Lament Bozena, Rachlewicz Krystyna, Latos-Grazyński Lechosław, Waluk Jacek
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warsaw, Poland.
Chemphyschem. 2002 Oct 18;3(10):849-55. doi: 10.1002/1439-7641(20021018)3:10<849::AID-CPHC849>3.0.CO;2-9.
Magnetic circular dichroism (MCD) spectra were obtained for the inverted and "normal" forms of doubly protonated 5,10,10,20-tetraphenylsapphyrin and for the inverted neutral form. In all these species, the same pattern of the signs of Faraday B terms, [+, -, +, -], is revealed for the four lowest singlet electronic transitions. This sequence is opposite to that observed in sapphyrins that are unsubstituted at the meso positions. The results can be accounted for by the reversed patterns of the orbital energy splittings in the two highest occupied pi orbitals (delta HOMO) and the two lowest unoccupied pi orbitals (delta LUMO). Indeed, the application of the perimeter model leads to the prediction that in the parent sapphyrin, delta HOMO < delta LUMO, whereas the opposite becomes true after fourfold phenyl substitution at the meso positions. These predictions are corroborated by the results of quantum-chemical calculations. The calculated values of delta HOMO-delta LUMO are quite small, which places sapphyrin close to the case of the so-called "soft chromophore", for which delta HOMO = delta LUMO. Titration of solutions containing the neutral chromophore with bases and acids leads to parallel changes in the electronic absorption and MCD spectra that indicate presence of the anionic and singly protonated species.
获得了双质子化的5,10,10,20-四苯基锌卟啉的反转形式和“正常”形式以及反转中性形式的磁圆二色性（MCD）光谱。在所有这些物种中，对于四个最低的单重态电子跃迁，揭示了相同的法拉第B项符号模式[ +, -, +, - ]。该序列与在中位未被取代的锌卟啉中观察到的序列相反。结果可以通过两个最高占据π轨道（δHOMO）和两个最低未占据π轨道（δLUMO）中轨道能量分裂的反转模式来解释。实际上，应用周边模型可以预测，在母体锌卟啉中，δHOMO < δLUMO，而在中位进行四倍苯基取代后情况则相反。这些预测得到了量子化学计算结果的证实。δHOMO - δLUMO的计算值非常小，这使得锌卟啉接近所谓“软发色团”的情况，即δHOMO = δLUMO。用碱和酸滴定含有中性发色团的溶液会导致电子吸收光谱和MCD光谱发生平行变化，这表明存在阴离子和单质子化物种。
