Tuning photophysics and nonlinear absorption of bipyridyl platinum(II) bisstilbenylacetylide complexes by auxiliary substituents

Density functional theory investigation of photoelectric conversion in graphene quantum dot/Ir(III) complex nanocomposites: the influence of π-conjugation in cyclometalating ligands

Using density functional theory (DFT), this study investigates the photoelectric performance of nanocomposites formed by coupling graphene quantum dots (GQDs) with Ir(III) complexes. The goal is to evaluate the influence of different π-conjugation levels in cyclometalating ligands and determine the most efficient ligand for energy conversion in the nanocomposite. The analysis covers seven distinct Ir(III) complexes, each featuring a common bpy ligand but differing diimine ligands. These complexes are linked to GQDs through amide connections. The study comprehensively examines electronic structure, absorption spectra, charge transfer, and chemical reactivity. Our results show that increased ligand π-conjugation causes a redshift in the absorption spectrum due to smaller highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps, ultimately enhancing light harvesting. This effect becomes more pronounced when GQDs are incorporated. For less-conjugated ligands, attaching GQDs enhances metal-to-ligand charge transfer, facilitating electron injection into TiO2. Moreover, higher conjugation and GQD coupling reduce chemical hardness while increasing chemical potential and electrophilicity, thus improving electron acceptance. Furthermore, strategic structural variations modify free energy changes for electron injection and ground-state regeneration. Notable is the inclusion of perylene and pyrene moieties in the ligand, which accelerates injection and extends recombination lifetimes, while GQD incorporation accelerates injection across all ligands. Additionally, photocurrent generation primarily influences energy conversion efficiency. Finally, adding GQDs enhances the first-order hyperpolarizability, further boosting light harvesting. This study demonstrates the potential of tuning ligand π-conjugation and GQD interfaces to optimize optoelectronic properties and charge transfer dynamics, thereby enhancing solar energy conversion in GQD/Ir(III) complex systems.

Two-photon absorption characterization and comparison of Au(I) fluorenyl benzothiazole complexes in the visible wavelength regime

We use the two-photon excited fluorescence method to determine the two-photon absorption (2PA) cross sections of three series of (fluorenyl benzothiazole) gold(I) complexes in the visible wavelength range from 570 to 700 nm. We compare the effect of ancillary ligand substitutions on the 2PA magnitudes and find that the ancillary ligand does not drastically affect either the magnitude or the shape of 2PA. Even so, moderate 2PA cross sections were measured that ranged from 10 to 1000 s of GM (Göppert-Mayer, =10^-50cm⁴s/photon), making these types of complexes nonlinear optical materials for two-photon absorbing applications.

Electronic and steric effects of platinum(ii) di-yne and poly-yne substituents on the photo-switching behaviour of stilbene: experimental and theoretical insights

A series of mono-, di-, and poly(platina-ynes) incorporating stilbene spacer units with the formulae trans-[R-C[triple bond, length as m-dash]C-Pt(PBu₃)₂-C[triple bond, length as m-dash]C-R] (R = (E)-1,2-diphenylethene), trans-[(Ph)-(Et₃P)₂PtC[triple bond, length as m-dash]C-R-C[triple bond, length as m-dash]CPt(PEt₃)₂(Ph)] (R = (E)-1,2-diphenylethene), and trans-[-(PⁿBu₃)₂PtC[triple bond, length as m-dash]C-R-C[triple bond, length as m-dash]C-]_n (R = (E)-1,2-diphenylethene), respectively, have been synthesized and characterized to explore the effects of ligand topology on the photoisomerization and photophysical properties of these materials. The structural and photophysical properties of the complexes have been investigated and compared with those of the previously reported mono-, di- and poly(platina-ynes) incorporating azobenzene spacers. We found that the organometallic species 1M, 2M and 1P undergo topology-dependent reversible trans-to-cis photoisomerization in CH₂Cl₂ solution. Computational modelling supported the experimental findings.

Towards better understanding of the photophysics of platinum(ii) coordination compounds with anthracene- and pyrene-substituted 2,6-bis(thiazol-2-yl)pyridines

The photophysical properties of platinum(ii) compounds with 4-(9-anthryl)-2,6-bis(thiazol-2-yl)pyridine (1) and 4-(1-pyrenyl)-2,6-bis(thiazol-2-yl)pyridine (2) were widely investigated.

Aggregation and Tunable Color Emission Behaviors of l-Glutamine-Derived Platinum(II) Bipyridine Complexes by Hydrogen-Bonding, π-π Stacking and Metal-Metal Interactions

An l-glutamine-derived functional group was introduced to the bis(arylalkynyl)platinum(II) bipyridine complexes 1-4. The emission could be switched between the ³ MLCT excited state and the triplet excimeric state through solvent or temperature changes, which is attributed to the formation and disruption of hydrogen-bonding, π-π stacking, and metal-metal interactions. Different architectures with various morphologies, such as honeycomb nanostructures and nanospheres, were formed upon solvent variations, and these changes were accompanied by ¹ H NMR and distinct emission changes. Additionally, yellow and red emissive metallogels were formed at room temperature due to the different aggregation behaviors introduced by the substituent groups on bipyridine. The thermoresponsive metallogel showed emission behavior with tunable colors by controlling the temperature. The negative Gibbs free-energy change (ΔG) and the large association constant for excimer formation have suggested that the molecules undergo aggregation through hydrogen-bonding, π-π, and metal-metal interactions, resulting in triplet excimeric emission.

