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The Localization of Hydrophilic Sites Within an Osmium Polypyridyl Compound Can Produce a Negative Activation Energy for Emission Decay by Anula Ranatunga; Robin C. Lasey; Michael Y. Ogawa is a Materials Science article available to read on EtoBox.

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The temperature dependence of the emission lifetimes of two structural isomers of an osmium polypyridyl complex are reported. The compounds Osbpy 2 4Y 4 H -dcbpy (1) and Osbpy 2 3Y 5-dcbpy (2), where 4Y 4 H -dcbpy 4Y 4 H -dicarboxy-2Y 2 H -bipyridine and 3Y 5-dcbpy 3Y 5-dicarboxy-2Y 2 H -bipyridine, dier only in the placement of their two hydrophilic carboxylate groups within the unique bipyridine ligand. In argon-saturated water, the emission life-time of 1 decreases with increasing temperature and can be ®t to the Arrhenius expression k obs k 0 expÀE a aRT to give values of k 0 2X6 AE 0X3 Â 10 8 s À1 and E a 330 AE 20 cm À1 . In contrast the emission of 2 measured in ethanol displays longer lifetimes at higher temperatures to give k 0 2X9 AE 0X3 Â 10 6 s À1 and E a À590 AE 20 cm À1 . Thus, the speci®c localization of the hydrophilic carboxylate groups in these molecules signi®cantly alters their photophysical properties and can produce negatively activated emission lifetimes.

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Author

Anula Ranatunga; Robin C. Lasey; Michael Y. Ogawa

Publisher

Elsevier Science; Elsevier ; Elsevier BV (ISSN 1387-7003)

Published

2001

Language

EN

Field

Materials Science (Physical Sciences)