Optically Triggered Planarization of Boryl-Substituted Phenoxazine : Another Horizon of TADF Molecules and High-Performance OLEDs

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journal

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Author(s)

  • Deng-Gao Chen
  • Tzu-Chieh Lin
  • Chi-Lin Chen
  • Yi-Ting Chen
  • Yi-An Chen
  • Gene-Hsiang Lee
  • Pi-Tai Chou
  • Chia-Wei Liao
  • Po-Chen Chiu
  • Chih-Hao Chang
  • Yi-Jyun Lien

Detail(s)

Original languageEnglish
Pages (from-to)12886-12896
Journal / PublicationACS Applied Materials and Interfaces
Volume10
Issue number15
Online published27 Mar 2018
Publication statusPublished - 18 Apr 2018

Abstract

We report the unprecedented dual properties of excited-state structural planarization and thermally activated delayed fluorescence (TADF) of 10-dimesitylboryl phenoxazine, i.e., PXZBM. Bearing a nonplanar phenoxazine moiety, PXZBM shows the lowest lying absorption onset at ∼390 nm in nonpolar solvents such as cyclohexane but reveals an anomalously large Stokes-shifted (∼14 500 cm-1) emission maximized at 595 nm. In sharp contrast, when a phenylene spacer is added between phenoxazine and dimesitylboryl moieties of PXZBM, the 10-(4-dimesitylborylphenyl)phenoxazine PXZPBM in cyclohexane reveals a much blue-shifted emission at 470 nm despite its red-shifted absorption maximized at 420 nm (cf. PXZBM). The emission of PXZBM further reveals solvent polarity dependence, being red-shifted from 595 nm in cyclohexane to 645 nm in CH2Cl2. For rationalization, the steric hindrance between phenoxazine and the dimesitylboryl unit in PXZBM caused a puckered arrangement of phenoxazine at the ground state. Upon electronic excitation, as supported by the femtosecond early relaxation dynamics, spectral-temporal evolution and energetics calculated along the reaction potential energy surfaces, the diminution of N → B electron transfer reduces π-conjugation and elongates the N-B bond length, inducing the fast phenoxazine planarization with a time constant of 890 ± 100 fs. The associated charge-transfer reaction from phenoxazine (donor) to dimesitylboryl unit (acceptor) results in a further red-shifted emission in polar solvents. In stark contrast, PXZPBM shows a planar phenoxazine and undergoes excited-state charge transfer only. Despite the distinct difference in excited-state relaxation dynamics, both PXZBM and PXZPBM exhibit efficient TADF capable of producing highly efficient orange and green organic light emitting diodes with peak efficiencies of 10.9% (30.3 cd A-1 and 18.7 lm W-1) and 22.6% (67.7 cd A-1 and 50.0 lm W-1).

Research Area(s)

  • thermally activated delayed fluorescence, N-donor, borane, phenoxazine, charge transfer, solvatochromism

Citation Format(s)

Optically Triggered Planarization of Boryl-Substituted Phenoxazine : Another Horizon of TADF Molecules and High-Performance OLEDs. / Chen, Deng-Gao; Lin, Tzu-Chieh; Chen, Chi-Lin; Chen, Yi-Ting; Chen, Yi-An; Lee, Gene-Hsiang; Chou, Pi-Tai; Liao, Chia-Wei; Chiu, Po-Chen; Chang, Chih-Hao; Lien, Yi-Jyun; Chi, Yun.

In: ACS Applied Materials and Interfaces, Vol. 10, No. 15, 18.04.2018, p. 12886-12896.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journal