Talk Session 1

"Intense photoluminesce from Cu doped CdSe nanotetrapods trigg16ered by ultrafast hole capture".

Brightly photoluminescent Cu-doped CdSe nanotetrapods (NTPs) have been prepared by a modified hot injection method. Their photoluminescence (PL) has a quantum yield of 38% and decays slowly over a few microseconds, while the PL in undoped NTPs has a rather small quantum yield of 1.7 % and decays predominantly in tens of picoseconds, with a minor component in the nanosecond time regime. PL spectra of doped NTPs are significantly Stokes shifted compared to the band edge (BE). Efficient PL quenching by a hole scavenger confirms the oxidation state of +I for the dopant ion and establishes hole capture by this ion to be the primary event that leads to the Stokes shifted PL. A fast decay of photoinduced absorption band, along with a similar decay in PL, observed in femtosecond optical gating experiment, yields a time constant of about a picosecond for the hole capture from the valence band (VB) by Cu+. The remarkably long PL lifetime in the doped NTPs is ascribed to the decrease in the overlap between the wavefunctions of the photogenerated electrons and the captured hole.3 Hot carrier relaxation processes, triggered by excitation at energies greater than the band gap, leave their signature in a rise time of few hundreds of femtoseconds, in the ground state bleach recovery kinetics. Hence, a complete picture of exciton dynamics in the doped NTPs has been obtained using ultrafast spectroscopic techniques working in tandem .

2,2'-Bipyridine Derived Doubly B-N Fused Bisphosphine-Chalcogenides, [C5H3N(BF2){NCH2P(E)Ph2}]2 (E = O, S, Se): Tuning of Structural Features and Photophysical Studies

Molecules with extended π-conjugation have drawn considerable interest in the last two decades because of their intriguing optical and electronic properties, and also their wide applications in organic light emitting diodes (OLEDs), organic field-effect transistors (OFETs), polymer solar cells (PSCs) etc. The incorporation of heteroatoms such as: boron, nitrogen and phosphorus assist in fine tuning the optical and electronic properties of natural π-conjugated materials. In contrast, the attachment of phosphorus functionalization into the B-N bridged organic π-conjugated small molecules or to replace B-N bond with a P-N or C-P bond to assess the influence is less extensive. In this context, we sought to investigate the effect of phosphine-chalcogenide (P=E) functionalities on doubly B-N fused π-conjugated molecules and assess their structural features and optoelectronic properties. 2,2′-bipyridine based bisphosphine 1 and its bischalcogenide derivatives 2-4 were synthesized and further reacted with BF3•Et2O/Et3N to form doubly B-N fused compounds 5-7 in excellent yields. The compounds were fully characterized by various spectroscopic methods and by single crystal X-ray diffraction studies. The X-ray structures of compounds 1-4 showed the existence of both intra- and intermolecular hydrogen bonding. In addition, intramolecular F•••H interactions observed in compounds 5-7 have been assessed by 1H NMR data. The effect of phosphorus-chalcogenides on electronic properties of doubly B-N fused system and their structural features has been investigated in detail and well supported by extensive experimental and DFT studies. Compound 6 (P=S) exhibited a very high quantum yield with ϕ = 0.56 in CH2Cl2, and highest single excited state lifetime of 4.26 ns. TD-DFT calculation revealed that the involvement of P=E bonds in the HOMO energy level of these compounds follows the increasing order: P=O < P=S < P=Se. Chalcogen atoms on phosphorus have shown notable influence on the structural distortions, UV-vis, fluorescence spectroscopy, fluorescence quantum yield and single excited state lifetime studies. The X-ray structure of 6•CH2Cl2 showed P=S•••H interactions with hydrogen atoms of dichloromethane. The results have demonstrated how a co-crystallized solvent molecule through weak interactions effect the structural features and hence their photophysical properties.

