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[求助]
将下面英文翻译成中文
The genesis of organometallic complexes and polymers took place over a century ago and their great diversity has made them applicable in many different areas of materials applications since the initial discovery [9–11]. Metal complexes have unique advantages in electronic and photonic applications, since the electronic states can be changed in a controlled fashion within easily accessible ranges [12]. Spin states may also be controlled by the strength and symmetry of the ligand field and the redox states of metal ions. Fig. 1 describes the difference in the energy level and elec-tronic transition involved in organic and organometallic emitters. In organic molecules (with negligible spin–orbit coupling), they emit only from the lowest excited singlet S 1 state. Because T 1 →S 0 emission is extremely weak, triplet excitation is lost through radiationless decay rather than photon emission and consequently the maximum emission quantum yield is limited to 25%. However, in triplet harvesting, electron–hole recombination leads to excitations having a triplet-to-singlet population ratio of 3:1 [13]. Excitation cascades down to the triplet and singlet manifolds, in
which internal conversion (IC) and intersystem crossing (ISC) ultimately give states residing in the lowest triplet metal-to-ligand charge transfer,
3 MLCT (T 1 ), which then emit photons. Facilitated ISC from a singlet excited state to other multiplet states (e.g. the triplet state) in the presence of heavy metal atom may be utilized to tune the excited state energetics, lifetimes, emission spectra and efficiencies [9]. Many of the transition metal complexes exhibit a sufficient excited state lifetime that permits various processes to occur, such as charge and energy transfer [14]. An additional merit in the use of metal complexes is the ability to organize organic ligandsinawell-definedandpredictablegeometry[9].Therefore,itis important to study the structural and electronic nature of the unit |
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