Tetrabromoterepthalic Acid in Designing Co-crystals and Salts: Modification of Optical Properties and Schottky Barrier Effect

Abstract

Herein, tetrabromoterepthalic acid (TBTA) is used as the potential co-crystal former with various organic base molecules containing free nitrogen atoms. The crystal structure of TBTA (compound 1) has been determined from powder X-ray diffraction (PXRD) data. In a systematic way, we have synthesized hydrated-TBTA (compound 2), two salts of TBTA [TBTA2––4,4′-bipy2+ (compound 3), 4,4′-bipy = 4,4′-bipyridine, and TBTA2––(3-AP+)2 (compound 4), 3-AP = 3-aminopyridine] and two co-crystals of TBTA [TBTA–DPTZ (compound 5), DPTZ = 3,6-di(pyridyl-2-yl)-1,2,4,5-tetrazine, and TBTA–(3-IP)2 (compound 6), 3-IP = 3-iodopyridine]. All of the compounds were characterized by structural, spectral, and thermal studies. Supramolecular structural analysis reveals that 1 forms a 2D supramolecular sheet structure by means of O–H···Br hydrogen bonding interactions and hydrated-2 forms a 3D supramolecular structure through water mediated hydrogen bonding interactions and π··· interactions. The O–H···N/O¯···H–N+ hydrogen bonding interactions between acid and base molecules give rise to 1D supramolecular chain structure in 3 and supramolecular trimers in 4, 5, and 6. Because of presence of charge assisted O¯···H–N+ hydrogen bonds between acid–base molecules, 3 and 4 form hydrogen bonds with solvent water molecules, and also both 3 and 4 form 3D supramolecular structures using both hydrogen bonding and π··· interactions. In co-crystal 5, solvent water molecules participate in crystallization in contrast to 6, and it has been observed that 5 forms 3D supramolecular structure, while 6 forms 2D supramolecular structure using both hydrogen bonding and π··· interactions. An investigation of intermolecular closed contacts has been carried out by Hirshfeld surface analysis, and associated 2D fingerprint plots reveal the similarities and differences of TBTA molecules in these six crystal structures. Photoluminescence spectra of all the compounds have been studied, and they reveal that with change of polarity around TBTA luminescent intensity of the compounds has been modified. I–V measurement indicates that 3 shows semiconducting behavior, and the ITO/3/Al sandwich structure acts as a Schottky barrier diode. The device exhibits an excellent rectification ratio (19 at ±1 V) with an ideality factor of 2.96. The semiconducting behavior of 3 is attributed to the formation charge assisted hydrogen bonding interactions between acid and base molecules.