Singlet Heterofission in Tetracene–Pentacene Thin‐Film Blends

Clemens Zeiser,Katharina Broch,Margherita Maiuri,Daniel Lepple,Luca Moretti,Giulio Cerullo

doi:10.1002/ange.202007412

Clemens Zeiser, Katharina Broch + Show 4 more

Open Access

https://doi.org/10.1002/ange.202007412

Copy DOI

Abstract

AbstractHeterofission is a photophysical process of fundamental and applied interest whereby an excited singlet state is converted into two triplets on chemically distinct chromophores. The potential of this process lies in the tuning of both the optical band gap and the splitting between singlet and triplet energies. Herein, we report the time‐domain observation of heterofission in mixed thin films of the prototypical singlet fission chromophores pentacene and tetracene using excitation wavelengths above and below the tetracene band gap. We found a time constant of 26 ps for endothermic heterofission of a singlet exciton on pentacene in blends with low pentacene fractions, which was outcompeted by pentacene homofission for increasing pentacene concentrations. Direct excitation of tetracene lead to fast energy transfer to pentacene and subsequent singlet fission, which prevented homo‐ or heterofission of a singlet exciton on tetracene.

Highlights

We investigated the photophysical properties of the blends by transient absorption (TA) spectroscopy, using the results of the neat films (Figures 1 c,d) for comparison
In order to determine the time constants of the dominating photophysical processes in the different blends, we performed a global analysis (GA) (Figures S8 and S10), which yielded two spectrally distinct species that can be assigned to singlets and triplets, as before. Comparing these results with the time constants extracted from the measurements with lexc = 620 nm (Figure 3), we find that the early photoinduced processes triggered at lexc = 520 nm occur with longer time constants
We investigated the photophysics of mixed thin films of TET and PEN using TA spectroscopy, selectively pumping either PEN alone or PEN and TET simultaneously

Summary

Introduction

For the efficient application of SF in solar cells, a balance between efficient generation of triplet pairs, facilitated by strong intermolecular interactions, and the subsequent separation of the triplet pairs into free triplets, for which weak intermolecular interactions are beneficial, has to be found.[8] Different approaches are being followed for the development of new, promising SF compounds, often based on covalently bound dimers of SF chromophores, aiming at the optimization of the intermolecular coupling or the energy alignment of singlet and triplet states These dimers or polymers of covalently bound SF chromophores exhibit intramolecular SF (iSF) and can be used to probe the impact of interaction strength and charge transfer state admixture on SF rates.[9,10,11,12,13,14,15]. Heterofission holds great potential for the application of SF in devices based on a controlled tuning of the exo- and endothermicity of the SF process and of the optical band gap

Objectives

Results

Discussion

Conclusion