The mechanism of energy transfer from donor to acceptor is important for various energy applications. Here, a hybrid organic-inorganic upconversion system is investigated, in which energy is transferred from CdSe nanocrystals (NCs) (sensitizer) to the triplet state of a transmitter down an energy cascade to a 9, 10-diphenylanthracene (DPA) annihilator. Then two DPA molecules in their triplet excited states collide with each other during triplet-triplet annihilation (TTA) to emit a photon higher in energy than the incident light. In order to explore the effect of isomeric substitutions on the transmitter for triplet energy transfer (TET) between NC donor and molecular acceptor, two groups of anthracene isomers have been applied as transmitter. The transmitters are anthracene carboxylic acid (ACA) and anthracene dithiocarbamate (ADTC), with substitutions on the 1-, 2- or 9- positions of the anthracene ring. Each isomeric acceptor is expected to bind in a unique orientation with respect to the NC donor. The upconversion quantum yield (QY) of different isomers and TET rate from CdSe NC to different isomers have been investigated separately using steady photon upconversion QY measurements and ultrafast transient absorption spectroscopy. The photon upconversion QYs show a trend where 9-ACA (12%) &gt; 1-isomers (3%)&gt; 2-isomers (1%)&gt; 9-ADTC (0.1%), which is reflected in the rates of TET where a maximum of 3.8 x107 s-1 for 9-ACA was obtained. The molecular excited state energy levels were measured both in solution and polymer hosts to relate structure to TET. This work confirms that molecular substitutions on anthracene dramatically affect excited states levels, which in combination with orbital overlap, critically affect Dexter-based TET.

Effect of substituents on anthracene transmitters on triplet transfer from CdSe nanocrystals

253rd National Meeting (2017)

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