Substituent Effect on Porphyrin Ring Distortion

以吡咯、二苯基吡咯和2,6-二氟或2,6-二氯苯甲醛为混合缩合剂，合成了一系列具有中位（2,6-二氟或二氯苯）取代基的卟啉。本文报道的卟啉化合物缩写如下：四芳基卟啉（TXPP）、六芳基卟啉（HXPP）、反-辛烷基卟啉（trans-OXPP）、顺-辛烷基卟啉（顺- oxpp）、十烷基卟啉（DecXPP）和十二烷基卟啉（DXPP），其中X=F或Cl。苯基取代基的增加对紫外光可见光谱有较大的影响，Soret谱带依次为TXPP<HXPP<trans-OXPP，顺式oxpp <DecXPP<DXPP，逐渐红移。但是，X=F系列和X=Cl系列的红移幅度不同。我们很容易认为，在X=F系列和X=Cl系列中，卟啉环畸变的幅度是不同的。氟原子孤对与卟啉π轨道之间的相互作用可能减少了卟啉环的畸变。根据这些卟啉的酸碱性质，推测卟啉环与中间苯基环的共轭作用对卟啉环畸变有影响。此外，从酸碱滴定实验中观察到TXPP （X=F和X=Cl）在酸单离子状态下具有不寻常的稳定性。

A series of porphyrin with meso-(2,6-difluoro- or dichlorophenyl) substituents has been synthesized by mixed condensation of pyrrole, diphenylpyrrole, and 2,6-difluoro- or 2,6-dichlorobenzaldehyde. The porphyrins reported here are abbreviated as follows: tetraaryl-lporphrins (TXPP), hexaarylporphyrins (HXPP), trans-octarylporphyrins (trans-OXPP), cis-octarylporphyrins (cis-OXPP), decaarylporphyrins (DecXPP), and dodecaarylporphyrins (DXPP), where X=F or Cl.Increase of the phenyl substituents have large effect on the UV-visible spectra, gradually red-shifting the Soret bands in the order of TXPP<HXPP<trans-OXPP,cis-OXPP<DecXPP<DXPP. However, the magnitude of the red shift is different between X=F series and X=Cl series. It is tempting to suppose that the magnitude of porphyrin ring distortion is different between X=F seris and X=Cl seris. It is possible that interaction between lone pair of fluorin atoms and porphyrin π orbitals reduce the porphyrin ring distortion.From the acid-base properties of these porphyrins, it is supposed that conjugation between porphyrin ring and meso-phenyl ring has influence upon the porphyrin ring distortion. Furthermore, an unusual stability in the acid monocation state of TXPP (X=F and X=Cl) is observed from the acid-base titration experiments.