An
electronic spectral and photophysical characterization of three
gold(I) complexes containing heterocyclic chromophores differing in
the number and arrangement of pyridine rings (pyridine, bipyridine,
and terpyridine, with the acronyms pD, bD, and tD respectively) was
performed. Quantum yields of fluorescence, internal conversion and
triplet state formation, together with the rate constants for singlet
to triplet intersystem crossing, S1 ∼ ∼ ∼
S0 internal conversion and fluorescence were measured in
order to equate the impact of fast triplet state formation on the
amount of triplets formed. The results showed a correlation between
the increase on the measured decay values of S1 (leading
to the main formation of T1) and the increase in the charge
transfer (CT) character of the lowest energy transition, as evaluated
from the orthogonality of the frontier orbitals. The measured triplet
state quantum yields range from ∼50–60% to 70%, whereas
the intersystem crossing rate constants differ by almost 2 orders
of magnitude, from 9.4 × 109 s–1 for tD to 8.1 × 1011 s–1 for bD.
This constitutes an evidence for the existence of a correlation between
the intersystem crossing and the internal conversion mechanisms.
We report the first example of an observable and reversible case of thermochromism due to the interaction of an alkylphosphonium (P) with a β-diketonate (1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dionate-fod) of an europium(iii) tetrakis-β-diketonate room temperature ionic liquid. This thermochromism is characterized by the conversion of a light yellow viscous liquid, at room temperature, to a reddish substance close to 80 °C. The reversibility of this optical effect was highlighted by the thermal stability of the Eu(iii) complex.
An unusual thermally sensitive anion–cation interaction, which is characteristic of the anion [Eu(FOD)4]−, occurs in the complex [CHOL][Eu(FOD)4] (1; CHOL=choline; FOD=1,1,1,2,2,3,3‐heptafluoro‐7,7‐dimethyl‐4,6‐octanedionate) and affects both quantum yield and thermochromic behavior. This prompted the design of an Eu3+‐based ratiometric thermometer that functions at temperatures up to 95 °C through a thermally excited state absorption of the Eu3+ ion. The reusable temperature‐sensitive luminescent complex showed a range of relative sensitivity between 0.45 % C−1 at 25 °C, with an increase to 7.0 % C−1 at 95 °C. Confinement of compound 1 in a transparent film of polysulfone resulted in a higher thermal stability of 1 while its luminescence showed a strong temperature dependence.
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