Modulation of trans-to-cis photoisomerization and photoluminescence of 1,2-bis(4-pyridyl)ethylene or 4-styrylpyridine coordinated to fac-tricarbonyl(5-chloro-1,10-phenathroline)rhenium(I)

Photochemical and photophysical properties of fac-[Re(CO)3(Clphen)(trans-L)]+ complexes, Clphen = 5-chloro-1,10-phenathroline and L = 1,2-bis(4-pyridyl)ethylene, bpe, or 4-styrylpyridine, stpy, were investigated to complement the understanding of intramolecular energy transfer process in tricarbonyl rhenium(I) complexes having an electron withdrawing group attached to polypyridyl ligands. These new compounds were synthesized, characterized and the photoisomerization quantum yields were accurately determined by 1H NMR spectroscopy. The true quantum yields for fac-[Re(CO)3(Clphen)(trans-bpe)]+ were constant (Φ = 0.55) at all investigated irradiation wavelengths. However, for fac-[Re(CO)3(Clphen)(trans-stpy)]+, similar true quantum yields were observed only at higher energy irradiation (Φ313 nm = 0.53 and Φ365 nm = 0.57), but it decreased significantly at 404 nm (Φ = 0.41). These results indicated different deactivation pathways for the trans-stpy complex photoisomerization. Quantum yields decreased as the 3ILtrans-L and 3MLCTRe→NN excited states become closer and the behavior was discussed in terms of the excited state energy gaps. Additionally, luminescence properties of photoproducts, fac-[Re(CO)3(Clphen)(cis-L)]+, were also investigated in different environments to analyze the relative energy of the 3MLCTRe→Clphen excited state for each compound.