Effect of substituents on the ultraviolet (UV) spectra of supermolecular system involving silver nanoparticles (AgNPs) and Schiff bases was investigated. AgNPs and 49 samples of model compounds (MC), bi-aryl Schiff bases containing hydroxyl (XBAY, involving 4-OHArCH¼NArY, 2-OHArCH¼NArY, XArCH¼NAr-4′-OH, and XArCH¼NAr-2′-OH), were synthesized. The size of AgNPs was characterized by transmission electron microscopy (TEM), and the UV absorption spectra of AgNPs, XBAYs, and MC-AgNPs mixed solutions were measured, respectively. The results show that (1) the size of AgNPs is larger in MC-AgNPs solutions than that in AgNPs solution due to the distribution of MC molecules on the surface of AgNPs; (2) the UV absorption wavelength of XBAYs changes in the action of AgNPs and their wavelength shift exists limitation between XBAY and MC-AgNPs solutions; and (3) the wavelength shift limit of MC-AgNPs (λ WSL ) is influenced by the substituents X and Y and the position of hydroxyl OH. The wavenumber Δν WSL of λ WSL can be quantified by employing the excited-state substituent constant σ ex CC and Hammett constant σ of substituents X and Y. Comparing with the 4-OH, the 4′-OH makes the Δν WSL a red shift, whereas the 2′-OH, comparing with the 2-OH, makes the Δν WSL a blue shift.
A series of biaryl Schiff bases containing the nitro groups, 4‐XArCH═NArNO2‐4′ (XBANO2‐4′) and 4‐NO2ArCH═NArY‐4′ (4‐NO2BAY), were synthesized. Also, the fish sperm DNA (fsDNA) and silver nanoparticles (AgNPs) solutions were prepared. By mixing these compounds with fsDNA or AgNPs solution and determining the ultraviolet absorption spectra of the mixture solutions, an interesting phenomenon was found: a new absorption peak λmax,lim appeared in the (XBANO2‐4′)‐AgNPs solution, which was longer than the wavelength of λmax of XBANO2‐4′ solution. The new absorption peak in the (XBANO2‐4′)‐AgNPs solution was the complex spectrum originating from the electron transfer between XBANO2‐4′ and AgNPs. Whereas this phenomenon was not observed in the (4‐NO2BAY)‐AgNPs solutions, a quantitative correlation analysis was carried out with the measured spectral data, and the results show that the wave number νmax,lim of the λmax,lim is mainly affected by the excited‐state substituent constant
σCCex()X rather than the ground Hammett constant σ of the X group. The redshift magnitude Δνmax,WSL, namely, Δνmax,WSL = (1/λmax) − (1/λmax,lim), of the wavelength λmax,lim is related to the highest occupied molecular orbital and lowest unoccupied molecular orbital of XBANO2‐4′. The discovery of this new phenomenon is helpful to understanding the interaction between AgNPs‐organic compound supramolecular systems.
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