Abstract
Two novel 1,3,5-trisubstituted pyrazoline derivatives—1-acetyl-3-(4-methoxyphenyl)-5-(6-methoxy-2-naphthyl)-pyrazoline (2a) and 1-(4-nitrophenyl)-3-(4-methoxyphenyl)-5-(6-methoxy-2-naphtyl)-pyrazoline (2b)—were synthesized and their structures were determined by single crystal X-ray crystallography. Both of the two crystals exhibit twisted structures due to the large dihedral angles between the pyrazolinyl ring and the aromatic ring at the 5-position (88.09° for 2a and 71.26° for 2b). The optical–physical properties of the two compounds were investigated. The fluorescent emission of 2b arises from the 1,3-disubstituted pyrazoline chromophores and exhibits a red shift in polar solvents and solid-state, which could be attributed to photo-induced intramolecular charge transfer (ICT) from N1 to C3 in the pyrazoline moiety and the intermolecular interactions within the crystal. The fluorescent emissions of 2a (λmax 358–364 nm) in solvents and solid-state both come from 6-methoxy-2-naphthyl chromophores, which are fairly insensitive to the solvent polarity.
Highlights
A development in the design and preparation of novel organic luminescent materials has recently been the subject of great interest from both academia and industry, including the fields of fluorescent biological labels, optical sensors, and organic light-emitting diodes (OLEDs) [1,2,3,4]
Two novel 1,3,5-trisubstituted pyrazoline derivatives were synthesized and their structures were confirmed by IR, 1H Nuclear Magnetic Resonance (NMR) and X-ray crystallographic analysis
Two novel 1,3,5-trisubstituted pyrazoline derivatives were synthesized and their structures were confirmed by IR, 1 H NMR and X-ray crystallographic analysis
Summary
A development in the design and preparation of novel organic luminescent materials has recently been the subject of great interest from both academia and industry, including the fields of fluorescent biological labels, optical sensors, and organic light-emitting diodes (OLEDs) [1,2,3,4]. Amongst the numerous organic luminescent materials, pyrazoline and its derivatives have received increasing attention due to their excellent electro–optical properties and wide range of applications [5,6,7,8,9,10]. 1-acetyl-pyrazoline derivatives show high sensitivity and selectivity towards different metal ions and can be used as fluorescent sensors [14]. Relevant research about the photophysical properties of 1-acetyl-pyrazoline derivatives, especially in solid-state, is rare. The two compounds contain the same substituent groups on 3- and 5-positions, but different electron-withdrawing groups on. The substituent groups on 1-position of the pyrazoline ring could primarily influence the photophysical properties [15]. Crystals 2018, 8, 467; doi:10.3390/cryst8120467 www.mdpi.com/journal/crystals dilute ethanolic sodium hydroxide solution at room temperature, according to the Claisen-Schmidt condensation given in the literature [16,17]
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