Infrared Spectroscopic Study of α-Cyano-4-hydroxycinnamic Acid on Nanocrystalline TiO₂Surfaces: Anchoring of Metal-Free Organic Dyes at Photoanodes in Dye-Sensitized Solar Cells

Abstract

Adsorption structures of the self-assembled thin films of α-cyano-4-hydroxycinnamic acid (CHCA) anchoring on TiO2 surfaces have been studied by using temperature-dependent diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy. From the presence of the strong ν(COO − ) band at ~1390 cm -1 along with the disappearance of the OH bands in the carboxylic acid group in the DRIFT spectra at room temperature, CHCA appeared to adsorb onto TiO2 surfaces as a carboxylate form. The absence of the out-of-plane benzene ring modes of CHCA in the DRIFT spectra suggests a rather vertical orientation of CHCA on TiO2. Above ~220 o C, CHCA seemed to start to thermally degrade on TiO2 surfaces referring from the disappearance of most vibrational modes in the DRIFT spectra, whereas the ν(C ≡ N) bands were found to remain relatively conspicuous as the temperature increased even up to ~460 o C.

Precise Identification and Manipulation of Adsorption Geometry of Donor−π–Acceptor Dye on Nanocrystalline TiO2 Films for Improved Photovoltaics

“…Previous investigations also support the above assignment. Red shift of CN stretch mode is similar to those observed for other molecules with the cyanoacrylic acid as an anchor. ,− Both experimental and theoretical works show that the vibration band located between 1600 cm –1 to 1630 cm –1 is a sensitive signature for hydrogen-bonded monodentate adsorption. , …”

Tetraalkylphosphonium-Based Ionic Liquids for a Single-Step Dye Extraction/MALDI MS Analysis Platform

“…Decomposition onset begins at 288, 254, and 350 °C for PR 4 -DHB, PR 4 -CHCA, and CY101, respectively. In the case of [PR 4 ][CHCA], gas phase FT-IR data collected from the TGA efflux (supplied as Supporting Information) show a strong CO 2 peak at ∼2400 cm −1 at 188 °C, a temperature that roughly corresponds to the onset of decomposition for solid CHCA . The maximal C−H peak (∼2900 cm −1 ) found at 42 min and 338 °C for [PR 4 ][CHCA] corresponds to the greatest rate of mass loss detected by TGA (39.4 min, 312 °C) and likely signals the decomposition of the phosphonium alkyl chains.…”

Vibrational analysis of α-cyanohydroxycinnamic acid

“…The only vibrational study done on the 4CHCA was the one reported by Dembereldorj and Joo [24], wherein they investigated the vibration modes of solid 4CHCA using attenuated total reflectance (ATR) infrared spectroscopy as well as using temperature-dependent diffuse reflectance (DRIFT) where the compound was anchored on titanium oxide (TiO 2 ) surfaces. Here we present the first reported vibrational study 4CHCA and its derivative (α-cyano-3-hydroxycinnamic acid, cyanocinnamic acid and p -coumaric acid, Fig.…”