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

Abstract

Donor‐spacer‐acceptor (D‐π‐A) architecture consists of triphenylamine (TPA) and phenanthrimidazole (MPPPI) namely, para‐linked 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 ‐ 426°C (mTPA‐MPPPI); Td ‐ 432 °C (pTPA‐MPPPI) with high glass transition temperature, Tg ‐ 124°C (mTPA‐MPPPI); Tg ‐ 115°C (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‐π‐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, ηc = 3.10 cd A‐1, ηp = 3.94 lm W‐1 and ηex = 4.05 %.

Robust luminogens as cutting-edge tools for efficient light emission in recent decades

“…Jayabharathi et al 144 synthesized D–π–A materials with HLCT behaviour ( p TPA-MPPPI/ m TPA-MPPPI) using phenyl as a spacer, which exhibited excellent thermal and photophysical properties [ λ abs : 271/268 nm; PL s,f : 432, 425/409, 412 nm; PLQY s,f : 82/78%; τ : 2.61/2.53 ns; T g , T d : 124, 426/114, 432 °C; and HOMO, LUMO: 5.20, 2.10/5.25, 2.30 eV, respectively]. The greater decrease in the twist angle in p TPA-MPPPI than m TPA-MPPPI leads to a more coplanar geometry in p TPA-MPPPI than m TPA-MPPPI.…”

Doped and non-doped blue organic light-emitting diodes based on AIEgens with high exciton utilization efficiency and external quantum efficiency

“…For structure-activity analysis, frontier molecular orbital (FMO) investigation of NSPI-DVP and CNSPI-DVP have been carried out by DFT method (Figure 1: Table 1). The excited state analysis have been made by TD-DFT method [26,27]. The twisted conformation of NSPI-4 DVP and CNSPI-DVP show C-H interactions rather than π-π interactions which leads to minimised the tight packing arrangement hence, these materials show mechanochromism i.e., response to external stimuli (grinding, fuming, annealing etc.).…”