DFT study of core-modified porphyrin isomers

B3LYP/6-311+G** calculations were performed systematically on 1,2 (syn) and 1,3 (anti) tautomeric forms of oxa- and thia- core-modified porphyrin isomers, which resulted in a total of 86 structures. The structural and energetic variation in all the isomers were analyzed. In corrphycene, hemiporphycene and porphycene the Z forms are more stable compared to the corresponding E forms in both the anti and syn oxa- and thiaporphyrin isomers. In contrast, in the syn isomeric forms of [3.0.1.0], [3.1.0.0] and [4.0.0.0] oxaporphyrins and in both syn and anti forms of thiaporphyrin isomers, Z forms are less stable. The HOMO and LUMO values are both negative and varied in a narrow zone, indicating no dramatic effect on the position of heteroatom substitution on the redox properties. The effect of geometric constraints due to the alteration of meso-bridge length and the hetero atom disposition in the porphyrin core on the relative stabilities of the isomers is analyzed