Non-symmetric 9,10-diphenylanthracene-based deep-blue emitters with enhanced charge transport properties

Abstract

Realization of efficient deep-blue anthracene-based emitters with superior film-forming and charge transport properties is challenging. A series of non-symmetric 9,10-diphenylanthracenes (DPA) with phenyl and pentyl moieties at the 2nd position and alkyl groups at para positions of the 9,10-phenyls were synthesized and investigated. The non-symmetric substitution at the 2nd position enabled to improve film forming properties as compared to those of the unsubstituted DPA and resulted in glass transition temperatures of up to 92 °C. Small-sized and poorly conjugated substituents allowed to preserve emission in the deep blue range (<450 nm). Substitution at the 2nd position enabled to achieve high fluorescence quantum yields (up to 0.7 in solution, and up to 0.9 in the polymer host), although it caused an up to 10-fold increase in the intersystem crossing rate as compared to that of the unsubstituted DPA. Further optimization of the film forming properties achieved by varying the length of the alkyl groups attached at the 9,10-phenyls enabled to attain very high hole drift mobilities (∼5 × 10(-3)-1 × 10(-2) cm(2) V(-1) s(-1)) in the solution-processed amorphous films of the DPA compounds.

Impact of non-symmetric 2,9,10-aryl substitution on charge transport and optical properties of anthracene derivatives

“…Absorption spectra of all 2,9,10-arylanthracene derivatives resembles those of unsubstituted anthracene [47] as well as its derivatives like 2-phenylanthracene [49] and other similar anthracene derivatives [26]. The absorption spectra of 2,9,10-arylanthracene compounds in solid state are redshifted for about 120-130 meV and slightly broadened in respect to those of in dilute solutions.…”

“…The additional substitution at the 2 nd position also helps to ensure amorphous state and improves charge transport properties of the films [10,30]. However the additional π-conjugation extension towards the long axis of the molecule results in the reorganization of singlet and triplet energy levels when the T n level emerges below S 1 leading to the efficient ISC recombination and low Φ F [26]. Despite the importance of the intersystem crossing, recent studies have suggested that the vibrational relaxation may also be the important pathway for the non-radiative decay in anthracene derivatives [31,32].…”

“…Further modifications with more bulky aryl groups at 9 th and 10 th positions [17,[26][27][28][29] greatly reduces the intermolecular interactions and enables to achieve amorphous thin films. The additional substitution at the 2 nd position also helps to ensure amorphous state and improves charge transport properties of the films [10,30].…”

“…However the structural modifications with phenyl moieties at 9 th and 10 th positions are insufficient to eliminate unwanted crystallization and fluorescence quenching in the films [10,26].…”

Fluorene- and benzofluorene-cored oligomers as low threshold and high gain amplifying media

“…It is worth noting that increasing compound concentration up to 10 wt % (for benzofluorenes) or 20 wt % (for fluorenes) had negligible influence on the U F and s, whereas further increase of the concentration up to 100 wt % resulted in roughly 2-fold drop of these values. Only 2-fold reduction of U F and s in the neat films is caused by enhanced nonradiative relaxation induced by exciton migration and infers rather weak emission quenching 7,16,17 and thereby weak intermolecular coupling. This was also confirmed by the small red shift of emission spectra as well as single exponential decay of the transients preserved up to the highest oligomer concentrations in PS.…”