Uzra Diwan

A Zn2+-responsive highly sensitive fluorescent probe and 1D coordination polymer based on a coumarin platform

A coumarin-based Schiff base (receptor 1) exhibited fluorescence enhancement selectively with Zn(2+) at a nanomolar level in near-aqueous medium (EtOH-H2O; 1:1, v/v). The response was instantaneous with a detection limit of 3.26 × 10(-9) M. The sensing event is supposed to incorporate a combinational effect of intramolecular charge transfer (ICT), chelation-enhanced fluorescence (CHEF) and C[double bond, length as m-dash]N isomerization mechanisms. Various spectroscopic methods, viz. IR, UV-visible, fluorescence and NMR in association with single crystal XRD studies, were used for thorough investigation of the structure of receptor 1 as well as of the sensing event. The Zn(2+) complex of receptor 1 exhibited a very nice 1D chain coordination polymeric framework in its single crystal XRD.

Harvesting red fluorescence through design specific tuning of ICT and ESIPT: an efficient optical detection of cysteine and live cell imaging

In this report, we constructed 2-(2-hydroxyphenyl)benzothiazole (HBT) based ratiometric fluorescent probe R1, highly selective for cysteine (Cys) in the red channel with a nanomolar detection limit. The rational combination of benzothiazole and benzothiazolium unit within the same molecular frame work act as “two-heads” that allowed the simultaneous harvesting of intramolecular charge transfer (ICT) as well as excited state intramolecular proton transfer (ESIPT). This coupling of dual mechanism in R1 provides selective colorimetric and ratiometric fluorescence response towards Cys from the mixture of various anions and amino acids including foremost interfering thiols viz. HS−, Hcy and GSH. R1 shows a weak ESIPT at 497 nm (green fluorescence, N*) which undergoes shifting to 625 nm (red channel K*) upon addition of Cys selectively. Henceforth, R1 was also utilized for marking Cys in live cell imaging in HeLa cells. The sensing phenomenon of R1 for Cys was studied through a number of spectroscopic techniques viz., NMR, IR along with HRMS studies. The density functional theory calculations further strengthened the experimental findings.