Comprehensive Understanding of Structure‐Controlling Factors of a Zinc Tetraphenylporphyrin Thin Film Using pMAIRS and GIXD Techniques

Abstract

The performance of an organic electronic device is significantly influenced by the anisotropic molecular structure in the film, which has long been difficult to predict especially for a solution process. In the present study, a zinc tetraphenylporphyrin (ZnTPP) thin film prepared by a solution process was chosen to comprehensively explore the molecular-arrangement mechanism as a function of representative film-preparation parameters: solvent, film-preparation technique, and thermal annealing. The anisotropic structure was first analyzed by using a combination of infrared p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) and grazing incidence X-ray diffraction (GIXD), which readily revealed the molecular orientation and crystal structure, respectively. As a result, the real dominant factor was found to be the evaporation time of the solvent that determines the initial two different molecular arrangements, types-I and -II, while the thermal annealing was found to play an additional role of improving the molecular order. The correlation between the molecular orientation and the crystal structure was also revealed through the individual orientation analysis of the porphyrin and phenyl rings.

Impact of Kinetically Restricted Structure on Thermal Conversion of Zinc Tetraphenylporphyrin Thin Films to the Triclinic and Monoclinic Phases

“…25 This result is supported by the weak XRD peak at 6.9° (Figure 3b) that corresponds to the monoclinic phase. 25,37 Of note is that another polymorph is also observed with a minor quantity in the FD-100 film by new band components at 762 and 748 cm -1 in the pMAIRS spectra ( Figure 3c), which are attributed to the triclinic phase 38 of ZnTPP as discussed later. Here, the (C-H) band of the 'phenyl' ring at 748 cm -1 appears mainly in the OP spectrum, which means that the 'phenyl' rings in the triclinic crystallites have the face-on orientation judging from the surface selection rule of pMAIRS.…”

“…According to the surface selection rule of pMAIRS, 21,22 when the (C-H) band appears stronger in the IP spectrum than that in OP one, the rings have the edge-on orientation; whereas the face-on orientation is revealed when the OP band is stronger than the IP one. 25 On this rule, the porphyrin ring in the 'FD' film is found to have the face-on orientation, since the (C-H)…”

Controlling Mechanism of Molecular Orientation of Poly(3-alkylthiophene) in a Thin Film Revealed by Using pMAIRS

“…Since both Chl and SC have a fast solvent-evaporation character, for example, the combination of Chl-SC gives a very short evaporation time. 24 In this paper, the films are systematically named as Chl-SC-X (X; spin-speed). Since the TCB needs a long evaporation time to have a dried film due to the low-volatile character, 24,26,32 the spin speed is fixed at 1500 rpm for the TCB-SC series.…”

“…24 In this paper, the films are systematically named as Chl-SC-X (X; spin-speed). Since the TCB needs a long evaporation time to have a dried film due to the low-volatile character, 24,26,32 the spin speed is fixed at 1500 rpm for the TCB-SC series. Since the evaporation time of the Chl-SC film, on the other hand, is a relatively short, the time can be controlled by changing the spin speed, X.…”

Physicochemical Nature of Perfluoroalkyl Compounds Induced by Fluorine

“…Since the RA spectrometry detects only the surface perpendicular component, however, it is difficult to conclude the R f group of MA‐R f 9 has a ‘perfectly’ perpendicular stance to the surafce. The pMAIRS technique works powerfully for this purpose, since it provides both in‐plane (IP) and out‐of‐plane (OP) spectra from an identical thin‐film sample. The IP and OP spectra corresponds to the conventional transmission and RA spectra, respectively…”