Non-linear optical, electrochemical and spectroelectro-chemical properties of amphiphilic inner salt porphyrinic systems

Three zwitterionic meso-substituted A(3)B- and AB(2)C-porphyrins containing one sulfonato alkylpyridinium substituent and three or two alkoxy-substituted phenyl groups were synthesized in good yield and fully characterized as to their physicochemical properties by a variety of techniques. This new series of inner salt donor-acceptor meso-substituted porphyrin derivatives were prepared for possible application as amphiphilic probes for membrane insertion in the area of combined second-harmonic and two-photon fluorescence cellular microscopy. To this end, the linear and nonlinear optical properties of the compounds were characterized, together with their electrochemical and spectroelectrochemical properties in non-aqueous media. The neutral design of such molecules enabled us to determine their second order non-linear properties, both by Electric Field Induced Second Harmonic Generation and Hyper-Rayleigh Scattering. Two-photon absorption cross sections of these dyes were also measured by the two-photon induced fluorescence method. The zwitterionic nature of the inner salt results in very specific solvent-dependent redox-properties, which could be rationalized in terms of solvent-dependent ion-pairing. The overall data electrochemical and photophysical data indicates that these new porphyrinic systems should be good probes for membrane potential sensing.