Ultraviolet And Fluorescence Properties Of Supermolecular System:Silver Nanoclusters With N-(Phenyl-ethylene)-Anilines

Effect of substituents on ultraviolet（UV）absorption spectra and fluorescence（FL）emission spectra of supermolecular system involving N-（phenyl-ethylene）-anilines and silver nanoparticles was investigated.Silver nanoparticles（AgNPs）and 77 samples of model compounds（MC）,N-（phenyl-ethylene）-anilines ZArC（Me）=NArY（ZPEAY,including 40compounds 2-H-XPEAY without ortho-hydroxyl group and 37 compounds 2-OH-XPEAY with ortho-hydroxyl group）were synthesized.The size of AgNPs was characterized by transmission electron microscopy（TEM）.And the UV absorption spectra and the FL emission spectra of AgNPs,ZPEAY and MC-AgNPs solutions were measured respectively.The spectra of ¹³C NMR and ¹H NMR of 2-OH-XPEAY were measured.The ¹³C chemical shift values of C（Me）=N bridge groups,δ_C[2-OH,C（Me）=N]were determined.The effect of substituents X and Y on theδ_C[2-OH,C（Me）=N]were investigated quantitatively.The substituent effects on the UV absorption spectra of MC-AgNPs supermolecular system were investigated quantitatively.The results show that:（i）the size of silver nanoparticles increases in AgNPs-ZPEAY solution,compared with it in AgNPs solution,due to the absorption of ZPEAY molecules on the surface of AgNPs;（ii）the UV absorption wavelength of ZPEAY changes in AgNPs-ZPEAY solution and there is a limitation for the wavelength shift(λ_WSL)between ZPEAY and AgNPs-ZPEAY system;（iii）there is a quantitative correlation between the wavenumberΔν_WSLSL ofλ_WSLSL and the substituent constants(Hammett constantσand excited-state substituent constantσ_CC^exof substituents X and Y;（iv）the intramolecular hydrogen bonding in 2-OH-XPEAY makes theλ_WSLSL a blue shift in AgNPs-ZPEAY system.By using the quantitative correlation analysis ofν_maxax of 2-OH-XPEAY and comparing the change regularity of theirν_maxax with that of 2-H-XPEAY and 2-OH-XBAY（2-OH-XArCH=NArY）,we obtained that the factors influencing theν_maxax of them are different.The addition of methyl group to the bridging group makes group-state polar electronic effect（σ）has important effects on theν_maxax of 2-H-XPEAY,whereas the influence of theσconstants of X and Y on theν_maxax of 2-OH-XBAY is negligible.The steric effect resulting from the methyl group at the bridging group contributes a blue shift to theλ_maxax of 2-OH-XPEAY.The intramolecular hydrogen bonding of 2-OH-XPEAY has influence on theλ_maxax of2-OH-XPEAY.Comparison of ¹³C NMR of C（Me）=N bond chemical shiftsδ_C[2-OH,C（Me）=N]in2-OH-XPEAY with that in 2-H-XPEAY was carried out.The results shows that the factors affecting theδ_C[2-OH,C（Me）=N]of 2-OH-XPEAY are quite different from that ofδ_C[C（Me）=N]of 2-H-XPEAY.A five-parameter correlation equation with correlation coefficient 0.9605 was obtained for quantifying theδ_C[2-OH,C（Me）=N].The result indicates that theδ_C[2-OH,C（Me）=N]of 2-OH-XPEAY is dominated by polar electronic effect of Y[σ（Y）]and excited-state substituent constant of Y[σ_cc^ex（Y）].Also theδ_C[2-OH,C（Me）=N]of2-OH-XPEAY was compared with theδc[C（Me）=N]of C（Me）=N bridge group in2-H-XPEAY.It shows there is no good linear relationship between theδ_C[2-OH,C（Me）=N]andδc[C（Me）=N]due to the intramolecular hydrogen bond in 2-OH-XPEAY.Therefore one cannot only use the change ofδc[C（Me）=N]to deduce the change ofδ_C[2-OH,C（Me）=N]in confirming the organic molecule structures with NMR spectra.