Dynamics of formation and decay of the exciplex created between excited Cu(II)-5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin and thymine CO groups in short oligothymidylates and double-stranded [poly(dA–dT)]2
✍ Scribed by Vladimir S Chirvony; Victor A Galievsky; Igor V Sazanovich; Pierre-Yves Turpin
- Book ID
- 104373526
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 259 KB
- Volume
- 52
- Category
- Article
- ISSN
- 1011-1344
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✦ Synopsis
Cationic water-soluble Cu(II)-5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (CuTMpyP 4q ) complexed with short oligothymidylates d(pT) n (ns1, 2, 3, 4, 5, 9, 12-18) can form exciplexes simultaneously with both CO groups of thymine, forming [(CuP) U dd -CO], and with surrounding water molecules, forming [(CuP) U dd -H 2 O], where (CuP) U dd is the Cu(II)-porphyrin in its excited (d,d) state. The contribution of the CO exciplex in the complexes with d(pT) n increases from 10% for ns1 up to 100% for ns9 and 12-18. For all n, the water-exciplex rise time is of the order of 1-3 ps, its lifetime being as long as 30-160 ps and depending on n. The CO-exciplex lifetime (;950 ps) is found to be independent of the length (n) of the oligothymidylate. The CO-exciplex rise time is found to be as long as ;100 ps. This implies that the excited triplet CuTMpyP 4q molecules, which form the CO exciplex, are protected during this time from the fast (;1 ps) quenching by water molecules. It is assumed that the dependence of the water-exciplex lifetime on n found for CuP complexes with d(pT) n , as well as the difference of CuP-exciplex lifetimes found for various axial ligands and surrounding oligomers, may result from a dependence of the (d,d) state lifetime of five-coordinate (non-planar) CuP on the polarity of the microenvironment.