Electron Transfer from Photoexcited TiO₂ to Chelating Alizarin Molecules: Reversible Photochromic Effect in Alizarin@TiO₂ under UV Irradiation

Abstract

Reduction of alizarin molecules coupled to TiO(2) nanoparticles (A@TiO(2)) occurs on UV irradiation in the presence of a sacrificial electron donor. Evidence is presented that reduction is mediated by conduction-band electrons and yields a 1,2,9,10-tetrahydroxyanthracene species which remains coupled to the TiO(2) nanoparticles. The spectrum of the reduced complex displays two overlapping broad bands centred at 480 and 650 nm which can harvest visible photons besides 900 nm, in agreement with theoretical predictions by TDDFT. The potential relevance of the dual-redox behaviour of strongly TiO(2) coupled anthraquinone dyes in the field of photocatalysis and in connection with their utilization in the development of dye-sensitized TiO(2) solar cells is briefly discussed.

Polymeric Adsorption of Methylene Blue in TiO2 Colloids—Highly Sensitive Thermochromism and Selective Photocatalysis

“…[24] Sometimes, strong adsorption can also form the organic molecule@TiO 2 hybrid nanosystem. [25][26][27][28] This research reports an interesting polymeric (MB + ) 2 and (MB + ) 3 adsorption of the MB molecule on a TiO 2 surface due to electrostatic attraction between TiO 2 and MB, resulting in the formation of an MB@TiO 2 polymeric sol. The investigation of the mechanism shows that the presence of TiO 2 provides a good surface condition for the MB polymerization.…”

DFT/TDDFT investigation on the UV-vis absorption and fluorescence properties of alizarin dye

“…Nowadays, alizarin is prepared synthetically and in recent years it has also been used as a sensitizer for dye-sensitized solar cells (DSC). [11][12][13][14][15][16][17][18][19][20] Due to the great interest in the chromatic properties of alizarin for different application fields, its photophysics and photochemistry have been widely investigated.…”

“…In particular, the structural and electronic properties of the ground state and electronic absorption spectra of alizarin [33][34][35][36] and alizarin metal complexes have been investigated [36][37][38][39] and the interaction of alizarin with TiO 2 surfaces studied in the context of DSC. [11][12][13][14][15][16][17][18][19][20] Recently, the Franck-Condon (FC) theory has been used to compute vibrationally resolved spectra to study the absorption spectra of alizarin 36 and the absorption and emission spectra of the umbelliferone-alizarin bichromophore, 40 allowing for a more meaningful comparison between simulated and experimental data.…”

TiO2–anthraquinone hybrids: from quantum-chemical design to functional materials

“…All these compounds are stable and easily available from both synthetic and natural sources, therefore they are compatible with the concept of green chemistry, however the application of organic solvents during the synthesis of dye-semiconductor hybrids cannot be avoided. Alizarin itself is a well-known photosensitizer of TiO 2 16,[30][31][32][33][34][35][36][37][38][39][40] and a preliminary report on quinizarin can also be found. 17 1 is a molecule composed of the central quinone ring, the catechol ring on the one side and the benzene ring on the opposite side.…”