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Revisited Dual Luminescence of 2,2′‐Dipyridylamine Hydrochloride in Solution and Physical Processes behind It
Author(s) -
Bulatov Evgeny,
Haukka Matti
Publication year - 2018
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201802726
Subject(s) - luminescence , chemistry , protonation , pyridinium , hydrochloric acid , hydrogen bond , photochemistry , solvent , dissociation (chemistry) , chloroform , methanol , solvatochromism , inorganic chemistry , molecule , materials science , organic chemistry , ion , optoelectronics
Reaction of 2,2′‐dipyridylamine (dpa) with hydrochloric acid results in formation of dpa hydrochloride (dpa⋅HCl), leading to substantial changes in its luminescent properties. Luminescence of dpa⋅HCl in solution has been previously interpreted as aggregation‐induced phenomenon. In this work, the emission properties of dpa⋅HCl in solution were revisited, focusing on the impact of methanol and chloroform solvents. Luminescence, absorption, and 1 H NMR spectroscopy were used to study physical state of the solute molecules and photophysical properties associated with them. The results clearly indicate that the concentration and solvent dependencies of luminescence are due to equilibrium between protonated dpaH + and neutral dpa forms, rather than aggregation in solution. In chloroform, strong emission with λ em ≈ 430 nm is associated with the cationic dpaH + form. Polar and hydrogen bonding methanol not only facilitates dissociation of dpaH + cation, but also seems to quench its luminescence through pyridinium hydrogen bond, and the residual weak emission at λ em ≈ 360 nm is associated with the neutral dpa form. The obtained results can be applied in design of new dpa based materials with desirable luminescent properties in both solution and solid state.