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Interplay of Fluorescence and Phosphorescence in Organic Biluminescent Emitters.

ABSTRACT: Biluminescent organic emitters show simultaneous fluorescence and phosphorescence at room temperature. So far, the optimization of the room-temperature phosphorescence in these materials has drawn the attention of research. However, the continuous-wave operation of these emitters will consequently turn them into systems with vastly imbalanced singlet and triplet populations, which is due to the respective excited-state lifetimes. This study reports on the exciton dynamics of the biluminophore NPB (N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1-biphenyl)-4,4-diamine). In the extreme case, the singlet and triplet exciton lifetimes stretch from 3 ns to 300 ms, respectively. Through sample engineering and oxygen quenching experiments, the triplet exciton density can be controlled over several orders of magnitude, allowing us to study exciton interactions between singlet and triplet manifolds. The results show that singlet-triplet annihilation reduces the overall biluminescence efficiency already at moderate excitation levels. Additionally, the presented system represents an illustrative role model to study excitonic effects in organic materials.

SUBMITTER: Salas Redondo C

PROVIDER: S-EPMC6614881 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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Interplay of Fluorescence and Phosphorescence in Organic Biluminescent Emitters.

Salas Redondo Caterin C Kleine Paul P Roszeitis Karla K Achenbach Tim T Kroll Martin M Thomschke Michael M Reineke Sebastian S

The journal of physical chemistry. C, Nanomaterials and interfaces 20170621 27

Biluminescent organic emitters show simultaneous fluorescence and phosphorescence at room temperature. So far, the optimization of the room-temperature phosphorescence in these materials has drawn the attention of research. However, the continuous-wave operation of these emitters will consequently turn them into systems with vastly imbalanced singlet and triplet populations, which is due to the respective excited-state lifetimes. This study reports on the exciton dynamics of the biluminophore NP ...[more]

PMID: 31303904

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Project description:The photophysical properties of a series of gold(i) [LAu(C[triple bond, length as m-dash]CR)] (L = PCy3 (1a-4a), RNC (5a), NHC (6a)) and gold(iii) complexes [Au(C^N^C)(C[triple bond, length as m-dash]CR)] (1b-4b) bearing heterocyclic arylacetylide ligands with narrow band-gap are compared. The luminescence of both series are derived from an intraligand transition localized on the arylacetylide ligand (ππ*(C[triple bond, length as m-dash]CR)) but 1a-3a displayed prompt fluorescence (τ PF = 2.7-12.0 ns) while 1b-3b showed mainly phosphorescence (τ Ph = 104-205 μs). The experimentally determined intersystem crossing (ISC) rate constants (k ISC) are on the order of 106 to 108 s-1 for the gold(i) series (1a-3a) but 1010 to 1011 s-1 for the gold(iii) analogues (1b-3b). DFT/TDDFT calculations have been performed to help understand the difference in the k ISC between the two series of complexes. Owing to the different oxidation states of the gold ion, the Au(i) complexes have linear coordination geometry while the Au(iii) complexes are square planar. It was found from DFT/TDDFT calculations that due to this difference in coordination geometries, the energy gap between the singlet and triplet excited states (ΔE ST) with effective spin-orbit coupling (SOC) for Au(i) systems is much larger than that for the Au(iii) counterparts, thus resulting in the poor ISC efficiency for the former. Time-resolved spectroscopies revealed a minor contribution (<2.9%) of a long-lived delayed fluorescence (DF) (τ DF = 4.6-12.5 μs) to the total fluorescence in 1a-3a. Attempts have been made to elucidate the mechanism for the origins of the DF: the dependence of the DF intensity with the power of excitation light reveals that triplet-triplet annihilation (TTA) is the most probable mechanism for the DF of 1a while germinate electron-hole pair (GP) recombination accounts for the DF of 2a in 77 K glassy solution (MeOH/EtOH = 4 : 1). Both 4a and 4b contain a BODIPY moiety at the acetylide ligand and display only 1IL(ππ*) fluorescence with negligible phosphorescence being observed. Computational analyses attributed this observation to the lack of low-lying triplet excited states that could have effective SOC with the S1 excited state.

Dataset Information

Interplay of Fluorescence and Phosphorescence in Organic Biluminescent Emitters.

Publications

Interplay of Fluorescence and Phosphorescence in Organic Biluminescent Emitters.

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