Sirimatayanant Saruti, Andruniów Tadeusz
Institute of Advanced Materials, Department of Chemistry, Wroclaw University of Science and Technology, Wyb. Wyspiańskiego 27, Wrocław 50-370, Poland.
J Chem Theory Comput. 2024 Sep 13;20(18):8118-26. doi: 10.1021/acs.jctc.4c00675.
We investigate here a systematic way to tune two-photon transition strengths (δ) and two-photon absorption (2PA) cross sections (σ) of the rhodopsin's chromophore 11--retinal protonated Schiff base (RPSB) via the modulation of the methyl groups pattern along its polyene chain. Our team employed the resolution of identity, coupled cluster approximate second order (RI-CC2) method with Dunning's aug-cc-pVDZ basis set, to determine the structural impact on δ, as well as its correlation to both transition dipole moments and permanent electric dipole moments. Seven structures were probed in vacuo, including five-double-bond-conjugated model of the native chromophore, shortened by the β-ionone ring (RPSB5), and its de/methylated analogues: 9-methyl, 13-methyl, planar and twisted models of 9,10-dimethyl and 9,10,13-trimethyl. Our results demonstrate that the magnitude of δ is dictated by both the position and number of methylated groups attached to its polyene chain as well as the degree of dihedral twist that is introduced due to the de/methylation. In fact, a strong correlation between δ enhancement and the presence of a C13-methyl group in the planar RPSB5 species is found. Trends in δ values follow the trends observed in their corresponding changes in the permanent dipole moment upon the S0-S1 excitation nearly exactly. The assessment of four DFT functionals, i.e., M11, MN15, CAM-B3LYP, and BHandHLYP, previously found most successful in predicting 2PA properties in biological chromophores, points to a long-range-corrected hybrid meta-GGA M11 as the top-performing functional, albeit still delivering underestimated δ and σ values by a factor of 3.3-5.3 with respect to the CC2 results. In the case of global-hybrid meta-NGA (MN15), as well as CAM-B3LYP and BHandHLYP functionals, this factor deteriorates significantly to 6.7-20.9 and is mostly related to significantly lower quality of the ground- and excited-state dipole moments.
我们在此研究一种系统的方法，通过调节视紫红质发色团11 - 视网膜质子化席夫碱（RPSB）多烯链上的甲基模式，来调整其双光子跃迁强度（δ）和双光子吸收（2PA）截面（σ）。我们的团队采用了分辨率恒等式耦合簇近似二阶（RI - CC2）方法以及邓宁的aug - cc - pVDZ基组，来确定结构对δ的影响，以及它与跃迁偶极矩和永久电偶极矩的相关性。在真空中探究了七种结构，包括天然发色团的五重双键共轭模型，去掉β - 紫罗兰酮环后缩短的模型（RPSB5），以及它的去甲基化/甲基化类似物：9 - 甲基、13 - 甲基、9,10 - 二甲基和9,10,13 - 三甲基的平面和扭曲模型。我们的结果表明，δ的大小由连接在其多烯链上的甲基化基团的位置和数量以及由于去甲基化/甲基化引入的二面角扭曲程度决定。事实上，在平面RPSB5物种中发现δ增强与C13 - 甲基基团的存在之间存在很强的相关性。δ值的趋势几乎与S0 - S1激发时其相应永久偶极矩变化中观察到的趋势完全一致。对四种DFT泛函（即M11、MN15、CAM - B3LYP和BHandHLYP）的评估，此前发现它们在预测生物发色团的2PA性质方面最为成功，结果表明长程校正的杂化元广义梯度近似（meta - GGA）M11是表现最佳的泛函，尽管相对于CC2结果，它仍然将δ和σ值低估了3.3 - 5.3倍。就全局杂化元非局部广义近似（MN15）以及CAM - B3LYP和BHandHLYP泛函而言，这个倍数显著恶化到6.7 - 20.9，并且主要与基态和激发态偶极矩的质量显著较低有关。
