A systematic femtosecond study on the two-photon absorbing D-π-A molecules–π-bridge nitrogen insertion and strength of the donor and acceptor groups

The two-photon absorption (2PA) properties of a series of dyes containing donor and acceptor groups connected via a π-electronic bridge were studied by using a femtosecond Z-scan technique. It was found that the nature of the π-electronic bridge does not substantially affect the measured 2PA intensities. In the case of the substituted azobenzenes the decrease of the strength of the donor and/or acceptor groups leads to decrease of the 2PA intensity, the effect of the acceptor strength being greater.