Synthesis and characterization of strongly two photon absorbing and photoswitchable azo molecules

• Symmetric photoswitchable two photon absorbing chromophores were synthesised.
• The TPA cross section of these molecules was measured by z-scan at 780 nm.
• The cis/trans isomerisation of these materials was also explored.

Here we describe the synthesis and characterization of a range of symmetric two photon absorbing chromophores containing photoswitchable Disperse Red-type donors. These have been incorporated into D–π–D molecules with 1-(2-ethylhexyloxy)-4-methoxybenzene and 9,9-bis(2-ethylhexyl)-fluorene π-cores, and D–π–A–π–D molecules based on a (2,6-dimethyl-pyran-4-ylidene)propanedinitrile acceptor core. The TPA cross section measured by z-scan at 780 nm was up to 298 GM for the D–π–A–π–D molecules and up to 1250 GM for the molecules with D–π–D architectures. As all of the compounds have azo groups as part of the π linker the cis/trans isomerisation of these materials was also explored. It is found that dyes based on the D–π–D architecture are more amenable to isomerisation and are also more stable in the cis form when compared to D–π–A–π–D chromophores.