Effect of Hydrogen Bonding on the Luminescence Lifetime and Device Resistance: A Case Study Based on Two New Related Cd-Based Coordination Polymers

Two new coordination polymers of formulas [Cd2(2,3-pzdc)(tz)2] (1) and [Cd2(2,3-pzdc)(dtz)2] (2) {2,3-pzdc = 2,3-pyrazine dicarboxylate, tz = 1,2,4-triazolate, dtz = 3,5-diamino-1,2,4-triazolate)} were synthesized via hydrothermal techniques. Both the compounds were characterized by single-crystal X-ray analysis, powder X-ray diffraction, Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). Single-crystal X-ray analysis shows that both the structures are three-dimensional in nature and connectivity-wise they are similar to each other. In compound 2, the presence of N–H···O hydrogen-bond interactions further stabilized the structure. Aqueous dispersion of both the compounds showed a strong dual emission─one at around 353 nm and another at 369 nm upon excitation at 280 nm. Lifetime studies from time-resolved spectra show 0.82 and 0.60 ns for compound 1 and 2.02 and 1.78 ns for compound 2. The higher lifetimes of the excited states in the case of compound 2 establish the role of hydrogen-bond interactions in reducing the nonradiative decay processes. To explore the junction properties at the Al/material interface of these Schottky barrier diodes, the dark J–V characteristics of both of the devices (ITO/PEDOT/compound 1/Al and ITO/PEDOT/compound 2/Al) were analyzed using the well-known Shockley diode equation. In both the devices (with compound 1 and compound 2), asymmetric behavior is observed under forward and reverse bias, indicating rectification. However, in the compound 2 device, the overall current magnitude is 10 times higher than that of the compound 1 device. The series resistance extracted for the compound 2 device is ≈ 22 times lower than that of the compound 1 device, indicating the higher conductivity of compound 2. This behavior indicates a probable role of hydrogen-bond interactions in the lower resistance and higher conductivity of compound 2 compared to compound 1.