1，8-二羟基-2-萘甲醛激发态双质子转移反应的MS-CASPT2//CASSCF研究

激发态双质子转移反应长期困扰着理论和实验科学家并成为了一个悬而未决的热点问题. 本文利用完全活化空间自洽场方法及其二阶微扰理论(MS-CASPT2//CASSCF)系统地研究了典型体系1，8-二羟基-2-萘甲醛(DHNA)的激发态双质子转移反应以及相关的激发态弛豫过程. 在MS-CASPT2//CASSCF水平下，本文优化了三个能量相近但结构不同的S₁态互变异构体，即S1-ENOL、S1-KETO-1和S1-KETO-2，以及两个关键的S₁/S₀锥形交叉点结构，即S1S0-KETO-1和S1S0-KETO-2. 其中，两个极小点S1-KETO-1和S1-KETO-2与实验上观测到的双荧光发射现象密切相关. 本文还利用MS-CASPT2//CASSCF方法计算了双质子转移反应的二维势能面以及从极小点到交叉点结构的线性内插路径；相应计算结果证实了DHNA体系具有分步的激发态双质子转移机制. 具体来说，从S1-ENOL到S1-KETO-1的第一个质子转移过程是无能垒的，而从S1-KETO-1到S1-KETO-2的第二个质子转移过程则需要克服一个大约6.0 kcal/mol的能垒. 此外，由于从S1-KETO-1 (S1-KETO-2)到S1S0-KETO-1 (S1S0-KETO-2)的线性内插路径显示DHNA体系需要翻越一个约为12.0 kcal/mol的能垒，因此DHNA体系将在S₁态上停留一段时间并发生双荧光发射现象. 当然，S₁/S₀锥形交叉点也会促使DHNA体系从S₁态内转换到S₀态，而这会一定程度上降低DHNA体系发射荧光的效率. 可以通过限制C5-C8-C9-O10二面角旋转来降低体系的内转换效率，进而提高DHNA体系的发光效率. 本工作不仅有助于理解激发态双质子转移机制，还有助于设计具有优异发光性能的新型分子材料.

Excited-State Double Proton Transfer of 1,8-Dihydroxy-2-Naphthaldehyde: a MS-CASPT2//CASSCF Study

Excited-state double proton transfer (ESDPT) is a controversial issue which has long been plagued with theoretical and experimental communities. Herein, we took 1,8-dihydroxy2-naphthaldehyde (DHNA) as a prototype and used combined complete active space selfconsistent field (CASSCF) and multi-state complete active-space second-order perturbation (MS-CASPT2) methods to investigate ESDPT and excited-state deactivation pathways of DHNA. Three different tautomer minima of S1-ENOL, S1-KETO-1, and S1-KETO-2 and two crucial conical intersections of S1S0-KETO-1 and S1S0-KETO-2 in and between the S₀ and S₁ states were obtained. S1-KETO-1 and S1-KETO-2 should take responsibility for experimentally observing dual-emission bands. In addition, two-dimensional potential energy surfaces (2D-PESs) and linear interpolated internal coordinate paths connecting relevant structures were calculated at the MS-CASPT2//CASSCF level and confirmed a stepwise ESDPT mechanism. Specifically, the first proton transfer from S1-ENOL to S1-KETO-1 is barrierless, whereas the second one from S1-KETO-1 to S1-KETO-2 demands a barrier of ca. 6.0 kcal/mol. The linear interpolated internal coordinate path connecting S1-KETO-1 (S1-KETO-2) and S1S0-KETO-1 (S1S0-KETO-2) is uphill with a barrier of ca. 12.0 kcal/mol, which will trap DHNA in the S₁ state while therefore enabling dual-emission bands. On the other hand, the S₁/S₀ conical intersections would also prompt the S₁ system to decay to the S₀ state, which could be to certain extent suppressed by locking the rotation of the C5?C8?C9?O10 dihedral angle. These mechanistic insights are not only helpful for understanding ESDPT but also useful for designing novel molecular materials with excellent photoluminescent performances.