A study of thermally activated delayed fluorescence in C60

Salazar, Filipa A.; Fedorov, Alexander; Berberan‐Santos, Mário N.

doi:10.1016/s0009-2614(97)00469-7

Cited by 83 publications

(63 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As shown e.g. by Salazar et al (1997), Bachilo et al (2000), Baleizão & Berberan-Santos (2007), and references therein, several reasons may contribute to the importance of PF in fullerenes: 1) very efficient intersystem conversion (ISC) channelling 100% of the energy of absorbed UV photons into the lowest triplet level T 1 (Fig. 2); 2) the very long lifetime of this level; 3) small energy splitting, ∆E ST = E S1 − E T1 , typically ∼0.3 eV for C 60 or C 70 compounds.…”

Section: Appendix A: Interstellar Accretion Of C + To C 60mentioning

confidence: 75%

See 1 more Smart Citation

Interstellar fullerene compounds and diffuse interstellar bands

Omont

2016

A&A

View full text Add to dashboard Cite

Recently, the presence of fullerenes in the interstellar medium (ISM) has been confirmed and new findings suggest that these fullerenes may possibly form from polycyclic aromatic hydrocarbons (PAHs) in the ISM. Moreover, the first confirmed identification of two strong diffuse interstellar bands (DIBs) with the fullerene, C + 60 , connects the long standing suggestion that various fullerenes could be DIB carriers. These new discoveries justify reassessing the overall importance of interstellar fullerene compounds, including fullerenes of various sizes with endohedral or exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of fullerene compounds is complex. In addition to fullerene formation in grain shattering, fullerene formation from fully dehydrogenated PAHs in diffuse interstellar clouds could perhaps transform a significant percentage of the tail of low-mass PAH distribution into fullerenes including EEHFs. But many uncertain processes make it extremely difficult to assess their expected abundance, composition and size distribution, except for the substantial abundance measured for C + 60 . EEHFs share many properties with pure fullerenes, such as C 60 , as regards stability, formation/destruction and chemical processes, as well as many basic spectral features. Because DIBs are ubiquitous in all lines of sight in the ISM, we address several questions about the interstellar importance of various EEHFs, especially as possible carriers of diffuse interstellar bands. Specifically, we discuss basic interstellar properties and the likely contributions of fullerenes of various sizes and their charged counterparts such as C + 60 , and then in turn: 1) metallofullerenes; 2) heterofullerenes; 3) fulleranes; 4) fullerene-PAH compounds; 5) H 2 @C 60 . From this reassessment of the literature and from combining it with known DIB line identifications, we conclude that the general landscape of interstellar fullerene compounds is probably much richer than heretofore realized. EEHFs, together with pure fullerenes of various sizes, have many properties necessary to be suitably carriers of DIBs: carbonaceous nature; stability and resilience in the harsh conditions of the ISM; existing with various heteroatoms and ionization states; relatively easy formation; few stable isomers; spectral lines in the right spectral range; various and complex energy internal conversion; rich Jahn-Teller fine structure. This is supported by the first identification of a DIB carrier as C + 60 . Unfortunately, the lack of any precise information about the complex optical spectra of EEHFs and most pure fullerenes other than C 60 and about their interstellar abundances still precludes definitive assessment of the importance of fullerene compounds as DIB carriers. Their compounds could significantly contribute to DIBs, but it still seems difficult that they are the only important DIB carriers. Regardless, DIBs appear as the most promising way of tracing the interstellar abundances of various fullerene compounds if the breakthr...

show abstract

Section: Appendix A: Interstellar Accretion Of C + To C 60mentioning

confidence: 75%

“…Salazar et al 1997;Anthony et al 2003;Baleizão et al 2011, and references therein). Its very well-behaved properties allow its use e.g.…”

