Derivados de aminofenil-naftoquinonas: síntese, propriedades fotofísicas e possíveis aplicações

Abstract

Naphtho-1,4-quinones are compounds easily found in nature and exhibit significant potential for biological and technological applications due to their redox, photophysical, and photochemical properties. The presence of two carbonyl groups in their structure imparts electron-accepting characteristics to these molecules, making them suitable for the design of new donor-acceptor (push-pull) dyes. These dyes essentially consist of an electron-rich fragment (donor) and an electron-deficient fragment (acceptor). When these groups are connected within the same molecule, photoexcitation results in intramolecular charge transfer (ICT), which reorganizes the electronic density in the excited state compared to the ground state. In this study, we present the synthesis, photophysical properties, and potential applications of naphtho-1,4-quinone derivatives with various electron-donating groups: Nmethylaniline (1), N,N’-dimethylaniline (2), 1,2,3,4-tetrahydroquinoline (3), 1-methyl-1,2,3,4- tetrahydroquinoline (4), diphenylaniline (5), triphenylaniline (6), 9-H-carbazole (7), and 10-Hphenothiazine (8). The products were synthesized via oxidative coupling in acetonitrile (ACN) in the presence of 10 mol% triflic acid, achieving yields ranging from 30-81%. Structural characterization was performed using FTIR, NMR (¹H/¹³C), HRMS, and XRD techniques. The photophysical studies were conducted using UV-vis absorption and steady-state/time-resolved fluorescence techniques. All synthesized molecules absorb in the visible region (400-700 nm). Molecules 1, 3, and 5 demonstrated potential as polarity-sensitive colorimetric sensors and were evaluated as possible ethanol sensors in polar media, showing applicability in detecting gasoline adulteration. Additionally, 1 to 5 exhibited negative acidichromism upon the addition of trifluoroacetic acid, while 6 and 7 showed positive acidichromism upon the addition triflic acid in ACN, with reversibility upon the addition of triethylamine. The pKa(ACN) values of these molecules were determined using UV-vis spectroscopy. Large Stokes shifts were observed in cyclohexane (88-181 nm), and the effect in paraffin pellets were evaluated. Compounds 5, 6, and 7 showed promise as fluorimetric sensors for detecting gasoline adulteration with longchain hydrocarbons. Furthermore, the intermolecular interaction between compounds 1 and 6 with human serum albumin (HSA) was investigated using spectroscopy. Finally, compounds 1, 5, 6, and 7 exhibited large singlet oxygen generation yields, making them promising candidates for use as type II photosensitizers, thereby broadening their potential technological and biomedical applications.