Jung Gregor, Gerharz Stephan, Schmitt Alexander
Biophysical Chemistry, Saarland University, Campus, Building B2 2, D-66123, Saarbruecken, Germany.
Phys Chem Chem Phys. 2009 Mar 7;11(9):1416-26. doi: 10.1039/b816695a. Epub 2009 Feb 3.
We reinvestigated the solvatochromism of 8-hydroxypyrene-1,3,6-trisulfonate (pyranine) in conjunction with that of 8-methoxypyrene-1,3,6-trisulfonate and of 1-hydroxypyrene (pyrenol) by use of 25 different solvents. Conclusions for the prediction of ESPT behaviour of synthetic dyes were drawn by comparison with the solvatochromism of p-hydroxystyryl Bodipy dyes. Solvents were chosen according to their Kamlet-Taft parameters alpha and beta for elucidating the acidicity of the dyes and the basicity of their conjugated bases in the ground and excited state. Comparison of the spectra of pyranine and pyrenol in solvents with varying beta-values revealed that the acidity of both dyes is similar therein. The well-known ESPT behaviour of pyranine in water is assigned to a change of the electronic state at alpha-values approximately 0.7 to 0.8. The high acidity of this excited state also appears in the vanishing solvatochromism of the photoproduct fluorescence. However, prediction of an ESPT tendency of synthetic dyes might fail when only fluorescence emission data are considered. We propose to refer instead to the energetic difference of the 0-0 transition in absorption together with the solvatochromism of the acidic form in aprotic solvents of similar polarity.
我们重新研究了8-羟基芘-1,3,6-三磺酸盐（吡喃宁）以及8-甲氧基芘-1,3,6-三磺酸盐和1-羟基芘（芘酚）在25种不同溶剂中的溶剂化显色作用。通过与对羟基苯乙烯基Bodipy染料的溶剂化显色作用进行比较，得出了关于合成染料ESPT行为预测的结论。根据其Kamlet-Taft参数α和β选择溶剂，以阐明染料在基态和激发态下的酸度及其共轭碱的碱度。比较吡喃宁和芘酚在具有不同β值的溶剂中的光谱表明，两种染料在其中的酸度相似。吡喃宁在水中众所周知的ESPT行为归因于α值在约0.7至0.8时电子态的变化。这种激发态的高酸度也出现在光产物荧光的溶剂化显色作用消失中。然而，当仅考虑荧光发射数据时，合成染料ESPT趋势的预测可能会失败。我们建议转而参考吸收中0-0跃迁的能量差以及类似极性的非质子溶剂中酸性形式的溶剂化显色作用。
