%0 Journal Article %J Journal of Physical Chemistry Letters %D 2016 %T Electrostatic interactions are key to C=O n-pi* shifts: an experimental proof %A Haldar, Tapas %A Bagchi, Sayan %X

Carbonyl n-pi* 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-pi* 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-pi*/fluorescence correlation. The IR/n-pi* correlation validates the key role of electrostatic stabilization of the ground state toward n-pi* shifts and demonstrates the electrostatic nature of carbonyl hydrogen bonds. n-pi* shifts show linear sensitivity to calculated electrostatic fields on carbonyls. Our results portray the potential for n-pi* absorption to estimate local polarity in biomolecules and to probe chemical reactions involving carbonyl activation/stabilization.

%B Journal of Physical Chemistry Letters %I AMER CHEMICAL SOC %C 1155 16TH ST, NW, WASHINGTON, DC 20036 USA %V 7 %P 2270-2275 %8 JUN %G eng %N 12 %9 Article %3

Foreign

%4 8.539 %R 10.1021/acs.jpclett.6b01052