Triplet-Triplet Annihilation Based Energy Upconversion Mechanism: Cyanine7 Dye Doped with Super Yellow and Rubrene Hosts

In this work, two case studies for energy upconversion mechanisms are presented; one via two photon absorption and the other one via triplet fusion mechanism. These are strongly required photophysical mechanisms in conjugated organic molecules, due to enhance the efficiency of organic electronic devices. During the investigations, Cyanine7 (Cye7) molecule is used as a sensitizer and for the host molecules rubrene and super yellow molecules are preferred due to their comparatively close locally excited triplet energy levels. The results show that upconverted delayed fluorescence arises from triplet-triplet annihilation mechanism in those particular sensitizer-host systems which gives rise to enhance the internal quantum efficiencies by populating the locally excited singlet states. Consequentially, for the first time Cye7 (near infrared) dye is used as a sensitizer in an energy upconversion experiment, and also two photon absorption mechanisms are reported in ppv based 'super yellow' polymer which has two photon absorption cross-section at 780 nmKeywords: Cyanine7 dye, delayed fluorescence, energy up-conversion, rubrene, super yellow

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