Abstract
The title pull-push chromophores, 2-[4-(di-methyl-amino)-benzyl-idene]-1H-indene-1,3(2H)-dione, C18H15NO2 (ID[1]) and (E)-2-{3-[4-(di-methyl-amino)-phen-yl]allyl-idene}-1H-indene-1,3(2H)-dione, C20H17NO2 (ID[2]), have donor-π-bridge-acceptor structures. The mol-ecule with the short π-bridge, ID[1], is almost planar while for the mol-ecule with a longer bridge, ID[2], is less planar. The benzene ring is inclined to the mean plane of the 2,3-di-hydro-1H-indene unit by 3.19 (4)° in ID[1] and 13.06 (8)° in ID[2]. The structures of three polymorphs of compound ID[1] have been reported: the α-polymorph [space group P21/c; Magomedova & Zvonkova (1978 ▸). Kristallografiya, 23, 281-288], the β-polymorph [space group P21/c; Magomedova & Zvonkova (1980 ▸). Kristallografiya, 25 1183-1187] and the γ-polymorph [space group Pna21; Magomedova, Neigauz, Zvonkova & Novakovskaya (1980 ▸). Kristallografiya, 25, 400-402]. The mol-ecular packing in ID[1] studied here is centrosymmetric (space group P21/c) and corresponds to the β-polymorph structure. The mol-ecular packing in ID[2] is non-centrosymmetric (space group P21), which suggests potential NLO properties for this crystalline material. In both compounds, there is short intra-molecular C-H⋯O contact present, enclosing an S(7) ring motif. In the crystal of ID[1], mol-ecules are linked by C-H⋯O hydrogen bonds and C-H⋯π inter-actions, forming layers parallel to the bc plane. In the crystal of ID[2], mol-ecules are liked by C-H⋯O hydrogen bonds to form 21 helices propagating along the b-axis direction. The mol-ecules in the helix are linked by offset π-π inter-actions with, for example, a centroid-centroid distance of 3.9664 (13) Å (= b axis) separating the indene rings, and an offset of 1.869 Å. Spectroscopic and electrochemical measurements show the ability of these compounds to easily transfer electrons through the π-conjugated chain.
Highlights
The title pull–push chromophores, 2-[4-(dimethylamino)benzylidene]-1Hindene-1,3(2H)-dione, C18H15NO2 (ID[1]) and (E)-2-{3-[4-(dimethylamino)phenyl]allylidene}-1H-indene-1,3(2H)-dione, C20H17NO2 (ID[2]), have donor– -bridge–acceptor structures
In the crystal of ID[1], molecules are linked by C—HÁ Á ÁO hydrogen bonds and C—HÁ Á Á interactions, forming layers parallel to the bc plane
In the crystal of ID[2], molecules are liked by C—HÁ Á ÁO hydrogen bonds to form 21 helices propagating along the b-axis direction
Summary
Organic molecules containing donor and acceptor groups connected by a conjugated -bridge (push–pull chromophores) are important in many areas of materials chemistry, especially organic electronics and optoelectronics. Applications of pull–push molecules can be related to their properties such as intramolecular charge transfer and specific molecular arrangements in the solid state. Intramolecular charge transfer from donor to acceptor via a -bridge defines their colour, light absorption and emission, hyperpolarizability and other optoelectronic effects. The spectroscopic properties of pull–push molecules are related to the donor and acceptor strength in these molecules and to the length of the -bridge. Many such compounds have been studied, but not all of their crystal structures have been reported. We have repeated the structural study of ID[1] in order to establish exactly which polymorph we obtained It was characterized by spectroscopic and electrochemical measurements.
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