No abstract

Small molecule thin films are the core of some organic optoelectronic devices. Their deposition by solution processes is an advantage for device fabrication and can be achieved via spin coating for small areas and slot-die or doctor blade for larger areas. Solution deposition of small molecule thin films is usually processed only with medium polarity solvents. Herein, the use and influence of solvents with several polarities and physicochemical properties to form small-molecule homogeneous thin films via the doctor blade technique over an area of 25 cm2 have been explored. Solvents with different polarity, heptane, chlorobenzene, N,N-dimethylformamide, acetonitrile, and methanol were used along with different deposition temperatures, from room temperature up to near the boiling temperature for each solvent. With heptane and chlorobenzene, smooth films with an average roughness of 3 nm and thickness of 100–120 nm were obtained. The film was homogeneous over the whole substrate for temperatures from room temperature to close to the boiling temperature of both solvents. On the other hand, with dimethylformamide, a film is observed when the deposition is conducted only at room temperature; when the deposition temperature increases, the formation of agglomerates of several sizes from 1 to 5 nm was observed. With acetonitrile, and methanol, no films were formed, and only nanoaggregates were created on the substrate due to the solvent high vapor pressure, and the agglomerate size depends on the deposition temperature. The measure of the contact angle of pure solvent and solutions indicated that wettability helps to film formation over the whole substrate. For heptane and chlorobenzene, a small angle was measured; meanwhile, the contact angle is large in acetonitrile leading to the formation of nanoaggregates. In the case of methanol solution, although it wets very well, no film is deposited because it has high volatility.

In the present study the molecular structure of compound 4‐(4,5‐diphenyl‐1H‐imidazol‐2‐yl)benzaldehyde [DPI‐BA] and its optoelectronic properties are reported. The SCXRD analysis revealed that DPI‐BA crystallizes in the Orthorhombic crystal system and Pca21 space group with Z=4. The intermolecular N‐H⋅⋅N interaction generates a one‐dimensional chain. An interesting halochromic behavior was observed for the DPI‐BA in THF:H2O (9:1) by varying the pH analysis. The fluorescence properties of neutral and acid‐base solutions were monitored by UV‐vis and 1D, 2D‐NMR studies. The HCl vapor was bubbled to the DPI‐BA in the DMSO‐d6 solution and the corresponding fluorescence wavelength changed from green (λem 501 nm) to blue (λem 459 nm). In the case of a basic pH solution was made by adding NaOH flakes to the DPI‐BA DMSO‐d6 solution and then the fluorescence wavelength changed from green to orange (λem 595 nm). The λmax of PL emission could be correlated to intermolecular charge transfer (ICT). The optical absorption and cyclic voltammetry measurement were performed to determine the bandgap. Besides, the quantitative analysis of intermolecular interactions through PIXEL, QTAIM, NBO, GIAO‐DFT methods and DFT studies was correlated to the experiments.