Thitipone Suwunwong

Influence of trimethoxy-substituted positions on fluorescence of heteroaryl chalcone derivatives

Three series of heteroaryl chalcones, (E)-1-(2-pyridyl)-3-(X)prop-2-en-1-one (Ia-Ic), (E)-1-(2-thienyl)-3-(X)prop-2-en-1-one (IIa-IIc), and (E)-1-(2-furyl)-3-(X)prop-2-en-1-one (IIIa-IIIc), where X = 2,4,5-trimethoxyphenyl (for series a), X = 2,4,6-trimethoxyphenyl (for series b), and X = 3,4,5-trimethoxyphenyl (for series c) were synthesised using basic catalysed aldol condensation and characterised using 1H NMR and FT-IR spectroscopies. Compound IIa was also characterised by single crystal X-ray analysis. The absorption and fluorescence emission spectra of these compounds revealed that the absorption and fluorescence depended on the heterocycle rings and trimethoxysubstituted phenyl rings linked to the enone system. The position of methoxy groups substantially affected the fluorescent properties. Compounds Ia-IIIa containing the 2,4,5-trimethoxyphenyl moiety exhibited the red-shift phenomenon and strong emission fluorescence.

(E)-1-(2-Thien-yl)-3-(3,4,5-trimethoxy-phen-yl)prop-2-en-1-one.

The molecule of the title heteroaryl chalcone, C16H16O4S, which consists of substituted thiophene and benzene rings bridged by the prop-2-en-1-one group, is slightly twisted. The dihedral angle between the thiophene and 3,4,5-trimethoxyphenyl rings is 12.18 (4)°. The three methoxy groups have two different conformations; two methoxy groups are coplanar [C—O—C—C torsion angles = −1.38 (12) and 0.47 (12)°] whereas the third is (-)-synclinal with the benzene ring. In the crystal structure, adjacent molecules are linked in a face-to-side manner into chains along the c axis by weak C—H⋯O(enone) interactions. These chains are stacked along the b axis by weak C—H⋯O(methoxy) interactions.

3-(4-Bromo-phen-yl)-5-[4-(dimethyl-amino)-phen-yl]-4,5-dihydro-1H-pyrazole-1-carbothio-amide.

The molecule of the title pyrazole derivative, C18H19BrN4S, is twisted. The central pyrazole ring, which adopts a flattened envelope conformation, is almost coplanar with the 4-bromophenyl ring, whereas it is inclined to the 4-(dimethylamino)phenyl ring making dihedral angles of 1.68 (6) and 85.12 (6)°, respectively. The dihedral angle between the two benzene rings is 86.56 (6)°. The dimethylamino group is slightly twisted from the attached benzene ring [C—C—N—C torsion angles = 8.4 (2) and 8.9 (2)°]. In the crystal, molecules are linked by intermolecular N—H⋯S hydrogen bonds into chains along [20]. The crystal is further stabilized by C—H⋯π interactions.

(E)-1-(2-Fur-yl)-3-(3,4,5-trimeth-oxy-phen-yl)prop-2-en-1-one.

The title molecule, C16H16O5, is twisted; the dihedral angle between the furan and 3,4,5-trimethoxyphenyl rings is 12.14 (13)°. The two methoxy groups at the meta positions of the benzene ring are close to being coplanar with the ring [C—O—C—C = −0.6 (3) and 1.4 (3)°], whereas the third methoxy group, at the para position, is (+)-anticlinal with respect to the benzene ring [C—O—C—C = 104.9 (2)°]. In the crystal, molecules are linked by weak C—H⋯O bonds to stack along the b axis and further C—H⋯O interactions consolidate the structure.

(E)-1-(2-Fur-yl)-3-(2,4,6-trimeth-oxy-phen-yl)prop-2-en-1-one.

In the title heteroaryl chalcone derivative, C16H16O5, the dihedral angle between the furan and benzene rings is 14.45 (6)°. The three methoxy groups are almost coplanar with their attached benzene ring [C—C—O—C torsion angles = 2.07 (17), −5.04 (17) and 2.85 (16)°]. An intramolecular C—H⋯O hydrogen bond occurs. In the crystal, adjacent molecules are linked into X-shaped chains along the c axis by weak C—H⋯O(enone) interactions. These chains are stacked along the b axis. C⋯O [3.3308 (13)–3.4123 (14) Å] short contacts are also observed.

