CORE ELECTRON CHEMICAL-SHIFTS IN CONJUGATED MOLECULES AND POLYMERS

Modern experiments and quantum calculations have revealed interesting trends in core electron spectra of oligomers and polymers. In particul ar, the core electron chemical shifts show salient features that are s tructurally dependent, but which have not been completely understood. From pi-electron theory we derive a model for core electron binding en ergy shifts in conjugated molecules and polymers. The alternant behavi or of the site dependent shifts in the linear and polycyclic hydrocarb ons are predicted by the model. The alternations show end-to-bulk ampl ification, respectively, damping for the cyclic and the linear polyene s. The polycyclic hydrocarbons show the strongest alternation effects for the bulk atoms, while for the polyenes the alternation is stronges t for the terminal atoms. The analysis is based on renormalized pertur bation theory and on the analytic solutions of the Huckel equations. T he theory and the proposed model can be applied also for investigation s of the influence of impurities on physical properties of polymers. ( C) 1995 American Institute of Physics.