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

Abstract

The powerful combination of p-polarized multiple-angle incidence resolution spectroscopy (pMAIRS) and grazing incidence X-ray diffraction (GIXD) is applied to the structural characterization of zinc tetraphenylporphyrin (ZnTPP) in vapor-deposited films as a function of the deposition rate. The deposition rate is revealed to have an impact on the initial film structure and its conversion by thermal annealing. The pMAIRS spectra reveal that a fast deposition rate yields a kinetically restricted amorphous film of ZnTPP having a “face-on orientation”, which is readily discriminated from another “randomly oriented” amorphous film generated at a slow deposition rate. In addition, the GIXD patterns reveal that the film grown at a slow deposition rate involves a minor component of triclinic crystallites. The different initial film structure significantly influences the thermal conversion of ZnTPP films. The randomly oriented amorphous aggregates with the triclinic crystallite seeds are converted to the thermodynamically stable phase (monoclinic) via the metastable triclinic phase. The kinetically restricted structure, on the other hand, is followed by a simple thermal conversion: the molecules are directly converted to the monoclinic one rather than the triclinic one.

Alternative Face-on Thin Film Structure of Pentacene

“…The discussion on the Vis-pMAIRS results can readily be supported by IR-pMAIRS measurements, which are powerful for revealing the molecular orientation of each normal mode as well as the molecular packing 34–36 . The most important bands are the C–H out-of-plane deformation vibration (γ(C–H)) bands of an aromatic ring that appear typically in a region less than 1000 cm −1 .…”

“…The most important bands are the C–H out-of-plane deformation vibration (γ(C–H)) bands of an aromatic ring that appear typically in a region less than 1000 cm −1 . On the surface selection rule (SSR) of pMAIRS 27 , the intensity ratio of the IP band to the OP one reveals the ring orientation 34–36 , since the IP and OP spectra have a common ordinate scale 33 .…”

Structure control of a zinc tetraphenylporphyrin thin film by vapor annealing using fluorine containing solvent

“…In the as-spun film, the amorphous structure is readily confirmed by four key bands at 798, 752, 719 and 700 cm -1 in Fig. 6a, which are known to be specific to the amorphous state (marked by 'A') [25,28]. In the HCFC-SVA film, on the other hand, the marker bands appear at different positions, and instead some characteristic bands of the triclinic phases (marked by 'T') appear apparently accompanying monoclinic phases (marked by 'Ma') with a very minor intensity, as found in Fig.…”

“…According to our former study, in a thin film, the monoclinic (Ma) phase has a thermodynamically stable structure; whereas the triclinic one has a metastable one [28], and no report is available for obtaining the triclinic one in a wet-processed film. The present study is thus the first report that the triclinic crystal is readily prepared by a 'wet process' in a thin film.…”

“…2b) is difficult to be prepared by a wet process using a good solvent [25]. Although the triclinic one can be obtained by the vapor deposition technique [28], a wet process is better when considering the merit of efficient mass-5 production.…”