Pescitelli Gennaro, Di Bari Lorenzo
Dipartimento Di Chimica E Chimica Industriale, Università Di Pisa, Pisa, Italy.
Chirality. 2017 Sep;29(9):476-485. doi: 10.1002/chir.22711. Epub 2017 Jun 21.
The electronic circular dichroism (ECD) spectra of two previously reported quassinoids containing a pair of enone chromophores are revisited to gain insight into the consistency and applicability of the exciton chirality method. Our study is based on time-dependent Density Functional Theory calculations, transition and orbital analysis, and numerical exciton coupling calculations. In quassin (1) the enone/enone exciton coupling is quasi-degenerate, yielding strong rotational strengths that account for the observed ECD spectrum in the enone π-π* region. In perforalactone C (2) the nondegenerate coupling produces weak rotational strengths, and the ECD spectrum is dominated by other mechanisms of optical activity. We remark the necessity of a careful application of the nondegenerate exciton coupling method in similar cases.
重新审视了两种先前报道的含有一对烯酮发色团的苦木素类化合物的电子圆二色性（ECD）光谱，以深入了解激子手性方法的一致性和适用性。我们的研究基于含时密度泛函理论计算、跃迁和轨道分析以及数值激子耦合计算。在苦木素（1）中，烯酮/烯酮激子耦合是准简并的，产生了很强的旋光强度，这解释了在烯酮π-π*区域观察到的ECD光谱。在穿孔内酯C（2）中，非简并耦合产生较弱的旋光强度，并且ECD光谱由其他光学活性机制主导。我们指出在类似情况下谨慎应用非简并激子耦合方法的必要性。
