A series of pyrimidine derivatives bearing one, two or three triphenylamine/9-ethylcarbazole substituents has been synthesized by Suzuki cross-coupling reaction. All compounds showed absorption bands in the UV region and the emission of violet-blue light upon irradiation. Protonation led to quenching of the fluorescence, although some derivatives remained luminescent with the appearance of a new red-shifted band in the spectra. Accurate control of the amount of acid enabled white photoluminescence to be obtained both in solution and in solid state.
The development of
fluorescence materials with
switched
on
/
off
emission has attracted great attention
owing to the potential application of these materials in chemical
sensing. In this work, the photophysical properties of a series of
original 2-(2′-hydroxyphenyl)pyrimidines were thoroughly studied.
The compounds were prepared by following well-established and straightforward
methodologies and showed very little or null photoluminescence both
in solution and in the solid state. This absence of emission can be
explained by a fast proton transfer from the OH group to the nitrogen
atoms of the pyrimidine ring to yield an excited tautomer that deactivates
through a nonradiative pathway. The key role of the OH group in the
emission quenching was demonstrated by the preparation of 2′-unsubstituted
derivatives, all of which exhibited violet or blue luminescence. Single
crystals of some compounds suitable for an X-ray diffraction analysis
could be obtained, which permitted us to investigate inter- and intramolecular
interactions and molecular packing structures. The protonation of
the pyrimidine ring by an addition of trifluoroacetic acid inhibited
the excited-state intramolecular proton transfer (ESIPT) process,
causing a reversible
switch on
fluorescence response
detectable by the naked eye. This acidochromic behavior allows 2-(2′-hydroxyphenyl)pyrimidines
to be used as solid-state acid–base vapor sensors and anticounterfeiting
agents. Extensive density functional theory and its time-dependent
counterpart calculations at the M06-2
X
/6-31+G** level
of theory were performed to rationalize all the experimental results
and understand the impact of protonation on the different optical
transitions.
White-light emission from single molecular systems has attracted a great deal of attention due to their advantages over multicomponent emitters. Azaheterocyclic push-pull derivatives have been demonstrated to be white emitters by combining neutral and protonated forms in the appropriate ratio, although limited cases of white-light emission have been reported from quinazoline derivatives. Herein, we describe a series of push-pull 4-substituted and 4,7-disubstituted quinazolines that show white photoluminescence both in solution and in the solid state. All of the materials were prepared by straightforward Suzuki-Miyaura crosscoupling reactions and the compounds exhibited remarkable emission solvatochromism. In some cases the presence of acid prompted the appearance of emission bands of complementary colors. Thus, multicolor photoluminescence, including white light, could be finely tuned by the controlled protonation of the electron-deficient quinazoline ring.
The photophysical properties of a series of conjugated push-pull (iso)quinolines have been studied. The compounds were synthesized by well-established and straightforward methodologies. The materials exhibited not only emission solvatochromism in a variety of non-polar solvents, but also tunable halochromism. Some of the compounds remained moderately luminescent after protonation and these had a red emissive form, which was used to obtain white light emission, both in solution and in thin film, by the controlled protonation of the initially blue-green emitting materials. This methodology has potential applications in white OLED fabrication with two forms of a single emitter in equilibrium.
Molecular hybridization consists of the combination of two or more non-identical pharmacophores in a single molecule. It has emerged as a promising strategy that allows the design of molecular frameworks with enhanced activity and affinity compared to their parent drugs. In this work, two novel hybrids that combine the well-known anticancer chemotherapeutic agent 5-fluorouracil with antioxidant coumarin derivatives have been synthesized and characterized by means of a copper-catalyzed azide-alkyne cycloaddition (CuAAC). The conjugates showed good antioxidant properties and a high tendency to aggregate and form stable nanoparticles in aqueous media, with regular shape and uniform size. These materials have proven to be preferential cytotoxic agents in vitro against human pancreatic cancer cells PANC-1, with an activity superior to free 5-fluorouracil. These results open up the possibility of exploiting the synergistic combination between 5-fluorouracil and coumarin derivatives and warrant further investigation of these hybrids as promising pancreatic anticancer agents.
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