同样传质子，核运动范围不一样#

蒽–酚–吡啶三单元里，光激发后可走质子耦合电子转移（PCET），也可走较新的质子耦合能量转移（PCEnT）。两者都伴随酚到吡啶的质子转移，但除了质子本身，哪些核运动在驱动反应、两条路径有何不同，此前不清楚。作者要找出这两条非绝热过程的核反应坐标，并比较其机制差异。

Fig.1 Anthracene−phenol−pyridine triads examined in this study, with the transferring proton highlighted in red. Note that the only difference between the triads is the group on the pyridine. We studied both PCET and PCEnT in triad 1, PCET in triad 3, and PCEnT in triad 4.

用二重态缝采样找反应坐标#

作者用E-SHAKE在二重态（diabatic）能级简并缝空间做约束分子动力学，取缝内最低能量点DMECP，以二重态能隙梯度作为反应坐标的零阶估计。三单元中，PCET反应坐标主要落在酚和蒽上，吡啶贡献仅0.031；PCEnT则贯穿整个三单元，三单元相对贡献约酚0.149、蒽0.690、吡啶0.150（triad 1，未计转移质子和亚甲基）。质子运动投影到供体–受体轴，PCET为−0.22，PCEnT为0.99和0.51；PCET中受体氮运动贡献很小，PCEnT中明显更大。PCET的DMECP处质子仍靠近酚氧（O–H/N–H约1.02/1.56 Å和1.02/1.59 Å），PCEnT的triad 4也如此，triad 1则已转移到氮。两者都无稳定中间体，作者判断均协同但可能异步，PCEnT可能更同步。二重态耦合在缝内变化大，均违反Condon近似；PCET的耦合穿过零，线积分几何相位约−1.04π和−1.03π，支持圆锥交叉；PCEnT未见此现象，更接近避免交叉。质子势重叠平方比PCEnT约21、PCET约5.6，作者据此推测PCEnT的动力学同位素效应可能更大，但明确说需完整速率计算确认。

Fig.2 Diabatic electronic couplings between the LES and CSS for PCET or between the LES and LEPT state for PCEnT versus the energy of its lower adiabatic surface relative to its DMECP. The color of each point is determined by the instantaneous temperature during the diabatic seam sampling. All diabatic seams appear to violate the Condon approximation in that the diabatic electronic coupling depends on the nuclear coordinates (i.e., it changes in the seam space). Only the LES–CSS diabatic coupling associated with PCET passes through zero in our seam sampling, indicating an energetically relevant intersection of adiabatic surfaces in the diabatic seam. Fig.3 Proton potential energy profiles and H vibrational wave functions for PCET (top) and PCEnT (bottom) in triad 1. The energy in each plot is relative to the minimum energy of the two proton potentials shown. We show the first two proton vibrational wave functions for each diabatic state. Note that PCET and PCEnT may involve nonadiabatic transitions between vibronic states not shown here.

能指导设计，还不能当定量预测#

理论上，这把PCET与PCEnT的核反应坐标和拓扑差异摆到一起：前者更局部、可经圆锥交叉，后者牵动受体和全分子。做光化学质子耦合体系、想偏向电荷转移或能量转移的人，可把吡啶受体运动和质子对齐程度当设计线索。边界很清楚：计算在气相、TDDFT级别，采样温度1–50 K并非物理温度，只用于充分采样；未传播非绝热动力学，未算速率和KIE，二重化方案也不唯一。原文未提供直接实验或器件转化证据，这些差异能否推广到其他三单元，作者自己说仍不清楚。