| Abstract
| - The dissociation constants of the 4-phosphonato-2,2‘:6‘,2‘ ‘-terpyridine ligand were measured by pH−NMR andpotentiometric titration methods. The 4-phosphonato-2,2‘:6‘,2‘ ‘-terpyridine ligand shows three measurable pKavalues at 5.99, 4.65, and 3.55 using the latter method. The fourth pKa was estimated to be below 2.Spectrophotometric titration of the ruthenium complex [Ru(P-terpy)(Me2bpy)(NCS)] (1) (P-terpy = 4-phosphonato-2,2‘:6‘,2‘ ‘-terpyridine and Me2bpy = 4,4‘-dimethyl-2,2‘-bipyridine) exhibits two ground-state pKa values at 6.0and below 4.0, which can be assigned to pKa1 and pKa2, respectively. The emission maximum of complex 1shows a blue shift with decreasing pH, and apparent pH-dependent excited-state lifetimes. Complex 1 shows twoexcited-state pK*a values at 6.5 (pK*a1) and below 4.5 (pK*a2). Comparison of the ground- and excited-state pKavalues of complex 1 demonstrates that the excited state has metal to 4-phosphonato-2,2‘:6‘,2‘ ‘-terpyridine ligandcharge-transfer character.
- The 4-phosphonato-2,2‘:6‘,2‘ ‘-terpyridine ligand shows three pKa values at 6.0, 4.65, and 3.55, and its ruthenium complex [Ru(P-terpy)(Me2bpy)(NCS)] (1) (P-terpy = 4-phosphonato-2,2‘:6‘,2‘ ‘-terpyridine and Me2bpy = 4,4‘-dimethyl-2,2‘-bipyridine) exhibits ground- and excited-state pKa values at 6.0 and 6.5, respectively. The emission intensity and lifetime of complex 1 increase with decreasing pH from 11 to 3.5.
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