Substituent Effect on Porphyrin Ring Distortion

以吡咯、二苯基吡咯和2，6-二氟苯甲醛或2，6-二氯苯甲醛为原料，通过混合缩合反应合成了一系列具有meso-（2，6-二氟苯基或二氯苯基）取代基的卟啉化合物。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）、反式-八芳基卟啉（trans-OXPP），cis-octarylporphyrins（cis-OXPP）、十芳基卟啉（DecXPP）和十二芳基卟啉（DXPP），其中X=F或Cl。苯基取代基的增加对紫外-可见光谱有很大的影响，使Soret带逐渐红移，顺序为TXPP<HXPP<trans-OXPP，顺式-OXPP <DecXPP<DXPP。然而，X=F系列和X=Cl系列之间的红移幅度是不同的。这是诱人的假设，卟啉环变形的大小是不同的X=F系列和X=Cl系列。这可能是由于孤对氟原子与卟啉π轨道之间的相互作用减小了卟啉环的畸变，从卟啉的酸碱性质推测，卟啉环与meso-苯环之间的共轭作用对卟啉环的畸变有影响。此外，从酸碱滴定实验中观察到TXPP（X=F和X=Cl）在酸性一价阳离子状态下的不寻常的稳定性。

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.