Arnbjerg Jacob, Jiménez-Banzo Ana, Paterson Martin J, Nonell Santi, Borrell José I, Christiansen Ove, Ogilby Peter R
Department of Chemistry, University of Aarhus, DK-8000 Arhus, Denmark.
J Am Chem Soc. 2007 Apr 25;129(16):5188-99. doi: 10.1021/ja0688777. Epub 2007 Mar 31.
Porphycenes are structural isomers of porphyrins that have many unique properties and features. In the present work, the resonant two-photon absorption of 2,7,12,17-tetraphenylporphycene (TPPo) and its palladium(II) complex (PdTPPo) has been investigated. The data obtained are compared to those from the isomeric compound, meso-tetraphenylporphyrin (TPP). Detection of phosphorescence from singlet molecular oxygen, O2(a(1)Delta(g)), produced upon irradiation of these compounds, was used to obtain two-photon excitation spectra and to quantify two-photon absorption cross sections, delta. In the spectral region of 750-850 nm, the two-photon absorption cross sections at the band maxima for both TPPo and PdTPPo, delta = 2280 and 1750 GM, respectively, are significantly larger than that for TPP. This difference is attributed to the phenomenon of so-called resonance enhancement; for the porphycenes, the two-photon transition is nearly resonant with a comparatively intense one-photon Q-band transition. The results of quantum mechanical calculations using density functional quadratic response theory are in excellent agreement with the experimental data and, as such, demonstrate that comparatively high-level quantum chemical methods can be used to interpret and predict nonlinear optical properties from such large molecular systems. One important point realized through these experiments and calculations is that one must exercise caution when using qualitative molecular-symmetry-derived arguments to predict the expected spectral relationship between allowed one- and two-photon transitions. From a practical perspective, this study establishes that, in comparison to porphyrins and other tetrapyrrolic macrocyclic systems, porphycenes exhibit many desirable attributes for use as sensitizers in two-photon initiated photodynamic therapy.
卟吩是卟啉的结构异构体，具有许多独特的性质和特征。在本工作中，对2,7,12,17-四苯基卟吩（TPPo）及其钯（II）配合物（PdTPPo）的共振双光子吸收进行了研究。将获得的数据与来自异构体化合物中位-四苯基卟啉（TPP）的数据进行了比较。通过检测这些化合物辐照时产生的单重态分子氧O₂(a¹Δg)的磷光，获得双光子激发光谱并量化双光子吸收截面δ。在750 - 850 nm的光谱区域，TPPo和PdTPPo在谱带最大值处的双光子吸收截面分别为δ = 2280和1750 GM，显著大于TPP的双光子吸收截面。这种差异归因于所谓的共振增强现象；对于卟吩，双光子跃迁几乎与相对较强的单光子Q带跃迁共振。使用密度泛函二次响应理论进行的量子力学计算结果与实验数据非常吻合，因此表明可以使用相对高级的量子化学方法来解释和预测此类大分子体系的非线性光学性质。通过这些实验和计算认识到的一个重要点是，在使用基于分子对称性的定性论据来预测允许的单光子和双光子跃迁之间的预期光谱关系时必须谨慎。从实际角度来看，本研究表明，与卟啉和其他四吡咯大环体系相比，卟吩在用作双光子引发光动力疗法的敏化剂方面表现出许多理想的特性。
