: Energy structure and carrier transfer

## TL;DR

This study investigates how the energy structure and charge transfer properties of aperiodic and fractal polymers, modeled after DNA, depend on their complex structural patterns, revealing correlations between complexity and transfer efficiency.

## Contribution

It introduces a comprehensive analysis of energy spectra and charge transfer in quasi-periodic and fractal polymers, highlighting the influence of structural complexity on transfer properties.

## Key findings

- I polymers favor charge transfer over D polymers.
- Charge transfer rates vary with structural complexity and sequence type.
- Comparison with periodic and random sequences shows distinct transfer behaviors.

## Abstract

We study the energy structure and the coherent transfer of an extra electron or hole along aperiodic polymers made of $N$ monomers, with fixed boundaries, using B-DNA as our prototype system. We use a Tight-Binding wire model, where a site is a monomer (e.g., in DNA, a base pair). We consider quasi-periodic (Fibonacci, Thue-Morse, Double-Period, Rudin-Shapiro) and fractal (Cantor Set, Asymmetric Cantor Set) polymers made of the same monomer (I polymers) or made of different monomers (D polymers). For all types of such polymers, we calculate the HOMO and LUMO eigenspectrum, the HOMO-LUMO gap and the density of states. We examine the mean over time probability to find the carrier at each monomer, the frequency content of carrier transfer (Fourier spectra, weighted mean frequency of each monomer, total weighted mean frequency of the polymer), and the pure mean transfer rate $k$. Our results reveal that there is a correspondence between the degree of structural complexity and the transfer properties. I polymers are more favorable for charge transfer than D polymers. We compare $k(N)$ of quasi-periodic and fractal sequences with that of periodic sequences (including homopolymers) as well as with randomly shuffled sequences. Finally, we discuss aspects of experimental results on charge transfer rates in DNA with respect to our coherent pure mean transfer rates.