Institute for Lasers, Life, and Biophotonics, VU University Amsterdam, De Boelelaan 1081, NL 1081 HV Amsterdam, The Netherlands.
J Chem Phys. 2012 Feb 7;136(5):054307. doi: 10.1063/1.3681259.
The electronic gas-phase absorption spectrum of the bent carbon-chain radical, HC(4)CHC(6)H with C(s) symmetry, is recorded in the 595 nm region by cavity ring-down spectroscopy through an expanding hydrogen plasma. An unambiguous spectroscopic identification becomes possible from a systematic deuterium labeling experiment. A comparison of the results with recently reported spectra of the nonlinear HC(4)CHC(4)H and HC(4)C(C(2)H)C(4)H radicals with C(2v) symmetry provides a more comprehensive understanding of the molecular behavior of π-conjugated bent carbon-chain systems upon electronic excitation. We find that the electronic excitation in the bent carbon-chain HC(4)CHC(2n)H (n = 1-4) series exhibits a similar trend as in the linear HC(2n+1)H (n = 3-6) series, shifting optical absorptions towards longer wavelengths for increasing overall bent chain lengths. The π-conjugation in bent HC(4)CHC(2n)H (n = 1-4) chains is found to be generally smaller than in the linear HC(2n+1)H (n = 3-6) case for equivalent numbers of C-atoms. The addition of an electron-donating group to the bent chain causes a slight decrease of the effective conjugation.
具有 C(s) 对称性的弯曲碳链自由基 HC(4)CHC(6)H 的电子气相吸收光谱通过腔内光衰荡光谱法在 595nm 区域中用膨胀氢等离子体记录。通过系统的氘标记实验可以进行明确的光谱识别。将结果与最近报道的具有 C(2v)对称性的非线性 HC(4)CHC(4)H 和 HC(4)C(C(2)H)C(4)H 自由基的光谱进行比较，为电子激发后π共轭弯曲碳链体系的分子行为提供了更全面的理解。我们发现，弯曲碳链 HC(4)CHC(2n)H(n=1-4)系列中的电子激发表现出与线性 HC(2n+1)H(n=3-6)系列相似的趋势，随着整体弯曲链长度的增加，光学吸收向更长的波长移动。对于等效数量的 C 原子，发现弯曲 HC(4)CHC(2n)H(n=1-4)链中的π共轭通常小于线性 HC(2n+1)H(n=3-6)情况。向弯曲链添加供电子基团会导致有效共轭略有减少。
