Pyrrolo[3,2-b]pyrroles-From Unprecedented Solvatofluorochromism to Two-Photon Absorption

摘要

A combined experimental and theoretical study of the two-photon absorption (2PA) properties of a series of quadrupolar molecules possessing a highly electron-rich heterocyclic core, pyrrolo[3,2-Npyrrole, is presented. In agreement with quantum-chemical calculations, large 2PA cross-section values, (sigma(2pA) approximate to 10(2)-10(3) GM (1 GM= 10(50) cm(4)s photon(-1)), are observed at wavelengths of 650 700 nm, which correspond to the two photon allowed but one-photon forbidden transitions. The calculations also predict that increased planarity of this molecule through removal of two N-substituents leads to further increase in the sigma(2PA) values. Surprisingly, the most quadrupolar pyrrolo[3,2-Npyrrole derivative, containing two 4-nitrophenyl substituents at positions 2 and 5, demonstrates a very strong solvatofluorochromic effect, with a fluorescence quantum yield as high as 0.96 in cyclohexane, whereas the fluorescence vanishes in DMSO.