biostudies-literatureUnknown7(1)Ma ZIn attempt to the obtain detailed geometric information of proton transfer compound (subsequently denote as SQBP) formed between squaric acid (SQ)and 4,4'-bipyridine(BP), and to investigate the mechanisms of pressure-induced double proton transfer and related structural phase transition, we carried out in-situ high pressure Raman spectroscopy of SQBP up to 20 GPa. A solid-solid phase transition together with double proton transfer phenomenon was confirmed by Raman spectroscopy at about 1.5 GPa, and the activation of C?=?O stretching mode in Raman spectra indicates a square-ring structure of SQ with four symmetric C?=?O bond formation. These results are further supported by first-principals calculations and in-situ high pressure infrared absorption spectroscopy. Additionally, Raman intensity analysis suggests that a higher-order phase transition with planar BP molecular structure occurred in the pressure range of 3~6?GPa. As a result, the ? electron delocalization effect in BP dominated the intensity enhancement of C?=?O stretching mode in SQ. To the best of our knowledge, this is the first time observation of the intensity enhancement of proton donor's normal modes induced by proton acceptor's ? electron delocalization.Scientific reports4677https://www.ebi.ac.uk/biostudies/studies/S-EPMC5498627biostudies-literatureHigh Pressure Spectroscopic Investigation on Proton Transfer in Squaric Acid and 4,4'-Bipyridine Co-crystal.PMC5498627Zhou MLi JSun CMa ZLiu CfalseHigh Pressure Spectroscopic Investigation on Proton Transfer in Squaric Acid and 4,4'-Bipyridine Co-crystal.In attempt to the obtain detailed geometric information of proton transfer compound (subsequently denote as SQBP) formed between squaric acid (SQ)and 4,4'-bipyridine(BP), and to investigate the mechanisms of pressure-induced double proton transfer and related structural phase transition, we carried out in-situ high pressure Raman spectroscopy of SQBP up to 20 GPa. A solid-solid phase transition together with double proton transfer phenomenon was confirmed by Raman spectroscopy at about 1.5 GPa, and the activation of C?=?O stretching mode in Raman spectra indicates a square-ring structure of SQ with four symmetric C?=?O bond formation. These results are further supported by first-principals calculations and in-situ high pressure infrared absorption spectroscopy. Additionally, Raman intensity analysis suggests that a higher-order phase transition with planar BP molecular structure occurred in the pressure range of 3~6?GPa. As a result, the ? electron delocalization effect in BP dominated the intensity enhancement of C?=?O stretching mode in SQ. To the best of our knowledge, this is the first time observation of the intensity enhancement of proton donor's normal modes induced by proton acceptor's ? electron delocalization.2017-01-01T00:00:00Z2017 Jul2021-02-19T22:19:02Z2019-03-27T02:49:33ZS-EPMC54986272868004410.1038/s41598-017-04980-3