Kusama Tomoya, Hirata Shuzo
Department of Engineering Science, University of Electro-Communications, Tokyo, Japan.
Front Chem. 2021 Nov 16;9:788577. doi: 10.3389/fchem.2021.788577. eCollection 2021.
The suppression of thermally driven triplet deactivation is crucial for efficient persistent room-temperature phosphorescence (RTP). However, the mechanism by which triplet deactivation occurs in metal-free molecular solids at room temperature (RT) remains unclear. Herein, we report a large RTP intensity change in a molecular guest that depended on the reversible amorphous-crystal phase change in the molecular host, and we confirm the large contribution made by the rigidity of the host in suppressing intermolecular triplet quenching in the guest. ()-(-)-2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl (()-BINAP) was doped as a guest into a highly purified ()-bis(diphenylphosphino)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl (()-H-BINAP) host. It was possible to reversibly form the amorphous and crystalline states of the solid by cooling to RT from various temperatures. The RTP yield ( ) originating from the ()-BINAP was 6.7% in the crystalline state of the ()-H-BINAP host, whereas it decreased to 0.31% in the amorphous state. Arrhenius plots showing the rate of nonradiative deactivation from the lowest triplet excited state (T) of the amorphous and crystalline solids indicated that the large difference in between the crystalline and amorphous states was mostly due to the discrepancy in the magnitude of quenching of intermolecular triplet energy transfer from the ()-BINAP guest to the ()-H-BINAP host. Controlled analyses of the T energy of the guest and host, and of the reorganization energy of the intermolecular triplet energy transfer from the guest to the host, confirmed that the large difference in intermolecular triplet quenching was due to the discrepancy in the magnitude of the diffusion constant of the ()-H-BINAP host between its amorphous and crystalline states. Quantification of both the T energy and the diffusion constant of molecules used in solid materials is crucial for a meaningful discussion of the intermolecular triplet deactivation of various metal-free solid materials.
抑制热驱动的三重态失活对于高效持久室温磷光（RTP）至关重要。然而，在室温（RT）下无金属分子固体中三重态失活发生的机制仍不清楚。在此，我们报道了分子客体中RTP强度的大幅变化取决于分子主体中可逆的非晶-晶相变化，并且我们证实了主体的刚性在抑制客体分子间三重态猝灭方面做出了巨大贡献。（）-（-）-2,2'-双（二苯基膦基）-1,1'-联萘（（）-BINAP）作为客体掺杂到高度纯化的（）-双（二苯基膦基）-5,5',6,6',7,7',8,8'-八氢-1,1'-联萘（（）-H-BINAP）主体中。通过从不同温度冷却至室温，可以可逆地形成固体的非晶态和晶态。在（）-H-BINAP主体的晶态中，源自（）-BINAP的RTP产率（）为6.7%，而在非晶态中降至0.31%。显示非晶态和晶态固体最低三重态激发态（T）非辐射失活速率的阿仑尼乌斯图表明，晶态和非晶态之间的巨大差异主要是由于从（）-BINAP客体到（）-H-BINAP主体的分子间三重态能量转移猝灭程度的差异。对客体和主体的T能量以及从客体到主体的分子间三重态能量转移的重组能进行的控制分析证实，分子间三重态猝灭的巨大差异是由于（）-H-BINAP主体在其非晶态和晶态之间扩散常数大小的差异。对固体材料中使用的分子的T能量和扩散常数进行量化对于有意义地讨论各种无金属固体材料的分子间三重态失活至关重要。
