Density and Dimensional Control of π-Electrons in Electrostatically Binding Naphthalenediimide Salts

Abstract

Dianionic bis­(benzenesulfonate)–naphthalenediimide (BSNDI 2– ) formed simple 2:1 cation–anion salts of (NH4 +)2­(BSNDI 2– ) (1), (CH3NH3 +)2­(BSNDI 2– ) (2), (C2H5NH3 +)2­(BSNDI 2– ) (3), [(C2H5)2NH2 +]2­(BSNDI 2– ) (4), and [(C2H5)3NH+]2­(BSNDI 2– ) (5). The thermal stability, crystal structure, electron transport properties, and dielectric response were evaluated for these systems in terms of π-electron density and dimensional crossover from two-dimensional (2D) and one-dimensional (1D) to zero-dimensional (0D) electronic structures. Systematic modification of the counter cations from NH4 + to simple alkylammoniums (CH3NH3 +, C2H5NH3 +, (C2H5)2NH2 +, and (C2H5)3NH+) for BSNDI 2– salts affected the packing π-density and dimensionality of NDI π-cores. All single crystals formed alternating cation–anion layers, where the intermolecular interactions in salts 1, 2, 3, 4, and 5 were observed as dense 2D brickstone, 1D column, 1D column, dilute 2D herringbone, and isolated 0D monomer arrangements, respectively. The π-electron occupation percentage in the unit cell of salts 1, 2, 3, 4, and 5 decreased in that order, at 96.2%, 87.8%, 83.8%, 78.8%, and 72.6%, respectively, where the intermolecular π–π interaction between BSINDI 2– anions was gradually diluted on increasing in the cation volume. The transfer integrals between the lowest unoccupied molecular orbital in salts 1–5 clearly indicated a dimensional crossover from 2D to 1D to 0D electronic structures. Flash-photolysis time-resolved microwave conductivity measurements of salts 1, 2, 3, and 4 helped determine the magnitude of electron carrier mobility, which followed the order 1 > 2 ≈ 3 ≈ 4. The dielectric response of salt 1 being an order of magnitude higher than those of salts 2–5 was associated with the protonic conductivity in the NH4 +···–SO3– electrostatic hydrogen-bonding network layer. Simple cation exchange in dianionic BSNDI 2– salts conventionally modified the intermolecular π–π interactions in terms of dimensionality, magnitude, and electron transport properties.

Preliminary chemical reduction for synthesizing a stable porous molecular conductor with neutral metal nodes

“…In the case of PMC-2, Rb + ions locating near the conductive pathways are disordered with a 50% occupancy, and this would cause a random charge localization and decrease the electrical conductivity. The calculated transfer integral between adjacent LUMO orbitals (255.8 meV) is larger than those of NDI-based organic semiconductors 47,48 and comparable to those of highly conducting molecular conductors. 49 Thus, the p-stacked array of NDI cores has the potential to exhibit a higher intrinsic conductivity if a random charge localization does not occur.…”

Electrostatic versus van der Waals Interactions in an n-Type Semiconducting Dianionic Naphthalenediimide Derivative with CnH2n+1NH3+ (n = 1–16)

“…The softness and hardness of the cation–anion crystal lattices were systematically modulated by replacing the alkali metal ions, and the electron transport property was dominated by the crystal lattice. , In the case of BSNDI 2– salts, inorganic M + cations, such as Na + , K + , and NH 4 + , were conventionally replaced with organic cations such as CH 3 NH 3 + , C 2 H 5 NH 3 + , (C 2 H 5 ) 2 NH 2 + , and (C 2 H 5 ) 3 NH + . This significantly changed the molecular assembly structures and showed a dimensional crossover from 2D, 1D, to 0D electronic structures . The electron density and dimensionality of the NDI π-cores in the molecular assembly were controlled by the counter cations.…”

“…This significantly changed the molecular assembly structures and showed a dimensional crossover from 2D, 1D, to 0D electronic structures. 71 The electron density and dimensionality of the NDI π-cores in the molecular assembly were controlled by the counter cations. For instance, CH 3 NH 3 + and C 2 H 5 NH 3 + in BSNDI 2− salts formed a 1D π-stacking structure without the effective intercolumn interaction, with transient electron conductivities being 2.9 × 10 −9 and 5.6 × 10 −9 m 2 V −1 s −1 at 298 K, respectively.…”

Crystal Lattice Design of H2O-Tolerant n-Type Semiconducting Dianionic Naphthalenediimide Derivatives

“…48 A simple cation exchange reaction from (Na + ) 2 (BSNDI 2− ) to (M + ) 2 (BSNDI 2− ) with M + = CH 3 NH 3 + , C 2 H 5 NH 3 + , (C 2 H 5 ) 2 NH 2 + , and (C 2 H 5 ) 3 NH + also modulated the packing structure of BSNDI 2− dianions, where the dimensional crossover from the 2D to 1D to 0D electronic structure was observed by increasing the cation volume. 52 Therefore, the introduction of electrostatic interactions into n-type semiconducting materials is a useful approach to simultaneously increasing the chemical stability and electron mobility. In addition to the designable cations, through the chemical modification of the anionic n-type semiconducting π molecule, various stable molecular assembly structures can be formed.…”

“…In addition, the electron mobilities in polycrystalline thin films of (Na + ) 2 ( BSNDI 2– ) and (K + ) 2 ( BSNDI 2– ) were observed at 0.22 and >0.0003 cm 2 V –1 s –1 , respectively . A simple cation exchange reaction from (Na + ) 2 ( BSNDI 2– ) to (M + ) 2 ( BSNDI 2– ) with M + = CH 3 NH 3 + , C 2 H 5 NH 3 + , (C 2 H 5 ) 2 NH 2 + , and (C 2 H 5 ) 3 NH + also modulated the packing structure of BSNDI 2– dianions, where the dimensional crossover from the 2D to 1D to 0D electronic structure was observed by increasing the cation volume . Therefore, the introduction of electrostatic interactions into n-type semiconducting materials is a useful approach to simultaneously increasing the chemical stability and electron mobility.…”