Spectroscopy and Photophysics of Bifunctional Proton Donor–Acceptor Indole Derivatives

Luminescent 1H-1,3-benzazaphospholes

2-R-1H-1,3-Benzazaphospholes (R-BAPs) are an interesting class of σ²P heterocycles containing P[double bond, length as m-dash]C bonds. While closely related 2-R-1,3-benzoxaphospholes (R-BOPs) have been shown to be highly photoluminescent materials depending on specific R substituents, photoluminescence of R-BAPs has been previously limited to an example having a fused carbazole ring system. Here we detail the synthesis and structural characterization of a new R-BAP (3c, R = 2,2'-dithiophene), and compare its photoluminescence against two previously reported R-BAPs (3a, R, R' = Me and 3b, R = 2-thiophene). The significant fluorescence displayed by the thiophene derivatives 3b (φ = 0.53) and 3c (φ = 0.12) stands in contrast to the weakly emissive methyl substituted analogue 3a (φ = 0.08). Comparative computational investigations of 3a-c offer insights into the interplay between structure-function relationships affecting excited state relaxation processes.

In vitro cytotoxicity of novel 2,5,7-tricarbo-substituted indoles derived from 2-amino-5-bromo-3-iodoacetophenone

A series of novel 2,5,7-tricarbo-substituted indoles were prepared via sequential Sonogashira and Suzuki-Miyaura cross-coupling of 2-amino-5-bromo-3-iodoacetophenone with terminal acetylenes and aryl/styrylboronic acids followed by palladium chloride-mediated heteroannulation of the incipient 5-aryl/styryl-substituted 2-amino-3-(arylalkynyl)acetophenones. These polycarbo-substituted indole derivatives were evaluated for potential in vitro antiproliferative activity against the human breast adenocarcinoma (MCF-7) and human cervical cancer (HeLa) cell lines. Compounds 6f, 6i, 6k, 6m and 6n were found to exhibit significant cytotoxicity and selectivity against the HeLa cells. Compounds 6i and 6m were chosen as representative examples to evaluate their pro-apoptotic efficacy against the HeLa cell line. The compounds induced apoptosis through cell membrane alteration and DNA fragmentation caspase-dependent pathways.

Molecular reorganization of selected quinoline derivatives in the ground and excited states—Investigations via static DFT

Quinoline derivatives are interesting objects to study internal reorganizations due to the observed excited-state-induced intramolecular proton transfer (ESIPT). Here, we report on computations for selected 12 quinoline derivatives possessing three kinds of intramolecular hydrogen bonds. Density functional theory was employed for the current investigations. The metric and electronic structure simulations were performed for the ground state and first excited singlet and triplet states. The computed potential energy profiles do not show a spontaneous proton transfer in the ground state, whereas excited states exhibit this phenomenon. Atoms in Molecules (AIM) theory was applied to study the nature of hydrogen bonding, whereas Harmonic Oscillator Model of aromaticity index (HOMA) provided data of aromaticity evolution as a derivative of the bridge proton position. The AIM-based topological analysis confirmed the presence of the intramolecular hydrogen bonding. In addition, using the theory, we were able to provide a quantitative illustration of bonding transformation: from covalent to the hydrogen. On the basis of HOMA analysis, we showed that the aromaticity of both rings is dependent on the location of the bridge proton. Further, the computed results were compared with experimental data available. Finally, ESIPT occurrence was compared for the three investigated kinds of hydrogen bridges, and competition between two bridges in one molecule was studied.