Hydration from lifetime determination

Following this study, Korovin and coworkers tested cryptands 23b-f which are used in time-resolved luminescent immunoassays (Mathis, 1993) for the sensitization of Ybm luminescence (Korovin et al., 2002b). From the lifetimes determined in both water and deuterated water, one calculates that the hydration number varies from 2 (23b), to 1.5 (23a, 23e), and finally to 1 (23c, 23d, 23f). Quantum yields were not determined, but luminescence intensities relative to the cryptate with 23a (in water, at room temperature) point to cryptands 23c and 23d being the best sensitizers of the Yb111 luminescence with a seven-fold enhancement, while cryptates with 23e and 23b are only 1.5- to 1.8-times more luminescent. 

Moreover, it is possible to determine the emission efficiency r] = Arad/ nrad of the emitting level, where the total decay rate is Atot = 1/r = Arad + nrad. and where the non-radiative component A rad depends on the vibronic couphng between the Eu ion and its chemical environment and r is the lifetime of the Do emitting level. It may be determined from lifetime measurements and the experimentally determined radiative component Arad- The hydrated Eu + S-diketonates tend to present lower values of emission quantum efficiencies, and emission quantum yields, in agreement with the well known effect of luminescence quenching due to the vibrational modes of the water molecule. 

However, a study of a few dyes of higher fluorescence quantum yield in polymer microparticles did not show any change in the fluorescence lifetime even though the modification of the fluorescence spectra was observed [4]. In this work, a new molecule (9-amino acridine hydrochloride hydrate, 9AAHH) is reported in which we have observed the effect of MDR in both, the steady state spectra and the fluorescence lifetimes. The dephasing time of 9AAHH in polymer matrix at room temperature have been determined from this study. 

Here Tq is equal to r+Ar, with the best value of Ar = 1.66 A determined empirically (52). The uncertainties in the absolute values of radius calculated using this equation are relatively large, however it is generally considered that useful relative values of pore size can be obtained on analysis of a series of materials. The values of diameter, Dpals calculated for the samples studied here are listed in Table 2. It is evident from Table 2 that the PALS technique is sensitive to similar pore sizes as Xe NMR, and that the values obtained are broadly consistent with those obtained by NMR, considering the assumptions used in calculation of pore diameters for both techniques. The results indicate that the sample 5 has substantially smaller free volume cavities than both sample 30 and the same sample hydrated to equilibrium. The value of the lifetime for sample 5 is very close to the value of 1.7 ns reported previously by this group for bulk PHEMA 19). 

---