Ultrabroadband two-quantum two-dimensional electronic spectroscopy

A recent theoretical study proposed that two-quantum (2Q) two-dimensional (2D) electronic spectroscopy should be a background-free probe of post-Hartree-Fock electronic correlations. Testing this theoretical prediction requires an instrument capable of not only detecting multiple transitions among molecular excited states but also distinguishing molecular 2Q signals from nonresonant response. Herein we describe a 2Q 2D spectrometer with a spectral range of 300 nm that is passively phase stable and uses only beamsplitters and mirrors. We developed and implemented a dual-chopping balanced-detection method to resolve the weak molecular 2Q signals. Experiments performed on cresyl violet perchlorate and rhodamine 6G revealed distinct 2Q signals convolved with nonresonant response. Density functional theory computations helped reveal the molecular origin of these signals. The experimental and computational results demonstrate that 2Q electronic spectra can provide a singular probe of highly excited electronic states. Published by AIP Publishing.