Optical and nonlinear optical properties of copper nanocomposite glasses annealed near the glass softening temperature

Copper nanocomposite glasses have been prepared by the ion-exchange method, and annealed at different temperatures up to and above the glass softening temperature. The absorption spectra, fluorescence spectra, and nonlinear optical transmission of the samples at 532 nm for nanosecond laser pulses, have been investigated. The optical and nonlinear optical properties of the glasses are found to be distinctly different below and above the glass softening temperature. For instance, thermal annealing up to the glass softening temperature makes the samples behave like saturable absorbers, while annealing at higher temperatures makes them behave like optical limiters. Such flexibility in controlling the optical nonlinearity in these materials makes them potential candidates for photonic applications.     

Self-location of acceptors as "isolated" or "stacked" energy traps in a supramolecular donor self-assembly: a strategy to wavelength tunable FRET emission

Control over supramolecular assemblies of donor and acceptor arrays in nanoscale dimension that facilitate efficient energy transfer resulting in tunable emission is an outstanding challenge. In pursuit of this goal, we have designed a supramolecular donor-acceptor organogel with tunable emission from green to red through controlled energy transfer by simply varying the acceptor concentration. Temperature-dependent UV/vis absorption, XRD, and AFM studies of the coassembly of 1 (donor) and 2 (acceptor) revealed the intercalation of 2 within the self-assembly of 1. Upon excitation of the decane gels of 1 with 0-2 mol % of 2, quenching of the emission of the former at 509 nm with the formation of the monomer emission of the latter at 555 nm is observed. Upon further addition of 2 (2-20 mol %), the emission was continuously red-shifted to 610 nm, which corresponds to the aggregate emission of 2. Consequently, a 98% quenching of the donor emission was observed at 509 nm. Fluorescence microscopic studies provided visual evidence for the color tuning of the FRET emission. Thus efficient trapping of excitons by "isolated" or "aggregated" acceptors through a subtle control of the self-assembly and the photophysical properties of the donor-acceptor building blocks allowed a continuous shifting of the emission color anywhere between green and red (lambdamax, 509-610 nm) in a supramolecular light harvesting system.     

Synthesis of 4-carboxy-4-pyridylpiperidines through palladium-catalyzed α-arylation of esters

A concise synthesis of 4-carboxy-4-pyridylpiperidines has been achieved. Key step is the palladium-catalyzed α-arylation of esters under basic conditions.