Synthesis, characterization and surface enhanced Raman spectroscopy study of a new family of different substituted cruciform molecular systems deposited on gold nanoparticles

Abstract

In this work, the adsorption and orientation on gold nanoparticles (AuNps) of a new family of cruciform systems consisting of thiophene rings and imino groups were studied. The structural modification and its influence on the adsorbate‐substrate interaction were evaluated by UV–Vis spectroscopy and Surface Enhanced Raman Spectroscopy (SERS). The absence of SERS spectrum for (N,N′‐bis(4‐(trifluoromethyl)benzylidene)‐2,5‐di (thiophene‐2‐yl)‐1,4‐diaminobenzene) CFF shows that the inclusion of a trifluoromethyl group (‐CF3) on the benzylidene fragment limits the interaction of the CFF system with the gold substrate, in contrast, to that obtained for (N, N′‐dibenzylidene‐2,5‐di (thiophene‐2‐yl) ‐1,4‐diaminobenzene) 2‐CF and (N, N′‐bis (4‐methoxybenzylidene) ‐2,5‐di (thiophene‐2yl) ‐1,4‐diaminobenzene) CMF, where the adsorption took place preferentially through the thiophene rings, resulting in partial quinoidization. On the other hand, the interaction for compound (N, N′‐bis (4‐methylenepyridinyl) ‐2,5‐di (thiophene‐2‐yl) ‐1,4‐diaminobenzene) CPy with the surface was conducted by means of the pyridinic fragments. The systematic modification of the bifunctional cruciform systems, with groups of different nature, makes it possible to rationalize the structural aspects that directly influence the adsorbate‐substrate interaction and molecular orientation on gold substrates. These structural parameters are the basis to the development of stable molecular assemblies, which can act as basic building blocks in the manufacture of molecular switches.

Concentration and Surface Chemistry Dependent Analyte Orientation on Nanoparticle Surfaces

“…SERS has been used to determine analyte orientation on materials surfaces. Some such studies include analyzing the orientation of phthalazine on silver, benzoic acid on silver, thiophenol on copper, silver, and gold, dipyridinic derivatives on gold nanoparticles, and cruciform systems on gold nanoparticles . However, each of these studies investigated one analyte concentration before determining analyte orientation.…”

“…Some such studies include analyzing the orientation of phthalazine on silver, 28 benzoic acid on silver, 29 thiophenol on copper, silver, and gold, 30 dipyridinic derivatives on gold nanoparticles, 31 and cruciform systems on gold nanoparticles. 32 However, each of these studies investigated one analyte concentration before determining analyte orientation. It is unknown whether the findings hold when the analyte concentration changes.…”

Resveratrol-Schiff Base Hybrid Compounds with Selective Antibacterial Activity: Synthesis, Biological Activity, and Computational Study

“…To do this, compound 7 was treated with SnCl 2 × 2H 2 O in acidic media to obtain compound 8 with a 91% yield. We confirmed this reduction reaction by checking the absence of signals at 1505 and 1346 cm −1 (-NO 2 stretching) [ 46 ]. Once the diamine derivative 8 was synthetized, we went on to obtain the dimeric and monomeric resveratrol-Schiff base derivatives 9 and 10 , respectively.…”

“…In order to obtain the resveratrol-Schiff base dimers and monomers ( 9 – 10 , respectively), it is first is necessary to obtain the 1,4-diaminobenzene core ( 8 , see Scheme 1 ). To do this, we started with 2,5-dibromoaniline ( 6 ) and performed an acetylation reaction using traditional procedures in acidic media, obtaining a 95% yield and confirming the desired product by the presence of a signal at 1667 cm −1 (C=O stretch) [ 30 , 46 ]. After this, the amide of compound 6 was selectively nitrated in para -position from the amide substituent, achieving an 81% yield and ensuring chemoselectivity by the steric hindrance of the -NHAc group, which blocks the ortho -oriented nitration, according to a previous report [ 46 ].…”

“…To do this, we started with 2,5-dibromoaniline ( 6 ) and performed an acetylation reaction using traditional procedures in acidic media, obtaining a 95% yield and confirming the desired product by the presence of a signal at 1667 cm −1 (C=O stretch) [ 30 , 46 ]. After this, the amide of compound 6 was selectively nitrated in para -position from the amide substituent, achieving an 81% yield and ensuring chemoselectivity by the steric hindrance of the -NHAc group, which blocks the ortho -oriented nitration, according to a previous report [ 46 ]. The obtained N -(2,5-dibromo-4-nitrophenyl)acetamide ( 7 ) identity was confirmed by referential signals at 1505 and 1346 cm −1 (-NO 2 stretching) and at 3296 cm −1 and 1673 cm −1 (amide fragment) [ 32 , 47 ].…”