<title>Polyurea with luminophor fragments in polymer chain: synthesis and spectral properties</title>

Abstract

A series of aliphatic polyureas with chromophore moieties in the polymer chain, such as 7-amino-2(4'-aminophenyl)benzoxazole, have been prepared. The absorption and fluorescence spectra of these polymers as well as corresponding chromophore-containing model urea (product of condensation of 7-amino-2(4'-amino-2'-hydroxyphenyl)benzoxazole and phenylisocyanate) were studied and compared. It was found that the special feature of the model compound and polyureas is the large value of Stokes shift due to the presence of a hydroxy group in the ortho-position to the nitrogen atom ofthe benzoxazole ring. The model ofthe excited-state proton transfer in molecules containing fragments of 2-(2'-hydroxyphenyl)benzoxazole has been used for the description of bathochromic shift in emission spectra of polymer solutions and films. According to this model, the proton remains predominantly on the phenol oxygen while in the ground state (enol form). Upon UV excitation, in the first excited singlet state, the phenol is a considerably stronger acid and the nitrogen is a stronger base. Thus, the proton is transferred from the oxygen site to the nitrogen site, and the isomer formed (5' *) is more stable than the isomer before proton transfer (Si*) S' can be then regarded as a vibrationally excited form of S. Then the molecule de-excites to the ground state, emitting a photon. In the ground state the enol form is again the more stable form and the proton will then transfer back to the oxygen. S'0 is also a vibrationally excited state of S0. Because of this process the absorption and fluorescence spectra of model urea and polyureas do not intersect and the value of Stokes shift is about 6000 cni'.

Electrochemical fluorescence switching properties of conjugated polymers composed of triphenylamine, fluorene, and cyclic urea moieties

“…The ability of these conjugated polymers to amplify their sensitivity on fluorescence responses is attributed to the efficient electronic delocalization and rapid transport of excitons along the π‐ conjugated backbone. Much research has been done on polyureas due to their outstanding thermal and mechanical properties 3–9. However, to our knowledge, fabrication of solid‐state electrofluorescent devices (EFD) using PU based materials has not been examined and reported.…”