Abe Manabu, Adam Waldemar, Borden Weston Thatcher, Hattori Masanori, Hrovat David A, Nojima Masatomo, Nozaki Koichi, Wirz Jakob
Department of Materials Chemistry and Frontier Research Center (HANDAI FRC), Graduate School of Engineering, Osaka University (HANDAI), Suita, Osaka 565-0871, Japan.
J Am Chem Soc. 2004 Jan 21;126(2):574-82. doi: 10.1021/ja038305b.
The effect of a 2,2-ethylene-ketal functionality on the singlet-triplet energy gap (Delta E(ST)) and on the first electronic transition in singlet cyclopentane-1,3-diyls (1) has been investigated. UDFT calculations predict a significant increase in the preference for a singlet ground state in the diradical with the cyclic ketal at C2 (1g; Delta E(ST) = -6.6 kcal/mol in C(2) symmetry and -7.6 kcal/mol in C(2v) symmetry), compared to the 2,2-dihydroxy- and 2,2-dimethoxy-disubstituted diradicals (1d, Delta E(ST) = -3.6 kcal/mol in C(2) symmetry, and 1e, Delta E(ST) = -3.4 kcal/mol in C(2) symmetry). Spiroconjugation is shown to be responsible for the larger calculated value of absolute value Delta E(ST) in 1g, relative to 1d and 1e. A strong correlation between the calculated values of Delta E(ST) and the computed electronic excitation energies of the singlet diradicals is found for diradicals 1d, 1e, and 1g and for 2,2-difluorocyclopentane-1,3-diyl (1c). A similar correlation between Delta E(ST) and lambda(calcd) is predicted for the corresponding 1,3-diphenylcyclopentane-1,3-diyls 3, and the predicted blue shift in the spectrum of 3g, relative to 3e, has been confirmed by experimental comparisons of the electronic absorption spectra of the annelated derivatives 2c, 2e, and 2g in a glass at 77 K. The wavelength of the first absorption band in the singlet diradicals decreases in the order 2e (lambda(onset) = 650 nm) > 2g (lambda(onset) = 590 nm) > 2c (lambda(onset) = 580 nm). The combination of these computational and experimental results provides a sound basis for reassignment of the first electronic absorption band in singlet diradicals 2c, 2e, and 2g to the excitation of an electron from the HOMO to the LUMO of these 2,2-disubstituted derivatives of cyclopentane-1,3-diyl.
研究了2,2 - 亚乙基缩酮官能团对单重态 - 三重态能隙（ΔE(ST)）以及单重态环戊烷 - 1,3 - 二基（1）中第一电子跃迁的影响。UDFT计算预测，与2,2 - 二羟基和2,2 - 二甲氧基双取代双自由基（1d，C2对称下ΔE(ST) = -3.6 kcal/mol，以及1e，C2对称下ΔE(ST) = -3.4 kcal/mol）相比，在C2位带有环状缩酮的双自由基（1g；C2对称下ΔE(ST) = -6.6 kcal/mol，C2v对称下ΔE(ST) = -7.6 kcal/mol）中，基态单重态的偏好性显著增加。结果表明，相对于1d和1e，螺共轭是导致1g中ΔE(ST)绝对值计算值更大的原因。对于双自由基1d、1e和1g以及2,2 - 二氟环戊烷 - 1,3 - 二基（1c），发现ΔE(ST)的计算值与单重态双自由基的计算电子激发能之间存在很强的相关性。对于相应的1,3 - 二苯基环戊烷 - 1,3 - 二基3，预测ΔE(ST)与λ(calcd)之间也存在类似的相关性，并且通过在77 K玻璃态下对稠合衍生物2c、2e和2g的电子吸收光谱进行实验比较，证实了相对于3e，3g光谱中的预测蓝移。单重态双自由基中第一吸收带的波长按以下顺序减小：2e（λ(onset) = 650 nm）> 2g（λ(onset) = 590 nm）> 2c（λ(onset) = 580 nm）。这些计算和实验结果的结合为将单重态双自由基2c、2e和2g中的第一电子吸收带重新归属为环戊烷 - 1,3 - 二基的这些2,2 - 二取代衍生物从最高占据分子轨道（HOMO）到最低未占据分子轨道（LUMO）的电子激发提供了可靠的基础。
