Papers by sumesh babuk Krishnan
Journal of Physical Chemistry A, Sep 26, 2019
Journal of Physical Chemistry B, Sep 8, 2020
Efficiencies of artificial photosynthetic and photocatalytic systems depend on their ability to g... more Efficiencies of artificial photosynthetic and photocatalytic systems depend on their ability to generate long-lived charge separated states in photoinduced electron transfer (PET) reactions. PET, in most cases, is followed by an ultrafast back electron transfer, which severely reduces lifetime and quantum yield of charge separated states. Generation of a long-lived charge separated state, thus is an important goal in the study of PET reactions. Herein we report that this goal is achieved using a hierarchically self-assembled anthracene-methyl viologen donor-acceptor system. Anthracene linked to two β-cyclodextrin molecules (CD-AN-CD) and methyl viologen linked to two adamantane units (AD-MV 2+-AD) form an inclusion complex in water, which further self-assembled into well-defined toroidal nanostructures. The fluorescence of anthracene is highly quenched in the self-assembled system due to PET from anthracene to methyl viologen. Irradiation
ChemistrySelect, Dec 14, 2020
The essay studies the contribution of Mor-iscos to Arabic studies. It concludes that the contribu... more The essay studies the contribution of Mor-iscos to Arabic studies. It concludes that the contributions of Moriscos in the Iberian peninsula remained modest. Some contributed actively to the knowledge of Arabic through their Arabic-Islamic learning. I show that the Mudejar convert known as Juan Andrés, who wrote one of the most influential treatises against Islam, was indeed a canon of the cathedral of Granada. I briefly discuss the contribution of Moriscos to the translations and interpretations of the Lead Books and studied their post-expulsion contribution to Arabic and Islamic studies. The last part focuses on the Dutch Republic, where, as a result of historical circumstances and contingent factors such as personal relations, Moriscos played an important role. Here, in addition to the study of the Arabic language itself, the physical sciences played a noteworthy role. This, I suggest, can be connected to the broad scope of the emergence of Arabic studies in Europe, which incorporated both the physical sciences and religion and philosophy , and an interest in North Africa itself because of developments in the physical sciences, including their application in daily life.
Chemistry: A European Journal, Jun 27, 2017
Supramolecular chirality was observed in a chargetransfer complex formed through the self-assembl... more Supramolecular chirality was observed in a chargetransfer complex formed through the self-assembly of -cyclodextrinlinked pyrene and adamantane-linked pyromellitic diimide in water. In the complex, the pyrene-pyromellitic diimide charge transfer interaction is reinforced several fold by the strong -cyclodextrinadamantane inclusion binding interaction as confirmed by 1 H NMR, absorption, fluorescence and isothermal titration calorimetry studies. The CT complex exhibited high stability as inferred from the temperature dependent absorption and NMR studies. The CT absorption band exhibited positive cotton effect indicative of supramolecular chirality for the complex. Twisted fibers were observed in the TEM, AFM and SEM experiments. A mechanism involving synergistic binding interactions leading to 2D sheet, followed by twisting of the sheet is proposed for the formation of twisted fibers. This system offers a chance to investigate the combination of supramolecular charge-transfer and supramolecular chirality and explore their synergistic effects.
Journal of Physical Chemistry A, Nov 22, 2022
Journal of Chemical Sciences, 2018
Equimolar amounts of native β-cyclodextrin (β-CD), pyrene-linked adamantane (PYAD) and tert-butyl... more Equimolar amounts of native β-cyclodextrin (β-CD), pyrene-linked adamantane (PYAD) and tert-butylpyromellitic diimide (PMDI) when dissolved in water self-assembled to form the supramolecular donor-acceptor system PYAD β-CD PMDI. The high affinity of adamantane derivatives for inclusion binding in the β-CD cavity and the propensity of PMDI to undergo rim-binding at the narrow rim of β-CD led to the formation of PYAD β-CD PMDI. The ternary complex PYAD β-CD PMDI was thoroughly characterized using various spectroscopic techniques. β-CD performs three functions in the self-assembled complex: (1) encapsulate the adamantane unit and keep the pyrene (PY) moiety above the secondary rim, (2) rim-bind PMDI and keep it at the primary rim, and (3) act as a spacer between pyrene and PMDI. Thus, the ternary complex can function as a donor-spacer-acceptor system capable of undergoing photoinduced electron transfer (PET). Upon excitation of the pyrene moiety in PYAD β-CD PMDI an electron is transferred from the excited pyrene to the PMDI ground state. Steady state and time resolved fluorescence experiments were carried out to study the PET in PYAD β-CD PMDI. Existence of the ternary system and PET processes taking place within it are further supported by laser flash photolysis experiments.
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 27, 2018
Hierarchical self-assemblies of β-cyclodextrin-linked pyrene and N-alkyl derivatives of pyromelli... more Hierarchical self-assemblies of β-cyclodextrin-linked pyrene and N-alkyl derivatives of pyromellitic diimides are studied in detail. The charge-transfer interaction between pyrene and pyromellitic diimide is augmented by β-cyclodextrin-pyromellitic diimide binding interactions in these cases. When the alkyl group is adamantyl, a 1:1 complex was formed with a very high association constant (K =1.82×10 m ). Here, the charge-transfer interaction is reinforced by inclusion binding of the adamantyl group in the β-cyclodextrin cavity leading to the formation of 2D sheets, which undergo twisting to give twisted fibres. When the alkyl group is tert-butyl, a 1:2 complex was formed with a high association constant (K =2.91×10 m ). A detailed analysis showed that the tert-butyl pyromellitic diimide undergoes both inclusion and rim-binding interactions with the β-cyclodextrin. The charge-transfer complex further self-assembled into chiral nanostructures as evident from SEM, TEM and AFM analys...
Molecules
Cholesta-5,7,9(11)-trien-3β-ol (9,11-dehydroprovitamin D3, CTL) is used as a fluorescent probe to... more Cholesta-5,7,9(11)-trien-3β-ol (9,11-dehydroprovitamin D3, CTL) is used as a fluorescent probe to track the presence and migration of cholesterol in vivo. We recently described the photochemistry and photophysics of CTL in degassed and air-saturated tetrahydrofuran (THF) solution, an aprotic solvent. The zwitterionic nature of the singlet excited state, 1CTL* is revealed in ethanol, a protic solvent. In ethanol, the products observed in THF are accompanied by ether photoadducts and by photoreduction of the triene moiety to four dienes, including provitamin D3. The major diene retains the conjugated s-trans-diene chromophore and the minor is unconjugated, involving 1,4-addition of H at the 7 and 11 positions. In the presence of air, peroxide formation is a major reaction channel as in THF. X-ray crystallography confirmed the identification of two of the new diene products as well as of a peroxide rearrangement product.
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Papers by sumesh babuk Krishnan