Abstract
The control of spins and spin to charge conversion in organics requires understanding the molecular spin-orbit coupling (SOC), and a means to tune its strength. However, quantifying SOC strengths indirectly through spin relaxation effects has proven difficult due to competing relaxation mechanisms. Here we present a systematic study of the g-tensor shift in molecular semiconductors and link it directly to the SOC strength in a series of high-mobility molecular semiconductors with strong potential for future devices. The results demonstrate a rich variability of the molecular g-shifts with the effective SOC, depending on subtle aspects of molecular composition and structure. We correlate the above g-shifts to spin-lattice relaxation times over four orders of magnitude, from 200 to 0.15 μs, for isolated molecules in solution and relate our findings for isolated molecules in solution to the spin relaxation mechanisms that are likely to be relevant in solid state systems.
Highlights
The control of spins and spin to charge conversion in organics requires understanding the molecular spin-orbit coupling (SOC), and a means to tune its strength
In this work we show that the g-factor of an unpaired spin from a charged molecule can be used as a measure of the effective SOC, over a wide range of SOC strengths
We compare a set of 32 fused-ring molecular semiconductors with systematically varying geometries and atomic substitutions, most of which are based on central thiophene or selenophene moieties that are commonly found in highmobility organic semiconductors
Summary
The control of spins and spin to charge conversion in organics requires understanding the molecular spin-orbit coupling (SOC), and a means to tune its strength. Despite its fundamental importance for device applications, quantifying SOC strengths in organics based on investigating spin relaxation has proven difficult due to the competing and hard to distinguish contribution from hyperfine interactions (HFI)[4], the coupling of the charge’s spin to nuclear spins. Both SOC and HFI have been used separately to explain the magnetoresistance[5] and spin diffusion length[6] in spin valves of the same organic material. A systematic quantitative study of SOC strengths has been hindered by the difficulty in isolating the effect of SOC on spin lifetimes, diffusion lengths or inverse spin hall voltages
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