The dynamics of palladium phthalocyanine excited states in magnetic fields at low temperatures

Abstract The spectral and transient behavior of both the first excited singlet and the lowest triplet state of randomly oriented palladium phthalocyanine (PdPc) molecules in a Shpol'skii matrix were investigated at liquid-helium temperatures with magnetic fields up to ≈ 63 kG. It is estimated that the expectation value of the orbital angular momentum in S 1 of a free molecule amounts to Λ ≳ 3.1 ℏ from which an orbital reduction factor q of ≈ 0.8 follow. The phosphorescence lifetimes (τ p ) of the observed field-split spin components differ substantially. At T =4.2 K and a field strength of ≈ 63 kG, the central component has τ p = 11.0 ± 1.0 μs and the low-energy component has τ p = 29 ± 2 μs, respectively. It is also found that at high fields very fast spin-lattice relaxation occurs among the triplet spin levels of the ẑ ⊥ H molecules. The interesting field and temperature dependence of the rates were discussed. The spectral intensity behavior and the related dynamic aspects of the energy transfer of the complex at T ≈ 25 K and liquid-helium temperatures were accounted for as well, assuming an acceptable model for the relaxation mechanism.