![]() ![]() Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are indispensable analytical techniques in modern life science and medicine, but their critically low sensitivity limits their applications. Because organic spin materials have advantages with their extremely small size, down to nanometers, and excellent bio-compatibility, it is worthwhile to research applications of the unique quintet state in quantum information science (QIS) and quantum biotechnologies 17– 19.ĭynamic nuclear polarization (DNP) of biomolecules is one of the fields where polarized electron spins can play a pivotal role 22– 29. To date, the spin aspect of SF has only been used to explain the microscopic mechanisms of SF. This model has explained well the experimental results of oriented crystalline samples 20, 21. According to the JDE model, the 5(TT) 0 quintet state of chromophore dimers can be generated as a nearly pure quantum state by making the exchange interaction between two chromophores sufficiently large and by making the principal axes of the two chromophores parallel to each other and to the Zeeman field 19. Among the five quintet spin sublevels, it has been reported that certain sublevels can be preferentially populated 13– 16. We explore the unique spin degree of freedom of SF for quantum technologies 17, 18. However, how to use this unique quintet state has not been fully demonstrated. SF provides the effective method to create spin-polarized quintet states in organic systems without using heavy metals. Note that the multiexcitonic nature offers a unique opportunity to construct quintet multiplicity owing to the presence of four half-filled orbitals. When the molecular assembly is larger than two molecules, the triplet-pair states may dissociate into two free triplets 9, 13– 16. The basic SF process is as follows: the singlet exciton S 1 undergoes a spin-allowed ultrafast transition to a triplet-pair state with overall-singlet multiplicity 1(TT), followed by an intersystem crossing (ISC) to the highest spin multiplicity state, a quintet triplet-pair 5(TT). Its unique electron degree of freedom has attracted much attention and has been studied intensively for decades. SF is a multiexciton generation process that can potentially surpass the theoretical limit of a single-junction solar cell if the split excitons are harvested as free electrons and holes 5. In particular, singlet fission (SF) 2– 12, which generates two triplet excitons from one singlet exciton, shows unique functions in terms of electron and spin degrees of freedom. Photo-excited states of organic assemblies have brought a number of unique opportunities to optoelectronics, taking advantage of the dual nature of singlet and triplet molecular excitons 1.
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