Section: Appendix A: Interstellar Accretion Of C + To C 60mentioning

confidence: 99%

Interstellar fullerene compounds and diffuse interstellar bands

Omont

2016

A&A

View full text Add to dashboard Cite

show abstract

“…4,5 In 2012, our group demonstrated that an OLED with a green TADF emitter composed of a carbazole donors (D) and a dicyanobenzene acceptor (A) can achieve an EQE as high as 19%, corresponding to an IQE of nearly 100%. 6 At the same time, pure blue and orange-red TADF OLEDs have also achieved high EQEs of 10% and 17.5%, respectively.…”

mentioning

confidence: 99%

Dicarbazolyldicyanobenzenes as Thermally Activated Delayed Fluorescence Emitters: Effect of Substitution Position on Photoluminescent and Electroluminescent Properties

Nomura

Miyazaki

et al. 2013

Chemistry Letters

View full text Add to dashboard Cite

We demonstrate two efficient blue-green thermally activated delayed fluorescence (TADF) compounds comprising a dimeric phenylcarbazole and four cyano substituents on the phenyl rings. A comparison of the 2,6-dicyano-substituted derivative (26IPNDCz) with the 3,5-dicyano-substituted derivative (35IPNDCz) shows that 26IPNDCz provides a larger dihedral angle and a lower decrease in the energy difference between the first singlet and triplet excited states (¦E ST ) and the TADF lifetime. An organic light-emitting diode based on 26IPNDCz afforded an external quantum efficiency of 10% with reduced efficiency roll-off.Organic light-emitting diodes (OLEDs) have attracted much interest recently because of their potential application in flat-panel displays and light sources. In OLEDs containing only fluorescent dyes, the internal quantum efficiency (IQE) is limited to 25% because of the exciton branching ratio of singlet states. Phosphorescent OLEDs containing noble-metal-based phosphors can harvest the remaining 75% triplet excitons and can thus achieve 100% internal quantum efficiency.1,2 However, the drawback of phosphorescent OLED materials is their cost. Recent progress in OLEDs development has focused on lowcost solutions to improve the device efficiency. A promising way is to harvest triplet excitons in fluorescent OLEDs by triplettriplet annihilation (TTA) or thermally activated delayed fluorescence (TADF). TTA comprises intermolecular fusion, in which one singlet and one ground state can be produced from two triplet states. Thus, the upper IQE limit of OLEDs made using TTA can increase to 63% (0.25 + 0.75 © 0.5). Assuming that the optical outcoupling is 0.20, the maximum external quantum efficiency (EQE) is estimated to be 13%. 3 In 2009, the EQE of TTA devices was reported to be 11%, which is very close to the theoretical limit.3 On the other hand, triplets can also be converted to singlets by reverse intersystem crossing (RISC) under thermal activation when the energy difference between the first singlet (S 1 ) and triplet (T 1 ) excited states (¦E ST ) is small enough. 4,5 In 2012, our group demonstrated that an OLED with a green TADF emitter composed of a carbazole donors (D) and a dicyanobenzene acceptor (A) can achieve an EQE as high as 19%, corresponding to an IQE of nearly 100%. 6 At the same time, pure blue and orange-red TADF OLEDs have also achieved high EQEs of 10% and 17.5%, respectively. 7a,7b However, their EQE roll-off at high current density is rather significant because of their long TADF lifetimes. We, thus, investigated the photophysical mechanism of TADF emitters in detail and further demonstrate molecular design principles.According to the Boltzmann statistics, a small ¦E ST is essential for the efficient thermally activated repopulation of the emissive S 1 state; this also governs the TADF lifetime. To achieve a small ¦E ST , a small overlap between the occupied and unoccupied orbitals involved in the excitation is necessary, CT in some cases.9,10 A comparison with the carbazolyldicyanobenz...

show abstract

“…Apart from a strong TADF, C 70 exhibits good photostability and has high molar absorption (e.g., 2 10 4 m À1 cm À1 at 470 nm). Note that other fullerenes, for example, a C 70 derivative, [22] fullerene C 60 , [23] and some C 60 derivatives, [24,25] also exhibit TADF, but in all these cases it is much weaker than that of C 70 .…”

Section: Introductionmentioning

confidence: 99%