Effects of extending the π-conjugation of the acetylide ligand on the photophysics and reverse saturable absorption of Pt(ii) bipyridine bisacetylide complexes

Extending the acetylide ligand π-conjugation diminishes the terminal substituent effect on the lowest excited states, but expands the triplet excited-state absorption to the near-IR region.

Controllable synthesis of nucleotide complex based on pH control: a small-molecule fluorescent probe as an auxiliary ligand to indicate the pre-organization of the nucleotide complex in solution

Different CMP-bpe-M(ii) (CMP = cytidine monophosphate, bpe = bis(4-pyridyl)ethylene, M(ii) = Mn(2+) and Co(2+)) complexes are synthesized controllably based on pH control and well studied by X-ray single-crystal diffraction analysis. Interestingly, the suitable pH conditions are explored by considering the pre-organization modes of CMP, bpe, and M(2+) in aqueous solution by fluorescence spectroscopy based on acid/basic titration. The organic base bpe serves as a small-molecule fluorescent probe to indicate the changes of pre-organization modes along with the changes of the solution acidity. Furthermore, a perfect self-complementary sugar-base hydrogen bond is first reported based on the crystal structure analysis in this work, and different chiralities and SHG activities of CMP-bpe-Mn(ii) complexes obtained at different pH values are studied.

Photophysical properties of trans-platinum acetylide complexes featuring N-heterocyclic carbene ligands

Platinum acetylide complexes featuring NHC-carbene ligands show enhanced photophysical properties relative to complexes with phosphine ligands.

Synthesis, photophysics and reverse saturable absorption of bipyridyl platinum(II) bis(arylfluorenylacetylide) complexes

A series of Pt(II) bipyridyl complexes with different aryl substituents (Ar = naphthyl (1a), anthryl (1b), pyrenyl (1c) and phenothiazyl (1d)) on the fluorenylacetylide ligands are synthesized and investigated. The influence of the aryl substituent on the photophysics of these complexes is systematically investigated by spectroscopic methods and simulated by time dependent density functional theory (TD-DFT). All complexes exhibit ligand-centered (1)π,π* transitions significantly admixed with the metal-to-ligand charge transfer ((1)MLCT)/ligand-to-ligand charge transfer ((1)LLCT) transitions in the UV and blue spectral region, and broad, structureless (1)MLCT/(1)LLCT absorption bands in the visible spectral region. All complexes are emissive in solution at room temperature, with the fluorescence originating predominantly from the (1)MLCT/(1)LLCT states. The triplet emitting state is dominated by the (3)π,π* state localized on the fluorenylacetylide motif and mixed with some (3)ML'CT character (metal-to-fluorenylacetylide ligand charge transfer) for 1a, 1b and 1d. For 1c, the phosphorescence predominantly originates from the pyrene localized (3)π,π* state. The variation in the photophysical properties is related to the twisting angle of the aryl substituent from the fluorenyl plane, which defines the conjugation between the substituents and fluorenylacetylide ligands and, consequently, alters the energy and intensity of absorption and emission in these complexes. also exhibit broadband triplet excited-state absorption in the visible spectral region. Therefore, they show strong reverse saturable absorption at 532 nm for nanosecond laser pulses as demonstrated by the nonlinear transmission experiment.

Microbial efflux systems and inhibitors: approaches to drug discovery and the challenge of clinical implementation

Conventional antimicrobials are increasingly ineffective due to the emergence of multidrug-resistance among pathogenic microorganisms. The need to overcome these deficiencies has triggered exploration for novel and unconventional approaches to controlling microbial infections. Multidrug efflux systems (MES) have been a profound obstacle in the successful deployment of antimicrobials. The discovery of small molecule efflux system blockers has been an active and rapidly expanding research discipline. A major theme in this platform involves efflux pump inhibitors (EPIs) from natural sources. The discovery methodologies and the available number of natural EPI-chemotypes are increasing. Advances in our understanding of microbial physiology have shed light on a series of pathways and phenotypes where the role of efflux systems is pivotal. Complementing existing antimicrobial discovery platforms such as photodynamic therapy (PDT) with efflux inhibition is a subject under investigation. This core information is a stepping stone in the challenge of highlighting an effective drug development path for EPIs since the puzzle of clinical implementation remains unsolved. This review summarizes advances in the path of EPI discovery, discusses potential avenues of EPI implementation and development, and underlines the need for highly informative and comprehensive translational approaches.