V-Shaped Methylpyrimidinium Chromophores for Nonlinear Optics

Synthesis of Pyridin-1(2H)-ylacrylates and the Effects of Different Functional Groups on Their Fluorescence

While fluorescent organic materials have many potential as well as proven applications and so have attracted significant attention, pyridine-olefin conjugates remain a less studied subset of such systems. Herein, therefore, we report on the development of the straightforward syntheses of pyridin-1(2H)-ylacrylates and the outcomes of a study of the effects of substituents on their fluorescent properties. Such compounds were prepared using a simple, metal-free and three-component coupling reaction involving 2-aminopyridines, sulfonyl azides and propiolates. The fluorescent properties of the ensuing products are significantly affected by the positions of substituents on the cyclic framework, with those located in central positions having the greatest impact. Electron-withdrawing groups tend to induce blue shifts while electron-donating ones cause red shifts. This work highlights the capacity that the micro-modification of fluorescent materials provides for fine-tuning their properties such that they may be usefully applied to, for example, the study of luminescent materials.

The arylvinylpyrimidine scaffold: a tunable platform for luminescent and optical materials

The incorporation of electron-withdrawing pyrimidine rings within π-extended systems allows access to a wide variety of fluorescent push-pull molecules that display emission properties highly sensitive to external stimuli. A suitable design of these compounds leads to interesting materials for a variety of optoelectronic applications. In this context, a vast number of arylvinylpyrimidine-based chromophores have been extensively studied during the last two decades. Along with the main synthetic pathways, this review summarizes the photophysical features of these active compounds having great potential and their most important applications as sensors and luminescence materials.

Tuning the Photophysics of Two-Arm Bis[(dimethylamino)styryl]benzene Derivatives by Heterocyclic Substitution

The identification of novel molecular systems with high fluorescence and significant non-linear optical (NLO) properties is a hot topic in the continuous search for new emissive probes. Here, the photobehavior of three two-arm bis[(dimethylamino)styryl]benzene derivatives, where the central benzene was replaced by pyridine, furan, or thiophene, was studied by stationary and time-resolved spectroscopic techniques with ns and fs resolution. The three molecules under investigation all showed positive fluorosolvatochromism, due to intramolecular charge-transfer (ICT) dynamics from the electron-donor dimethylamino groups, and significant fluorescence quantum yields, because of the population of a planar and emissive ICT state stabilized by intramolecular hydrogen-bond-like interactions. The NLO properties (hyperpolarizability coefficient and TPA cross-section) were also measured. The obtained results allowed the role of the central heteroaromatic ring to be disclosed. In particular, the introduction of the thiophene ring guarantees high fluorescent quantum yields irrespective of the polarity of the medium, and the largest hyperpolarizability coefficient because of the increased conjugation. An important and structure-dependent involvement of the triplet state was also highlighted, with the intersystem crossing being competitive with fluorescence, especially in the thiophene derivative, where the triplet was found to significantly sensitize molecular oxygen even in polar environment, leading to possible applications in photodynamic therapy.