Thomas Simil, Kim Kwang S
Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Korea.
Phys Chem Chem Phys. 2014 Nov 28;16(44):24592-7. doi: 10.1039/c4cp03169e.
Linear and non-linear optical properties of indeno[2,1-b]fluorene (1) and its structural isomers with 20 π-electrons have been studied using many body methods. As compared to other π electron systems of similar conjugation length, the experimentally measured optical gap (vertical excitation energy) and the singlet-triplet gap of 1 are quite small. The diradical character calculated using the ab initio density matrix renormalization group (DMRG) of 1 is the largest among its isomers, which explains its lowest singlet-triplet gap. The optical gaps calculated by the DMRG method, employing the long-range interacting Pariser-Parr-Pople model, show good agreement with the experimental values as compared to those calculated by DFT, MP2, and CASPT2 methods. Using correlated Hamiltonian and the DMRG approach, the third harmonic generation coefficient is found to correlate well with the diradical character.
采用多体方法研究了茚并[2,1-b]芴（1）及其具有20个π电子的结构异构体的线性和非线性光学性质。与具有相似共轭长度的其他π电子体系相比，实验测得的1的光学能隙（垂直激发能）和单重态-三重态能隙相当小。使用从头算密度矩阵重整化群（DMRG）计算得到的1的双自由基特征在其异构体中是最大的，这解释了其最低的单重态-三重态能隙。与通过DFT、MP2和CASPT2方法计算得到的值相比，采用长程相互作用的巴黎-帕尔-波普尔模型的DMRG方法计算得到的光学能隙与实验值吻合良好。使用相关哈密顿量和DMRG方法，发现三次谐波产生系数与双自由基特征具有良好的相关性。
