Acid–base strength and acido(fluoro)chromism of three push–pull derivatives of 2,6-distyrylpyridine

Abstract

The acidochromism and acid–base properties of 2,6-distyrylpyridine (2,6-DStP) derivatives bearing on the sides push/pull substituents (namely two dimethylamino, one nitro, and one methoxy and two nitro groups in the case of 2,6-bis[(E)-2-(4-dimetylaminophenyl)ethenyl]pyridine, 2-[(E)-2-(4-nitrophenyl)ethenyl],6-[(E)-2′-(4′-methoxyphenyl)ethenyl]pyridine and 2,6-bis[(E)-2-(4-nitrophenyl)ethenyl]pyridine, respectively) were investigated by stationary and time-resolved spectroscopies. The sensitivity of the absorption and emission spectrum to the medium acidity was found to enhance in the dimethylamino-derivative relative to the unsubstituted 2,6-DStP, also because of the second protonation by the N(CH3)2 group. Spectrophotometric titrations, also processed by a global fitting approach, gave pKa values, for the protonation of the central pyridine, higher in the derivatives with electron-donor unities and lower in compounds bearing electron-acceptor groups. A fluorometric titration was performed in the case of the dimethylamino-derivative thanks to non-negligible emission efficiencies for both neutral and protonated species, unveiling an attractive naked-eye acido(fluoro)chromism from green to yellow upon pyridine protonation, and then to purple with the second protonation involving the lateral N(CH3)2 substituent. Due to the extremely short excited-state lifetimes, as resulted from femtosecond transient absorption experiments, the pKa values for the excited state (pKa*) were estimated through the Förster cycle, revealing that the monoprotonated species of the dimethylamino-derivative would become upon excitation the only stable form in a wide range of pH. Graphical abstract

Synthesis, Photochemistry, Computational Study and Potential Application of New Styryl-Thiophene and Naphtho-Thiophene Benzylamines

“…Both heterostilbenes 6 and 7 with methoxy substituents in metaand para-position showed in the NMR spectra of their photoproducts 13 and 14 signals for the presence of aldehydes (see ESI). The amino-thienostilbenes 2-8 and their photoproducts 9-15 were completely characterized by 1 H and 13 C NMR spectroscopy and HRMS analyses (Figure 5, Experimental and ESI, Figures S1-S79). The formation of the photoproducts 9-15 was generally accompanied by the appearance of some high-molecular-weight products, which were not investigated.…”

“…The second thiophene is stabilized by π-π stacking with Phe329, His438, and Trp82. Newly synthesized styryl-thiophene and naphtho-thiophene benzylamines (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) were also evaluated for biological activity in three different assays. First, the potential anti-inflammatory activity was tested by measuring TNFα production in human PBMCs following compound treatment and LPS stimulation.…”

“…The investigation of the photoreactivity of heterostilbenes showed potential applications in optoelectronics [8], as well as starting materials for photochemical reactions [9,10]. Photophysical properties of furo-and thienostilbenes were investigated [11], and heterostilbenes have found application in so-called NLO materials (nonlinear optical materials) [12,13]. Such materials are crucial in quantum electronics, telecommunications technology [14], and nanotechnology [15,16].…”

“…According to our previous experience in the field of the synthesis and photochemistry of heterostilbene molecules [27][28][29], we herein designed, synthesized, and photochemically transformed the new amino-thienostilbenes (Figure 1I) as interesting structures with potential biological activity and specific chemical and photophysical characteristics. so-called NLO materials (nonlinear optical materials) [12,13]. Such materials are crucial in quantum electronics, telecommunications technology [14], and nanotechnology [15,16].…”

Amphiphilicity-Controlled Localization of Red Emitting Bicationic Fluorophores in Tumor Cells Acting as Bio-Probes and Anticancer Drugs

“…Small organic fluorescent molecules are pivotal for a myriad of research applications ranging from optoelectronics [1,2], light-harvesting [3], sensing [4][5][6][7][8][9], to the medical and biological fields, particularly for bioimaging [10][11][12], disease diagnostics and cancer therapeutics [13,14]. Jointly to long-wavelength emission, which guarantees deeper penetration in biological tissues [15], other properties such as aromaticity, flexibility, photostability in physiological environments, lipophilicity, and solubility in an aqueous medium are sought-after features for designing bioavailable probes and drug-like molecules [16][17][18][19].…”