Kinetics of the Photoexcited States in Thin Films of Metallo-Supramolecular Polymers With Ditopic Thiophene-Bridged Terpyridine Ligands

Miroslav Menšík; David Rais; Muhammed Arshad Thottappali; Pinar Güloğlu; Petr Toman; Jiří Vohlídal; Jiří Pfleger

doi:10.3389/fchem.2021.766121

Kinetics of the Photoexcited States in Thin Films of Metallo-Supramolecular Polymers With Ditopic Thiophene-Bridged Terpyridine Ligands

Front Chem. 2022 Jan 20:9:766121. doi: 10.3389/fchem.2021.766121. eCollection 2021.

Authors

Miroslav Menšík¹, David Rais¹, Muhammed Arshad Thottappali^{1

2}, Pinar Güloğlu¹, Petr Toman¹, Jiří Vohlídal³, Jiří Pfleger¹

Affiliations

¹ Institute of Macromolecular Chemistry, Czech Academy of Sciences, Prague, Czechia.
² Faculty of Mathematics and Physics, Charles University, Prague, Czechia.
³ Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Prague, Czechia.

Abstract

Managing the excited-state decay by a supramolecular structure is a crucial issue for organic photovoltaics. We show that in thin films of metallo-supramolecular polymers made of bis(terpyridine-4'-yl)terthiophenes and $Z n^{2 +}$ coupling ions, the photoexcited states generated by ultrashort laser pulses at the wavelength of 440 nm decay by the bi-molecular annihilation predominantly controlled by the Förster transfer between singlet states. During this bi-molecular annihilation of singlet states, intermediate hot triplet pairs are formed, which subsequently dissociate into long-living diffusing triplet states. It explains a significant shortening of the triplet state rise time with increasing pump fluence. The diffusion coefficient of triplets showed power-law time dependence, with its exponent proportional to the pump fluence, decreasing thus the diffusivity of triplets.

Keywords: metallo-supramolecular polymers; polythiophene; singlet and triplet excitons; time-dependent diffusion coefficient; transient absorption spectroscopy.