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Here, we report our investigations on the development of novel, metal-free, organic materials able to harvest triplet states using efficient thermal activated delayed fluorescence (TADF), and dual fluorescence-phosphorescence emissions at room temperature (RT-DFP). These materials show enormous potential in different technological applications, including the development of materials for oxygen,[1] and temperature[2] sensing, optical power limiters,[3] bio-imaging,[4] and in organic light emitting diodes (OLEDs).[5]
TADF, also known as E-type delayed fluorescence, has gained very rapid interest as a mechanism to improve efficiencies in OLEDs, due to the possibility of harvesting approx. 100% of the excitons formed from charge recombination, without requiring the use of expensive and scarce materials such as iridium or platinum.[6] As TADF, the observation of RT-DFP in pure organic materials has also potential for many technological applications, and in particular in sensing applications. Recently, organic materials with long lived triplet photo-induced absorption were used to develop optical power limiters for low light levels.[7] Magnetic modulation over visible room temperature phosphorescence using weak magnetic fields was also reported.[8] Moreover, RT-DFP in principle, can be also used as a way to harvest triplet states in OLEDs and produce light directly from both singlet and triplet states, which may allow the design of metal free organic white emitters for lighting applications.
In this talk, the complex and rich photophysics of materials showing very efficient TADF and RT-DFP is discussed in detail, showing how a simple change on the molecular structure allows switching-off the strong TADF and opening the channel for efficient RT-DFP to be observed.[9] The role of the energy ordering of electronic states on the efficiency of both mechanisms is also discussed, giving clear guidelines for the design of new emitters, and opening the way for TADF and RT-DFP to be explored in technological applications.
References
[1] Feng, Y. et al., Analyst, 2012, 137, 4885.
[2] Wolfbeis, O.S., Adv. Mater. 2008, 20, 3759.
[3] Zhou, G. et al., Adv. Funct. Mater. 2009, 19, 531.
[4] Zhang,G. et al,. Nat. Mater. 2009, 8, 747.
[5] Chaudhuri, D. et al., Angew. Chem. Int. Ed. 2013, 52, 1.
[6] Dias, F.B. et al. Adv. Mater. 2013, 25, 3707.
[7] Hirata,S. et al., Nat. Mater. 2014, 13, 938.
[8] Mani, T. et al., J. Phys. Chem. Lett. 2012, 3, 3115.
[9] Ward, J.S. et al., Chem. Commun., 2016,52, 2612-2615
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