Competitive hydrogen bonding influences of fluorophore- urea-adenine system in water: Photophysical and photochemical approaches

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2020-08, Vol.237, p.118409, Article 118409
• Main Authors: Anupurath, Sumita, Krishnan, Anju, Namasivayam, Dhenadhayalan, Rajaraman, Vasanthi, Rajendran, Kumaran
• Format: Article
• Language: English
• Subjects: Acridinedione; Adenine; Fluorescence; Hydrogen bonding; Transient absorption; Urea
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2020.118409

Photophysical and photochemical investigation of photoinduced electron transfer (PET)-based acridinedione dye (ADR1) with urea in the presence of a nitrogenous base (adenine) were carried out in water. Urea suppresses the PET resulting in a fluorescence enhancement and the extent of binding is correlated and governed by the number of urea molecules surrounding the close vicinity of dye. On the contrary, adenine forms a true 1:2 complex with dye. Presence of adenine in dye-urea microenvironment results in the displacement of dye from the vicinity of urea molecules. The stability of dye-urea network in the presence of adenine reveals that the microenvironment of dye is governed and influenced by both urea and adenine. Introduction of adenine to dye-urea results in the formation of several hydrogen bonding assemblies that are competitive and influences the excited state characteristics of ADR1 dye. The micro assemblies comprise dye-urea (DU), dye-adenine (DA), urea-adenine (UA), urea-water (UW), urea-urea (UU), and adenine-water (AW) framework and the existence of several competitive hydrogen bonding results in a large variation in fluorescence properties of ADR1 dye. The presence of several assemblies also signifies that no confined phase selectively of DU or DA assemblies exist in any stoichiometric proportion in the aqueous phase. The binding constant, the variation in the fluorescence lifetime and its relative amplitude of DA in the presence of urea authenticate that the binding nature of dye-urea-adenine (DUA) is dependent on the several hydrogen bonding assemblies that coexist at any concentration. The extent of hydrogen bonding of DA is found to be entirely different from that of urea. Further, urea resulted in changes in the transient absorption peak of dye with a large variation in lifetime and shift of the transient absorption peaks. Fluorescence spectral techniques are used as an efficient tool in elucidating the binding nature of DU framework in the presence of non-fluorescent hydrogen-bonding solute like adenine. [Display omitted] •Photophysical nature of acridiendione dye with adenine and adenine on dye-urea complex.•Dye forms 1:2 complex with adenine and 1:1 with urea · Binding of dye-adenine is hydrogen bonding, hydrophobic influences with hydrogen bonding with urea•Insight into photochemistry of PET dye with urea is imparted•Urea influences the triplet lifetime and the formation of radicals