Alia Joseph D, Flack Joseph A
Division of Science and Mathematics, University of Minnesota Morris 600 E 4th St USA
NYITCOM at Arkansas State University P. O. Box 2206, State University AR 72467 USA.
RSC Adv. 2020 Nov 26;10(70):43153-43167. doi: 10.1039/d0ra06774a. eCollection 2020 Nov 23.
The computed vertical energy, , from the equilibrium geometry of the initial electronic state is frequently considered as representative of the experimental excitation/emission energy, = / . Application of the quantum mechanical version of the Franck-Condon principle does not involve precise specification of nuclear positions before, after, or during an electronic transition. Moreover, the duration of an electronic transition is not experimentally accessible in spectra with resolved vibrational structure. It is shown that computed vibronic spectra based on TDDFT methods and application of quantum mechanical FC analysis predict = / with a 10-fold improvement in accuracy compared to for nine cyanine dyes. It is argued that part of the reason for accuracy when this FC analysis is compared to experiment as opposed to is the unspecified verticality of transitions in the context of the quantum version of the FC principle. Classical FC transitions that preserve nuclear kinetic energy before and after an electronic transition were previously found to occur at a weighted average of final and initial electronic state molecular geometries known as the r-centroid. Inspired by this approach a qualitative method using computed vertical and adiabatic energies and the harmonic approximation is developed and applied yielding a 5-fold improvement in accuracy compared to . This improvement results from the dominance of low frequency vibronic transitions in the cyanine dye major band. The model gives insight into the nature of the redshift when qPCR dye EvaGreen is complexed to λDNA and is applicable to the low frequency band of similar non cyanine dyes such as curcumin. It is found that the computed vibronic cyanine dye spectra from time-dependent FC analysis at 0 K and 298 K show decreased intensity at higher temperature suggestive of increased intensity with restricted motion shown when cyanine dyes are used in biomedical imaging. A 2-layer ONIOM model of the DNA minor groove indicates restricted motion of the TC-1 dye excited state in this setting indicative of enhanced fluorescence.
从初始电子态的平衡几何结构计算得到的垂直能量(E_{00})，常被视为实验激发/发射能量(E_{ex}/E_{em})的代表，即(E_{ex}/E_{em}=E_{00})。弗兰克 - 康登原理的量子力学版本的应用并不涉及电子跃迁之前、之后或期间核位置的精确指定。此外，在具有分辨振动结构的光谱中，电子跃迁的持续时间在实验上是无法获取的。结果表明，基于含时密度泛函理论（TDDFT）方法计算得到的振转光谱以及量子力学弗兰克 - 康登（FC）分析的应用，对于九种花青染料而言，预测的(E_{ex}/E_{em}=E_{00})的准确度比(E_{ex}/E_{em})提高了10倍。有人认为，当将这种FC分析与实验进行比较时，与(E_{ex}/E_{em})相比准确度提高的部分原因是在FC原理的量子版本背景下跃迁的垂直性未明确指定。先前发现，在电子跃迁前后保持核动能的经典FC跃迁发生在最终和初始电子态分子几何结构的加权平均值处，即r - 质心。受此方法启发，开发并应用了一种使用计算得到的垂直和绝热能量以及简谐近似的定性方法，与(E_{ex}/E_{em})相比，准确度提高了5倍。这种提高源于花青染料主带中低频振转跃迁的主导作用。该模型深入了解了qPCR染料EvaGreen与λDNA复合时红移的本质，并且适用于类似的非花青染料如姜黄素的低频带。研究发现，在0 K和298 K下，通过含时FC分析计算得到的花青染料振转光谱在较高温度下强度降低，这表明当花青染料用于生物医学成像时，随着运动受限强度增加。DNA小沟的两层ONIOM模型表明，在这种情况下TC - 1染料激发态的运动受限，这表明荧光增强。
