To explore the effect of substituent attached to aromatic ring and the length of diamine chain in salen-type Schiff base molecules on the fluorescence emission spectra (FL_em), the FL_em of 63 diamine-salicylaldehyde condensates in an ethanol solution were obtained. The influence of substituent electronic effects and chain lengths on the wavenumber (ν_em) of fluorescence emission wavelengths (λ_em) was subsequently studied. The results show that the length of the diamine chain in the target compound has an effect on the ν_em, which can be quantified by the alkyl polarizability effect index (PEI), where compounds with alkyl of higher PEI have lower ν_em. Second, the λ_em of salen-type Schiff bases can be quantified by an equation of the seven parameters, PEI, σ(X)_─OH, σ(X)_─CH═N, , , and , form where the stability and predictive ability of the obtained equation was confirmed by leave-one-out cross validation. Lastly, it was observed that the influence on the λ_em of substituent X attached to the aromatic ring is related to its position relative to OH or CH═N groups as reference, whose Hammett constants (σ(X)_─OH, σ(X)_─CH═N) and the excited-state substituent constants ( , ) of the substituents X with varying locating methods have different effects on the λ_em; and that there is a “homoring competition effect” of substituent.

中文翻译：

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烷基极化效应和取代基的同化竞争效应对Salen型席夫碱荧光发射光谱的影响

为探讨芳环上的取代基和salen型席夫碱分子中二胺链的长度对荧光发射光谱(FL _em )的影响，获得了63种二胺-水杨醛缩合物在乙醇溶液中的FL _em。随后研究了取代基电子效应和链长对荧光发射波长 ( λ _em )的波数 ( ν _em ) 的影响。结果表明，目标化合物中二胺链的长度对ν _em有影响，可以通过烷基极化效应指数（PEI）来量化，其中具有较高PEI的烷基的化合物具有较低的ν _em。其次，萨伦型席夫碱的λ _em可以通过七个参数的方程来量化，PEI , σ (X) _─OH , σ (X) _─CH=N , , ,和, 形成其中的稳定性和预测性通过留一法交叉验证证实了所得方程的能力。最后，观察到芳环上的取代基X对λ _em的影响与其相对于OH或CH=N基团作为参考的位置有关，其哈米特常数( σ (X) _─OH , σ(X) _─CH=N ) 和取代基 X的激发态取代基常数 ( , ) 对λ _em有不同的影响；并且存在取代基的“同位竞争效应”。