In PtOEP/TAB system (Figure , Figure -S7), the EPR linewidth was narrowed in the mixture of toluene(T): paraffin(P) = 1:1 (v/v) solvent due to a rapid change in the orientation of triplet-exciton relative to the external magnetic field. In contrast, in the T:P = 1:19 solvent, the narrowing effect is suppressed, and broad EPR spectra were observed due to the anisotropy of the spin-spin dipole interaction (Figure ). In the T:P = 1:9 mixture of the PtOEP/DPA system (Figure ), the motional narrowing is suppressed, as well as in the PtOEP/TAB system with T:P = 1:19. In these viscous solutions, the total splitting widths of the spectra (c.a.120 mT) by the fine structures are comparable for both TAB and DPA. The spin density is distributed to two anthracene moieties in TAB, whereas the spin density is localized in one anthracene unit in DPA (Figure ). The difference of spin distribution means that the ZFS parameter in DPA is larger than those in TAB. Therefore the equal widths of observed dipolar splitting indicate a motional narrowing effect on the spectrum for DPA in the T:P = 1:9 solvent since the molecular radius of DPA is much smaller than that of TAB.