Influence of π-Conjugated Backbone Length and Tail Chain Number on Self-Assembly Structures of 4,6-Diamino-1,3,5-triazine Derivatives Revealed by STM

4,6-Diamino-1,3,5-triazine (DT) derivatives typically exhibit excellent liquid crystal properties, attracting numerous researchers interested in enhancing their performance. In this paper, two DT molecules (DT−10 and DT−12) are employed to elucidate the effects of their backbone length and number of branches in the tail chains on self-assembled nanostructures using scanning tunneling microscopy (STM) at the 1-octanoic acid/highly ordered pyrolytic graphite interface, compared to our previous report (2TDT−n, n = 10,12,16,18). DT−10 features a short backbone and a trialkoxy chain tail, whereas DT−12 possesses a long backbone and bifurcated chain tails. STM results reveal that DT−10 assembles into a cross-shaped nanostructure with DT head groups arranged in a head-to-head configuration stabilized by a pair of N–H···N hydrogen bindings (HBs). In contrast, DT−12 assembles into a two-row linear pattern, where DT head groups exhibit a side-by-side arrangement mediated by a pair of N–H···N HBs. Comparison with our previous findings indicates that although variations in backbone length and tail chain branching can modulate the nanostructural features of DT derivatives, the chain length of DT molecules emerges as a pivotal factor governing their assembly architecture.