Design, Synthesis, and Photophysical Properties of 5-Aminobiphenyl Substituted [1,2,4]Triazolo[4,3-c]- and [1,2,4]Triazolo[1,5-c]quinazolines.

Two series of novel [1,2,4]triazolo[4,3-c]- and [1,2,4]triazolo[1,5-c]quinazoline fluorophores with 4'-amino[1,1']-biphenyl residue at position 5 have been prepared via Pd-catalyzed cross-coupling Suzuki-Miyaura reactions. The treatment of 2-(4-bromophenyl)-4-hydrazinoquinazoline with orthoesters in solvent-free conditions or in absolute ethanol leads to the formation of [4,3-c]-annulated triazoloquinazolines, whereas [1,5-c] isomers are formed in acidic media as a result of Dimroth rearrangement. A 1D-NMR and 2D-NMR spectroscopy, as well as a single-crystal X-ray diffraction analysis, unambiguously confirmed the annelation type and determined the molecular structure of p-bromophenyl intermediates and target products. Photophysical properties of the target compounds were investigated in two solvents and in the solid state and compared with those of related 3-aryl-substituted [1,2,4]triazolo[4,3-c]quinazolines. The exclusion of the aryl fragment from the triazole ring has been revealed to improve fluorescence quantum yield in solution. Most of the synthesized structures show moderate to high quantum yields in solution. Additionally, the effect of solvent polarity on the absorption and emission spectra of fluorophores has been studied, and considerable fluorosolvatochromism has been stated. Moreover, electrochemical investigation and DFT calculations have been performed; their results are consistent with the experimental observation.

3-Aryl-5-aminobiphenyl Substituted [1,2,4]triazolo[4,3-c]quinazolines: Synthesis and Photophysical Properties.

Amino-[1,1']-biphenyl-containing 3-aryl-[1,2,4]triazolo[4,3-c]quinazoline derivatives with fluorescent properties have been designed and synthesized. The type of annelation of the triazole ring to the pyrimidine one has been unambiguously confirmed by means of an X-ray diffraction (XRD) method; the molecules are non-planar, and the aryl substituents form the pincer-like conformation. The UV/Vis and photoluminescent properties of target compounds were investigated in two solvents of different polarities and in a solid state. The samples emit a broad range of wavelengths and display fluorescent quantum yields of up to 94% in toluene solutions. 5-(4'-Diphenylamino-[1,1']-biphenyl-4-yl)-3-(4-(trifluoromethyl)phenyl)-[1,2,4]triazolo[4,3-c]quinazoline exhibits the strongest emission in toluene and a solid state. Additionally, the solvatochromic properties were studied for the substituted [1,2,4]triazolo[4,3-c]quinazolines. Moreover, the changes in absorption and emission spectra have been demonstrated upon the addition of water to MeCN solutions, which confirms aggregate formation, and some samples were found to exhibit aggregation-induced emission enhancement. Further, the ability of triazoloquinazolines to detect trifluoroacetic acid has been analyzed; the presence of TFA induces changes in both absorption and emission spectra, and acidochromic behavvior was observed for some triazoloquinazoline compounds. Finally, electronic-structure calculations with the use of quantum-chemistry methods were performed for synthesized compounds.

Push-Pull Structures Based on 2-Aryl/thienyl Substituted Quinazolin-4(3H)-ones and 4-Cyanoquinazolines.

Design and synthesis of 2-(aryl/thiophen-2-yl)quinazolin-4(3H)-ones and 4-cyano-2-arylquinazolines with Et2N-, Ph2N- or carbazol-9-yl- electron donating fragment are described. The key photophysical properties of these compounds have been studied by UV/Vis absorption and fluorescence spectroscopy in solvents of different polarity (toluene and MeCN). 2-(Aryl/thiophen-2-yl)quinazolin-4(3H)-ones show fluorescence in blue-green region in toluene solution with quantum yields up to 89% in the case of 2-(4'-N,N-diphenylamino[1,1'-biphenyl]-4-yl)-quinazolin-4(3H)-one. Moreover, triphenylamino derivative based on quinazolin-4(3H)-one with para-phenylene linker displays the highest quantum yield of 40% in powder. The fluorescence QY of Et2N and Ph2N derivatives decrease when going from toluene to MeCN solution, whereas carbazol-9-yl counterparts demonstrate strengthening of intensity that emphasizes the strong influence of donor fragment nature on photophysical properties. 4-Cyanoquinazolines are less emissive in both solvents, as well as, in solid state. The introduction of cyano group into position 4 leads to orange/red colored powder and dual emission bands. Some molecules demonstrate the increase in emission intensity upon addition of water to MeCN solution. According to frontier molecular orbitals (HOMO, LUMO) calculations, the energy gap of 4-cyanoquinazoline decreases by more than 1 eV compared to quinazolin-4-one, that is consistent with experimental data.

Substituted 2-(2-hydroxyphenyl)-3H-quinazolin-4-ones and their difluoroboron complexes: Synthesis and photophysical properties.

2-(2-Hydroxyphenyl)-3H-quinazolin-4-ones with diverse substituents at phenol ring and their six-membered difluoroboron complexes have been synthesized via few-stage approach. The photophysical properties of target compounds have been investigated in two solvents as well as in the solid state. The nature of substituents and substitution point in the phenol moiety of ligands and resulting BF2-complexes on the photophysical properties of dyes have been explored. The complex bearing two t-Bu groups proved to be the most emissive in solid state, whereas its 5-methoxy and 4-diethylamino counterparts possess strong emission in toluene solution. The dyes exhibited large Stokes shifts which was attributed to excited state intramolecular proton transfer (ESIPT). Additionally, fluorescence of quinazolinones in the mixture of THF/water was studied. All ligands demonstrated emission enhancement with increase of water fraction which was due to aggregation induced emission.