A density functional study of the optical spectra and nonlinear optical properties of heteroleptic tetrapyrrole sandwich complexes: The porphyrinato-porphyrazinato-zirconium(IV) complex as a case study

Time-dependent density functional theory calculations are presented for the excitation energies and oscillator strengths of the title mixed sandwich. They prove to agree very well with the experimental data, providing that an accurate description of the salient features of the UV-vis spectrum is giv en. The nature of the excitations, intraligand (excitonic) or interligand ( charge-resonance), is discussed and compared to previous theoretical deduct ions for bisporphyrins. An experimental measurement of the first hyperpolar izability beta (-2 omega; omega, omega), related to a second harmonic gener ation, yielded a large, negative beta at omega = 0.65 eV and, by extrapolat ion, also a large, negative static value. This suggests that this complex h as very interesting nonlinear optical properties. Our calculations, however , show beta to have a pole very close to the laser frequency used in the ex periment, with large, negative beta values only in its vicinity. Off-resona nce values of beta at omega < 0.6 eV are small and positive.