Energetics and couplings in oligoacene-based singlet fission: Efficient and accurate density functional theory tells the story

Lin, Zhou

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https://hdl.handle.net/2142/100743 Copy

Description

Title

Energetics and couplings in oligoacene-based singlet fission: Efficient and accurate density functional theory tells the story

Author(s)

Lin, Zhou

Contributor(s)

• Iwasaki, Hikari
• Van Voorhis, Troy
• Ye, Hong-Zhou

Issue Date

2018-06-18

Keyword(s)

Mini-symposium: New Ways of Understanding Molecular Spectra

Abstract

In the sub-picosecond singlet fission (SF) process, two coherent triplet excitons (1 (T1T1)) are generated from one singlet exciton (S1) through a mysterious “multi-exciton” (1ME) intermediate: S1 ←→ 1ME ←→ 1 (T1T1) −→ 2T1. a Organic semiconducting materials that undergo exothermic SF double the efficiency associated with high-energy incident photons and allow the photovoltaics to exceed the Shockley–Queisser limit of 33.7%.b Understanding the character of 1ME serves as the key to deciphering the ultrafast SF mechanism. Based on a popular hypothesis, the complete SF procedure involves two steps of charge transfer (CT) and 1ME is a superposition of localized and charge-separated excited states.c However, the straightforward experimental and theoretical evidence to support this hypothesis is still in darkness due to the challenges to measure ultrafast photochemistry and to describe charge-separated and multiply-excited energy levels. Herein we modeled the local SF reactions occurring in hexacene, pentacene and bis(6,13-bis(triisopropylsilylethynyl)pentacene)benzene in the crystalline or solution phase. The efficient and accurate density functional theory (DFT) based approaches developed in the earlierd and present study were utilized to evaluate energies of S1, 1ME and 1 (T1T1), as well as the non-adiabatic coupling between each pair of them. Our results shed light on the roles of localized and charge-separated excited states in the complete SF mechanism and propose the strategy for the rational design of oligoacene-based SF materials.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100743

DOI

10.15278/isms.2018.MH07

Copyright and License Information

Copyright 2018 Zhou Lin

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