Electronic characterisation and significant second-order NLO response of 10,20-diphenylporphyrins and their Zn-II complexes substituted in the meso position with pi-delocalised linkers carrying push or pull groups

This work describes the synthesis and the electronic characterisation by electronic absorption spectroscopy, cyclic voltammetry and dipole moments of diphenyl porphyrins and their Zn-II complexes substituted at the meso position by a pseudo-linear pi-delocalised substituent carrying an electron-donor or an electron-withdrawing group. The second-order NLO response was investigated by the EFISH technique working with a nonresonant incident wavelength of 1.907 mu m. This work confirms the ambivalent role of the polarisable porphyrin ring, which, already in the ground state, acts as a donor or acceptor depending on the nature (acceptor or donor) of the substituent in the meso position, as was pointed out in our previous work on tetraphenyl porphyrins substituted at the beta-pyrrolic position. The second-order NLO response has been discussed by comparing the nature of the substituent (electron donor or acceptor) and the kind of substitution (beta pyrrolic or meso). This comparison evidenced a significant increase of the electron-donor properties of NBu2 or NMe2 when they are connected to the meso position or to the beta-pyrrolic position, probably because of an auxiliary donor effect of the electron-rich porphyrin ring. When the substituent is the electron-withdrawing NO2 group, the substituent position (meso or beta pyrrolic) is influential, with the existance of a significant increase in the second order NLO response when substitution occurs at the meso position. (c) Wiley-VCH Verlag GmbH & Co.