Molecular structure of unsubstituted oxadiazolic analog of ortho -POPOP and peculiarities of conformational structure of this class of sterically hindered organic compounds

Photophysical Parameters, Excitation Energy Transfer, and Photoreactivity of 1,4-Bis(5-phenyl-2-oxazolyl)benzene (POPOP) Laser Dye

“…Derivatives of 1,2-bis-(5-phenyloxazol-2-yl)benzene [23][24][25] are ortho analogs of the well-known scintillation luminophore POPOP [ They belong to the class of efficient fluorescent organic compounds with abnormally high Stokes shifts [26]. In contrast to their planar paraisomers [27], molecules of the title series are characterized by essential nonplanarity caused by the steric repulsion of two bulky heterocyclic moieties introduced into the orthopositions of the central benzene ring [28].…”

5-(4-Fluorophenyl)-2-[2-(5-phenyl-1,3-oxazol-2-yl)phenyl]-1,3-oxazole

“…All the already examined crystal structures of the ortho-analogs of POPOP are characterized by essentially different angles between the planes of the central phenylene and each of the attached heterocyclic rings. Thus, two quasi-planar fragments containing two and three aromatic or heteroaromatic rings could be defined for the ortho-POPOPs molecules in crystals (Doroshenko, 1994(Doroshenko, , 1997(Doroshenko, , 2000b(Doroshenko, , 2002b).…”

“…For background to the practical applications of 1,2-bis-(5phenyl-oxazol-2-yl)benzene (ortho-POPOP) analogs (spectroscopic and fluorescence kinetics data), see: Doroshenko et al (1996Doroshenko et al ( , 1999Doroshenko et al ( , 2000aDoroshenko et al ( ,c, 2002a, Kirichenko et al (1998). For related structures, see: Doroshenko et al (1994Doroshenko et al ( , 1997Doroshenko et al ( , 2000bDoroshenko et al ( , 2002b. Table 1 Hydrogen-bond geometry (Å , ).…”

“…Synthesis of the title compound was conducted according to the procedure presented on Fig. 4: 1 g (0.0038 mol) of 2-(5-phenyl-oxazol-2-yl)benzoic acid (Doroshenko, 1994(Doroshenko, , 2000b(Doroshenko, , 2002b 4-F-ω-Amino-acetophenone hydrochloride: 6.5 g (0.046 mol) of hexamethylenetetramine was added portionwise at continuous stirring to the solution of 10 g (0.046 mol) of 4-F-ω-Br-acetophenone in 70 ml of chloroform. The reaction mixture was stirred during 5 h, then the precipitated solid was filtered, washed with chloroform, dried and mixed with 25 ml of concentrated HCl in 70 ml of ethanol.…”

“…The scheme of the synthesis of the title compound. General procedure is analogous to that of Doroshenko (1994Doroshenko ( , 2000bDoroshenko ( , 2002b).…”