Localization of electronic and vibrational energy in the jet-cooled m-cyanophenol/o-cyanophenol dimer: laser induced fluorescence and fluorescence-dip IR spectra

Abstract

The mixed o-cyanophenol/m-cyanophenol dimer has been studied by laser-induced fluorescence and infrared fluorescence dip spectroscopy, in the region of the hydride stretch. DFT calculations have been carried out in conjunction with the experimental work. The most stable form of the dimer contains o-cyanophenol in its trans form and the cis isomer of m-cyanophenol. It exhibits a planar structure bound by a double hydrogen bond, similar to that observed in the homo (o-cyanophenol)₂ or (m-cyanophenol)₂ dimers. Its vibrational spectrum shows two strong bands assigned to the v(OH) stretch modes localized on each sub-unit. Electronic excitation localized on each moiety has been identified on the basis of dispersed fluorescence spectra. The lower-energy electronic state corresponds to the excitation of the cis m-cyanophenol sub-unit, while that localized on the trans o-cyanophenol moiety occurs 215 cm⁻¹ higher in energy. No electronic energy transfer has been evidenced following excitation of the mixed dimer, up to 409 cm⁻¹ excess energy.

Acknowledgements

We thank the ‘Centre de Ressources Informatiques’ (Orsay University) for the allotment of computer resources.