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Please use this identifier to cite or link to this item: http://repository.iitr.ac.in/handle/123456789/20828
Title: Phenanthroimidazole-based bipolar carbazoles featuring cyano substituents to realize efficient deep-blue electroluminescence with an external quantum efficiency of nearly 6%
Authors: Sharma A.
Thomas K.R.J.
Nagar M.R.
Jou J.-H.
Published in: Materials Advances
Abstract: Developing deep-blue bipolar materials with high quantum yields remains a crucial issue in organic light-emitting diodes. The excited-state characteristics of dyes play a pivotal role in controlling the photoluminescence (PL) and electroluminescence (EL) outcomes. Here, a series of carbazole-phenanthroimidazole dyads with and without phenyl spacer units have been designed and synthesized. The functional properties are tunable by substitution of cyano units at various positions on the carbazole. The cyano-featured dyes exhibit a bathochromic shift in their emission spectra that is attributable to the contribution of a charge-transfer component in the excited state, which is further confirmed by solvatochromism studies. Accordingly, the dyes showed larger Stokes shifts due to a significant reorganization of the molecular structure in the excited state. The enhanced CT component is expected to benefit the exciton utilization efficiency of singlet energy states, thereby offering better EL performances. All dyes showed excellent thermal stability upon cyanation of carbazole-phenanthroimidazole derivatives. Electrochemical studies revealed stabilization of the lowest unoccupied molecular orbitals (LUMOs) upon the addition of cyano units to the central carbazole and realized maximum stabilization for the dyes containing cyano units at the C2 and C7 positions. The dyes were utilized as dopant emitters in solution-processed OLED devices and exhibited pure blue emission with a CIEx,y coordinate of (0.16, 0.06) and an external quantum efficiency of 5.7%. This journal is © The Royal Society of Chemistry.
Citation: Materials Advances, 2(19): 6326-6338
URI: https://doi.org/10.1039/d1ma00604e
http://repository.iitr.ac.in/handle/123456789/20828
Issue Date: 2021
Publisher: Royal Society of Chemistry
ISSN: 26335409
Author Scopus IDs: 57210795172
57280016500
57209416736
35083609400
Author Affiliations: Sharma, A., Organic Materials Laboratory, Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, 247667, India
Thomas, K.R.J., Organic Materials Laboratory, Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, 247667, India
Nagar, M.R., Department of Material Science and Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan
Jou, J.-H., Department of Material Science and Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan
Funding Details: K. R. J. T. is thankful to the Science and Engineering Research Board (SERB), New Delhi (CRG/2018/003729), and the Council of Scientific and Industrial Research (CSIR), New Delhi (02(0371)/19/EMR-II), for financial support. A. S. is grateful to the University Grant Commission (UGC), Government of India, for a research fellowship. Council of Scientific and Industrial Research, India, CSIR: 02(0371)/19/EMR-II; University Grants Commission, UGC; Science and Engineering Research Board, SERB: CRG/2018/003729
Corresponding Author: Thomas, K.R.J.; Organic Materials Laboratory, India; email: krjt@cy.iitr.ac.in
Appears in Collections:Journal Publications [CY]

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