In this regard, the triplet exciton-radical coupled systems and the intramolecular triplet-pairs generated by singlet fission (SF) can produce a variety of spin multiplicities simultaneously or sequentially, and thus are candidates for creating advanced molecular functions of the quantum information. In mechanism of electron spin polarization in chromophore-radical systems, it is known that the interaction between a singlet exciton and a radical moiety generated by photoexcitation produces the doublet and quartet spins in the pair by the excited triplet and radical moieties in the linked systems. By using time-resolved electron paramagnetic (TREPR) measurements, Ishii and Yamauchi et al. pioneered the spin polarization mechanism that takes spin-orbit coupling (SOC) into account in the doublet (D)-quartet (Q) spin conversion in the linked systems. The SOC effects have been developed applying the perturbation treatments in several D-Q systems. On the other hand, reversed quartet spin polarization was found and was explained by Q-D spin conversion by the zero-field splitting (ZFS) in a functionalized fullerene-radical linked systems, as reported by Corvaja and coworkers. Wasielewski and coworkers invoked the ZFS interaction causing the quick D-Q spin conversion using the Fermi's golden rule expression to understand the spin polarization of the quartet states. This resembles to the radical-triplet pair mechanism (RTPM) by which the spin polarization of a radical is created by the ZFS interaction of the triplet moiety during radical-exciton collision and subsequent diffusion separation in the radical-triplet pairs undergoing the Q-D spin conversion as an activation process for the dynamic electron spin polarization in the ground state radical. In the intramolecular triplet-pairs (TT) generated by SF, the singlet-quintet interconversion has been explained by the activation motions of the TT states as the vibronic effect: the anisotropic conformation dynamics in the TT state generates the electron spin polarization in the quintet state ( 5 TT) because the ZFS interactions at the thermally activated TT states allows the singlet TT to create the 5 TT spinsublevel selectively, when the spin-spin exchange interaction (6J) is repeatedly modulating and when the magnitude of the 6J is less than the thermal energy of kBT. In this regard, even though the thermal energy is less than 100 cm -1 , the terahertz conformation vibrations can be invoked to play a role for the anisotropic quintet spin polarization even at the cryogenic condition at 80 K because the 6|J| energy can resonate with the low-frequency vibrations (around 100 cm -1 or less) to cause the singletquintet decoherence as the Markov relaxation process. From the above findings, it is highly expected that the above molecular conformation dynamics would play a key role for the D-Q spin conversion in the linked chromophore-radical systems. However, no theoretical prediction has been examined on the quartet spin polarization originating from the thermal activation motion relevant to the sublevel spin selectivity. Richert and coworkers reported the fine structures of the spin-polarized excited quartet state in a perylene diimide (PDI)-tetrathiaryl trityl radical linked systems (Fig. ) at room temperature. We thus revisited this linked system to investigate the vibronic effects on electron spin polarization to understand mechanism of the quantum information generation in the fluid environment.