# First-Principles Calculation of Triplet Exciton Diffusion in Crystalline Poly($p$-phenylene vinylene)

## TL;DR

This study uses first-principles electronic structure and quantum dynamics to calculate triplet exciton diffusion in crystalline PPV, revealing high intrachain mobility and anisotropic diffusion constants relevant for optoelectronic device design.

## Contribution

It provides a detailed quantum dynamical analysis of triplet exciton migration in crystalline PPV, introducing a master-equation approach for nanoscale systems.

## Key findings

- High intrachain diffusion coefficient of 3.03 cm^2/s along the backbone.
- Anisotropic diffusion with interchain D_a=0.89×10^{-2} and D_b=1.49×10^{-2} cm^2/s.
- Rapid triplet migration facilitates efficient energy transfer in organic devices.

## Abstract

Understanding and controlling exciton transport is a strategic way to enhance the optoelectronic properties of high-performance organic devices. In this article we study triplet exciton migration in crystalline poly($p$-phenylene vinylene) polymer (PPV) using comprehensive electronic structure and quantum dynamical methods. We solve the coupled electron-nuclear dynamics for the triplet energy migrating between two neighboring Frenkel sites in J- and H-aggregate arrangements. From the two-site model we extract key parameters for use with a master-equation approach that allows us to treat nanosize systems where time-dependent Schr\"odinger equation becomes intractable. We calculate the transient exciton density evolution and determine the diffusion constants along the principal crystal axes of the PPV. The triplet diffusion is characterized by two distinctive components: fast intrachain, and slow interchain. At room temperature the interchain diffusion coefficients are found to be $D_a=0.89\cdot10^{-2}$ cm$^2$s$^{-1}$ and $D_b=1.49\cdot10^{-2}$ cm$^2$s$^{-1}$ along the respective $\bar{a}$- and $\bar{b}$-axes, and the intrachain is $D_c=3.03$ cm$^2$s$^{-1}$ along the fast $\bar{c}$-axis. The exceptionally high exciton mobility along the $\pi$-conjugated backbone facilitates rapid triplet migration over long distances. Our results can be utilized in the design of efficient energy conversion and light-emitting devices with desired solid-state properties.