A simple color change detection by the naked-eye using untreated paper for a biologically relevant fluoride (F^–) anion in water is a challenge. New non-planar push-pull chromophore involving intramolecular charge-transfer (ICT) from urea donor in 2,3-disubstituted-1,1,4,4-tetracyanobuta-1,3-diene (TCBD) turns out to be an efficient system for detecting F^– ion giving various output signals. But, replacing phenyl (Ph) at C₃-position with 4-(dimethylamino)phenyl (DMA) led to the absence of colorimetric and fluorometric detections due to the masking and quenching, nature of strong ICT by the DMA. NMR and electrochemical studies revealed that the sensing mechanism is governed by H-bonding as well as the deprotonation of N–H attached with TCBD moiety which reduces the HOMO–LUMO gap and causes the dramatic color change. Coupled with excellent sensitivity (3 ppm) and specificity towards F^–, a successful demonstration of cheap tissue paper-based visual strip-detection in aqueous is presented.

中文翻译：

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含取代基的多途径氟化物信号的细微变化，包括使用尿素受体功能化的基于1,1,4,4-Tetracyanobuta-1,3-Diene的推挽发色团的纸条比色检测

通过使用未经处理的纸张为生物学相关的氟化物裸眼一个简单的颜色变化检测（F ^- ）的阴离子在水中是一个挑战。新型的非平面推挽生色团涉及尿素供体的2,3-二取代-1,1,4,4-tetracyanobuta-1,3-diene（TCBD）中的分子内电荷转移（ICT）系统，用于检测˚F ^-离子给各种输出信号。但是，在C ₃处取代苯基（Ph）4-（二甲基氨基）苯基（DMA）的正位置导致了比色和荧光检测的缺失，这是由于DMA掩盖和猝灭了强ICT的性质。核磁共振和电化学研究表明，传感机理受氢键以及与TCBD部分相连的N-H的去质子作用的控制，这减少了HOMO-LUMO间隙并引起剧烈的颜色变化。结合出色的灵敏度（3 ppm）和对F ^–的特异性，成功证明了廉价的薄页纸基于视觉的条带检测水溶液。