Tuning interfacial charge separation by molecular twist: a new insight into coumarin-sensitized TiO2 films

Verma, Sandeep ; Ghosh, Hirendra N. (2014) Tuning interfacial charge separation by molecular twist: a new insight into coumarin-sensitized TiO2 films Journal of Physical Chemistry C, 118 (20). pp. 10661-10669. ISSN 1932-7447

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Official URL: http://pubs.acs.org/doi/abs/10.1021/jp5023696

Related URL: http://dx.doi.org/10.1021/jp5023696

Abstract

The 7-aminocoumarin class of dyes exhibits significant molecular twisting in their electronic excited state, which has important consequences on the reaction mechanism involving the intramolecular charge-transfer (ICT) state. In this work, the relationship between the molecular structure of coumarin dye and charge separation on TiO2 surface has been explored using 7-(dialkylamino)coumarin-3-carboxylic acid dyes C343 and D1421. The alkylamino group in the form of tethered constraint geometry of the julolidyl ring of coumarin C343 and rotation free geometry of 7-N,N′-diethylamino moiety of coumarin D1421 compel planar and twisted ICT (TICT) excited states in polar solvents, respectively. The femtosecond transient absorption studies show that both the charge-transfer states participate in directional electron injection from coumarin dye into the conduction band of the TiO2 semiconductor substrate. The TICT state formation in the excited state minimizes the donor and acceptor orbital overlap and causes slow back electron-transfer reaction. Current–voltage and incident photon-to-current efficiency measurements verify the beneficial electronic decoupling of the TICT state producing superior photovoltaic response of dye-sensitized solar cells based on coumarin D1421. This work presents tuning of interfacial charge separation by molecular twist at the electron-donating site in D-π-A dye/TiO2 systems.

Item Type:Article
Source:Copyright of this article belongs to American Chemical Society.
ID Code:101986
Deposited On:27 Jan 2017 17:36
Last Modified:27 Jan 2017 17:36

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