Hybridised-Local and Charge-Transfer Excited States in Donor-Spacer-Acceptor Molecules for Efficient OLEDs: Combined Experimental and Theoretical Study

摘要

Donor-spacer-acceptor (D-p-A) architecture consists of triphenylamine (TPA) and phenanthrimidazole (MPPPI) namely, paralinked pTPA-MPPPI and meta-linked mTPA-MPPPI was designed and synthesized using phenyl as spacer. The photophysical and electroluminescent behaviour of these two isomers were comparatively investigated. These compounds exhibit excellent thermal stabilities, decomposition temperature, Td - 4268C (mTPA-MPPPI); Td - 432 8C (pTPA-MPPPI) with high glass transition temperature, Tg - 1248C (mTPA-MPPPI); Tg - 1158C (pTPA-MPPPI). Meta linked mTPA-MPPPI isomer exhibit NUV emission compared to para linked isomer, however, with the loss of efficiency. Theoretical calculation and photophysical experiments have been implemented to verify the excited state properties of pTPA-MPPPI and mTPA-MPPPI and indicates that these twisting D-p-A molecules exhibit a hybridised local and charge transfer (HLCT) excited state. The mTPA-MPPPI based device exhibit EL emission at 407 nm with FWHM of 42 nm corresponding to CIE coordinates of (0.16, 0.087) whereas the pTPA-MPPPI device exhibit higher electroluminescent efficiencies, hc = 3.10 cd A-1, hp = 3.94 lm W-1 and hex = 4.05 %.