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Insight into the mechanism and outcoupling enhancement of excimer-associated white light generation.

ABSTRACT: Fundamental insight into excimer formation has been gained by using 9,10-bis[4-(9-carbazolyl)phenyl]anthracene] (Cz⁹PhAn) as a probe. Cz⁹PhAn exhibits a highly emissive blue fluorescence in solution and is found to emit a panchromatic white light spectrum (400-750 nm) in film, powder and single crystal, in which an additional excimer band appears at ?550 nm. Detailed structural analyses, emission relaxation dynamics and a theoretical approach conclude the formation of an anthracene*/phenyl ring excimer through an overlap between ?* (anthracene) and ? (phenyl ring) orbitals in a face-to-edge stacking orientation. The rate of excimer formation is determined to be 2.2 × 10⁹ s^-1 at room temperature, which requires coupling with lattice motion with an activation energy of 0.44 kcal mol^-1. Exploiting Cz⁹PhAn as a single emitter, a fluorescent white organic light emitting diode (WOLED) is fabricated with a maximum external quantum efficiency (?_ext) of 3.6% at 1000 cd m^-2 (4.2 V) and Commission Internationale de L'Eclairage (CIE) coordinates of (0.30, 0.33). The white-light Cz⁹PhAn reveals a preferred orientation of the transition dipole moment in the emitting layer to enhance light outcoupling. This non-doped, single component (Cz⁹PhAn) WOLED greatly reduces the complexity of the fabrication process, rendering a green and cost-effective alternative among the contemporary display/lighting technologies.

SUBMITTER: Chen YH

PROVIDER: S-EPMC6007176 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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Insight into the mechanism and outcoupling enhancement of excimer-associated white light generation.

Chen Ying-Hsiao YH Tang Kuo-Chun KC Chen Yi-Ting YT Shen Jiun-Yi JY Wu Yu-Sin YS Liu Shih-Hung SH Lee Chun-Shu CS Chen Chang-Hsuan CH Lai Tzu-Yu TY Tung Shih-Huang SH Jeng Ru-Jong RJ Hung Wen-Yi WY Jiao Min M Wu Chung-Chih CC Chou Pi-Tai PT

Chemical science 20160212 6

Fundamental insight into excimer formation has been gained by using 9,10-bis[4-(9-carbazolyl)phenyl]anthracene] (Cz9PhAn) as a probe. Cz9PhAn exhibits a highly emissive blue fluorescence in solution and is found to emit a panchromatic white light spectrum (400-750 nm) in film, powder and single crystal, in which an additional excimer band appears at ∼550 nm. Detailed structural analyses, emission relaxation dynamics and a theoretical approach conclude the form ...[more]

PMID: 29997847

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Project description:The dark-colored viologen radical cations are unstable in air and easily fade, thus greatly limiting their applications. If a suitable substituent is introduced into the structure, it will have the dual function of chromism and luminescence, which will broaden its application field. Here, Vio1·2Cl and Vio2·2Br were synthesized by introducing aromatic acetophenone and naphthophenone substituents into the viologen structure. The keto group (-CH2CO-) on the substituents is prone to isomerize into the enol structure (-CH[double bond, length as m-dash]COH-) in organic solvents, especially in DMSO, resulting in a larger conjugated system to stabilize the molecular structure and enhance fluorescence. The time-dependent fluorescence spectrum shows obvious keto-to-enol isomerization-induced fluorescence enhancement. The quantum yield also increased significantly (T = 1 day, ΦVio1 = 25.81%, ΦVio2 = 41.44%; T = 7 days, ΦVio1 = 31.48%, and ΦVio2 = 54.40%) in DMSO. The NMR and ESI-MS data at different times further confirmed that the fluorescence enhancement was caused by isomerization, and no other fluorescent impurities were produced in solution. DFT calculations show that the enol form is almost coplanar throughout the molecular structure, which is conducive to stabilizing the structure and enhancing fluorescence. The fluorescence emission peaks of the keto and enol structures of Vio12+ and Vio22+ were at 416-417 nm and 563-582 nm, respectively. The fluorescence relative oscillator strength of Vio12+ and Vio22+ enol structures is significantly higher than that of keto structures (f value changes from 1.53 to 2.63 for Vio12+ and from 1.62 to 2.81 for Vio22+), indicating stronger fluorescence emission of the enol structure. The calculated results are in good agreement with the experimental results. Vio1·2Cl and Vio2·2Br are the first examples of isomerization-induced fluorescence enhancement of viologen derivatives, which shows strong solvatofluorochromism under UV light, making up for the disadvantage that it is easy for a viologen radical to fade in air, and providing a new strategy for designing and synthesizing viologen materials with strong fluorescence.

Dataset Information

Insight into the mechanism and outcoupling enhancement of excimer-associated white light generation.

Publications

Insight into the mechanism and outcoupling enhancement of excimer-associated white light generation.

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