A DFT study on Electronic Excitations, Charge Transfer and NLO Properties of Visible Absorbing Squaraine and Thiosquaraine dyes

Density functional calculations have been performed to see the effect of sulfur substitution in place of oxygen at central four membered acceptor squarate ring on electronic excitations, charge transfer and second order non-linear optical properties in visible absorbing squaraines (SQ). Molecules oxy-thiosquaraines (OSQ) and thiosquaraines (SSQ) have showed red shift in absorption as compared to their corresponding SQ molecules. The lowest five electronic excitations for all the molecules have been calculated by using TDDFT method. Further, effect of electron donating and electron withdrawing groups on absorption maxima have been studied. The large red shifts in case of electron withdrawing group within the same series of molecules (SQ, OSQ and SSQ) are due to destabilization of HOMO and stabilization of LUMO levels. Charge transfers in these molecules are reported by using VMOdes. Second hyperpolarizabilities (áγñ) for these molecules are calculated by SOS method. This study may helpful in synthesizing new C-N bonding SQ, OSQ and SSQ dyes which are further useful in NLO applications

Dicyanomethylene substituted oxocarbon dianions: A comparative computational study

A comparative and computational study of various dicyanomethylene substituted dianions of squarate (SQ1-SQ3), croconate (CR1-CR4) and rhodizonate (RH1-RH7) with absorption in the visible to the near-infrared region (300-800 nm) is reported. Rhodizonate dianions show ~100 nm red-shifted absorption as compared to corresponding croconate dianions. Similarly, croconate dianions show ~100 nm red-shifted absorption as compared to the corresponding squarate dianions. Further, on increasing the number of dicyanomethylene substitutions on the central ring, there is a change in electronic properties (absorption shifts toward longer wavelength). The drastic changes in absorption properties are due to the variation in size of the central ring as shown by DFT, TDDFT and SAC-CI data

A DFT study on electronic excitations, charge transfer and NLO properties of visible absorbing squaraine and thiosquaraine dyes

370-377Density functional calculations have been performed to see the effect of sulfur substitution in place of oxygen at central four membered acceptor squarate ring on electronic excitations, charge transfer and second order non-linear optical properties in visible absorbing squaraines (SQ). Molecules oxy-thiosquaraines (OSQ) and thiosquaraines (SSQ) have shown red shift in absorption as compared to their corresponding SQ molecules. The lowest five electronic excitations for all the molecules have been calculated by using TDDFT method. Further, effect of electron donating and electron withdrawing groups on absorption maxima have been studied. The large red shifts in case of electron withdrawing group within the same series of molecules (SQ, OSQ and SSQ) are due to destabilization of HOMO and stabilization of LUMO levels. Charge transfers in these molecules are reported by using VMOdes. Second hyperpolarizabilities (áγñ) for these molecules are calculated by SOS method. This study may be helpful in synthesizing new C-N bonding SQ, OSQ and SSQ dyes which are further useful in NLO applications

Glutathione as a potent inhibitor against SARS CoV-2 Main protease (Mpro): Molecular docking and dynamics simulations

The emergence of a zoonotic pathogen causing disease entitled as novel coronavirus disease 2019 (COVID-19) which keeps rapid spreading and has become a pandemic threat for the entire world. Right now no medications are approved for coronaviral infection, albeit some of the medications have been attempted. Chloroquine, hydroxychloroquine, remdesivir, favipiravir, lopinavir and ritonavir are broadly used for the treatment of COVID-19. To study the interactions of glutathione with COVID-19 main protease and spike glycoprotein, computational approaches like molecular docking and molecular dynamics (MD) simulation studies are explored. The ligand-receptor interactions of glutathione-Mpro (PDB: 6LU7) and glutathione-spike glycoprotein (PDB: 6VSB) complexes were explored by using molecular docking tools. Further glutathione-Mpro complex was subjected to MD simulation study. MD simulation results shows the protein stability by exploring the RMSD and RMSF of the protein. The MD simulation also shows ligand-protein interactions as well as ligand properties. The present study concludes that glutathione shows better interactions with COVID-19 main protease in comparison to the above mentioned drugs which were used for the treatment of SARS-CoV-2

Dicyanomethylene substituted oxocarbon dianions: A comparative computational study

1121-1127A comparative and computational study of various dicyanomethylene substituted dianions of squarate (SQ1-SQ3), croconate (CR1-CR4) and rhodizonate (RH1-RH7) with absorption in the visible to the near-infrared region (300-800 nm) is reported. Rhodizonate dianions show ~100 nm red-shifted absorption as compared to corresponding croconate dianions. Similarly, croconate dianions show ~100 nm red-shifted absorption as compared to the corresponding squarate dianions. Further, on increasing the number of dicyanomethylene substitutions on the central ring, there is a change in electronic properties (absorption shifts toward longer wavelength). The drastic changes in absorption properties are due to the variation in size of the central ring as shown by DFT, TDDFT and SAC-CI data

