What question did this study set out to answer?

This research aims to identify the energetics of higher singlet states in a TADF emitter using advanced spectroscopic techniques.

March 25, 2026Open Access

Accessing S n≥2 States of a TADF Emitter by Femtosecond NIR Spectroscopy

Key Points

This research aims to identify the energetics of higher singlet states in a TADF emitter using advanced spectroscopic techniques.
Characterized a TADF emitter using femtosecond UV-Vis and near infrared spectroscopy.
Probed spectral changes across a wavelength range of 350 to 1600 nm.
Conducted experiments in various solvents including cyclohexane, toluene, 1,2-dimethoxyethane, and acetonitrile.
Identified low-lying higher singlet excitations contributing to intersystem crossing.
Noted significant solvent dependence on transition energies between S1 and Sn≥2 states.
Provided insights into dielectric and vibrational relaxation following S1 excitation.

Abstract

A thermally activated delayed fluorescence (TADF) emitter consisting of a triarylamine (TAA) donor and a 1,4-dicyanobenzene (DCN) acceptor moiety was characterized by femtosecond UV-Vis and near infrared (NIR) spectroscopy. The combination of the two techniques allows to probe spectral changes of the emitter in a range extending from 350 to 1600 nm. With the approach, low-lying higher singlet excitations (Sn≥2) contributing to intersystem crossing via spin vibronic mechanisms can be located energetically. Due to the charge transfer (CT) character of the S1 state, the transition energies S1→Sn≥2 are strongly solvent dependent as experiments on TAA-DCN dissolved in cyclohexane, toluene, 1,2-dimethoxyethane, and acetonitrile indicate. The experiments also hold information on dielectric and vibrational relaxation ensuing S1 excitation.

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