Simple water clusters of Coumarins 151 and 152A studied by IR–UV double resonance spectroscopy

The hydrogen-bonded clusters Coumarin 151/(H2O)1 and Coumarin 152A/(H2O)1 have been studied via IR–UV double-resonance spectroscopy. Each cluster exists in two structural forms having distinct electronic properties. Evidence is presented to show that the structures involve water hydrogen bonded to groups at opposite ends of the molecular dipole. These results were supported by semiempirical structure calculations and, for C151, by infrared measurements in the S1 state.