Ab initio study of structural, electronic, optical, and vibrational properties of ZnxSy (x?+?y?=?2 to 5) nanoclusters

An ab initio study of the stability, structural, electronic. and optical properties has been performed for 46 zinc sulfide nanoclusters Zn _x S _y (x + y = n = 2 to 5). Five out of them are seen to be unstable as their vibrational frequencies are found to be imaginary. A B3LYP-DFT/6-311G(3df) method is employed to optimize the geometries and a TDDFT method is used for the study of the optical properties. The binding energies (BE), HOMO-LUMO gaps and the bond lengths have been obtained for all the clusters. For the ZnS₂, ZnS₃, and ZnS₄ nanoclusters, our stable structures are seen to be different from those obtained earlier by using the effective core potentials. We have also considered the zero point energy (ZPE) corrections ignored by the earlier workers. For a fixed value of n, we designate the most stable structure the one, which has maximum final binding energy per atom. The adiabatic and vertical ionization potentials (IP) and electron affinities (EA), charges on the atoms, dipole moments, optical properties, vibrational frequencies, infrared intensities, relative infrared intensities, and Raman scattering activities have been investigated for the most stable structures. The nanoclusters containing large number of S atoms for each n is found to be most stable. The HOMO-LUMO gap decreases from n = 2–3 and then increases above n = 3. The IP and EA both fluctuate with the cluster size n. The optical absorption is quite weak in visible region but strong in the ultraviolet region in most of the nanoclusters except a few. The optical absorption spectrum or electron energy loss spectrum (EELS) is unique for every nanocluster and may be used to characterize a specific nanocluster. The growth of most stable nanoclusters may be possible in the experiments.     

Quantum chemical study on gas phase decomposition of ferulic acid

Ferulic acid, representing phenolic fraction of bio-oil, is considered to be a model compound in this study for its decomposition into various end products such as ethylbenzene, eugenol, cis-isoeugenol, vanillin, 4-ethylguaiacol, guaiacol, and acetovanillone using density functional theory approach. Results of bond dissociation energies indicate that cleavage of methyl group from ferulic acid is the lowest energy-demanding bond scission amongst all 14 bond cleavages. Primary end product by decomposition of ferulic acid is found to be ethylbenzene and its production occurs through the formation of intermediate products such as 4-hydroxycinnamic acid, cinnamic acid and styrene. Demethoxylation of ferulic acid gives rise to the production of 4-hydroxycinnamic acid which further undergoes the formation of cinnamic acid by dehydroxylation reaction route. The formation of cinnamic acid in this study is carried out using three reaction schemes 1–3 and its further reduction to ethylbenzene is performed using two reaction possibilities. Finally, favourable pathway is found to be decarboxylation of cinnamic acid to produce vinylbenzene followed by the production of ethylbenzene using hydrogenation of C=C chain double bond. Furthermore, thermochemistry of each reaction scheme is performed at atmospheric pressure and at a wide range of temperature of 598–898 K.     

Advances in the Chemistry of 2,4,6-Tri(thiophen-2-yl)-1,3,5-triazine

Heterocyclic systems are now considered to be an integral part of material chemistry. Thiophene, selenophene, furan, pyrrole, carbazole, triazine and others are some such examples worth mentioning. 2,4,6-Tri(thiophen-2-yl)-1,3,5-triazine is a C_3h-symmetric system with thiophene as the donor unit and s-triazine as the acceptor unit. This review gives an insight into the advances made in the thienyl-triazine chemistry over the past two to three decades. The synthetic pathways for arriving at this system and all its important derivatives are provided. The major focus is on the materials synthesized using the thienyl-triazine system, including star molecules, linear and hyperbranched polymers, porous materials and their diverse applications. This review will play a catalytic role for new dimensions to be explored in thienyl-triazine chemistry.