Changing optical nonlinearities of homoleptic bis(phthalocyaninato) rare earth praseodymium double-decker complexes by the redox reaction

We report the third-order nonlinear optical properties of the homoleptic bis(phthalocyaninato) rare earth double-decker complex Pr(OOPc)2 (1), the oxidized species [Pr(OOPc)2]+ (2), and the reduced species [Pr(OOPc)2]- (3), by performing the femtosecond-pulsed Z-scan experiments at the wavelength of 800 nm. It is found that the second-order hyperpolarizability in complex molecules decreases in the order of 1>2>3. More interestingly, the observed nonlinear absorption process changes from two-photon absorption in the oxidized 2 to saturable absorption in the reduced 3. The results demonstrate that the nonlinear optical properties of sandwich-type phthalocyanine rare earth complexes could be altered by the redox reaction. Furthermore, the figures of merit of three complexes were evaluated for nonlinear photonic applications in optical limiter, saturable absorber, or all-optical switch.