Aggregation induced enhanced emission of diphenylamine and pyridine based conjugated organic materials

Aggregation induced emission enhancement (AIEE) was studied for diphenylamine and pyridine based donor–acceptor conjugated moieties (DPA-PA-1-3). These moieties were synthesized from Knoevenagel condensation and great solubility in organic solvents such as toluene, tetrahydrofuran, ethyl acetate, dichloromethane, chloroform etc due to various alkyl chains. AIEE process was investigated from absorption/fluorescence spectroscopy and scanning electron microscopy. The absorption maximum of DPA-PA-1-3 appeared at 437, 433, 444 nm in THF solution. The optical band gaps are 2.33, 2.29, and 2.25 eV calculated from thin film absorption edges. After aggregation using different water fractions, the absorption of conjugated moiety was red shifted to 12 nm (j-aggregation) and there was no change in optical band gap. The photoluminescence spectra of three molecules were exhibited a maximum peak at 511, 515, 529 nm with greenish fluorescence in chloroform solution and 553, 541, 554 nm as in thin film state. DPA-PA-1-3 showed a delay fluorescence decay time (τ1) of 35, 16 and 14 µs respectively. Aggregation-induced emission (AIE) phenomenon of DPA-PA-1-2 was also observed and fluorescence intensity was enhanced with different water fractions. The lower electrochemical band gaps 1.90 and 1.80 eV was observed by cyclic voltammetry. The morphological images were indicated that spherically shaped particles were observed with lower surface roughness. These types of low bandgap materials have much attention for their various potential applications in optoelectronic devices.