An investigation on hydrogen bonding between 3-methylindole and ethanol using trilinear decomposition of fluorescence excitation–emission matrices

Abstract

The multi-state fluorescence characteristics of 3-methylindole (MI) make its spectra rich in chemical information and the spectral interpretation rather challenging. The trilinear decomposition method could be appropriate for this task and provide a deeper insight into the hydrogen bonding to MI. Taking the excitation fluorescence spectra together with the emission counterparts to formulate a three-way data array and solving the data array using the Alternating Trilinear Decomposition (ATLD) algorithm is beneficial for studying hydrogen bonding to MI in several aspects. Firstly, making full use of the excitation spectra could guarantee that the experimentally collected data contain sufficient information necessary for investigating signals originated from the weak interactions buried in the strong interaction background. Secondly, the resolution of a three-way data array could theoretically guarantee the uniqueness of the resolved component spectra with actual physical meaning. Thirdly, the ATLD algorithm resolves spectra of complex mixture and determines the spectra of corresponding individual components of different states without disturbing the complex chemical equilibrium involved. The hydrogen bonding interaction of MI with other molecules has been studied using the ATLD algorithm. A detailed investigation has been undertaken for the 1La and 1Lb states as the lowest excited singlet states which dominate the fluorescence emission of MI depending on the effect of other molecules and the surrounding microenvironment. The hydrogen bonding between indole derivatives and other molecules has been examined and some association constants involving hydrogen bond formation have been estimated and compared with theoretical simulation results or experimental observations of previous researchers.