Charge Polarity Control in Organic Transistors of Mixed and Segregated Complexes Based on Diaminonaphthalene and Pyrene

Organic cocrystals of diaminonaphthalene (DAN) and diaminopyrene (DAP) with bromanil (BA) and tetracyanoquinodimethane (TCNQ) are an exemplar system for understanding the charge-transport process, where from the viewpoint of partition theory, orbital symmetry plays a crucial role in controlling the carrier charge polarity of transistors. In the mixed-stack complexes of BA and other p-quinone acceptors, a comparatively weak donor, 1,5-DAN, shows p-channel characteristics owing to the counteractive contribution of the next highest occupied molecular orbital for electron transport. This characteristic behavior occurs because the BA molecule, situated on top of the amino group, overlaps with half of the DAN molecule. By contrast, the BA and TCNQ complexes of a stronger donor, 1,6-DAP, exhibit n-channel transport due to the cooperative path and orthogonal orbitals. Similarly, TCNQ complexes of variously substituted DAN show n-channel transport, where the TCNQ molecules are located on top of the DAN molecules. However, when the carbon electrodes of (1,5-DAN)(BA) are replaced by silver, electron transport appears due to the competitive effect of the Schottky barriers. In a highly conducting segregated complex of (1,6-DAP)(TCNQ), ambipolar transistor characteristics are observed without subtracting the bulk current by using carefully prepared thin-film transistors.


Charge-transfer degree
The charge transfer degree  of the TCNQ complexes were estimated from the bond lengths b ~ d and the C≡N stretching mode C≡N of the IR spectra by using the following formula.S5).
Transistor properties           When the amino group is regarded as the "para" position of the side ring, the HOMO and HOMO-2

Inter-stack transfer integrals
It has been reported that when there are hydrogen bonds, inter-stack transfer integrals are extraordinarily large, which typically amount to one third of the intra-stack transfer integrals. 54The same is observed when the hydrogen bond exists between the donor and acceptor molecules.The triad method affords considerable inter-stack effective transfer integrals along the hydrogen bonds (Table S6), which sometimes amount to more than half of the intra-stack effective transfer integrals.
Hydrogen bonds appear between almost coplanar molecules.It is characteristic that these intra-stack effective transfer integrals are approximately the same for electron and hole.However, the partition method gives practically zero (< 1 meV) effective transfer integrals for the same interactions, and physical meaning of these inter-stack transfer integrals is not certain.
Table S6.Inter-stack effective transfer integrals along the hydrogen bonds (meV).

Molecular orbital levels of diaminonaphthalenes
In 1,5-DAN, the HOMO and HOMO-1 come from the antibonding and bonding combinations of the same orbital (Figure 6(b)).Since orbital overlap is important in controlling transistor properties, the molecular orbitals are analyzed.Figure S11(a) demonstrates how molecular orbitals of naphthalene are influenced by successive amino group substitutions at various positions.Naphthalene HOMO and HOMO-2 have a horizontal node, while HOMO-1 has vertical nodes.Addition of an amino group at the 1 (pink) and 2 (green) positions significantly increases the HOMO energy levels.2-Substitution increases the (green) HOMO-1 energy level, whereas 1-substitution leads to an insignificant increase of the (pink) HOMO-1 level.In general, when the molecular orbital has a large amplitude at the amino substituted carbon, the energy level increases significantly, whereas when the amino carbon corresponds to a node of the molecular orbital, the energy level does not change largely.For diamino substitutions, amino groups at 1 and 8 positions considerably increase the (pink) energy level of HOMO-2 (horizontal node) superseding energy of HOMO-1 (vertical node), resulting in shape exchange between HOMO-2 and HOMO-1.Accordingly, the (pink) HOMO-1 of 1,5-DAN (rightmost in Figure S11(a)) comes from the naphthalene HOMO-2, and has a similar horizontal node to the HOMO.Addition at positions 2 and 3, however, even reduces the (green) HOMO energy of 2,3-DAN as the out-of-plane lone pairs on nitrogen do not contribute to the increase in the energy level, but rather the inductive effect is more significant due to the steric hinderance from the neighboring hydrogen on the nitrogen molecules.2,6-DAN and 1,5-DAN are moderately strong donors; the HOMO levels go up by 1 eV in comparison with the parent naphthalene, and are situated around -5 eV.By contrast, 2,3-DAN is a much weaker donor with the HOMO level around -5.2 eV.
The same principle applies to pyrene (Figure S11(b)).The 1-substitution (pink) increases the HOMO level, but does not increase HOMO-1.The opposite happens in the 2-substitution (green).As a result, HOMO and HOMO-1 are approximately degenerated in 2-aminopyrene, whereas 1aminopyrene has a large (1.3 eV) gap between HOMO and HOMO-1.In 1,6-DAP, HOMO-2 is nearly degenerated with HOMO-1.Although this orbital is still HOMO-2, the mechanism of the cancellation is entirely the same as 1,5-DAN (Table S5(c)).
In aminoacenes, energy levels of orbitals with a large amplitude at the amino substituted carbon go up, but at the same time have a large overlap with BA LUMO.As a consequence, it is likely that complexes forming half-molecule overlap suffer from the cancellation of electron transport and show p-channel transport.

