Balance between Triplet States in Photoexcited Orthogonal BODIPY Dimers

Yuri E Kandrashkin; Zhijia Wang; Andrei A Sukhanov; Yuqi Hou; Xue Zhang; Ya Liu; Violeta K Voronkova; Jianzhang Zhao

doi:10.1021/acs.jpclett.9b01741

Balance between Triplet States in Photoexcited Orthogonal BODIPY Dimers

J Phys Chem Lett. 2019 Aug 1;10(15):4157-4163. doi: 10.1021/acs.jpclett.9b01741. Epub 2019 Jul 11.

Authors

Yuri E Kandrashkin¹, Zhijia Wang², Andrei A Sukhanov¹, Yuqi Hou², Xue Zhang², Ya Liu², Violeta K Voronkova¹, Jianzhang Zhao²

Affiliations

¹ Zavoisky Physical-Technical Institute FRC Kazan Scientific Center of RAS , Sibirsky Tract 10/7 , Kazan 420029 , Russia.
² State Key Laboratory of Fine Chemicals, School of Chemical Engineering , Dalian University of Technology , E-208 West Campus, 2 Ling Gong Road , Dalian 116024 , P.R. China.

PMID: 31283880
DOI: 10.1021/acs.jpclett.9b01741

Abstract

The intersystem crossing (ISC) and the triplet states in two representative BODIPY orthogonal dimers were studied with time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The electron spin polarization (ESP) of the triplet state of the dimers, accessed with spin-orbit charge-transfer ISC, is different from that of the monomer (spin-orbit coupling-induced ISC). The TREPR spectra show that the triplet state initially formed by charge recombination is localized on either of two subunits, with different preference and ESP patterns. On the basis of the relative orientation of the respective zero field splitting principal axes, the T_x state on one subunit and the T_z state on another subunit in the dimer are overpopulated. The balance between the two triplet states is confirmed by the temperature dependency of the population ratio. No quintet state was detected with TREPR down to 20 K; thus, the recently proposed singlet fission ISC mechanism is excluded.