Exploring matrix isolated carbenes and bis‐carbenes with electronic spectroscopy as a guide

Singlet carbenes exhibit very informative electronic spectra, which vary as a sensitive function of substituents and geometries. In particular, the lowest energy σ–p type excitations for singlet carbenes range broadly from the short wavelength UV to the near IR. Substituent effects on the energy of this key electronic transition can be rationalized by very simple orbital mixing arguments, and parallel similar influences on singlet–triplet energies. Besides providing valuable electronic information on singlet carbenes and bis-carbenes which have been studied by low temperature matrix isolation methods, UV/Vis spectroscopy has often guided investigations of conformation-dependent photochemistry of these species. Insights learned from experimental and calculated UV/visible spectra of a broad range of matrix isolated singlet carbenes and bis-carbenes are described. Copyright © 2010 John Wiley & Sons, Ltd.