Calculated mobilities
Mobility is calculated according to the Marcus theory. 68,S12,S13 ℎ The factor including the reorganization energy  is designated as F. S14 Table S7 shows the calculated results.If  is nearly the same,  is proportional to t square.In general,  decreases with extending aromatic rings; for example, naphthalene (189) to pentacene (99 meV), S15 and dithiophene (365) to sexithiophene (253 meV).S16 Although TCNQ is a small molecule, TCNQ has a small  (258 meV) compared with other donors and acceptors.S13,S17 This affords by one order larger F = 0.50 eV -1 than F = 0.042 eV -1 in BA ( = 483 meV).Although it is difficult to prepare thin films of TCNQ, a large mobility close to 1 cm 2 V -1 s -1 has been observed in TCNQ.S18-S20 Recently, significant isomer dependence of  has been reported in fused thiophenes.S21 Accordingly, a small  has a significant impact to .

Estimation of Schottky barriers
Schottky barrier B is usually smaller than the pristine energy level difference, M -EH.

B = c(M -EH)
For silicon, the actual barrier B is by c = 0.27 times smaller than the difference of the work functions.S23-S26 The c values estimated from electrode material dependence of mobility in organic transistors are listed in Table S8.From this, we have used the average c = 0.07 in Table 3.Such remarkable reduction of Schottky barrier has been attributed to surface states or defects, S22 and interfacial charge transfer and dipole formation. 70The figure attached to Table S8 demonstrates that eq 2 is universally applicable to inorganic metals such as Au, Cu, Ag, and Mg, though Ca is somewhat deviated.

Figure S2 .
Figure S2.Observed charge-transfer transition plotted against (a) the difference of the individual donor and acceptor levels (Figure 1), and (b) the D HOMO and A LUMO difference calculated from the dimer (TableS5).

Figure S10 .
Figure S10.Calculated (a) intermolecular energy, and (b) energy level shift for proton transfer in (1,6-DAP)(TCNQ).54 have the same symmetry at the side ring.Then, the contribution of HOMO-2 cancels the HOMO interaction analogously to (1,5-DAN)(BA), and this phase becomes hole dominant.The same mechanism applies to -(1,6-DAP)(CA) as well (TableS5(f)).Although the crystal structure of -(1,6-DAP)(BA) has been solved using a space group Pn, 41 the structure seems centrosymmetric.After moving the DAP molecule to the origin and averaging, the calculation has given essentially the same result: 3/28 meV.

Figure S11 .
Figure S11.Calculated energy levels and molecular orbitals of (a) amino naphthalene, and (b) amino pyrene.

Table S5 .
Energy difference, transfers, and contributions to superexchange transfers (meV) in the

Table S7 .
Transfer integral t, reorganization energy , and calculated mobility 

Table S8 .
c values obtained from electrode dependence.