Highly sensitive two-photon chromophores applied to three-dimensional lithographic microfabrication: design, synthesis and characterization towards two-photon absorption cross section

A series of D-pi-A-pi-D type chromophores were synthesized by the dehydration reaction of 4-R2N-benzaldehye (R=Ph, Bu-n, Et, Me) and diaminomaleonitrile (corresponding to the chromophores 1, 2, 3 and 4, respectively), in which a polar imino double bond (-C=N-) replaced the double bond (-CH=CH-) in the pi-conjugated centers. Femtosecond laser induced fluorescence intensity was used to evaluate two-photon absorption (TPA) cross sections, delta, using a USB-2000 CCD. Results show a change of terminal groups from Ph2N- to Me2N- influenced the delta value significantly through a change of the quantum yield, phi. However, the two-photon absorption peak position was only slightly affected. The chromophores 2 and 3 were found to afford polymers in the presence of the functional triacrylate monomer at low laser power at 755 and 820 nm. This demonstrated that the enhanced delta value was not a main factor in the improvement of chromophore two-photon photosensitivity. Such information can be useful in the design of more efficient two-photon chromophores for imaging and power-limiting applications.