Small molecules with ene-diol anchoring groups such as catechol form localized molecule-semiconductor charge-transfer complex with TiO2 nanoparticles. We have shown in an earlier investigation that ultrafast luminescence dynamics and corresponding anisotropy can be used to probe the localized/delocalized nature of the transitions and the charge-transfer dynamics. In this work, efforts were focused to understand the donor and acceptor strength of small molecule on the localized/delocalized nature of the charge-transfer transitions and correlate them to charge separation dynamics. The investigated molecules, as seen in figure1, include 4-nitrocatechol, 3-methoxy catechol and 3,4-dihydroxy benzoic acid, 3,4-dihydroxy benzonitrile and 3,4-dihydroxy benzaldehyde, and aminosalicyclic acid. The femtosecond fluorescence upconversion and transient absorption measurements are utilized to probe the charge-transfer dynamics in these catechol derivatives sensitized TiO2 nanoparticles. Interesting charge-transfer dynamics is observed. The ultrafast luminescence dynamics and anisotropy measurements have shown that increasing the donor strength of the catechol led to relatively more delocalized charge-transfer transitions than the catechol derivatives with an acceptor. The transient absorption dynamics have shown that the charge recombination is slowed down with increasing donor strength of catechol suggesting that the hole is localized away from the surface of the nanoparticle and thus increasing the charge separation. In addition, the charge recombination dynamics for catechols in solution and thin films are found to be entirely different. Though the solution phase measurements have shown ultrafast charge recombination for catechol sensitized TiO2 nanoparticles, the thin film investigations have shown long-lived charge separation suggesting that the chromophores with catechol can be used in solar cell and photocatalytic applications.                                                        

Ultrafast charge-transfer luminescence dynamics in catechol derivatives sensitized TiO<sub>2</sub> nanoparticles

247th National Meeting (2014)

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Ultrafast charge-transfer luminescence dynamics in catechol derivatives sensitized TiO2 nanoparticles

Ultrafast charge-transfer luminescence dynamics in catechol derivatives sensitized TiO₂ nanoparticles