...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >On the Nature of the Fluorescent State in β-Nitrotetraarylporphyrins
【24h】

On the Nature of the Fluorescent State in β-Nitrotetraarylporphyrins

机译：关于β-硝基四芳基卟啉中荧光状态的性质

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

2-NO_2-5,10,15,20-tetraphenylporphyrin (H_2TPP-NO_2) is shown to exist in solution as an equilibrium mixture of two NH tautomers with different spectral and photophysical properties. At 77 K in a rigid glass solution the fluorescence spectra of the tautomers contain two well-resolved narrow bands that are slightly (～300 cm~(-1)) Stokes-shifted with respect to the corresponding Q_(X00) absorption bands, with the spectrum of the more stable tautomer being ～500 cm~(-1) red-shifted as compared to the spectrum of the less stable tautomer. At room temperature, the tautomers show almost identical broad and structureless fluorescence spectra, markedly red-shifted relative to the longest wavelength absorption band. The Stokes shift increases with an increase of solvent polarity, being as large as ～2000 cm~(-1) in N,N-dimethylformamide. Fluorescence lifetimes of the tautomers are found to be markedly (about a factor of 2) different, with both decreasing with an increase of solvent polarity. The reasons for these peculiar fluorescence properties can be understood on the basis of semiempirical quantum chemical calculations. Charge-transfer (CT) states are found to be located between the porphyrinic Q and B states for both tautomers, and a different energy of the CT states gives rise to different fluorescence lifetimes of the tautomers. The calculations also predict a lowering of the Q_x state energy and an increase of its dipole moment μ with a decrease of the angle θ between the plane of the NO_2 group and the porphyrin plane (relative to the ground-state equilibrium geometry with θ = 80°). We suggest that, in solution, such an increase in the μ value should result in an increase of the stabilization interaction between the polar porphyrin and solvent molecules and, consequently, in flattening of the Q_x state energy curve as a function of θ and a shift of the minimum of this curve to θ values less than 80°. Both quantum chemical calculations and picosecond transient absorption measurements of the S_1 → S_n absorption show that the fluorescent O_x state of H_2TPP-NO_2 has mainly ~1(π,π~*) character with a relatively small charge-transfer admixture.
机译：2-NO_2-5,10,15,20-四苯基卟啉（H_2TPP-NO_2）以两种不同光谱和光物理性质的NH互变异构体的平衡混合物形式存在于溶液中。在刚性玻璃溶液中，在77 K时，互变异构体的荧光光谱包含两个分辨良好的窄带，相对于相应的Q_（X00）吸收带，这些窄带发生了斯托克斯位移（〜300 cm〜（-1））。与较不稳定的互变异构体的光谱相比，较稳定的互变异构体的光谱红移了约500 cm〜（-1）。在室温下，互变异构体显示出几乎相同的宽广且无结构的荧光光谱，相对于最长的波长吸收带明显红移。斯托克斯位移随溶剂极性的增加而增加，在N，N-二甲基甲酰胺中最大达到〜2000 cm〜（-1）。发现互变异构体的荧光寿命显着不同（约2倍），两者均随着溶剂极性的增加而降低。这些特殊的荧光特性的原因可以根据半经验量子化学计算来理解。发现两个互变异构体的电荷转移（CT）状态位于卟啉Q和B状态之间，并且不同的CT状态能量导致互变异构体的荧光寿命不同。计算还预测，随着NO_2基团平面与卟啉平面之间的角度θ减小（相对于θ= 80的基态平衡几何形状），Q_x态能量会降低，偶极矩μ会增加。 °）。我们建议，在溶液中，μ值的这种增加应导致极性卟啉与溶剂分子之间的稳定相互作用增加，因此，Q_x状态能曲线随θ和位移的变化而变平该曲线的最小值的θ值小于80°。 S_1→S_n吸收的量子化学计算和皮秒瞬态吸收测量均表明，H_2TPP-NO_2的荧光O_x状态主要具有〜1（π，π〜*）特征，且电荷转移混合物较小。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号