Spectral Heterogeneity of PRODAN Fluorescence in Isotropic Solvents Revealed by Multivariate Photokinetic Analysis

Abstract

This paper describes a multivariate analysis of the fluorescence emission of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) in a series of isotropic solvents of differing polarity and hydrogen-bonding ability. Multivariate methods distill the essential features from spectral data matrices so that the structural details that are embedded within the data are revealed to the analyst. In the aprotic solvents investigated, the analysis reveals a pair of emission components that have emission maxima that scale with the orientational polarizability. In the alcohols, short-lived, polarity-independent blue bands tentatively attributed to neutral hydrogen-bonded solute-solvent complexes form and relax prior to emission from paired bands that have Stokes shifts that scale with the solvent hydrogen-bonding ability rather than the polarity. In water, the short-lived blue bands were not observed, but the shift in the paired bands did scale with the solvent hydrogen-bonding ability.

A New Interpretation of the Absorption and the Dual Fluorescence of Prodan in Solution

“…the amount of photons emitted from the lower energy excited state is smaller in water than in cyclohexane. This finding is in agreement with the previous study performed in ethanol/water mixture 14 and ethanol/buffer mixture. 15 However, it is in conflict with the second consequence of the common hypothesis discussed above.…”

“…The emission spectrum of Prodan is very peculiar because it is broad and asymmetric and is composed by dual emission in several distinct environments, from nonpolar to polar solutions [12][13][14][15] and also in biological systems. 7,11,16 The explanation for these dual emission is still a matter of discussion.…”

“…[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Other studies recognize some limitations of this hypothesis, suggesting that more investigation is necessary to fully understand the dual fluorescence of Prodan. 8,10,[14][15][16][17][18][19]36,38 Therefore, understanding the origin of the dual emission decay mechanism is critical to improve the applications of Prodan and its derivative as fluorescent probes in biological environments.…”

“…Therefore, a new hypothesis for the dual fluorescence of Prodan (and Laurdan) in homogeneous solvents is possible, where the two emission bands would come from two different excited electronic states. 10,14,15 To verify this possibility, or Initially, the electronic transition energies of Prodan in some solvents were calculated and compared with the experimental data of the first band of the UV-visible absorption spectra. This motivated us to obtain again the experimental absorption spectrum and analyze also the broadening of the band.…”

Does PRODAN Possess an O-TICT Excited State? Synthesis and Properties of Two Constrained Derivatives

“…This behavior is shown graphically in Figure 3 using Catalan's solvent acidity parameter to characterize the H-bond donating ability of the solvent 16. It should be noted that the effect of H-bonding solvents on the fluorescence of 1 continues to be an active area of investigation 3, 17-20…”