Nonlinear optical properties as a guide to aromaticity in congeneric pentapyrrolic expanded porphyrins: pentaphyrin, sapphyrln, isosmaragdyrin, and orangarin

Various spectroscopic techniques are employed to study the relationship between the nonlinear optical properties and aromaticity in congeneric pentapyrrolic expanded porphyrins. The compounds with high aromaticity are shown to exhibit higher two-photon absorption.