2-Amino-6-methylpyridinium nitrophenolate nitrophenol: An organic multiple charge-transfer complex with large second harmonic generation for optoelectronics applications

• Published in: Journal of thermal analysis and calorimetry 2018-11, Vol.134 (2), p.1059-1070
• Main Authors: Babu, B., Chandrasekaran, J., Jayaramakrishnan, V., Ho, Mon-Shu, Thirupugalmani, K., Chandrasekar, S., Thirumurugan, R.
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Chemistry; Chemistry and Materials Science; Inorganic Chemistry; Measurement Science and Instrumentation; Physical Chemistry; Polymer Sciences
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-018-7386-5

Organic co-crystals fashioned with two or more different constituents through intermolecular non-covalent interactions (hydrogen and halogen bonds) gain cumulative research considerations as of their applications in ambipolar charge transport, nonlinear optics (NLO), light-driven actuator, liquid crystal material and electronics industry. In this contribution, charge-transfer (CT) interactions and the corresponding physicochemical and nonlinear properties of bulk organic, CT co-crystal of 2-amino-6-methylpyridinium nitrophenolate nitrophenol (2A6MPNN) were comprehensively investigated. CT crystals were fabricated by the facile solvent evaporation strategy and crystallized with an extensive hydrogen bonding network existed between the aromatic donor (D) and acceptor (A). The organic salt formation of phenol–pyridine co-crystal was investigated by using 1 H NMR, 13 C NMR and FTIR. More importantly, we show that the CT interactions in co-crystals are related to their molecular packing which eventually leads to distinct optoelectronic properties. The convincing evidence for multiple CT was found by UV–Vis spectral measurements, i.e., both π–π and n–π* interactions (between 4-nitrophenol and 2-amino-6-methylpyridine) are simultaneously present and additionally new feature band arises at 408 nm. Remarkably, upon photoexcitation at 374 nm in the solid state, CT displays an unusual emission around 572 nm, which is probably attributed for the shallow traps of the ion pairs, along with a usual phenolate-centered green emission. Thermal analysis was performed using TG/DTA/DSC and Modulated DSC studies. NLO response on CT powder (for diverse particle sizes) indicates a phase matchability and NLO coefficient about 1.8-fold larger than that of urea.