No abstract

Two new pyrrolylquinoline-substituted heteroaromatic-containing compounds bearing a central boron bridge have been prepared by a short, high-yielding sequence consisting of Suzuki-coupling of 8-bromoquinoline and N-Boc 2-pyrroleboronic acid, thermolytic tert-butyloxycarbonyl deprotection, and subsequent boron chelation (either using boron trifluoride or triphenylborane). Both derivatives display longer wavelength absorption maxima (λabsmax) than a previously reported indolopyridine-BPh2 analogue, in agreement with the smaller HOMO-LUMO energy gap predicted by DFT quantum chemical calculations. Both of the pyrrolylquinoline-boron chelates display weak emission (quantum yields 0.3–0.9%) and the BPh2 complex displays a very broad, long-wavelength emission (λemmax = 715 nm, MeCN), which may be due to dimer emission and results in a large pseudo-Stokes’ shift (7753 cm−1) for this compound.

The novel tetrahedral 10-(4-carboxyphenyl)-2,8-diethyl-5,5-difluoro-1,3,7,9-tetramethyl- 5H-di-pyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide [NՈNBF2] BODIPY complex was prepared in a very good yield and via one-pot synthesis. The desired [NՈNBF2] has been used as a model complex for XRD/HSA interactions and DFT/B3LYP/6-311G(d,p) computations. The tetrahedral geometry around the boron center was demonstrated by DFT optimization and XRD-crystallography. The 1H, 11B, and 19F-NMR spectra were used also to support the high symmetrical BODIPY via π‑extended phenomena. Moreover, the values of the DFT-calculated structural bond lengths/angles and DFT-IR were matched to the corresponding experimental XRD and IR parameters, respectively. The crystal lattice interactions were correlated to Hirshfeld surface analysis (HSA) calculations. Calculations of the Mulliken Atomic Charge (MAC), Natural Population Analysis (NPA), Global reactivity descriptors (GRD), and Molecular Electrostatic Potential (MEP) quantum parameters were performed to support the XRD/HSA interactions result. Analysis of the predicted Density of States (DOS), molecular orbital, and time-dependent density functional theory (TD-DFT) calculations have been combined to explain the experimental UV-vis spectra and electron transfer behavior in [NՈNBF2] complex using MeOH and other four solvents.

This study presents the design and characterization of new monochromatic light-harvesting systems based on inorganic porous materials hybridized with organic dye molecules within their structure. A new fluorescent BOPHY dye was prepared, characterized optically and used as both reference and synthetic precursor for two alkoxysilane derivatives that were incorporated separately within a silica structure. The dyes, one bearing one alkoxysilane group and the other one two, were co-condensed with tetraethyl orthosilicate to form a hybrid organo-silica framework, where they are found at specific locations. The structure of the new materials was analysed by powder XRD and TEM, which confirmed the presence of the hexagonal pore arrangement typical of mesoporous MCM-41 silica particles. The steady-state and time-resolved analysis showed that the particles where the dyes are most dispersed within the framework retain the highest fluorescence quantum yield, up to 0.63, in the green-yellow region of the visible spectrum. On the other hand, increasing the content of BOPHY units in the solid matrix seem to favour non-radiative deactivation pathways and aggregation phenomena, which lower the efficiency of light emission. The materials also exhibit interesting properties, such as a dual excited-state decay and fluorescence anisotropy. The short fluorescence lifetime, about 2 ns, matches the typical singlet lifetime of BOPHY dyes, whereas the long component, up to 20 ns, is attributed to delayed fluorescence, which could take place via charge recombination. Optical anisotropy experiments revealed that all materials show polarised light emission to a significant extent and, for most samples, it was also possible to determine a polarisation transfer decay trace, from 400 to 800 ps This is ascribed to the occurrence of energy migration between neighbouring dye units within the silica structure.