Mono-, di- and tri- substituted S-triazine as anti cancer agents: A comparative molecular docking study

816-822In this paper, a series of 1,3,5-triazine derivatives with mono-, di-, tri- substitutions at 2,4,6 positions of S-triazine have been designed. The molecular docking studies have been carried out against cancer therapeutic target protein (Heat Shock Protein 90, HSP90). The most active structure has been predicted based on the binding energy and mode of interactions of compounds with the help of molecular modeling software AUTODOCK Vina. Of all the substitutions (mono-, di- and tri-) of 1,3,5-triazine derivatives, trisubstituted triazine i.e. tri-4 shows better activity than mono- and di- substitutions having binding affinity −12.1 kcal/mol. This is due to the presence of strong π-π interactions of hydrophobic substituted part of 1,3,5-triazine with phenylalanine 138 (PHE138) present in the hydrophobic region of HSP90

A novel twisted Donor-Acceptor structures with cyano substituents for advancements in Near-Infrared Red TADF Emitters

The designing and development of near-infrared (NIR) red emitters have attracted significant attention owing to the challenges of achieving the necessary energy levels for harvesting both singlet and triplet excitons and their unique requirements for this spectral range. Herein, we have reported the designing and synthesis of two novel red TADF emitters 4,4\u27-(3,6-bis(9,9-dimethylacridin-10(9H)-yl)dibenzo[a,c]phenazine-11,12-diyl)dibenzonitrile (Ac-PhCNDBPZ) and 4,4\u27-(3,6-di(10H-phenoxazin-10-yl)dibenzo[a,c]phenazine-11,12-diyl)dibenzonitrile (PXZ-PhCNDBPZ) having twisted donor-acceptor structures. A cyano substituent helps to increase the wavelength towards the redshift. These emitters show near-IR emissions at 602 and 698 nm. This work proves that the cyano substituent and rigid acceptor with a strong donor could be an effective approach to exploring high-efficiency red near-infrared TADF materials

Strategic Approach to Pyrazinoquinoxaline Molecular Design for Enhanced Performance

The availability of affordable organic compounds with thermally activated delayed fluorescence (TADF) properties represents a unique class of materials for addressing key challenges in organic electronics. In this context, we have successfully designed and synthesised three novel hybrid molecules 2-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)-3,7,8-triphenylpyrazino[2,3-g]quinoxaline (tCz-PyrQx), 4-(tert-butyl)-N-(4-(tert-butyl)phenyl)-N-(4-(3,7,8-triphenylpyrazino[2,3-g]quinoxalin-2-yl)phenyl)aniline (tDPA-PyrQx), and 2-(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)-3,7,8-triphenylpyrazino[2,3-g]quinoxaline (Ac-PyrQx) comprising electron-donating 3,6-di-tert-butyl-9H-carbazole, bis(4-(tert-butyl)phenyl)amine, and (9,9-dimethyl-9,10-dihydroacridine) with electron-accepting pyrazinoquinoxaline groups. The incorporation of highly planar and rigid pyrazinoquinoxaline electron-accepting moieties holds significant importance due to their unique properties like efficient charge transfer, and reduced steric hindrance. Their planar structure facilitates strong π-π stacking interactions and efficient charge transfer within the molecular framework, leading to improved exciton formation and enhanced reverse intersystem crossing (RISC) rates, which are critical for TADF processes. The three different electron-donating groups with pyrazinoquinoxaline were synthesised with the view of tuning the photophysical and electrochemical properties of the hybrids

Ultrafast Excited State Relaxation Dynamics of New Fuchsine‐ a Triphenylmethane Derivative Dye

An all-inclusive investigation of the ultrafast excited state relaxation dynamics of a triphenylmethane derivative molecule, New Fuchsine (NF), using a combined approach of density functional theory (DFT), femtosecond transient absorption spectroscopy (fs-TAS), and photoluminescence spectroscopy is presented in this work. The DFT calculations confirmed the formation of twisted molecular structure in the excited state of NF in ethanol solution with bond rotation of ≈86°. TAS measurements of NF solution exhibited ultrafast ground state-recovery pathway via a conical intersection confirming an ultrafast structural reorientation. On the contrary, TAS measurements of NF thin-film exhibited a longer excited-state lifetime suggesting a hindered molecular twisted state formed as an intermediate step. Photophysical kinetic models are proposed to globally fit the fs-TAS data establishing the twisted intramolecular charge transfer (TICT) state mediated ground state recovery for NF in solution and thin film, respectively. Temperature-dependent photoluminescence study of NF film provided a clear insight into the effect of rotational motion of phenyl rings in NF molecules over the TICT mediated emission. © 2021 Wiley-VCH GmbH