Fine-Tuning of β-Substitution to Modulate the Lowest Triplet Excited States: A Bioinspired Approach to Design Phosphorescent Metalloporphyrinoids.

Abstract

Learning nature's approach to modulate photophysical properties of NIR porphyrinoids by fine-tuning β-substituents including the number and position, in a manner similar to naturally occurring chlorophylls, has the potential to circumvent the disadvantages of traditional "extended π-conjugation" strategy such as stability, molecular size, solubility, and undesirable π-π stacking. Here we show that such subtle structural changes in Pt(II) or Pd(II) cis/trans-porphodilactones (termed by cis/trans-Pt/Pd) influence photophysical properties of the lowest triplet excited states including phosphorescence, Stokes shifts, and even photosensitization ability in triplet-triplet annihilation reactions with rubrene. Prominently, the overall upconversion capability (η, η = ε·Φ(UC)) of Pd or Pt trans-complex is 10(4) times higher than that of cis-analogue. Nanosecond time-resolved infrared (TR-IR) spectroscopy experiments showed larger frequency shift of ν(C═O) bands (ca. 10 cm(-1)) of cis-complexes than those of trans-complexes in the triplet excited states. These spectral features, combining with TD-DFT calculations, suggest the strong electronic coupling between the lactone moieties and the main porphyrin chromophores and thus the importance of precisely positioning β-substituents by mimicking chlorophylls, as an alternative to "extended π-conjugation", in designing NIR active porphyrinoids.

• Authors: Xian-Sheng Ke, Hongmei Zhao, Xiaoran Zou, Yingying Ning, Xin Cheng, Hongmei Su, Jun-Long Zhang
• Journal: Journal of the American Chemical Society (J Am Chem Soc) Vol. 137 Issue 33 Pg. 10745-52 (Aug 26 2015) ISSN: 1520-5126 [Electronic] United States
• PMID: 26247480 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Luminescent Agents
• Metalloporphyrins
• Photosensitizing Agents
• Platinum
• Palladium

Topics

• Biomimetics (methods)
• Drug Design
• Luminescent Agents (chemistry)
• Metalloporphyrins (chemistry)
• Models, Molecular
• Molecular Conformation
• Palladium (chemistry)
• Photosensitizing Agents (chemistry)
• Platinum (chemistry)
• Stereoisomerism