Spectral investigations on 2‐methyl‐1,4‐naphthoquinone: solvent effects, host–guest interactions and SERS

Optical absorption and fluorescence emission spectroscopic techniques were employed to investigate the solvent effects on 2‐methyl‐1,4‐naphthoquinone (2‐mNQ) and the molecular recognition of 2‐mNQ in calix(8)arene. The orientation of 2‐mNQ on a silver surface was analysed by SERS. The optical absorption and fluorescence emission spectra of 2‐mNQ in different solvents reveal the n → π* transition and the observed features show that the singlet excited state is more stabilized in polar protic solvents by intermolecular hydrogen bonding and in polar aprotic solvents by dipole–dipole interaction. The evidence for the formation of inclusion complexes of calix(8)arene with 2‐mNQ in dichloromethane was obtained by optical absorption and fluorescence emission studies. From the observations, the existence of association of molecules is proposed and the association constant is evaluated. The orientation of 2‐mNQ on a silver surface was studied by SERS measurements, and was found to be ‘flat‐on.’ Copyright © 2003 John Wiley & Sons, Ltd.