Understanding Strong Two-Photon Absorption in -Conjugated Porphyrin Dimers via Double-Resonance Enhancement in a Three-Level Model
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- 作者：Mikhail Drobizhev ; Yuriy Stepanenko ; Yuliya Dzenis ; Aliaksandr Karotki ; Aleksander Rebane ; Peter N. Taylor ; and Harry L. Anderson
- 刊名：Journal of the American Chemical Society
- 出版年：2004
- 出版时间：December 1, 2004
- 年：2004
- 卷：126
- 期：47
- 页码：15352 - 15353
- 全文大小：66K
- 年卷期：v.126,no.47(December 1, 2004)
- ISSN：1520-5126
文摘
We present the two-photon absorption (2PA) spectra of a series of conjugated porphyrin dimers and show that they possess extremely large intrinsic (femtosecond) peak 2PA cross sections, up to 
2 = 1 × 104 GM in the near-IR region; these are among the highest values measured for any organic molecule. Moreover, we demonstrate that the second-order perturbation theory applied to a simple three-level model gives a perfect quantitative description of the observed 2PA cross section. By comparing all the factors of the three-level model for dimers with those of corresponding monomer (for which 2 = 20 GM), we explain an ~500-fold cooperative enhancement in 2 and find that the most important factor is the strength of excited-state transition. The matrix element of dipole moment of this transition amounts gigantic values of 30-40 D for conjugated porphyrin dimers, which can be accounted for a large delocalization radius (large electron-hole separation) in this state. We also demonstrate efficient generation of singlet oxygen upon one- and two-photon excitation of these porphyrin dimers, which can be useful for two-photon initiated photodynamic therapy of cancer.
2 = 1 × 104 GM in the near-IR region; these are among the highest values measured for any organic molecule. Moreover, we demonstrate that the second-order perturbation theory applied to a simple three-level model gives a perfect quantitative description of the observed 2PA cross section. By comparing all the factors of the three-level model for dimers with those of corresponding monomer (for which 2 = 20 GM), we explain an ~500-fold cooperative enhancement in 2 and find that the most important factor is the strength of excited-state transition. The matrix element of dipole moment of this transition amounts gigantic values of 30-40 D for conjugated porphyrin dimers, which can be accounted for a large delocalization radius (large electron-hole separation) in this state. We also demonstrate efficient generation of singlet oxygen upon one- and two-photon excitation of these porphyrin dimers, which can be useful for two-photon initiated photodynamic therapy of cancer.