Cationic Two-Photon Absorption Chromophores with Double- and Triple-Bond Cores in Symmetric/Asymmetric Arrangements

Two-photon absorption (TPA) properties of a series of cationic, linear pi-conjugated systems with donor(D)/acceptor(A) substitution have been examined systematically in terms of the type and length of the pi-conjugation core and symmetric and asymmetric D/A-arrangement. The TPA spectra of the chromophores measured by the femtosecond open-aperture Z-scan method reveal that the double-bond core results in much more intense TPA than the triple-bond one, with a significant red shift of the TPA peak while the TPA becomes more intense as the chain is extended for the triple-bond core compounds with a little red shift. It is also found that the difference in the D/A-arrangement gives a small difference in the amplitude of the TPA spectrum although the spectral shapes differ considerably.