Two-dimensional asynchronous spectrum with auxiliary cross peaks in probing intermolecular interactions

Abstract

A new approach called “asynchronous spectrum with auxiliary peaks (ASAP)” is proposed for generating a 2D asynchronous spectrum to investigate the intermolecular interaction between two solutes (P and Q) dissolved in the same solution. In the ASAP approach, a virtual substance S with an isolated peak assumed to be at ν_S is introduced, while the characteristic peaks of P and Q are actually observed at ν_P and ν_Q. The concentrations series of P, Q and S are specifically designed so that a spectral portion that has nothing to do with the intermolecular interaction between P and Q is completely removed from the 2D asynchronous spectrum. Auxiliary cross peaks around (ν_P, ν_S) and (ν_Q, ν_S) can be used to reveal spectral variation caused by intermolecular interaction, which cannot be observed on conventional cross peaks appearing around the spectral coordinates (ν_P, ν_P), (ν_P, ν_Q), (ν_Q, ν_P), (ν_Q, ν_Q). For example, variation of the absorptivity of P caused by an intermolecular interaction between P and Q can be probed from the auxiliary cross peaks around (ν_P, ν_S) when Q does not even have any characteristic peak in the observed spectral range.