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

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-pi-D molecules with 1-(2-ethylhexyloxy)-4-methoxybenzene and 9,9-bis(2-ethylhexyl)-fluorene pi-cores, and D-pi-A-pi-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-pi-A-pi-D molecules and up to 1250 GM for the molecules with D Tc D architectures. As all of the compounds have azo groups as part of the pi linker the cis/trans isomerisation of these materials was also explored. It is found that dyes based on the D-pi-D architecture are more amenable to isomerisation and are also more stable in the cis form when compared to D-pi-A-pi-D chromophores. (C) 2014 Elsevier Ltd. All rights reserved.