Temperature-Dependent Semiconducting Behavior of an Organic Cocrystal Driven by the Stacking Mode of Interaction of a 4,4′-Bipyridine Molecule

Abstract

Organic cocrystals based on H-bonding as well as π-stacking interactions between 4,4′-bipyridine−pyromellitic acid (1) and 4,4′-bipyridine−phthalic acid (2) are reported. Cocrystals 1 and 2 were fully characterized by single-crystal X-ray diffraction and NMR and IR spectroscopy. The single-crystal X-ray diffraction shows the H stacking pattern of the adjacent 4,4′-bipyridine molecules in the construction of a 3D chain structure for cocrystal 1. Cocrystal 2, however, formed a zigzag 3D chain where the adjacent 4,4′-bipyridyl molecules are involved in a J-stacking mode. Experimental conductivity measurements of the cocrystals 1 and 2 with a Keithley 4200 SCS parameter analyzer showed the temperature-dependent semiconducting behavior in the case of cocrystal 1, whereas cocrystal 2 remained as an insulator. The favorable H-stacking interaction of 4,4′-bipyridine molecules which is the prime origin of semiconductivity in cocrystal 1 may become out of phase due to the free rotation along the C−C bond of 4,4′-bipyridine with an increase in temperature. Although the semiconducting behavior of a material increases with increasing temperature and decreases in resistivity, in the case of cocrystal 1 due to the probable phase transition of the 4,4′-bipyridyl molecules the material became an insulator with an increase in temperature from 20 °C to higher temperature, whereas the semiconducting behavior was restored after cooling the crystals to 20 °C again. The theoretical study conducted with the optimized structures of 1 and 2 showed the higher electron hopping rate in the case of cocrystal 1 as compared to 2 which can account for the charge conduction in the case of 1.

1,3,5‐Benzene Tricarboxylic Acid Based Cocrystals With Selective Semiconductivity via H‐coupled Charge Transfer

“…In this process, internal geometry changes from charged state to neutral and vice versa. This is the energy barrier in the charge transport process and similar to the reorganization energy (λ) and can be calculated as λ = λ 1 + λ 2 = (Ε 4 ‐ Ε 1 ) + (Ε 2 ‐ Ε 3 )“; where E 1 is the ground state energy of the neutral molecule, E 2 is the energy of the charged molecule on neutral geometry, E 3 is the ground state energy of the charged molecule and E 4 is the energy of neutral molecule on charged molecule geometry [24] …”

“…The construction of semiconducting supramolecular cocrystals based on pyromellitic acid and orthophenylene diamine as well as 4,4' bipyridine has been recently reported by our group. [24,25] Organic cocrystals through complementary H-bonding interaction is well-known in crystal engineering and active pharmaceutical ingredients (API). [2,[26][27][28][29][30][31][32][33][34][35] Many supramolecular polymeric functional materials are known to be formed via H-bonding interactions.…”

“…The development of electronic materials based on H‐bonding interactions is well‐known since the time of organic metals [1,16,17,19,20,23] but the H‐bond involving carboxylic acid amine systems has been surprisingly less explored. The construction of semiconducting supramolecular cocrystals based on pyromellitic acid and orthophenylene diamine as well as 4,4’ bipyridine has been recently reported by our group [24,25] . Organic cocrystals through complementary H‐bonding interaction is well‐known in crystal engineering and active pharmaceutical ingredients (API) [2,26–35] .…”