Annihilation Dynamics of Molecular Excitons Measured at a Single Perturbative Excitation Energy.

Exciton-exciton annihilation (EEA) is a ubiquitous phenomenon, which may limit the efficiency of photovoltaic devices. Conventional methods of determining EEA time scales rely on measuring the intensity dependence of third-order signals. In this work, we directly extract the annihilation rate of molecular excitons in a covalently joined molecular trimer without the need to perform and analyze intensity dependent data by employing fifth-order coherent optical spectroscopy signals emitted into ±2k⃗1 ∓ 2k⃗2 + k⃗3 phase matching directions. Measured two-dimensional line shapes and their time traces are analyzed in the framework of the many-body version of the Frenkel exciton model, extended to incorporate annihilation dynamics. Combining double-sided Feynman diagrams with explicit simulations of the fifth-order response, we identify a single peak as a direct reporter of EEA. We retrieve an annihilation time of 30 fs for the investigated squaraine trimer.

Hypoglycemic and antidiabetic profile of the aqueous root extracts of Leptadenia hastata in albino rats.

This study was designed to evaluate the antidiabetic profile and the hypoglycaemic activity of aqueous root extracts of L. hastata in normal and alloxan-induced diabetic rats model. Eighty five albino rats were used for this study out of this thirty five were used subjected to experimental diabetes by the use of alloxan at a dose of 160 mg kg(-1) body weight. Seven experimental groups of five rats per group (A-G) were used for this study. A standard antidiabetic drug (insulin) group (B) and normal saline group (G) serves as positive control. The blood glucose lowering activity of the extract, insulin and normal saline groups were monitored at 0, 1, 3, 6, 12 and 18 hpost extract administration. On the other hand the remaining fifty albino rats were used to determine the acute toxicity and the hypoglycemic activity of the extract. The blood glucose levels of the rats were monitored at 0, 7, 14, 21 and 28 days post extract administration. Oral administration of aqueous root extract at 600 and 800 mg kg(-1) b.wt have significantly (p < 0.05) decreased the blood glucose in diabetic albino rats. On the other hand the hypoglycemic activity of the aqueous root extract on normal rats at dose of 1000 mg kg(-1) b.wt have significantly (p < 0.05) decreases blood glucose level in normal albino rats. The results of the current study have demonstrated the antidiabetic and hypoglycaemic effects of L. hastata aqueous root extracts and underscore its potentials in the management of diabetes mellitus especially following prolonged use in days.