Sakashita, RyuichiRyuichiSakashitaOka, YasutakaYasutakaOkaAkimaru, HisanoriHisanoriAkimaruKesavan, Praseetha E.Praseetha E.KesavanIshida, MasatoshiMasatoshiIshidaToganoh, MotokiMotokiToganohIshizuka, TomoyaTomoyaIshizukaMori, ShigekiShigekiMoriFuruta, HiroyukiHiroyukiFuruta2025-09-042025-09-042017-08-010022-326310.1021/acs.joc.7b01770https://d8.irins.org/handle/IITG2025/30123Pyridylethenyl-substituted N-confused porphyrins (NCPs) were synthesized, and their cis–trans isomerization was studied. Among four possible isomers, trans-3H and cis-2H types of structures, of which aromaticity and absorption/emission properties differ largely, were isolated. The cis-isomer was largely stabilized by the intramolecular hydrogen bonding between the pyrrolic-NH and the pyridinic-N in the vicinity. The thermal cis–trans isomerization proceeded even at 30 °C, which was significantly accelerated by the pyridine added to the system. The kinetic studies revealed that the isomerization reaction was second-order and the activation energy of the thermal isomerization from cis to trans isomer was ΔG0⧧cis→trans = 35.7 kcal/mol at 298 K, which is significantly smaller than that of Ni complex (42.3 kcal/mol). An intermolecular proton transfer induced cis–trans isomerization mechanism was proposed.en-USMolecular structureIsomerizationTautomerismPyridinesPyrrolesArticlehttps://v2.sherpa.ac.uk/id/publication/77971520-6904pp. 8686-8696Article23123456789/372