Solvatochromic characteristics of dansyl molecular probes bearing alkyl diamine chains Sorin Mocanu, Gabriela Ionita, Iulia Matei ⁎ “Ilie Murgulescu” Institute of Physical Chemistry of the Romanian Academy, 202 Splaiul Independentei, Bucharest 060021, Romania abstract article info Article history: Received 25 March 2020 Received in revised form 22 April 2020 Accepted 24 April 2020 Available online 27 April 2020 A series of dansyl-based fluorescent probes bearing linear alkyl-1,n-diamine chains of different length (DA 1.n , n =2–8, 10, 12) was characterized in terms of the absorptive and emissive features in solvents of different po- larity and hydrogen bond donor/hydrogen bond acceptor character. The probes show solvent-dependent absorp- tion, a feature that is uncommon among dansyl derivatives. The dual emission of DA 1.n probes is strong in non- aqueous solvents and is influenced by the chain length and interactions with the solvent. Solvent effects on the spectral parameters were rationalized on the basis of the Kamlet-Taft and Catalán solvatochromic models, in order to quantify the degree of polarity-driven and hydrogen bonding interactions. A comparative discussion of the results predicted by the two models was made. In ground state, the DA 1.n probes act as hydrogen bond ac- ceptors. In excited state, hydrogen bonding is less favoured, the solute-solvent interactions being governed by the increasing polarity of the solvent that results in a large bathochromic shift of the emission. A comparison was made with the spectral features previously reported for the corresponding series of bis-dansyl fluorescent probes (2DA 1.n ). © 2020 Elsevier B.V. All rights reserved. 1. Introduction Solute-solvent interactions are at the core of solution chemistry, af- fecting reaction rates, positions of chemical equilibria and product yields [1], as well as altering molecular geometries, electronic distribu- tions and, consequently, spectroscopic data [2]. Interactions with the microenvironment are reflected in changes in the position, shape and intensity of the absorption and emission bands, which are generally termed as solvatochromic effects. The mechanism responsible for these effects is the differential solvation of the ground and excited states of solute molecules. The extent of solvation depends on the intermolec- ular forces between solute and neighbouring solvent molecules, which can be classified into non-specific (global) interactions, determined by polarity and polarizability effects, and specific (local) interactions such as hydrogen bonding involving hydrogen bond donor (HBD)/hydrogen bond acceptor (HBA) and electron-pair donor (EPD)/electron-pair ac- ceptor (EPA) molecules. The overall solvent effect recorded experimentally can be unraveled into its various contributions by the use of solvatochromic models such as those developed by Kamlet et al. [3] and, more recently, Catalán [4,5]. These models are based on linear solvation energy relationships be- tween a measured spectroscopic parameter and several solvent scales of polarity, HBD and HBA character. Comprehensive reviews of solvatochromic models can be found in the paper published by Reichardt more than two decades ago [2] and in a more recent book chapter [6]. The reliability of the Kamlet-Taft and Catalán multiparametric models over other solvatochromic models reported in the literature is that they employ solvent scales obtained by averag- ing solvent effects over a variety of standard molecular probes, specific to each model. The prerequisite for a molecular probe is its sensitivity to the proper- ties of the microenvironment, leading to characteristic solvatochromic behaviour. Continuous development of new probes has allowed re- searchers to focus their attention on systems that have been less studied in the past, including solvent mixtures [7], micellar solutions [8], bio- polymers [9] and solid surfaces [10]. Other applications of solvatochromic probes include identifying the solvent composition at which the phase transition occurs in polymers [11] and gels [12], and the investigation of micropolarity and local mobility of amino acid chains [13]. In our previous studies, we reported the synthesis and photophysical parameters of several series of molecular probes: i) dual probes bearing a pyrene fluorescent moiety and a TEMPO paramagnetic moiety liked by oligoethylene glycol chains [14,15], ii) dual probes bearing a dansyl fluorescent moiety and a TEMPO paramagnetic moiety liked by alkyl chains [16], and iii) bis-dansyl fluorescent probes bearing alkyl- diamine linkers of increasing length (2DA 1.n )[17]. The spectral features of these probes were analysed in water solutions of cyclodextrins [14,16,17], pluronics [15] and polymeric gels [14,16], proving their Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 237 (2020) 118413 ⁎ Corresponding author. E-mail address: iuliamatei@icf.ro (I. Matei). https://doi.org/10.1016/j.saa.2020.118413 1386-1425/© 2020 Elsevier B.V. All rights reserved. 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