Fluorescence upconversion and transient absorption techniques are used to explain the source of the intense red/near-infrared emission of crystalline 4-dimethylamino-2′-hydroxychalcone. We found that the initially excited enol form undergoes tautomerization in 3 ps to form the keto tautomer. The latter is stable in the ground state as a consequence of J-type aggregation in the crystal packing and is manifested in an absorption peak at 550 nm that spectrally overlaps with the short-lived enol emission, leading to self-reabsorption and adding a factor to the complete depletion of the enol emission. Relaxation of the keto tautomer takes place in the form of intense fluorescence (600–750 nm) with 1.7 ns lifetime. The different spectroscopy in solution is due to vibrational cooling (300 fs), followed by solvation dynamics (5 ps in methanol) and twisting of the hydroxyphenyl ring (16 ps), before relaxation of the enol tautomer in the form of weak green fluorescence with 350 ps lifetime.

中文翻译：

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晶体2-羟基查耳酮衍生物的红色/近红外强荧光起源的新见解：来自激发态飞秒动力学的全面描述

荧光上转换和瞬态吸收技术被用来解释晶体4-二甲基氨基-2'-羟基查耳酮强烈的红色/近红外发射的来源。我们发现最初激发的烯醇形式在3 ps内经历互变异构化，从而形成酮互变异构体。后者由于晶体堆积中的J型聚集而在基态下稳定，并表现为在550 nm处的吸收峰，该吸收峰在光谱上与短暂的烯醇发射重叠，从而导致自重吸收并增加了一个因子。完全耗尽烯醇排放物。酮互变异构体的弛豫以强荧光（600-750 nm）的形式发生，寿命为1.7 ns。溶液中不同的光谱是由于振动冷却（300 fs），