Urea-functionalized 4-ethynylbenzenes undergo facile formal [2 + 2] cycloaddition followed by retroelectrocyclization upon reaction with tetracyanoethylene, yielding 1,1,4,4-tetracyanobuta-1,3-dienes-based push–pull chromophores. Unlike the N,N′-dialkylamino group, urea functionalization provides easy access to further functionalization on these chromophores. The resulting chromophores exhibit unexpected white light emissions apart from various inherent properties like intramolecular charge-transfer band and redox behavior.

The stable organic diradicals that exhibit strong intramolecular ferromagnetic exchange interactions are suitable building blocks for organic magnetic materials (OMMs). Based on the ab initio calculations, here, we report the electronic and magnetic properties of 1,2,4-benzotriazinyl-based mono- and diradicals (known as Blatter’s radicals). The quantum mechanical calculations based on the density functional theory (DFT) reveal the merostability of the superstable Blatter’s radicals. The stability could further be enhanced by tuning the spin densities on the radical centers via the extended π-conjugation. The magnetic exchange interactions (2J) have been investigated for Blatter’s radical coupled to the nitronyl nitroxide radical (i.e., Bl-NN) as the prototypical system that has recently been synthesized by Rajca et al.. The broken-symmetry (BS) approach within the standard DFT and constraint spin-density DFT (CDFT) methods are applied to compute the exchange interactions, while for wave function-based multireference methods, the spin symmetry-adopted (e.g., CASSCF/NEVPT2) approach is applied. It is observed that the CBS-DFT provides much better 2J values as compared to the standard BS-DFT. The multireference calculations based on the minimal active space [i.e., CAS­(2,2)] incorporating the delocalized magnetic orbitals provide quite reliable exchange interactions. After validating the applied computational methods, a number of ferromagnetically coupled hybrid diradicals are modeled by coupling Blatter’s monoradical with various known stable organic radicals. A few of them turned out to be quite promising candidates for the building block of OMMs.

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 2,3disubstituted-1,1,4,4-tetracyanobuta-1,3-diene (TCBD) turns out to be an efficient system for detecting Fion 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 stripdetection in aqueous is presented.

The molecular topology in the single-molecular nano-junctions through which the de-Broglie wave propagates plays a crucial role in controlling the molecular conductance. The enhancement and reduction of the conductance in para and meta connected molecules due to constructive and destructive Quantum Interference (QI) respectively are quite well established. Herein, we investigated the effect of localized spin centers on spin transportation using organic radicals as molecular junctions. The role of the localized spins on the QI as well as on spin filtering capability is investigated employing density functional theory in combination with non-equilibrium Green s function (NEGF-DFT) techniques. Various organic radicals including nitroxy (NO˙), phenoxy (PO˙) and methyl (CH 2˙) attached to the central benzene ring of pentacene with different terminal connections (para and meta) to gold electrodes are examined. Due to more obvious QI effects, para connected pentacene is found to be more conductive than meta one. Surprisingly, on incorporating a radical center, along with spin filtering, a significant reversal of QI effects is observed which manifests itself in such a way that the conductance of meta coupled radicals is found to be more than para by two orders of magnitude. The anomaly in QI patterns induced by radical center is analyzed and discussed in terms of orbital and structural perspectives.

The development of stimuli responsive systems that can switch between two distinct spin states under the application of an external stimuli has always remained an illusory challenge. Here, we report...