Mrituanjay D. Pandey

Silver-guided excimer emission in an adenine-pyrene conjugate: fluorescence lifetime and crystal studies

This Communication describes a novel adenine-pyrene conjugate (1) and its solid-state structure with silver and copper ions. Single-crystal studies of metal complexes of 1 offer insight into molecular interactions and provide a basis to rationalize possible interactions in the solution state, leading to excimer formation. The robust nature of this interaction was further confirmed by deposition of the silver complex on a graphite surface, which exhibited a remarkable resemblance to its solid-state structure. The structural basis of selective excimer formation in the presence of Ag(+) ions presents a viable approach for ratiometric detection of these ions.

Synthesis, structure, and two-photon absorption studies of a phosphorus-based tris hydrazone ligand (S)P[N(Me)N=CH-C6H3-2-OH-4-N(CH2CH3)2]3 and its metal complexes.

A phosphorus-supported multidentate ligand (S)P[N(Me)N=CH-C(6)H(3)-2-OH-4-N(CH (2)CH(3))(2)](3) (1) has been used to prepare mononuclear complexes LM [M = Fe (2) Co (3)] and trinuclear complexes L(2)M(3) [M = Mn (4), Ni (5), Zn (6), Mg (7), Cd (8)]. In both 2 and 3 the ligand binds the metal ion in a facial coordination mode utilizing three imino nitrogen (3N) and three phenolic oxygen (3O) atoms. The molecular structures of L(2)Mn(3), L(2)Ni(3), L(2)Zn(3), L(2)Mg(3), and L(2)Cd(3) (4-8) are similar; two trihydrazone ligands are involved in coordination to hold the three metal ions in a linear fashion. Each of the trishydrazone ligands behaves as a trianionic hexadentate ligand providing three imino and three phenolic oxygen atoms for coordination to the metal ions. The coordination environment around the two terminal metal ions is similar (3N, 3O) while the central metal ion has a 6O coordination environment. Third-order non-linear optical properties of these compounds as measured by their two-photon absorption (TPA) cross section reveals that while 1 does not possess obvious TPA activity, complexes 2 (3213 GM) and 4 (3516 GM) possess a large TPA cross section at 770 nm.

Two-photon-absorption technique for selective detection of copper(II) ions in aqueous solution using a dansyl-pyrene conjugate.

In recent years, there has been an increase in research activity in the quest for materials possessing large nonlinear optical activity. At present, two-photon absorption (TPA) cross-section analysis of molecules is one of the most extensively used techniques in various applications such as frequency up-converted lasing, two-photon dynamic therapy, precision high resolution laser three-dimensional (3D) micro-nanofabrication, two-photon photopolymerization, optical power limiting, 3D fluorescence imaging. The design of molecules that can lead to high TPA values is based on several strategies. One of the important ways of achieving TPA appears to be increasing the delocalization pathway of electrons within molecules. In addition, the presence of donor and acceptor units within the molecule that are in conjugation with each other (donor-p-bridge-acceptor, D p A) seems to favor the nonlinear optical (NLO) behavior. Interestingly, most of the design of third-order NLO materials is based on organic substances. However, more recently there have been several reports suggesting that inorganic coordination complexes as well as organometallic compounds can also be designed to achieve NLO behavior. Recently, we reported that certain transition metal complexes derived from a tripodal phosphorusbased trihydrazone ligand showed excellent third-order NLO behavior. This observation suggested to us the possibility of using TPA enhancement as a method for the selective detection of metal ions in aqueous solution. Fluorescence-based sensors are well-known for metal-ion detection applications. On the other hand, TPA-based sensors are very rare. Herein, we report the synthesis, characterization, and selective copper(II)-ion sensing capability of a novel dansyl–pyrene conjugate (1). Interestingly, whilst 1 can be used as a fluorescence-based sensor (by fluorescence quenching) of copper(II) ions, TPA enhancement upon interaction with copper(II) ions allows a more-reliable and positive detection of these metal ions in aqueous solution. To the best of our knowledge, this is the first report on the use of the TPA technique for detecting copper(II) ions in aqueous solutions. The synthesis of 1 was achieved in good yield by the condensation of 1-pyrenemethylamine hydrochloride with dansyl chloride (Scheme 1). Compound 1 is soluble in many common organic solvents and shows the presence of a