<p>Herein, we explore a new strategy in the chemo-sensor field for fluorescence amplification upon binding with metal ions based on controlled participation of the nitrogen lone pair orbital. The basic architecture of the sensor entails a fluorophore, the sp2 hybridized nitrogen lone pair (-C═N-), and a chelator site referred to as the control part. Though nonplanar and nonfluorescent, compound IC1 achieved pseudo planarity from binding with Zn2+ as indicated by the increased fluorescence signal. Its other analogue (IC2) is also planar, and unlike IC1-Zn2+ was fluorescent with a lack of binding affinity to metal ions. The time-dependent density functional theory (TDDFT) calculations revealed that the fluorescence amplification was due to the blocking of the nitrogen lone pair orbital; unlikely geometrical rearrangements were insignificant. This could indicate a breakthrough concept in the future design of fluorescent turn-on sensors.</p>
H. Sung Jung, Ko, K. Chul, Lee, J. Hong, Kim, S. Hoon, Bhuniya, S., Lee, J. Yong, Kim, Y., Kim, S. Jin, and Kim, J. Seung, “Rationally Designed Fluorescence Turn-On Sensors: A New Design Strategy Based on Orbital Control”, Inorganic Chemistry, vol. 49, pp. 8552-8557, 2010.