High Charge-Carrier Mobility in an Amorphous Hexaazatrinaphthylene Derivative

Abstract

An isomeric mixture of a tris(pentafluorobenzyl ester) derivative of hexaazatrinaphthylene forms stable amorphous films with an effective charge-carrier mobility of 0.02 cm2/Vs, while the pure 2,8,15-isomer exhibits widely differing morphologies and carrier mobilities (0.001-0.07 cm2/Vs), depending critically on the processing conditions.

Synthesis, Ionisation Potentials and Electron Affinities of Hexaazatrinaphthylene Derivatives

“…The LUMO of 1 ( Figure 3) has a 2 '' symmetry and is qualitatively similar to that previously reported for 3 (R = H). [6] Qualitatively similar LUMOs are obtained for C s -2 a, C s -2 b, 6', 6'' and 7-9, with the addition of small coefficients on the p-accepting carbonyl groups of the ester derivatives 2 a and 2 b (see Supporting Information for reference [2]). The calculated changes in the bond lengths between the neutral molecule and the radical anion for compounds 2 a, 2 b, 6', 6'' and 7-9 are similar to those for 1.…”

“…[4] Recently we investigated the pentafluorobenzyl triester, 2 b, and, using the space-charge limited current technique, determined mobilities of 0.07 and 0.02 cm 2 V À1 s À1 for the C s isomer and as-synthesised isomer mixture, respectively. [2] Energy-level considerations based on electrochemical measurements suggest that hexaazatrinaphthylene derivatives are likely to function as electron-transport materials and that the mobilities we reported for 2 b in reference [2] are likely to represent electron mobilities. Further support for the ease of electron injection relative to hole injection comes from direct measurements of the solid-state ionisation potentials (IPs) of 1 [2] and 3 a [5] as 6.6 and 5.9 eV, respectively, and of the solid-state electron affinity (EA) of 1 as À2.4 eV.…”

“…[2] Energy-level considerations based on electrochemical measurements suggest that hexaazatrinaphthylene derivatives are likely to function as electron-transport materials and that the mobilities we reported for 2 b in reference [2] are likely to represent electron mobilities. Further support for the ease of electron injection relative to hole injection comes from direct measurements of the solid-state ionisation potentials (IPs) of 1 [2] and 3 a [5] as 6.6 and 5.9 eV, respectively, and of the solid-state electron affinity (EA) of 1 as À2.4 eV. [2] Recently, we reported the EA of trisA C H T U N G T R E N N U N G {2,5-bis(3,5-bis-trifluoromethyl-phenyl)-thieno} [3,4-b,h,n]-1,4,5,8,9,12-hexaazatriphenylene (6; i.e., an analogue of a hexaazatrinaphthylene in which the outer benzene rings are replaced with thiophene rings fused to the hexaazatriphenylA C H T U N G T R E N N U N G ene core through their 3-and 4-positions) to be À4.59 eV, considerably more exothermic than that of 1.…”

“…Most work has concerned esters derived from the 2,8,14-and 2,8,15-tricarboxylic acid (2) [1,2] or 2,3,8,9,14,15-hexa(alkylsulfanyl) (3) [3][4][5][6] and 2,3,8,9,14,15-hexaA C H T U N G T R E N N U N G (alkoxy) derivatives (4). [7,8] Analogues with more extensive p-systems, such as 5, have also been reported.…”

“…Further support for the ease of electron injection relative to hole injection comes from direct measurements of the solid-state ionisation potentials (IPs) of 1 [2] and 3 a [5] as 6.6 and 5.9 eV, respectively, and of the solid-state electron affinity (EA) of 1 as À2.4 eV. [2] Recently, we reported the EA of trisA C H T U N G T R E N N U N G {2,5-bis(3,5-bis-trifluoromethyl-phenyl)-thieno} [3,4-b,h,n]-1,4,5,8,9,12-hexaazatriphenylene (6; i.e., an analogue of a hexaazatrinaphthylene in which the outer benzene rings are replaced with thiophene rings fused to the hexaazatriphenylA C H T U N G T R E N N U N G ene core through their 3-and 4-positions) to be À4.59 eV, considerably more exothermic than that of 1. [10] In addition, this material can be n-doped with cobaltocene, which greatly enhances electron injection into the material.…”