New thioxanthene-Phenothiazine derivatives:synthesis, characterization and third-order nonlinear optical (NLO) properties

In this paper, two novel thioxanthene - phenothiazine derivatives (TPTZ1 and TPTZ2) were successfully synthesized based on phenothiazine and thiochromone. The structures of these two organic compounds were characterized by various spectroscopic techniques. The third order nonlinear optical (NLO) properties of TPTZ1 and TPTZ2 have been investigated by using the Z-scan technique under irradiance of 20ps pulse laser at 532 nm. It is discovered that TPTZ1 and TPTZ2 show the obvious reverse saturable absorption (RSA) characteristics and the typical saturable absorption (SA) characteristics, respectively. The nonlinear absorption coefficients ((3) and nonlinear refractive indices (n2) of TPTZ1 and TPTZ2 are calculated to be the order of 10- 11 m/W and 10-18 m2/ W. The opposite nonlinear absorption behavior and the size difference of the nonlinear refraction indices may result from the differences in the electronic structure due to the different substituents for the two organic compounds. The figure-of-merit (FOM) of TPTZ2 is larger than that of TPTZ1 and even reaches 10.43 at the incident energy of 30 nJ. Their excellent NLO properties may allow them to be potentially applied in the photonic field.