Effect of proton-donor solvent and structural flexibility of prodan and laurdan molecules on their spectral-luminescent properties

Abstract

535.37The influence of structural flexibility on dipole moments, energy-level locations, and charge distributions in prodan and laurdan molecules was studied. A quantum-chemical calculation of isolated prodan and laurdan molecules in the fluorescent state geometry was conducted. Rate constants for radiative and non-radiative processes and fluorescence quantum yields for these probe molecules were calculated. Interaction centers of prodan and laurdan with a proton-donor solvent were estimated quantitatively. The possibility of using fluorescent probes for estimating the polarity of proton-donor and proton-acceptor solvents was shown.Keywords: fluorescent probe, prodan, laurdan, structural flexibility, proton-donor properties, fluorescence quantum yield.Introduction. Fluorescent probes such as prodan (6-propionyl-2-dimethylaminonaphthalene) and laurdan (6-dodecanoyl-2-dimethylaminonaphthalene) are widely used in biological and biophysical research [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The fluorescence properties of prodan and laurdan have been described in the literature as simultaneously existing local-excited (LE) and twisted internal charge-transfer (TICT) states. However, the latter term should be used very arbitrarily because the state has been observed only at very low temperatures [2]. These states are strongly delocalized at temperatures near ambient and above [2]. It has been shown [5] that the positions of fluorescence maxima in phospholipids bilayers depend on the phase state of the phospholipids, i.e., 435 and 440 nm for the short-wavelength band in the gel phase; 515 and 490 nm, for prodan and laurdan in the liquid-crystalline phase. Two fluorescence bands (430 and 500 nm) were observed for laurdan in glycerin with λ ex = 380 nm at room temperature. The short-wavelength band at 430 nm disappeared as the temperature was raised to 370 K.The large shifts of prodan and laurdan fluorescence bands in solvents of different polarity have been explained by the significant change of dipole moment in the excited state as compared with the ground state. According to formulas for calculating common effects of solvents [16,17], changing the prodan dipole moment from 5.5 to 10.2 D causes a shift of the S 0 → S 1 -transition [18,19] in its fluorescence spectra of 770 cm -1 and 800 cm -1 on going to isopropanol and water, respectively, from a non-polar solvent [19,20]. The experimental shifts in fluorescence spectra of prodan were 3790 and 5520 cm -1 in isopropanol and water, i.e., the size of the dipole moment and its change from

Analytical Time-Dependent Long-Range Corrected Density Functional Tight Binding (TD-LC-DFTB) Gradients in DFTB+: Implementation and Benchmark for Excited-State Geometries and Transition Energies

“…When analyzing the performance of a method, it must be pointed out that the orientation of substituents can play an important role for optical properties of a dye; see, for instance, refs − . As some molecules in the benchmark set show different symmetries in the excited state than in the ground state with respect to the reference geometries, a couple of molecules were selected in the following analysis for a qualitative comparison of the LC-DFTB2/OB2 0.3 (base) results.…”

Conformal transitions of the laurdan molecule in the absorption and fluorescence spectra

“…The conformations of molecules at angles of 60° (the deviation maximum), 30° (the intermediate angle), and 0° (because the optimized structure was planar) were examined (see Table 1). Only two conformations (0 and 60°) were previously considered in [10]. Table 1 tabulates the energies (in cm -1 ), oscillator forces of transitions and dipole moments (in D), and electron states calculated by the INDO method.…”

“…This value can be considered as an approximate estimate of the conformal barrier. Following [10], we assumed that the geometric laurdan structure in the excited state was planar. However, as demonstrated in [5], the laurdan molecule in the excited state has both planar and non-planar conformations.…”

“…The geometry of the excited state of the molecule was calculated using the procedure described in [10]. …”

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

“…Possibly also with an internal twist of the fluorophore (TICT). [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.…”