Department of Chemistry
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Item The Japan Society of Applied Physics, find out more The Japan Society of Applied Physics, find out more Observing Enhanced Phosphorescence and Electroluminescence from Triplet Emitter by Quantum Dot Doping(IOP, 2005-05-27) Laskar, Inamur RahamanLuminescent CdSe/ZnS core-shell-type quantum dots (QDs) were synthesized by chemical colloidal methods. The photoluminescence (PL) intensity of a triplet emitter [bis(4-trifluoromethyl)-2-phenylbenzothiazolatoacetylacetonate–iridium(III) (Ir complex 1) and bis(4-methyl)-2-phenylbenzothiazolatoacetylacetonate–iridium(III) (Ir-complex 2)] was dramatically enhanced when bluish-green emitting CdSe/ZnS QDs were incorporated into these compounds. Experimental results indicate that the emissive region of QDs substantially overlaps with the low-energy absorption bands of Ir-complexes, indicating that the photons were absorbed by both the QDs and the Ir-complexes and that the energy absorbed by the QDs was transferred efficiently to the Ir-complex triplet emitter, resulting in the observed enhancement of PL intensity. A slow quenching of QDs emission was observed in a prepared set of solutions with gradual increasing of Ir complex concentration at a fixed QDs concentration in thin film PMMA matrix, which supports the energy transfer from Ir complex to QDs. In the fabricated double-layer electroluminescent (EL) devices, the emitting layer contained either only Ir-complex or a mixture of Ir-complex and CdSe/ZnS QDs with a specific molar ratio [Ir-complex/QDs = 1/0 (D-I); 1/0.5 (D-II), ..., 1/10 (D-V)]. The EL intensity and the luminance efficiency for D-II were higher (luminescence yield = 19.3 cd A-1) than those of the other devices. The PL and EL enhancement of the triplet emitter were also strongly supported by using ZnSe QDs rather than CdSe/ZnS QDs.Item One-pot synthesis of strong solid state emitting mono-cyclometalated iridium(iii) complexes: study of their aggregation induced enhanced phosphorescence(RSC, 2012) Laskar, Inamur RahamanStrong solid-state greenish-blue emitting, mono-cyclometalated iridium complexes, [Ir(ppy)(PPh3)2(H)(Cl)], 2a and [Ir(F2ppy)(PPh3)2(H)(Cl)], 2b [ppyH = 2-phenylpyridine; F2ppyH = 2-(2′,4′-difluoro)phenylpyridine], have been synthesized by a convenient route. The ‘aggregation induced enhanced phosphorescence (AIEP)’ activity exhibited by these complexes has been rationalized.Item Aggregation induced phosphorescence” active “rollover” iridium(iii) complex as a multi-stimuli-responsive luminescence material(RSC, 2015) Laskar, Inamur RahamanOn reaction of 2,2′-bipyridine with iridium(III), an “aggregation induced phosphorescence (AIP)” active “rollover” complex, [Ir(PPh3)2(bipy-H)(Cl)(H)] (bipy-H = κ2-N,C-2,2′-bipyridine) or [Ir(bipy-H)], is obtained. The emission colour changes from bluish-green to yellowish-orange and vice versa after repeated protonation and deprotonation of [Ir(bipy-H)], respectively, which unequivocally supports its reversible nature. [Ir(bipy-H)] is sensitive to acids with different pKa values. Tuning of the emission properties can be achieved in the presence of acids with different pKas. This behaviour allows the complex, [Ir(bipy-H)], to function as a phosphorescent acid sensor in both solution and the solid state, as well as a chemosensor for detecting acidic and basic organic vapours. The protonated form, [Ir(bipy-H)H+], which is generated after protonation of [Ir(bipy-H)] can be used as a solvatochromic probe for oxygen containing solvents, and also shows vapochromic properties. The emission, absorption and 1H NMR spectra of [Ir(bipy-H)] under acidic and basic conditions demonstrate its reversible nature. DFT based calculations suggest that changes in the electron affinity of the pyridinyl rings are responsible for all these processes.Item Highly sensitive explosive sensing by “aggregation induced phosphorescence” active cyclometalated iridium(iii) complexes(RSC, 2015) Laskar, Inamur RahamanTwo phosphorescent complexes [Ir(o-CHOppy)(PPh3)2(H)Cl] (1) and [Ir(ppy)(PPh3)2(H)Cl] (2) exhibiting ‘aggregation induced phosphorescent emission (AIPE)’ properties have been found to be very sensitive to the detection of picric acid (PA). The detection limit for PA has been checked and was found to be 264 nM and 65 nM for complexes 1 and 2, respectively.