We have explored the electronic natures of representative expanded porphyrins, - and -hexaphyrins, to investigate the interplay between the aromaticity and antiaromaticity that is brought by two electron oxidation/reduction processes. The excited singlet and triplet states of hexaphyrin in solution exhibit lifetimes of 125 ps and 1.8 μs, respectively, as revealed by various time-resolved spectroscopic measurements. On the other hand, hexaphyrin shows faster singlet and triplet lifetimes than those of hexaphyrin, which is largely in accordance with the perturbation of aromaticity due to the π electron formulation of [4n] in hexaphyrins. The two-photon absorption cross-section values at 1200 nm for hexaphyrins show ca. 9890 GM which is > 102 larger than those of porphyrins. The reduced TPA values of 2600 and 810 GM of hexaphyrin and perfluorinated hexaphyrin, respectively, match well with their relatively short excited-state lifetimes. Overall, the enhanced excited-state lifetimes for various hexaphyrins go in line with the increased TPA cross-section values and the ring planarity.
ASJC Scopus subject areas
- Colloid and Surface Chemistry