Liu Haonan, Isoda Ryuichi, Doi Marina, Muto Koichiro, Ando Shinji
Department of Chemical Science and Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan.
J Phys Chem B. 2024 Aug 8;128(31):7690-7701. doi: 10.1021/acs.jpcb.4c03946. Epub 2024 Jul 25.
To investigate the correlation between the aggregated state and photoluminescence (PL) mechanism of dual fluorescent (FL) and phosphorescent (PH) polyimides (PIs), the photophysical processes of FL-type , PH-type , and their corresponding imide model compounds ( and ) dispersed in poly(methyl methacrylate) (PMMA) films were analyzed at elevated pressures up to 8 GPa using a diamond anvil cell. Dibromo-substituted demonstrated a shorter wavelength absorption than owing to the larger dihedral angle in the biphenyl moiety. Both MCs exhibited red-shifts in their absorption spectra with increasing pressure, indicating planarization occurred at the biphenyl moieties associated with the compression of the free volume in PMMA. The PL intensity of increased with increasing pressure, while its quantum yield (Φ) decreased sharply due to the enhanced energy transfer via the Förster mechanism. In contrast, the PH quantum yield (Φ) of monotonically increased at lower pressures, while it showed excitation wavelength-dependent behaviors at higher pressures: Φ remained unchanged under excitation at 340 nm but gradually increased under excitation at 365 nm. This fact suggests that, at higher pressures, 365 nm excitation promoted intersystem crossing (ISC) from excited singlet states at higher energy levels. Using this phenomenon, a significant pressure-induced PH enhancement (PIPE) was observed for up to 0.9 GPa upon excitation at 365 nm, which is a rare phenomenon for organic polymers. This study indicates that even in colorless and optically transparent amorphous polymers, an enhancement of PH due to restricted molecular motion and intensified ISC outweighs the deactivation due to intermolecular energy transfer under certain pressures, leading to an increase in Φ.
为了研究双荧光（FL）和磷光（PH）聚酰亚胺（PI）的聚集态与光致发光（PL）机制之间的相关性，使用金刚石对顶砧池在高达8 GPa的高压下分析了分散在聚甲基丙烯酸甲酯（PMMA）薄膜中的FL型、PH型及其相应的酰亚胺模型化合物（ 和 ）的光物理过程。二溴取代的 由于联苯部分中较大的二面角，其吸收波长比 短。随着压力增加，两种模型化合物的吸收光谱均发生红移，表明与PMMA中自由体积压缩相关的联苯部分发生了平面化。 的PL强度随压力增加而增加，而其量子产率（Φ）由于通过Förster机制增强的能量转移而急剧下降。相比之下， 的PH量子产率（Φ）在较低压力下单调增加，而在较高压力下表现出与激发波长相关的行为：在340 nm激发下Φ保持不变，但在365 nm激发下逐渐增加。这一事实表明，在较高压力下，365 nm激发促进了来自较高能级激发单重态的系间窜越（ISC）。利用这一现象，在365 nm激发下，观察到 高达0.9 GPa的显著压力诱导磷光增强（PIPE），这对于有机聚合物来说是一种罕见的现象。这项研究表明，即使在无色且光学透明的无定形聚合物中，由于分子运动受限和ISC增强导致的PH增强在一定压力下超过了分子间能量转移导致的失活，从而导致Φ增加。
