Chemical Modification toward Long Spin Lifetimes in Organic Conjugated Radicals

Abstract

Organic semiconductors for spin-based devices require long spin relaxation times. Understanding their spin relaxation mechanisms is critical to organic spintronic devices and applications for quantum information processing. However, reports on the spin relaxation mechanisms of organic conjugated molecules are rare and the research methods are also limited. Herein, we study the molecular design and spin relaxation mechanisms by systematically varying the structure of a conjugated radical. We found that solid-state relaxation times of organic materials are largely different from that in solution state. We demonstrate that substitution of a lower gyromagnetic ratio nucleus (e. g. D, Cl) on the para-position of the aryl rings in the triphenylmethyl (TM) radical can significantly improve their coherence times (T ). Flexible thin films based on such radicals exhibit ultra-long spin-lattice relaxation times (T ) up to 35.6(6) μs and T up to 1.08(4) μs under ambient conditions, which are among the longest values in films. More importantly, using the TM radical derivative (5CM), we observed room-temperature quantum coherence and Rabi cycles in thin film for the first time, suggesting that organic conjugated radicals have great potentials for spin-based information processing.

Measurement of quantum coherence in thin films of molecular quantum bits without post-processing

“…Consequently, thus far, spin dynamics measurements of thin films, including the determination of phase memory or quantum coherence time have been carried out either ex situ by dissolving the films, 10 or by cutting thin films on flexible substrates into pieces so that they fit into standard electron paramagnetic resonance (EPR) tubes. 11,12 Both are rather unsatisfactory and do not allow moving forward towards device application.…”

A Stable Triplet‐Ground‐State Conjugated Diradical Based on a Diindenopyrazine Skeleton

“…To further confirm the triplet ground state of diradical m ‐DIP2 , we performed Rabi cycles at 100 K through an echo‐detected nutation experiment (Figure 4 c). [21] The Rabi frequency would exhibit a linear function to the magnetic B 1 field and, if g ‐values are kept unchanged, the slope of an S= 1 species would be √2 times that of an S= 1/2 species [20b, 22] (Figure 4 d). The dependence of the Rabi frequency to the B 1 field strength was measured as 4.4 MHz/G for m ‐DIP2 , and 2.8 MHz/G for a standard S= 1/2 substance ( 5CM ), indicating that the Rabi oscillation of m ‐DIP2 at 100 K resulted from S= 1 species.…”

“…The dependence of the Rabi frequency to the B 1 field strength was measured as 4.4 MHz/G for m ‐DIP2 , and 2.8 MHz/G for a standard S= 1/2 substance ( 5CM ), indicating that the Rabi oscillation of m ‐DIP2 at 100 K resulted from S= 1 species. Subsequently, we obtained T 1 and T m [23] of m ‐DIP2 via an inversion recovery method (π‐T‐π/2‐ τ ‐π‐ τ ‐echo) and magnetization echo induced by Hahn‐echo pulse sequences [21] (Figure S9). The spin‐echo decay curves were fitted with exponential decay to extract T 1 of 4.3 ms and T m of 3.0 μs at 100 K. The long T 1 of m ‐DIP2 indicated its potential for medium‐term storage of spin‐based bits.…”

Stability of radical-functionalized gold surfaces by self-assembly and on-surface chemistry

“…PTM is a very persistent and stable radical that shows a long coherence time at room temperature, being a strong potential candidate for quantum technologies. 24 Previously, self-assembled monolayers (SAMs) of PTM on gold substrates have been investigated to study their transport properties. [21][22][23]25 The radical character of the layers was proved by several techniques (UV-vis, cyclic voltammetry, EPR, NEXAFS and UPS); however, a careful and in-depth characterization of the stability of these radical SAMs has not been carried out so far.…”