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Thermal-Induced Twisting and Photoinduced Planarization of Salicylideneaniline in Alcohols.
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2020-03-03 , DOI: 10.1021/acs.jpca.9b09526 Karunakaran Ponnusamy 1 , Kannan Ramamurthy 1 , Selvaraju Chellappan 1
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2020-03-03 , DOI: 10.1021/acs.jpca.9b09526 Karunakaran Ponnusamy 1 , Kannan Ramamurthy 1 , Selvaraju Chellappan 1
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Thermofluorochromism and photochromism of salicylideneaniline (SA) in alcohol were investigated using steady-state and time-resolved fluorescence and absorption spectroscopy. The planar trans-enol form of SA in alcohols is converted into the twisted trans-enol form on heating. This conversion results change in the emission maximum from the 530 to the 440 nm region with an increase in fluorescence intensity, which confirms the absence of intramolecular hydrogen bonding between imine nitrogen and phenolic hydrogen in the twisted trans-enol form. The activation barrier for thermal-induced formation of the twisted trans-enol form in methanol was determined experimentally and was found to be 20.15 ± 2.22 kcal/mol. The rotation of the phenolic C7-C8 and C7-N1 bond followed by breaking of the intramolecular hydrogen bond and formation of an intermolecular hydrogen bond with alcohol solvent molecules results in the thermally stable twisted trans-enol form in alcohol solvents. The biexponential nature of the fluorescence decay of the twisted trans-enol form of SA confirms that the emission originates from multiple (π-π* and n-π*) excited states. On photolysis under UV light, the twisted trans-enol form is converted back into the planar trans-enol form. The time-resolved absorption and excitation-resolved fluorescence spectrum of SA in methanol confirm the existence of the twisted cis-keto form as a transient photochromic intermediate in the light-induced planarization of SA in alcohols. In alcohols, an interplay between the intra- and intermolecular hydrogen-bonding controls excited-state reaction dynamics and conformational relaxation of SA, which are responsible for the photochromism of salicylideneaniline.
中文翻译：
乙醇中水杨基苯胺的热诱导扭曲和光诱导平面化。
使用稳态和时间分辨荧光和吸收光谱法研究了水杨基苯胺（SA）在酒精中的热荧光色度和光致变色现象。加热时，SA在醇中的平面反式-烯醇形式转化为扭曲的反式-烯醇形式。这种转换导致发射最大值从530 nm到440 nm区域变化，并且荧光强度增加，这证实了在扭曲的反式烯醇形式下，亚胺氮与酚氢之间不存在分子内氢键。通过实验确定了在甲醇中热诱导形成扭曲的反式烯醇形式的活化势垒，发现该活化势垒为20.15±2.22 kcal / mol。酚C7-C8和C7-N1键的旋转，随后分子内氢键的断裂，以及与醇溶剂分子的分子间氢键的形成，导致在醇溶剂中热稳定的扭曲的反式-烯醇形式。扭曲的反式-烯醇形式的SA的荧光衰减的双指数性质证实了发射源于多个（π-π*和n-π*）激发态。在紫外光下光解时，扭曲的反式烯醇形式转化回平面的反式烯醇形式。SA在甲醇中的时间分辨吸收和激发分辨荧光光谱证实了扭曲的顺式-酮形式的存在是在酒精中SA的光诱导平面化过程中的瞬时光致变色中间体。在酒精中
更新日期：2020-03-03
中文翻译：
乙醇中水杨基苯胺的热诱导扭曲和光诱导平面化。
使用稳态和时间分辨荧光和吸收光谱法研究了水杨基苯胺（SA）在酒精中的热荧光色度和光致变色现象。加热时，SA在醇中的平面反式-烯醇形式转化为扭曲的反式-烯醇形式。这种转换导致发射最大值从530 nm到440 nm区域变化，并且荧光强度增加，这证实了在扭曲的反式烯醇形式下，亚胺氮与酚氢之间不存在分子内氢键。通过实验确定了在甲醇中热诱导形成扭曲的反式烯醇形式的活化势垒，发现该活化势垒为20.15±2.22 kcal / mol。酚C7-C8和C7-N1键的旋转，随后分子内氢键的断裂，以及与醇溶剂分子的分子间氢键的形成，导致在醇溶剂中热稳定的扭曲的反式-烯醇形式。扭曲的反式-烯醇形式的SA的荧光衰减的双指数性质证实了发射源于多个（π-π*和n-π*）激发态。在紫外光下光解时，扭曲的反式烯醇形式转化回平面的反式烯醇形式。SA在甲醇中的时间分辨吸收和激发分辨荧光光谱证实了扭曲的顺式-酮形式的存在是在酒精中SA的光诱导平面化过程中的瞬时光致变色中间体。在酒精中
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