Two-photon absorption properties of a series of symmetrically substituted stilbenes and asymmetrically substituted stilbene-type derivatives with the same conjugated length have been investigated. The effective two-photon absorption cross sections, δTPA, as large as 62.0 × 10−48 cm4 s photon−1 for D-π-D molecules and 48.5 × 10−48 cm4 s photon−1 for D-π-A counterparts have been observed. The effect of these two types of chromophores on the peak position of the linear absorption, one-photon fluorescence as well as two-photon absorptivity is reported. Dipole moment change between the ground and the first excited states (Δµge), and the transition dipole moment between the first and second excited states (Mee′)
have also been calculated. It was found that the asymmetrically substituted derivatives possess relatively large Δµge, whereas the symmetrical counterparts show an increase in Mee′. Although a large two-photon absorption resonance is due to the simultaneously high values of Mee′ and Δµge, correlated to intramolecular charge transfer, the former function is larger. These results obtained have demonstrated that the magnitude and the peak position of two-photon absorption depend not only on the amount but also on the direction of the intramolecular charge transfer.
研究了一系列具有相同共轭长度的对称取代
二苯乙烯和不对称取代
二苯乙烯类衍
生物的双光子吸收特性。观察到 D-π-D 分子的有效双光子吸收截面 δ
TPA 高达 62.0 × 10-48 cm4 s 光子-1,D-π-A 分子的有效双光子吸收截面 δ
TPA 高达 48.5 × 10-48 cm4 s 光子-1。报告了这两种发色团对线性吸收峰值位置、单光子荧光以及双光子吸收率的影响。此外,还计算了基态和第一激发态之间的偶极矩变化(Δµge)以及第一激发态和第二激发态之间的过渡偶极矩(Mee′)。结果发现,不对称取代的衍
生物具有相对较大的 Δµge,而对称的衍
生物则显示出 Mee′ 的增大。虽然较大的双光子吸收共振是由于 Mee′ 和 Δµge 值同时较高所致,但与分子内电荷转移有关,前者的函数较大。这些结果表明,双光子吸收的大小和峰值位置不仅取决于分子内电荷转移的量,还取决于分子内电荷转移的方向。