Abstract
In several fields of research, like e.g. photosensitization, photovoltaics, organic electroluminescent devices, dynamic nuclear polarization, or pulsed dipolar electron paramagnetic resonance spectroscopy, triplet state kinetics play an important role. It is therefore desirable to tailor the kinetics of photoexcited triplet states, e.g. by exploiting the intramolecular heavy-atom effect, and to determine the respective kinetic parameters. In this work, we set out to systematically investigate the photoexcited triplet state kinetics of a series of haloanthracenes by time-resolved electron paramagnetic resonance spectroscopy in combination with synchronized laser excitation. For this purpose, a procedure to simulate time traces by solving the differential equation system governing the triplet kinetics numerically is developed. This way, spin lattice relaxation rates and zero-field triplet life times are obtained concurrently by a global fit to experimental data measured at three different cryogenic temperatures.
Highlights
Photoexcited triplet states found numerous applications in several fields of research like, for example, photovoltaics [1], photosensitization [2], photon upconversion at low light intensities via triplet-triplet annihilation [3], and organic electroluminescent devices [4]
In the current manuscript we show that the exact differential equation system can be solved numerically to yield triplet decay as well as spin-lattice relaxation (SLR) kinetic parameters describing the experimental kinetic data in intermediate temperature regimes
The electron paramagnetic resonance (EPR) transients of each magnetic field are integrated for optimized signal-to-noise ratio (SNR)
Summary
Photoexcited triplet states found numerous applications in several fields of research like, for example, photovoltaics [1], photosensitization [2], photon upconversion at low light intensities via triplet-triplet annihilation [3], and organic electroluminescent devices [4]. In nuclear magnetic resonance (NMR) spectroscopy, dynamic nuclear polarization (DNP) by photoexcited triplet states is used to increase its sensitivity. [5] Here, utilizing the much higher polarization of optically excited triplet electron spins [6] 1H NMR spin polarizations of 70% and more were achieved. [7, 8] In another recent development, the triplet state was successfully employed for distance measurements in the nanometer range by triplet-doublet DEER and LaserIMD. In order to achieve high polarization transfer in DNP, the triplet spin polarization has to persist for long times.
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