Development of Novel Two Photon Absorbing Chromophores

There has been much interest in the development of two-photon absorbing materials and many efforts to understand the nonlinear absorption properties of these dyes. We have recently explored a new type of two photon absorbing dye containing a platinum center with ligands that vary in length that contain electron withdrawing benzothiazole. With increased pi-pi*conjugation we expect to observe a red shift in the absorption properties of the material. We have investigated the photophysical properties of the platinum chromophores using a variety of experimental techniques. Previously we determined that the singlet and triplet excited states are responsible for nearly all of the nonlinearity in the nanosecond regime accept the two photon mechanism that is primarily used for excitation. Therefore we would like to tune the photophysical properties of both the singlet and triplet excited state in these materials. To our surprise we found there is quite a bit of red shifting due to a metal-to-ligand charge transfer from the platinum to the ligand rather than the expected shifting due to increased pi-pi*conjugation. However, with increased ligand length the chromophore does take on more pi-pi* character.