02258nas a2200253   4500008004100000022001400041245012900055210006900184260000800253300001200261490000600273520138200279653001401661653003801675653002001713653002201733653001501755100001801770700002001788700002101808700002201829700002301851856013001874       2020                        eng d  a2367-093200aConjunctive photoluminescence enhancement through plasmonic and photonic band-gap pathways in a chiral self-assembled system0 aConjunctive photoluminescence enhancement through plasmonic and   cAUG  a582-5910 v43 a<p>We describe two parallel pathways for enhancing the intrinsic photoluminescence of an organic emitter dispersed in a liquid crystal (LC) medium. The pathways have independent origins: (i) Metal enhanced fluorescence (MEF) incorporating gold nanoparticles having an organic shell of pro-mesogenic cholesterol esters; and (ii) Matching the photonic band gap (PBG) due to the helical structure in a self-assembled chiral system with the excitation wavelength. This unprecedented combination of both pathways achieves a level of photoluminescence exceeding the sum of the contribution from the individual methods. This conjunctive protocol results in an overall enhancement by a factor of 37 between the emitter dispersed in a non-chiral LC and that appealing to both MEF and PBG pathways. Circular polarized luminescence measurements also show that this protocol helps in effective discrimination of chiral light achieving a large dissymmetry factor whose magnitude (+0.33) is comparable to the highest recorded to date. Electric field switching between two states is also shown to result in appreciable fluorescence modulation. Being generic in nature the protocol employed can be adapted to a variety of situations with the large magnitude as well the modulation level suitable for applications such as biosensors, various analyte detection, and other photonic devices.</p>
10achirality10acircularly polarized luminescence10aliquid crystals10aphotonic band-gap10aplasmonics1 aBaral, Marlin1 aPrasad, Krishna1 aBhat, Sachin, A.1 aNayak, Rashmi, A.1 aYelamaggad, C., V.  uhttps://library.ncl.res.in/content/conjunctive-photoluminescence-enhancement-through-plasmonic-and-photonic-band-gap-pathways02813nas a2200241   4500008004100000022001400041245016300055210006900218260000900287300000800296490000700304520194400311653001602255653002202271653001102293653002002304653002502324100003002349700002102379700002402400700002302424856012402447       2020                        eng d  a0250-470700aWide thermal range, exclusive occurrence of technically significant chiral nematic phase: synthesis and mesomorphism of cholesterol-based non-symmetric dimers0 aWide thermal range exclusive occurrence of technically significa  cAUG   a1880 v433 a<p>Fifteen new non-symmetric chiral dimers belonging to three different series have been synthesized and evaluated for their mesomorphic properties. They are formed by interlinking cholesterol with salicylaldimine (SAN) cores (with reverse imine groups) via an omega-oxyalkanoyloxy spacer. Within a series, the length of the terminaln-alkoxy tails has been varied for a fixed even-parity spacer. Three even-parity spacers such as 4-oxybutanoyloxy, 6-oxyhexanoyloxy and 8-oxyoctanoyloxy have been used to join two cores, whereas the terminal tails such asn-butyloxy,n-hexyloxy,n-octyloxy,n-decyloxy andn-dodecyloxy chains have been attached to the SAN core. Microscopic and calorimetric experimental results show that all the dimers behave identically exhibiting the chiral nematic (N*) phase solely, which was authenticated by powder X-ray diffraction studies carried out on some selected samples. In the vast majority of the cases, this phase is thermodynamically stable, and while cooling, it exists over a wide thermal range covering room temperature (RT) due to supercooling. This finding is notable given the fact that the N* phase possesses technologically significant optical properties. At RT, the N* phase displayed one of the iridescent colours characteristically caused by interference and diffraction of the reflected and scattered light. A comparative study reveals that the lengths of both the terminal chain and central spacer influence the clearing temperature of the dimers, and also the temperature range of the N* phase. The selective reflection measurements revealed that the pitch of the N* phase is either temperature sensitive or temperature insensitive. Temperature-dependent circular dichroism (CD) spectra were recorded for the planar texture of the N* phase formed by a dimer, as a representative case. The presence of an intense negative CD band suggests the left-handed screw sense of the N* phase helix.</p>
10aCD activity10acholesteric phase10adimers10aliquid crystals10aselective reflection1 aNayak, Rashmi, Ashwathama1 aBhat, Sachin, A.1 aRao, D., S. Shankar1 aYelamaggad, V., C.  uhttps://library.ncl.res.in/content/wide-thermal-range-exclusive-occurrence-technically-significant-chiral-nematic-phase