Structure, vibrations and Raman modes in electron doped metal phthalocyanines

Identifying and understanding the vibrational frequency shifts caused by electron addition to metal phthalocyanine (MPc) molecules is the main goal of the present work. Among other things, it should be useful in establishing the amount of charge-transfer level recently reported in potassium doped solid MPc films. Choosing MgPc as our working case, we calculated by density functional methods the full vibration spectrum of the neutral and of the negatively charged molecule, with and without Jahn-Teller distortion. In the negative ion MgPc- we found that although individual modes behave differently, the generality of modes undergoes a negative frequency shift of about 10 cm(-1) for a single extra electron added in the eg affinity level. We calculated the Raman intensities and made qualitative connection with recent data on K-doped CuPc films. The detailed features and parameters of the static Jahn-Teller effect in a phthalocyanine molecular ion are obtained as a byproduct.