Interactions between a tetraanionic porphyrin and the methylviologen dication in methanol studied by fluorescence quenching reaction
✍ Scribed by Sanjay Pant; Hiroyasu Ohtaka-Saiki; Makoto Takezaki; Toshihiro Tominaga
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- English
- Weight
- 506 KB
- Volume
- 90
- Category
- Article
- ISSN
- 0167-7322
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✦ Synopsis
Pluorescence decay curves for 5,10,15,20-tetrakis(4-sulfonatopheny1)-21H,23H-porphine tetraanion (TPPS4) have been measured in the absence and presence of the methylviologen dication &IV'+) with various ionic strengths in methanol. In the presence of MV2+ the fluorescence decays can be expressed by a double exponential function, Z(t) = Ztexp(-tiq) + Zzexp(-ti%). The contribution by the faster decay component to the total fluorescence signal increases with increasing MV2+ concentration. The faster decay process is attributed to fluorescence from the excited state of a solvent-separated ion pair (SW) formed between TPPS4-and MV2+, and the slower process is attributed to fluorescence from free TPPS4-ions in the solution. Rate constants for the quenching of fluorescence from free TPPS" by MV2+ (&) and formation constants for the SSJP (KSSJF) were calculated and both are found to decrease with increasing ionic strength. The decrease in k, and KssIp values cau be interpreted in terms of the shielding of electrostatic attraction between the ions.