A research group led by Prof. HAN keli from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) developed a highly efficient triplet acceptor for polarity tuned triplet-triplet annihilation upconversion (TTA UC). The study was published as a letter in The Journal of Physical Chemistry Letters.

Triplet–triplet annihilation upconversion (TTA UC) was intensively investigated for developing efficient photosensitizers and emitters. (Image by LIU Ya) 

Photon upconversion by triplet-triplet annihilation with advantages of low excitation power and high quantum yields has applications in organic light emitting diode, photo(electro)chemistry, solar cell devices and biological imaging.

Recently, the developing of new families of upconversion emitters/triplet energy acceptors for TTA UC has attracted great attention. However, the excited state energy levels of the emitters could only be tuned by chemical modifications. Emission wavelength tunable TTA UC system with only one emitter has not been reported yet.

In this study, the scientists constructed an emission wavelength tunable TTA UC system using a novel hetero-bichromophore dyad with solvatochromic emission as triplet acceptor/emitter. High TTA UC quantum yield (Φuc) up to 25.5% was achieved and the upconversion emission of the solvent polarity tuned TTA UC system could be fine-tuned from cyan to yellow by changing the media polarity.

In addition, they investigated the detail photophysical properties of the HB-An dyad by using steady-state and femtosecond/nanosecond transient absorption spectroscopies and quantum chemical calculations, in order to uncover the relationship between molecular structure and its excited state properties.

The study constructs efficient emission wavelength tunable TTA UC systems and is beneficial for developing new family of TTA UC emitters.

The above work was supported by the National Natural Science Foundation of China. And it is dedicated to the 70th anniversary of DICP. (Text by Liu Ya)