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Abstract A proper understanding of excited state properties of indole derivatives can lead to rational design of efficient fluorescent probes. The optically active and excited states of a series of substituted indoles, where a substituent was placed on position four, were calculated using equation of motion coupled cluster and time dependent density functional theory. The results indicate that most substituted indoles have a brighter second excited state corresponding to experimental absorption maxima, but a few with electron withdrawing substituents absorb more on the first excited state. Absorption on the first excited state may increase their fluorescence quantum yield, making them better probes. Electronic structure methods were found to predict the energies of the systems with electron withdrawing substituents more accurately than those with electron donating substituents. The excited states of both states correlated well with electrophilicity, similar to the experimental trends for the absorption maxima. Overall, these computational studies indicate that theory can be used to predict excited state properties of substituted indoles, when the substituent is an electron withdrawing group.
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Oxidative Photocyclization of Aromatic Schiff Bases in Synthesis of Phenanthridines and Other Aza-PAHs
The oxidative photocyclization of aromatic Schiff bases was investigated as a potential method for synthesis of phenanthridine derivatives, biologically active compounds with medical applications. Although it is possible to prepare the desired phenanthridines using such an approach, the reaction has to be performed in the presence of acid and TEMPO to increase reaction rate and yield. The reaction kinetics was studied on a series of substituted imines covering the range from electron-withdrawing to electron-donating substituents. It was found that imines with electron-withdrawing substituents react one order of magnitude faster than imines bearing electron-donating groups. The 1H NMR monitoring of the reaction course showed that a significant part of the Z isomer in the reaction is transformed into E isomer which is more prone to photocyclization. The portion of the Z isomer transformed showed a linear correlation to the Hammett substituent constants. The reaction scope was expanded towards synthesis of larger aromatic systems, namely to the synthesis of strained aromatic systems, e.g., helicenes. In this respect, it was found that the scope of oxidative photocyclization of aromatic imines is limited to the formation of no more than five ortho-fused aromatic rings.
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- Award ID(s):
- 1800329
- PAR ID:
- 10262209
- Date Published:
- Journal Name:
- International Journal of Molecular Sciences
- Volume:
- 21
- Issue:
- 16
- ISSN:
- 1422-0067
- Page Range / eLocation ID:
- 5868
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/ijms21165868
