Energies and couplings of local excitations and charge transfer states control the nature of singlets and triplets in PDI aggregates.

Quantum chemistry is employed to estimate the effects that the structural modification of 1,5- and 9,10-anthraquinones produces in their electronic structure, in the pursuit of a common strategy to improve the electrochemical and singlet fission features on conjugated quinones.

The modulation of intermolecular interactions upon aggregation induces changes in excited state properties of organic molecules that can be detrimental for some optoelectronic applications but can be exploited for others. The time-dependent density functional theory (TDDFT) is a cost-effective approach to determining the exciton states of molecular aggregates, and it has been shown to provide reliable results when coupled with the appropriate choice of the functional. Here we apply a general procedure to analyze the aggregates’ exciton states derived from TDDFT calculations in terms of diabatic states chosen to coincide with local (LE) and charge-transfer (CT) excitations within a restricted orbital space. We apply the approach to study energy profiles, interstate couplings, and the charge-transfer character of singlet and triplet exciton states of perylene di-imide aggregates (PDI). We focus on the intermolecular displacement along the longitudinal translation coordinate, which mimics different amounts of slip-stacking observed in PDI crystals. The analysis, in terms of symmetry-adapted Frenkel excitations (FE) and charge-resonance (CR) states and their interactions, discloses how the interchange of the H/J character for small longitudinal shifts, previously reported for singlet exciton states, also occurs for triplet excitons.

Intermolecular interactions modulate the electro-optical properties of molecular materials and the nature of low-lying exciton states. Molecular materials composed by oligoacenes are extensively investigated for their semiconducting and optoelectronic properties. Here, we analyze the exciton states derived from time-dependent density functional theory (TDDFT) calculations for two oligoacene model aggregates: naphthalene and anthracene dimers. To unravel the role of inter-molecular interactions, a set of diabatic states is selected, chosen to coincide with local (LE) and charge-transfer (CT) excitations within a restricted orbital space including two occupied and two unoccupied orbitals for each molecular monomer. We study energy profiles and disentangle inter-state couplings to disclose the (CT) character of singlet and triplet exciton states and assess the influence of inter-molecular orientation by displacing one molecule with respect to the other along the longitudinal translation coordinate. The analysis shows that (CT) contributions are relevant, although comparably less effective for triplet excitons, and induce a non-negligible mixed character to the low-lying exciton states for eclipsed monomers and for small translational displacements. Such (CT) contributions govern the L_a/L_b state inversion occurring for the low-lying singlet exciton states of naphthalene dimer and contribute to the switch from H- to J-aggregate type of the strongly allowed B_b transition of both oligoacene aggregates.

This article describes the enhanced sensitivity to a viscous medium by a molecular rotor based fluorophore (RBF), TPSI I. The TPSI I molecule is designed in such a way that it consists of a rotor and a fluorophore with a π-rich bridge between them. TPSI I is a light-responsive material in solution as well as in the solid state. The structural design of the molecule allows flexible rotation and photo-induced cis–trans isomerization both in the solid state as well as in solution. These combined attributes of TPSI I are responsible for the ultrasensitive viscosity response of the new material, which was verified through the Förster–Hoffmann equation. According to this equation, the derived ‘x’ value is 1.02 (x is related to the sensitivity) which is the highest among the contemporary reports for RBFs. The facts were evidenced both by experimental as well as theoretical data. The ultrasensitivity towards viscosity was further analyzed in in vitro studies by detecting the subtle changes in the alteration of intracellular viscosity in normal and cancerous cells. An alteration of intracellular viscosity in cells treated with viscosity modulators was also confirmed using a previously well-established viscosity measurement technique, dynamic measurement through the piezoelectric patch. Our research offers a detailed mechanism to improve viscosity sensors and an efficient probe for detecting minute changes in intracellular viscosity.

In this study, cyclometallated gold(III) compounds were evaluated for their capability to promote C-Se coupling reactions under biocompatible conditions, and their chemoselectivity towards selenium-containing substrates compared to sulfur-containing analogs. The compounds exhibited varying degrees of selectivity towards selenium-containing compounds, with [Au(bnopy)Cl₂] showing rapid C-Se bond formation. Competitive reactions with selenium and sulfur substrates highlighted the preference for selenium, especially for [Au(Mephpy)Cl₂], even in the presence of excess sulfur substrates. This selectivity was further confirmed in selenopeptide models mimicking the GPx active site, where arylation of selenocysteine was observed. The compounds were further investigated as inhibitors of selenoprotein glutathione peroxidase (GPx) isoenzymes, specifically GPx1 and GPx4. The six-membered metallacycles [Au(bnpy)Cl₂] and [Au(bnopy)Cl₂] exhibited potent inhibition of the GPx1 isoenzyme, particularly when co-incubated with reducing agents, while in vitro GPx4 inhibition was overall less pronounced. Notably, [Au(Mephpy)Cl₂] showed inhibition of GPx1 with no cross-inhibition of the non-selenoprotein glutathione reductase (GR). LC/MS studies identified selenocysteine (Sec51) as the primary arylation site on GPx1 by [Au(bnpy)Cl₂], highlighting its chemoselectivity. Finally, we demonstrated that the selectivity towards Sec could also be translated to an intracellular setting, using a A375 GPx4 WT cell line and an A375 GPx4 U46C mutant. Viability assays revealed a modest decrease in the IC50 for GPx4 WT cells compared to U46C mutants for both [Au(bnpy)Cl₂] and [Au(Mephpy)Cl₂]. More clearly, a proliferation assay over six days showed greater effect in GPx4 WT cells compared to the U46C mutant when treated with [Au(Mephpy)Cl₂], an effect further enhanced by co-treatment with iFSP1. This indicates a GPx4 Sec-dependent response to treatment in A375 cells and warrants further mechanistic studies.