Spectroscopic studies of the molecular organization of 4-([1,2,4] triazolo [4,3-a] pyridin-3-yl)-6-methylbenzene-1,3-diol in selected solvents

The paper presents the results of spectroscopic studies of 4-([1,2,4] triazolo[4,3-a] pyridin-3-yl)-6-methylbenzene-1,3-diol (TPBD), which indicate that the molecular organization of the compound is altered in different solvents and at different concentrations. The results were obtained from two solvents: methanol and propan-2-ol. Methanol represents a group of solvents in which monomers are the predominant molecular form of TPBD. Propan-2-ol belongs to a group of solvents in which TPBD additionally forms aggregates (dimers or N-aggregates). At concentration C-0 = 0.05 x 10(-3) M, TPBD has a monomeric form in Mt-OH and an additional dimeric form in Pr-OH. Circular dichroism (CD) and resonance light scattering (RLS) spectra revealed predominance of aggregated TPBD forms already at low concentrations of the compound in the methanol solvent. In turn, monomeric and dimeric forms of the compound dominated at low concentrations in propan-2-ol. Formation of additional dimers or N-aggregates in propan-2-ol was observed only at high concentrations of the compound (C-10 = 1.36 x 10(-3) M-C-20 = 4.90 x 10(-3) M). The presence of monomers and dimers in the Pr-OH solution yielded two bands (at 408 and 502 nm, respectively) in the fluorescence emission spectrum. Additionally, it was found that dimeric molecular form was characterized by reduction of the amplitude-weighted average fluorescence lifetimes in comparison with the monomeric form.