Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
Phys Chem Chem Phys. 2011 Jul 28;13(28):12912-9. doi: 10.1039/c0cp02821e. Epub 2011 Jun 21.
The absorption spectra and excited state dipole moments of four differently substituted fulvenes have been investigated both experimentally and computationally. The results reveal that the excited state dipole moment of fulvenes reverses in the first excited singlet state when compared to the ground state. The oppositely polarized electron density distributions, which dominate the ground state and the first excited singlet state of fulvenes, respectively, reflect the reversed π-electron counting rules for aromaticity in the two states (4n + 2 vs. 4n, respectively). The results show that substituents indeed influence the polarity of fulvenes in the two states, however, cooperative interactions between the substituents and the fulvene moiety are most pronounced in the ground state.
四种不同取代的富烯的吸收光谱和激发态偶极矩已通过实验和计算进行了研究。结果表明，与基态相比，富烯的第一激发 singlet 态的激发态偶极矩发生反转。在基态和第一激发 singlet 态中分别占主导地位的相反极化的电子密度分布，反映了两种状态下芳香性的π电子计数规则的反转（分别为 4n+2 和 4n）。结果表明，取代基确实会影响两种状态下富烯的极性，但取代基和富烯部分之间的协同相互作用在基态时最为明显。
