Acceptor number of room temperature ionic liquid determined by the Raman spectrum of diphenylcyclopropenone

Raman spectrum of diphenylcyclopropenone has been measured in various liquids including room temperature ionic liquids. We found a good linear correlation between the solvent acceptor number and the vibrational frequency of the C=C and C=O stretching mode. From the correlation, we have successfully determined acceptor number of several room temperature ionic liquids.