Jana Atanu, Jang So Young, Shin Jae-Yoon, Kumar De Arijit, Goswami Debabrata, Kim Dongho, Bharadwaj Parimal K
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India.
Chemistry. 2008;14(34):10628-38. doi: 10.1002/chem.200801396.
Two-photon absorption (TPA) properties of a laterally nonsymmetric aza cryptand with attached side arms have been investigated. This series of Schiff base derivatives supports the mechanistic approach for enhancing the TPA process, which is usually dictated by molecular geometry, pi-bridging, delocalization length, and corresponding charge-transfer possibilities. The results described here suggest that on increasing the branching units, the TPA cross-section, sigma((2)), can be tuned to a larger value. The TPA activity is "switched on" when a metal atom enters the cavity and serves as a conduit of electronic delocalization. The sigma((2)) value increases as the donor strength increases. The maximum value is obtained on moving from the single-branched system to the nearly threefold symmetry. This serves as a useful synthetic strategy for designing novel octupolar molecules with high sigma((2)) values. Theoretical calculations at the B3LYP functional with the 6-31G* basis set under DFT formalism provide supporting evidence that the communication between the side arms through the metal d orbital and more ordered geometry of chromophores leads to a smaller HOMO-LUMO gap, which has a great influence upon the electronic properties of the molecules.
对一种带有连接侧臂的横向不对称氮杂穴醚的双光子吸收（TPA）特性进行了研究。这一系列席夫碱衍生物支持增强TPA过程的机理方法，该过程通常由分子几何结构、π桥连、离域长度以及相应的电荷转移可能性决定。此处描述的结果表明，增加支化单元时，TPA截面σ(2)可调节至更大的值。当金属原子进入空腔并作为电子离域的通道时，TPA活性“开启”。σ(2)值随供体强度的增加而增大。从单支化体系到接近三重对称时可获得最大值。这为设计具有高σ(2)值的新型八极分子提供了一种有用的合成策略。在DFT形式下使用6 - 31G*基组的B3LYP泛函进行的理论计算提供了支持证据，即通过金属d轨道的侧臂之间的通信以及发色团更有序的几何结构导致较小的HOMO - LUMO能隙，这对分子的电子性质有很大影响。
