Investigation of structure-property relationships of multi-branched two-photon absorption chromophores based on π-conjugation core

To investigate the effect of conjugated-core structure of multi-branched chromophore on linear and nonlinear optical properties, three novel multi-branched organic chromophores, 3-(3,5-bis(9-butyl-9H-carbazol-6-yl)phenyl)-6-(4-(2,6-diphenylpyidin-4-yl)styryl)-9-butyl-9H-carbazole (W1), 1-(9-butyl-9H-carbazol-6-yl) phenyl)-3,5-bis(3-(4-(2,6-diphenylpyidin-4-yl)styryl)-9-butyl-9H-carbazole-6-yl)benzene (W2) and 1,3,5-tri(3-(4-(2,6-diphenylpyidin-4-yl)styryl)-9-butyl-9H-carbazole-6-yl)benzene (W3) have been synthesized and characterized. Their linear absorption, one- and two-photon fluorescence properties have been investigated. All these chromophores show intense one-photon fluorescence and high fluorescence quantum yields. When exited by a Ti:sapphire laser, these chromophores exhibit strong two-photon-excited fluorescence. The two-photon absorption cross sections of W1, W2 and W3 were calculated to be 69 GM, 112 GM and 173 GM in DMF, respectively. The ratio of the three compounds from the experiment is 1:1.6:2.5. Structure-property relationships are discussed based on photophysical data and theoretical calculation, which indicate a linear enhancement in one- and two-photon absorption and emission in going from W1 via W2 to W3.