Inclusion of higher excitations in coupled cluster theory via dual-exponential wave-operator: ground and excited state energetics and treatment of large chemical systems

In this talk, we will present the genesis of a dual exponential Ansatz based recursive similarity transformed Coupled Cluster (CC) methodology, which is capable to incorporate high rank excitations in an affordable manner. The method is proved to be extremely accurate over a large class of molecular systems, which is ensured by a balanced treatment of dynamical correlation and screened Coulomb interactions. The method is referred to as iterative n-body excitation inclusive CCSD (iCCSDn). We shall demonstrate the superiority of the proposed method by applying to determine the stabilization energetics of the ubiquitous water clusters. In order to go beyond small to medium sized molecules, we have further developed and integrated iCCSDn methodology to Fragment Molecular Orbital (FMO) based methods which allow us to treat very large chemical systems without unduly sacrificing the accuracy. In the resulting FMO-iCCSDn scheme, the molecule/cluster is broken into several small fragments based on some physically motivated fragmentation schemes, and the dynamical correlation is included via iCCSDn for the individual fragments, where the zeroth order function for each fragment is constructed in a self-consistent manner in the presence of all other fragments. Finally, we shall present the Linear Response (LR) formulation based on a better ground state description through the iCCSDn methodology. Towards this, we construct a time averaged Lagrangian, and the first order perturbed amplitudes are obtained by taking its derivative with respect to the Lagrange parameters. The excitation energy is obtained by diagonalizing the LR matrix in the frequency domain. We will show some pilot numerical applications to prove the efficacy of our method.

Lipidome reprogramming in pancreatic cancer under hypoxia

Cancer cells display altered cellular lipid metabolism, including disruption in endogenous lipid synthesis, storage, and exogenous uptake for membrane biogenesis and functions. Altered lipid metabolism and, consequently, lipid composition impacts cellular function by affecting membrane structure and properties, such as fluidity, rigidity, membrane dynamics, and lateral organization. Hypoxia, a state of oxygen deprivation, is most prevalent in pancreatic cancer, and is one of the major factors implicit in tempering lipid metabolism. Hypoxia induced alterations in lipid composition; membrane structure and properties involved in metastasis and invasion and remains unknown in pancreatic cancer. So herein, we want to provide an overview of Lipidome reprogramming of pancreatic cancer under hypoxia and how this lipidomic reprogramming affects attributed membrane biophysical properties.

Transition Metal Complexes of Acyclic Singlet Carbene Stabilized by Heteroatoms and its Application in Homogeneous Catalysis

N-heterocyclic carbenes (NHCs) are state-of-the-art ligands in organometallic chemistry. Although N-heterocyclic diaminocarbenes (NHCs) have emerged as an important class of ligands in catalysis, their N, O-congeners, cyclic aminooxycarbenes (CAOCs) have not been frequently encountered as ancillary ligands despite having a different electronic profile. The structural variety of CAOCs is rather limited because both bonds of oxygen are incorporated in the heterocyclic core and due to this, oxygen lone pair in CAOCs does not exert the same level of steric protection as the flanking N substituents in NHCs. In contrast, acyclic aminooxycarbenes (AAOCs) could impose the steric bulk if the nitrogen substituents are large enough to position the oxygen substituent towards the metal center in the preferred conformation. Since this area is very less explored, only a handful metal complexes have been reported in literature till now. In this work, a series of four AAOC ligand precursors have been synthesized. Subsequent metalation has been performed on ligand AAOC and (AAOC)gold(I) chloride complexes have been isolated. Furthermore, (AAOC)Au(III) tribromide have been synthesized. Synthesized ligand precursors and the corresponding gold complexes have been characterized by Single Crystal X-Ray crystallography. The four metal complexes (AAOC)gold(I) chloride have been used as catalysts in hydrohydrazination reaction of terminal alkyne with hydrazide derivative. Total synthesis has been done by using these (AAOC)gold chloride complexes .