In a generic synthesis approach, all three CsPbX3 (X=Cl, Br and I) perovskite nanocrystals having near unity quantum yields is reported. This has been achieved by injecting the desired amount of ...preformed alkylammonium halide salts which acted as a dual source providing halide ions and the capping agent to an equimolar amount of non‐halide Pb and Cs precursors in a reaction flask at an optimized reaction temperature. The composition sensitivity of Pb to Cs ratio, high temperature reaction, and injection of ammonium halide remained the key parameters for obtaining the high quantum yields. Details of the reaction process, use of different reagents and setting up the reaction parameters are reported.
Three colors: A rational synthesis of CsPbX3 (X=Cl, Br, and I) nanocrystals gives all three perovskites with near unity photoluminescence quantum yield. Careful analysis of the reaction chemistry and the parameters allows a generic reaction to be developed.
This paper deals with the synthesis, characterization, and photophysical behaviors of three Ru(II)–terpyridine complexes derived from a terpyridyl-imidazole ligand (tpy-HImzPh 3 Me 2 ), wherein a ...terpyridine moiety has been coupled with a dimethylbenzil unit through a phenylimidazole spacer. The three complexes display strong emission at RT having excited-state lifetimes in the range of 2.3–43.7 ns, depending upon the co-ligand present and the solvents used. Temperature-dependent emission spectral measurements have demonstrated that the energy separation between emitting metal-to-ligand charge transfer state and non-emitting metal-centered state is increased relative to that of Ru(tpy)22+. In contrast to our previously studied Ru(II) complexes containing similar terpyridyl-imidazole motif but differing by peripheral methyl groups, significant enhancement of RT emission intensity and quantum yield and remarkable increase of emission lifetime occur for the present complexes upon protonation of the imidazole nitrogen(s) with perchloric acid. Additionally, by exploiting imidazole NH motif(s), we have examined their anion recognition behaviors in organic and aqueous media. Interestingly, the complexes are capable of visually recognizing cyanide ions in aqueous medium up to the concentration limit of 10–8 M. Computational studies involving density functional theory (DFT) and time-dependent DFT methods have been carried out to obtain insights into their electronic structures and to help with the assignment of absorption and emission bands.
We synthesized and thoroughly characterized a new family of diarylethene-conjugated mononuclear Ru(II)-terpyridine complexes and investigated in detail their photophysical, electrochemical, and ...spectroelectrochemical behaviors. Interestingly, the compounds show moderately strong room-temperature luminescence predominantly from their 3MLCT state with luminescence lifetime varying between 8.43 and 22.82 ns. Because of the presence of diarylethene unit, all the monometallic complexes underwent trans-to-cis photoisomerization upon interaction with UV light with substantial changes in their absorption and luminescence spectra. Reverting back from the cis to the trans form is also made possible upon treatment with visible light or by heat. Trans-to-cis isomerization leads to almost complete quenching of luminescence, while backward cis-to-trans isomerization gives rise to restoration of the original luminescence for all the complexes. Thus, “on–off” and “off-on” emission switching was made possible upon successive interaction of the complexes with UV and visible light. Computational investigation involving density functional theory (DFT) and time-dependent DFT methods was done for proper assignment of the experimental absorption and emission spectral bands in the complexes. Finally, experimentally observed trend on the absorption and emission spectral behaviors of the complexes upon photoisomerization was also compared with the calculated results.
We have undertaken a thorough investigation on pH-responsive optical and redox switching behaviors of our recently reported
trans
form of bis-tridentate Ru(
ii
) luminophores, (H
2
...pbbzim)Ru(tpy-pvp-X)
2+
where X = H, Me, Cl, NO
2
, and Ph. The complexes possess two benzimidazole protons in their second coordination sphere, which became acidic upon coordinating influence of Ru
2+
and could be successively deprotonated with the increase of pH. The effect of pH on photophysical and electrochemical behaviours of the complexes was thoroughly studied. Substantial quenching of emission together with the red-shift of both absorption (color change) and emission bands is noticed for all complexes upon dissociation of NH protons. Absorption
vs.
pH data were employed for determination of ground-state p
K
a
values, while excited-state p
K
a
(p
K
a
*) values were estimated by employing the Förster cycle based equation. The electronic nature of X induces a small but finite effect on the p
K
a
values and a linear correlation is found by plotting p
K
a
vs.
Hammett
σ
p
parameters of X. Proton-coupled electrochemical behaviours were investigated within the pH range of 1-10. From the
E
1/2
vs
. pH plot, acid dissociation constants in different protonation states of the complexes were estimated in both Ru
2+
and Ru
3+
states. Compared with their protonated forms which exhibit reversible oxidation within 0.91-0.95 V, the oxidation potential of the doubly deprotonated forms shifted remarkably to the cathodic region (0.61-0.66 V). In essence, the present complexes act as potential pH-responsive colorimetric, emission and redox switches.
Ru(
ii
)-Terpyridine complexes exhibit pH-responsive colorimetric, emission and redox switching behaviours.
