Electrostatic Interactions Are Key to CO n‑π* Shifts: An Experimental Proof Tapas Haldar Sayan Bagchi 10.1021/acs.jpclett.6b01052.s001 https://acs.figshare.com/articles/journal_contribution/Electrostatic_Interactions_Are_Key_to_C_O_n_Shifts_An_Experimental_Proof/3413047 Carbonyl n-π* transitions are known to undergo blue shift in polar and hydrogen-bonding solvents. Using semiempirical expressions, previous studies hypothesized several factors like change in dipole moment and hydrogen-bond strength upon excitation to cause the blue shift. Theoretically, ground-state electrostatics has been predicted to be the key to the observed shifts, however, an experimental proof has been lacking. Our experimental results demonstrate a consistent linear correlation between IR (ground-state phenomenon) and n-π* frequency shifts (involves both ground and excited electronic-states) of carbonyls in hydrogen-bonded and non-hydrogen-bonded environments. The carbonyl hydrogen-bonding status is experimentally verified from deviation in n-π*/fluorescence correlation. The IR/n-π* correlation validates the key role of electrostatic stabilization of the ground state toward n-π* shifts and demonstrates the electrostatic nature of carbonyl hydrogen bonds. n-π* shifts show linear sensitivity to calculated electrostatic fields on carbonyls. Our results portray the potential for n-π* absorption to estimate local polarity in biomolecules and to probe chemical reactions involving carbonyl activation/stabilization. 2016-06-01 00:00:00 ground state IR probe chemical reactions correlation Electrostatic Interactions carbonyl hydrogen bonds shift