Syntheses and Spectroscopic Studies of Novel Chlorins with Fused Quinoxaline or Benzimidazole Ring Systems and the Related Dimers with Extended Conjugation
✍ Scribed by Andrei N. Kozyrev; V. Suresh; Suresh Das; Mathias O. Senge; Masayuki Shibata; Thomas J. Dougherty; Ravindra K. Pandey
- Book ID
- 104202670
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- French
- Weight
- 253 KB
- Volume
- 56
- Category
- Article
- ISSN
- 0040-4020
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✦ Synopsis
AbstractÐCondensation of 13 2 -oxopyropheophorbide a 1 with various aromatic diamines under acid-catalyzed conditions afforded a series of novel chlorins with fused quinoxaline or benzimidazole polyaromatic ring systems. This methodology was extended for the preparation of laterally bridged pyropheophorbide a dimers. Reaction of 1 with 1,2,4,5-benzenetetramine produced a bis-quinoxaline-bridged symmetrical chlorin dimer 16 and an unsymmetrical benzimidazole/pyrazine bridged analog 17. Spectroscopic data of novel conjugated dimers show a signi®cant perturbation of the extended bis-chlorin p-system in a coplanar arrangement. The excited state properties of some novel chlorin derivatives 4±6, 14, and dimers 16 and 17, which contain two laterally bridged pheophorbides have been examined. Compounds 4±6, 16 and 17 are weakly ¯uorescent (f f 0.08±0.16) with singlet state lifetimes ranging from 2±5 ns. These compounds show high intersystem crossing ef®ciencies (f T 0.39±0.58). A close match was observed between the quantum yields for singlet oxygen generated and their triplet quantum yields. The excited state of 14 undergoes deactivation mainly through a non-radiative route with ¯uorescence and triplet state quantum yields being negligible.The monomeric and dimeric structures of annulated chlorins show a characteristic vinylogous-type enolization of the 12-methyl group adjacent to the fused ring systems. The crystallographic and the modeling studies of these novel chlorins indicated a rigid construction of condensed aromatic heterocycles in a planar arrangement.