“…Derivatives of 2-pyrazoline with aryl radicals in positions 1, 3 and 5 are known from the middle 50-th as blue-to-green fluorescent dyes, possessing relatively high quantum yields [1,2]. During decades of their history, fluorescent pyrazolines had found wide practical application as optical brightening agents [3,4], spectra shifters in scintillation techniques [5,6], components of electroluminescent devices [7][8][9], fluorescent ligands for metals cations [10][11][12][13][14], intracellular pH probes [15,16], etc. They were extensively studied in the crystalline state [17], polymer matrices [9,18], in Langmuir-Blodgett films [19] and in donor-acceptor molecular complexes with electron-deficient compounds [20,21].…”