A new intramolecular charge transfer receptor as a selective ratiometric ‘off-on’ sensor for Zn

A new intramolecular charge transfer (ICT) probe 3 is found to display a highly selective photophysical response in the presence of Zn²⁺, among various biologically significant metal ions examined. The absorption band of 3 is red shifted by 84 nm and the fluorescence intensity increases 13-fold in the presence of Zn²⁺. The binding interaction follows the order Zn²⁺ > Cd²⁺ > Mg²⁺ > Ba²⁺ > Ca²⁺ > K⁺ ≅ Na⁺ ≅ Li⁺ and the stability constant for 3 + Zn²⁺ is over an order of magnitude higher compared to biologically competing Ca²⁺ and Mg²⁺.     

Single chemosensor for highly selective colorimetric and fluorometric dual sensing of Cu(II) as well as ‘NIRF’ to acetate ion

A novel fluorescent probe for the copper(II) ion in mixed aqueous media, based on fluorescence quenching mechanism with noticeable color change from light to dark yellow, was designed and synthesized. It also exhibited high selectivity for acetate in acetonitrile over other common anions in the near infrared region (NIR) accompanied with exciting color changes from light yellow to pink. Hence sensor 1 ascertains its dual chemosensing ability toward Cu(II) and acetate ions as evidenced by competitive experiments.     

Exploring the Franck–Condon region of a photoexcited charge transfer complex in solution to interpret femtosecond stimulated Raman spectroscopy: excited state electronic structure methods to unveil non-radiative pathways

We present electronic structure methods to unveil the non-radiative pathways of photoinduced charge transfer (CT) reactions that play a main role in photophysics and light harvesting technologies. A prototypical π-stacked molecular complex consisting of an electron donor (1-chloronaphthalene, 1ClN) and an electron acceptor (tetracyanoethylene, TCNE) was investigated in dichloromethane solution for this purpose. The characterization of TCNE:π:1ClN in both its equilibrium ground and photoinduced low-lying CT electronic states was performed by using a reliable and accurate theoretical–computational methodology exploiting ab initio molecular dynamics simulations. The structural and vibrational time evolution of key vibrational modes is found to be in excellent agreement with femtosecond stimulated Raman spectroscopy experiments [R. A. Mathies et al., J. Phys. Chem. A, 2018, 122, 14, 3594], unveiling a correlation between vibrational fingerprints and electronic properties. The evaluation of nonadiabatic coupling matrix elements along generalized normal modes has made possible the interpretation on the molecular scale of the activation of nonradiative relaxation pathways towards the ground electronic state. In particular, two low frequency vibrational modes such as the out of plane bending and dimer breathing and the TCNE central C C stretching play a prominent role in relaxation phenomena from the electronic CT state to the ground state one.

We present electronic structure methods to unveil the non-radiative pathways of photoinduced charge transfer (CT) reactions that play a main role in photophysics and light harvesting technologies.     

An inorganic phosphate (Pi) sensor triggers ‘turn-on’ fluorescence response by removal of a Cu ion from a Cu-ligand sensor: determination of Pi in biological samples

A fluorescent ligand that displays a high selectivity for Cu²⁺ has been synthesized. On complexation with Cu²⁺, the fluorescence of the ligand is quenched. Inorganic phosphate ions decomplex Cu²⁺ displaying a fluorescence enhancement that can even be seen with naked eyes. The method was successfully used in quantitative determination of inorganic phosphates in serum, urine, and saliva samples.     

Anomalous fluorescence and low-temperature absorption spectra of naphtho[1,8-cd][1,2,6] thiadiazine and its derivatives: an example of second excited state emission (S2 → S0)

An anomalous fluorescence near 380 nm is detected from heptane solutions on naphtho[1,8-cd][1,2,6] thiadiazine (1), 6,7-dihydroacenaphtho[5,6-cd][1,2,6]thiadiazone (2), its unsaturated derivative (4), and the tetrachloro derivative of 1 (3), when these substances are excited into the S₀→S₂ absorption band near 350 nm. Excitation spectra verify that S₂→S₀ fluorescence is occurring. The measured lifetimes of each fluorescence are 2.2, 3.3, 0.3, 0.4 ns respectively for 1,2,3, and 4. Radiative and non-radiative rate constants are presented. Compounds 1 and 2 exhibit unusual low-temperature absorption spectra at 77 K in 3-methylpetane matrix. The disappearance of the long-wavelength transition at 650 nm is accompanied by a new transition near 450 nm at 77 K. It is theorized that a ground-state dimer can explain these observations.