Tunable Chiral Second-Order Nonlinear Optical Chromophores Based on Helquat Dications

Fourteen new dipolar cations have been synthesized, containing methoxy or tertiary amino electron donor groups attached to helquat (Hq) acceptors. These Hq derivatives have been characterized as their TfO^– salts by using various techniques including NMR and electronic absorption spectroscopies. UV–vis spectra show intense, relatively low energy absorptions with λ_(max) ≈ 400–600 nm, attributable to intramolecular charge-transfer (ICT) excitations. Single-crystal X-ray structures have been solved for two of the chromophores, one as its PF_6^– salt, revealing centrosymmetric packing arrangements (space groups Pbca and P1̅). Molecular quadratic nonlinear optical (NLO) responses have been determined directly by using hyper-Rayleigh scattering (HRS) with a 800 nm laser, and indirectly via Stark (electroabsorption) spectroscopy for the low energy absorption bands. The obtained static first hyperpolarizabilities β_0 range from moderate to large: (9–140) × 10^(–30) esu from HRS in MeCN and (44–580) × 10^(–30) esu from the Stark data in PrCN. The magnitude of β_0 increases upon either extending the π-conjugation length or replacing a methoxy with a tertiary amino electron donor substituent. Density functional theory (DFT) and time-dependent DFT calculations on selected tertiary amino chromophores confirm that the low energy absorptions have ICT character. Relatively good agreement between the simulated and experimental UV–vis absorption spectra is achieved by using the CAM-B3LYP functional with the 6-311G(d) basis set. The β_(tot) values predicted by using DFT at the same level of theory are large ((472–1443) × 10^(–30) esu in MeCN). Both the theoretical and experimental results show that para-conjugation between Hq and electron donor fragments is optimal, and enlarging the Hq unit is inconsequential with respect to the molecular quadratic NLO response

Helquat Dyes: Helicene-like Push–Pull Systems with Large Second-Order Nonlinear Optical Responses

Helquat dyes combine a cationic hemicyanine with a helicene-like motif to form a new blueprint for chiral systems with large and tunable nonlinear optical (NLO) properties. We report a series of such species with characterization, including determination of static first hyperpolarizabilities β_0 via hyper-Rayleigh scattering and Stark spectroscopy. The measured β_0 values are similar to or substantially larger than that of the commercial chromophore E-4′-(dimethylamino)-N-methyl-4-stilbazolium. Density functional theory (DFT) and time-dependent DFT calculations on two of the new cations are used to probe their molecular electronic structures and optical properties. Related molecules are expected to show bulk second-order NLO effects in even nonpolar media, overcoming a key challenge in developing useful materials

Characterization of an in vitro transcription system from rinderpest virus

An in vitro transcription system for rinderpest virus (RPV) is described. Ribonucleoprotein complexes isolated from RPV-infected Vero cells, human lung carcinoma cells, or detergent-disrupted purified virions synthesized authentic RPV mRNAs for the N, P, M, F and H genes as identified by dot blot hybridization analysis with individual cDNA clones. The relative abundance of the mRNAs synthesized in vitro decreased from the 3? end of the genome to the 5? end, very similar to that observed with measles virus transcription in vitro. The transcription by purified virions was stimulated three-fold by the addition of infected human lung carcinoma cell lysate, demonstrating the involvement of host factor(s) in mRNA synthesis

Gas inducing type mechanically agitated contactors

The rate of gas induction was measured in 0.57, 1.0, and 1.5 m i.d. gas inducing types of mechanically agitated contactors (GIMAC). The ratio of impeller diameter to vessel diameter was varied in the range 0.13 < D/T < 0.59. The effect of impeller submergence from the top and impeller clearance from the bottom was investigated in detail. The effect of impeller speed was studied in the range 0.13 < N < 13.5 r/s. A model has been developed for the critical speed for gas induction, and for the rate of gas induction with the description of forced vortex structure in the impeller region. A unified theme has been proposed for the understanding of phenomena such as the critical speed for gas induction and the rate of gas induction. The physical significance of model parameters has been interpreted on the basis of flow information in the impeller region

Mechanism of gas induction in a self-inducting impeller

The gas induction characteristics of a stator-rotor-type self-inducing impeller were investigated in the cases without and with gas line resistance. To understand the hydrodynamics near the impeller, and to characterize the mechanism of gas induction, the local liquid velocity was measured with a laser Doppler anemometer. The effect of impeller speed, impeller submergence, and gas line resistance on the volumetric flow rate of liquid, as well as the rate of gas induction, was investigated. The dominant role of local gas holdup was identified and the mechanism of gas induction was established, with the help of an energy balance

Power consumption in gas-inducing-type mechanically agitated contactors

Power consumption was measured in 0.57, 1.0, and 1.5 m i.d. gas inducing type of mechanically agitated contactors (GIMAC) using single and multiple impellers. The ratio of impeller diameter to vessel diameter was varied in the range of 0.13 < D/T < 0.59. The effect of liquid submergence from the top and impeller clearance from the vessel bottom was investigated in detail. In the case of multiple impeller systems, six different designs were investigated. The designs included pitched blade downflow turbine (PBTD), pitched blade upflow turbine (PBTU), downflow propeller (PD), upflow propeller (PU), straight bladed turbine (SBT) and disc turbine (DT). The effect of interimpeller clearance was studied for the multiple impeller system. The effect of impeller speed was studied in the range of 0.13 < N < 13.5 rotations/s. A mathematical model has been developed for power consumption before and after the onset of gas induction