We report here the synthesis and structural characterization of a new class of homoleptic terpyridine complexes of Ru(II) containing styrylbenzene moieties to improve room-temperature luminescence ...properties. Solid-state structure determination of 2 was done through single-crystal X-ray diffraction. Tuning of photophysical properties was done by incorporating both electron-donating and electron-withdrawing substituents in the ligand. The complexes exhibit strong emission having lifetimes in the range of 10.0–158.5 ns, dependent on the substituent and the solvent. Good correlations were also observed between Hammett σp parameters with the lifetimes of the complexes. Styrylbenzene moieties in the complexes induce trans–trans to trans–cis isomerization accompanied by huge alteration of their spectral profiles upon treating with UV light. Reversal of trans–cis to trans–trans forms was also achieved on interacting with visible light. Change from trans–trans to the corresponding trans–cis form leads to emission quenching, whereas trans–cis to the corresponding trans–trans form leads to restoration of emission. In essence, “on–off” and “off–on” photoswitching of luminescence was observed. Calculations involving density functional theory (DFT) and time-dependent-DFT methods were performed to understand the electronic structures as well as for appropriate assignment of the absorption and emission bands.
•DFT study on the mechanism of Co(III)-catalysed 3+3 annulations.•Regioselectivity of Co(III) for ligand insertion into Co-C bond.•Energetic Span Model reveals the TDTS of the path.•Effect of level ...of theory on the global activation energy barrier.•Effect of various substituents on various step of reaction.
C-H annulation of anilide with benzylallene under the catalysis of Co(III)-complex has been studied theoretically by employing density functional theory (DFT) to find out the plausible mechanistic path. Our findings reveal that the C-H activation prefers the formation of a four-membered cobalta benzoazetidine intermediate rather than six-membered 1,2,4-cobalta benzoxazine intermediate to generate the product. This fact reveals a new mechanism in contrast to the mechanism proposed earlier. The metal mediated annulation of various anilides include six steps - coordination of substrate with catalyst, N-H metalation, C-H metalation, insertion of benzylallene, proton abstraction and migration insertion. Moreover, it reveals regioselectivity of cobalt for allene insertion. The effect of substituents on the mechanism has also been studied and the high energetic span obtained for this catalytic cycle implies that very high temperature is required for this reaction. It is consistent with the experimental result.
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A mild C-H activation reaction catalysed by an Ir(
iii
)-complex to generate chromones from salicylaldehydes at room temperature has been studied theoretically to explore the reaction mechanism. The ...DFT study reveals that the key point of the catalytic cycle is cyclometallation, more precisely it is in the C-H metallation step where the significance of the metal becomes obvious. The favourable pathway includes several steps, namely, coordination of the substrate with the metal catalyst, O-H metallation, C-H metallation, denitrogenation, migration insertion, proton transfer, and demetallation. On removal of one pivalic acid, the metal is activated and the C-H metallation proceeds
via
oxidative addition followed by reductive elimination. The DFT study clearly indicated that, although there are two possibilities for cyclometallation, it only proceeds
via
O-H metallation followed by stepwise C-H metallation. The effect of substituents on the mechanism was also been studied. The low energetic span obtained for this catalytic cycle implies that the reaction can proceed at room temperature, and this is consistent with the experimental result.
A mild C-H activation reaction catalysed by an Ir(
iii
)-complex to generate chromones from salicylaldehydes at room temperature has been studied theoretically to explore the reaction mechanism.
In a generic synthesis approach, all three CsPbX
(X=Cl, Br and I) perovskite nanocrystals having near unity quantum yields is reported. This has been achieved by injecting the desired amount of ...preformed alkylammonium halide salts which acted as a dual source providing halide ions and the capping agent to an equimolar amount of non-halide Pb and Cs precursors in a reaction flask at an optimized reaction temperature. The composition sensitivity of Pb to Cs ratio, high temperature reaction, and injection of ammonium halide remained the key parameters for obtaining the high quantum yields. Details of the reaction process, use of different reagents and setting up the reaction parameters are reported.
Synthesis, characterization and thorough investigation of the photophysical and electrochemical properties of a new category of emissive homo- and heteroleptic Ru(
ii
)-complexes derived from the ...4′-(
p
-triphenylphosphonium methyl phenyl)-2,2′:6′,2′′-terpyridinebromide (tpy-PhCH
2
PPh
3
Br) ligand have been executed in this work. Incorporation of the PhCH
2
PPh
3
+
Br
−
group at the terpyridine motif appropriately adjusts the triplet metal-to-ligand charge transfer (
3
MLCT) and metal-centered (
3
MC) excited states so that the complexes luminesce at room temperature (RT) having lifetimes within the range of 6.82-9.63 ns. The RT emission characteristics of the complexes get further enhanced
via
aggregation phenomena through the use of different solvent/non-solvent mixtures (DMSO/H
2
O and DMSO/PhCH
3
mixtures). Temperature dependent emission spectral measurements indicate that the emission intensity, quantum yield and lifetime increase upon dropping down the temperature, thereby designated as the on-state, while the increase of temperature causes a reduction of the said properties, indicating the off-state and the process is fully reversible. Taking advantage of the active methylene group coupled with a phosphonium motif, anion sensing characteristics of the complexes are investigated systematically in DMSO through the use of various optical channels and spectroscopic tools. The complexes are very much sensitive to fluoride and to a lesser extent acetate and dihydrogen phosphate among the studied anions. In essence, the complexes function as sensors for temperature and fluoride ion. Computational investigations were also executed
via
density functional theory (DFT) and time-dependent (TD)-DFT to obtain a clear understanding of the electronic structures of the metalloreceptors, appropriate assignment of the spectral bands and their mode of interaction with selected anions.
Luminescent homo- and heteroleptic Ru(
ii
)-terpyridine complexes display an aggregation-induced emission enhancement and act as multi-channel sensors for selective anions as well as temperature-induced molecular switches.
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