Synthesis and photostability of 1,4-bis(5-phenyloxazol-2-yl)benzene (POPOP) structural isomers and their trimethylsilyl derivatives

Abstract

In this work, a versatile synthetic method for preparation of linear phenyloxazoles and their organosilicon derivatives under mild conditions via a combination of van Leusen and direct C-H arylation reactions is reported. It was used for the synthesis of a novel trimethylsilyl (TMS) derivative of blue laser dye 1,4-bis(5-phenyloxazol-2-yl)benzene (POPOP) and its structural isomer 1,4-bis(2-phenyloxazol-5-yl)benzene (isoPOPOP) with and without TMS substituents. All of the compounds demonstrated high photoluminescence quantum yields and large molar extinction coefficients, which further increased for their TMS derivatives. Measurements of accelerated photodegradation of the dyes in diluted THF solutions revealed that POPOP-type compounds are twice more stable than their isoPOPOP-type isomers, independent of the presence or absence of TMS substituents. Cyclic voltammetry (CV) investigations revealed that POPOP-type dyes are more electrochemically stable as compared to their isoPOPOP-type isomers. Quantum chemical TD DFT calculations of the frontier energy levels of the dyes were in a good agreement with the experimental data obtained by CV. Single-crystal X-ray diffraction experiments revealed significant structural differences between crystal lattices of the dyes. Due to facile synthesis and excellent optical properties as well as high photo-and thermo-stability the novel luminescent dyes may find wide application in organic photonics.

Highly luminescent crystals of a novel linear π-conjugated thiophene–phenylene co-oligomer with a benzothiadiazole fragment

“…Most probably, the decrease in the luminescence intensity is associated with a destruction of the system of conjugated bonds of the benzothiadiazole fragment during the photo-oxidation. Similar processes of photo-oxidative degradation were observed for compounds containing oxazole fragments (Skorotetcky et al, 2017).…”

Recent Advances in the Synthesis of Oxazole-Based Molecules via van Leusen Oxazole Synthesis

“…The synthetic scheme of the two kinds of linear phenyloxazoles was exhibited, in which method A (Scheme 18) comprises fewer reaction stages compared with the preparation of the exact 1,4-bis(5phenyloxazol-2-yl)benzene (POPOP) structure (Scheme 18, method B). Due to the concise and efficient synthesis and excellent optical properties as well as high photo-and thermo-stability, the novel luminescent dyes might find broad application in organic photonics [58]. In 2016, Vinary Kumar and co-workers described a novel modified van Leusen protocol for the preparation of 5-(het)aryl oxazoles 73.…”

“…The synthetic scheme of the two kinds of linear phenyloxazoles was exhibited, in which method A (Scheme 18) comprises fewer reaction stages compared with the preparation of the exact 1,4-bis(5phenyloxazol-2-yl)benzene (POPOP) structure (Scheme 18, method B). Due to the concise and efficient synthesis and excellent optical properties as well as high photo-and thermo-stability, the novel luminescent dyes might find broad application in organic photonics [58]. In the following year, the Ponomarenko group invented various synthetic routes for the preparation of linear phenyloxazoles and their trimethylsilane (TMS) group substituted derivatives, which could serve as the novel luminescent dye under a mild condition, by a combination of the van Leusen process and direct C-H arylation reaction.…”

A new linear phenyloxazole–benzothiadiazole luminophore: crystal growth, structure and fluorescence properties

“…Recently, linear conjugated oligomers consisting of a combination of various heterocyclic groups, for example, thiophene-phenylenes (Hotta et al, 2004;Sung et al, 2007;Yamao et al, 2007;Postnikov et al, 2014;Kudryashova et al, 2016;Kazantsev et al, 2017b;Parashchuk et al, 2018), furan-phenylenes (Koskin et al, 2017;Kazantsev et al, 2017a;Sonina et al, 2018), oxazole-phenylenes (Yan et al, 2013;Skorotetcky et al, 2017;Sverbil et al, 2020 etc. ) have attracted great interest.…”

“…Our recent studies have shown that an oligomer containing a central BTD fragment, six conjugated thiophene and phenylene groups, and terminal trimethylsilyl substituents crystallizes well from solutions in the form of needle crystals of centimetre scale and is characterized by a high quantum yield of fluorescence in solutions and in the crystalline state (Postnikov et al, 2019b). In terms of optical properties, oligomers consisting of phenylene and oxazole groups are among the most efficient luminophores (Yan et al, 2013;Skorotetcky et al, 2017). In this regard, it is very interesting to develop new molecules based on BTD, oxazole and phenylene groups.…”