Can hydrogen bonds improve the hole-mobility in amorphous organic semiconductors? Experimental and theoretical insights

Abstract

Five hole-transporting triphenylamine derivatives containing methoxy and methyl groups are synthesized and investigated. The hole-mobility increases in the presence of methyl-and methoxy substituents, exceeding 10 -2 cm 2 /Vs in the case of the methyl groups. Quantum mechanical calculations on these compounds indicate very different dipole moments and intermolecular interaction strengths, with intriguing correlations to the trend in hole-mobility. Temperature dependent hole-mobility measurements indicate disorder dominated hole transport. The values of the energetic disorder parameter (σ) decrease upon methyl and methoxy substitutions despite the increase in dipole moments. This trend is discussed as a function of the interaction energy between adjacent molecules, the dipole moment, the molecular polarizability, and the conformational degree of freedom. Our results indicate that the global decrease of σ upon methyl and methoxy substitutions is dominated by the the larger decrease in the geometrical randomness component of the energetic disorder. A direct correlation is established between the decrease in geometrical randomness and the increase in intermolecular interaction energies, mainly stemming from the additional C-H….π,O,N hydrogen bonds induced by methyl and methoxy groups. the dipolar-moments on the energetic disorder, 6,7 methoxy substitutions are then expected to result in degraded-or improved charge transport properties, partly depending on the (respectively) important-or negligible increase of the molecular dipole moments. As will be shown in this study, the

Aggregation‐Enhanced Emission and Thermally Activated Delayed Fluorescence of Derivatives of 9‐Phenyl‐9H‐Carbazole: Effects of Methoxy and tert‐Butyl Substituents

“…Despite the same core of molecules, hole ( μ h ) and electron ( μ e ) mobilities for the layers of NCFMCz1 and NCFTCz were found to be different depending on the nature of substituents attached to carbazole moiety (Figure b). This observation can apparently be explained by variation in the geometrical randomness component which mainly stems from the additional C−H⋅⋅⋅π, O, N hydrogen bonds induced by methoxy groups as it was previously shown for triphenylamine derivatives . The differences in charge mobility parameters of the studied derivatives were apparently also determined by the differences in the energetic disorder parameters for electrons and holes in these carbazole and benzonitrile derivatives differently substituted by methoxy and tert ‐butyl groups.…”

“…This observation can apparently be explained by variation in the geometricalr andomness componentw hich mainly stems from the additional CÀH···p,O ,N hydrogen bonds induced by methoxy groups as it was previously shown for triphenylamine derivatives. [29] The differences in chargem obility parameters of the studied derivatives were apparently also determined by the differences in the energetic disorderp arameters for electrons and holes in these carbazole and benzonitrile derivatives differently substituted by methoxy and tert-butyl groups. In addition, the differences in charge mobility parameters of the studied derivatives can be related to the different carrierh opping distance in solid-statel ayers.…”

Rational Synthesis of Tetrahydrodibenzophenanthridine and Phenanthroimidazole as Efficient Blue Emitters and their Applications

“…Interestingly, FWHM of toluene solutions of substituted compounds 3b – j was lower in comparison to FWHM of 77 nm observed for the solution of non‐substituted compound 3a . The shapes of PL spectra were similar to the shape of PL spectrum of DMF solution of PI . PL spectra of the solutions of 3a – j in toluene were red‐shifted in comparison to PL spectrum of the solution of PI.…”

Synthesis of Linear and V‐Shaped Carbazolyl‐Substituted Pyridine‐3,5‐dicarbonitriles Exhibiting Efficient Bipolar Charge Transport and E‐Type Fluorescence

“…Additionally,h ydrogen bonds formedb ytert-butyl groups improve the holetransporting property of 9. [27] Attemptingt oi ncrease electron mobility,t he tert-butyl-substituted carbazole unit was replaced with ac yano-substituted carbazole moietyi nt he structure of compound 12.A sw as previously shown, the introduction of strong electron-withdrawing cyano groups in the carbazole core led to am anifestation of electron-transporting ability in addition to hole-transporting properties characteristic of carbazole derivatives. [28] X-ray analysiss howed that molecules of 12 interactb yp-p interactions between antiparallel 3,6-dicyano-9H-carbazolyl moieties( Figure S7 a) with ad istance of 3.55 .…”