(E)-1-(4-Bromo-phen-yl)-3-(2,4,6-trimethoxy-phen-yl)prop-2-en-1-one.

The molecule of the title chalcone derivative, C18H17BrO4, is twisted, the dihedral angle between the 4-bromophenyl and 2,4,6-trimethoxyphenyl rings being 39.17 (6)°. The three methoxy groups are oriented in two different conformations whereby two methoxy groups are coplanar, whereas the third is twisted with respect to the attached benzene ring [C—O—C—C torsion angles of −2.84 (18), −2.80 (18) and −9.31 (18)°]. Weak intramolecular C—H⋯O interactions generate two S(5) and one S(6) ring motifs. In the crystal structure, molecules are linked into supramolecular sheets parallel to the bc plane by weak C—H⋯O interactions. These sheets are stacked along the a axis. The crystal structure is further stabilized by weak C—H⋯π interactions.

6-(4-Amino­phen­yl)-4-(4-eth­oxy­phen­yl)-2-meth­oxy­nicotinonitrile

In the title molecule, C21H19N3O2, the central pyridine ring makes dihedral angles of 14.46 (9) and 34.67 (8)° with the 4-amino- and 4-ethoxy-substituted benzene rings, respectively. The ethoxy group is essentially coplanar with the attached benzene ring [C—O—C—C torsion angle = 178.70 (16)°] as is the methoxy group with the pyridine ring [C—O—C—N torsion angle = −3.0 (3)°]. In the crystal, molecules are linked by N—H⋯N hydrogen bonds into chains along [201]. Weak C—H⋯O hydrogen bonds and C—H⋯π interactions are also present.

6-(4-Bromo­phen­yl)-2-eth­oxy-4-(4-ethoxy­phen­yl)nicotinonitrile

The molecule of the title nicotinonitrile derivative, C22H19BrN2O2, is non-planar, the central pyridine ring making dihedral angles of 7.34 (14) and 43.56 (15)° with the 4-bromophenyl and 4-ethoxyphenyl rings, respectively. The ethoxy group of the 4-ethoxyphenyl is slightly twisted from the attached benzene ring [C—O—C—C = 174.2 (3)°], whereas the ethoxy group attached to the pyridine ring is in a (+)syn-clinal conformation [C—O—C—C = 83.0 (3)°]. A weak intramolecular C—H⋯N interaction generates an S(5) ring motif. In the crystal structure, the molecules are linked by weak intermolecular C—H⋯N interactions into screw chains along the b axis. These chains stacked along the a axis. π–π interactions with centroid–centroid distances of 3.8724 (16) and 3.8727 (16) Å are also observed.

(Z)-3-(9-Anthr­yl)-1-(4-methoxy­phen­yl)prop-2-en-1-one

The title chalcone derivative, C24H18O2, which consists of the substituted 4-methoxyphenyl and anthracene rings bridged by the prop-2-en-1-one unit, exists in a cis configuration. The molecule is twisted, the interplanar angle between the benzene and anthracene rings being 69.50 (10)°. The methoxy group is coplanar with the attached benzene ring [C—O—C—C angle = 2.9 (3)°]. In the crystal structure, molecules are linked into chains along the a axis by a weak C—H⋯O(enone) interaction. The chains are stacked along the c axis. A C—H⋯π interaction involving the benzene ring is observed.

(E)-3-(Anthracen-9-yl)-1-(4-bromo­phen­yl)prop-2-en-1-one

In the title molecule, C23H15BrO, the prop-2-en-1-one unit is planar and it makes dihedral angles of 20.9 (1) and 45.8 (1)°, respectively, with the 4-bromophenyl ring and the anthracene ring system. The interplanar angle between the 4-bromophenyl ring and the anthracene ring system is 35.52 (7)°. In the crystal structure, molecules are linked into dimers by C—H⋯Br hydrogen bonds, and the dimers are linked into a zigzag network parallel to the bc plane by weak C—H⋯O hydrogen bonds and C—H⋯π interactions involving the central benzene ring of the anthracene ring system.