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A Spectroscopic and Computational Study of Propofol Dimers and Their Hydrated Clusters



Propofol (2,6-diisopropylphenol, PPF) homodimers and their complexes with one water molecule are analyzed by means of mass-resolved excitation spectroscopy. Using two-color resonance-enhanced multiphoton ionization (REMPI) the S1 electronic spectra of these systems are obtained, avoiding fragmentation. Due to the large size of these species, the spectra present a large abundance of lines. Using UV/UV hole-burning spectroscopy, two isomers of PPF2 are found and the existence of at least three isomers for propofol2(H2O)1 (PPF2W1) is demonstrated. Comparison with the structures calculated at the M06-2X/6-311++G(d,p) and M06-2X/6-31+G(d) levels of theory shows that the main driving forces in PPF2 are several C[BOND]H⋅⋅⋅π interactions accompanied by dipole–dipole interaction between the OH moieties. On the other hand, there is evidence for the formation of cyclic hydrogen-bond structures in the heterotrimers. A comparison of the results obtained herein with those of similar systems from previously published studies follows.