The outstanding organic nonlinear optical material of 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) also exhibits fluorescence. While a strong fluorescence would add value to DAST in opening door to new applications such as sensing, it's underlying mechanism remains unclear and is expected to vary with the experimental conditions. To this end, DAST in the solution phase, with solutions in various polar solvents, and in the solid phase, with thin films annealed at different temperatures, were prepared and investigated. Results show that only one fluorescence peak at around 600–610 nm was present in the DAST solutions, and the increase of the solvent polarity leads to a red-shift of the fluorescence peak and a decrease of the fluorescence intensity. Rather differently, two fluorescence emission peaks were measured from the DAST solid thin films, and particularly, the peak at the higher frequency in 570–589 nm is excited by the charge transfer from the donor (dimethylamino group) to acceptor (pyridyl groups) of DAST cations, while the other peak at the lower frequency in 710–723 nm is assigned to the charge transfer from the anions to cations in DAST. After having been annealed at a high temperature of 150 °C, the fluorescence intensity of the peak at 587 nm of DAST solid film decreases evidently, due to the molecular reabsorption. This work provides insight to the fluorescence properties of DAST and points to avenues to alter or improve the emission characteristics and efficiency.

4 - N,N-二甲氨基-4'- N'优异的有机非线性光学材料-methyl-stilbazolium tosylate (DAST) 也显示荧光。虽然强荧光将为 DAST 增加价值，为传感等新应用打开大门，但其潜在机制仍不清楚，预计会随实验条件而变化。为此，制备并研究了溶液相中的 DAST，在各种极性溶剂中的溶液，以及在固相中，薄膜在不同温度下退火。结果表明，DAST 溶液中仅存在 600-610 nm 附近的一个荧光峰，溶剂极性的增加导致荧光峰红移和荧光强度降低。不同的是，从 DAST 固体薄膜中测量了两个荧光发射峰，特别是，在 570-589 nm 的高频峰被 DAST 阳离子从供体（二甲氨基）到受体（吡啶基）的电荷转移激发，而在 710-723 nm 低频处的另一个峰被指定为DAST 中从阴离子到阳离子的电荷转移。经150°C高温退火后，由于分子重吸收，DAST固体薄膜587 nm处峰的荧光强度明显降低。这项工作提供了对 DAST 荧光特性的深入了解，并指出了改变或改善发射特性和效率的途径。而在 710-723 nm 较低频率处的另一个峰被指定为 DAST 中从阴离子到阳离子的电荷转移。经150°C高温退火后，由于分子重吸收，DAST固体薄膜587 nm处峰的荧光强度明显降低。这项工作提供了对 DAST 荧光特性的深入了解，并指出了改变或改善发射特性和效率的途径。而在 710-723 nm 较低频率处的另一个峰被指定为 DAST 中从阴离子到阳离子的电荷转移。经150°C高温退火后，由于分子重吸收，DAST固体薄膜587 nm处峰的荧光强度明显降低。这项工作提供了对 DAST 荧光特性的深入了解，并指出了改变或改善发射特性和效率的途径。