Effects of surface-anchoring mode and aggregation state on electron injection from chalcogenorhodamine dyes to titanium dioxide

Dye aggregation identified by vibrational coupling using 2D IR spectroscopy

“…The efficiency of charge transfer depends on many factors, including the photosensitizer electronic orbitals, conjugation of the linker, and the anchoring groups. [5][6][7][8][9][10][11][12][13][14][15] For example, differing levels of conjugation have been shown to inject electrons with different, sometimes multiexponential, kinetics, and different binding groups also show different efficiencies of charge transfer. 11,12 Dye orientation on the surface also has a large effect, as a dye molecule that is lying flat usually has different electron transfer rates than those perpendicular to the surface.…”

Change in spectral properties of dyes upon immobilization on silicon surfaces: a combined theoretical and experimental study

“…3 a CPK model structure of dye A for theoretical calculations (a) attached using (i) APTES-(ii) PEI. b Spectra of dye A in the immobilised state involving experimental and theoretical spectra of (i) non-interacting dye molecule with both linkers (ii) interacting and non-interacting dye molecules with APTES linker (iii) interacting and non-interacting dye molecules with PEI linker ◂ Considering that the theoretical spectra indicates that only covalent bond formation does not cause such magnitude of red shift in absorption maxima, a possible reason is formation of aggregates [28] which was indicated in the case of dye A. Formation of such aggregates upon immobilization of carboxylate dyes on different surfaces has been reported by Mulhern et al [28] and Choi et al [53].…”

“…This study would help design sensors with bi-functional dyes. While the effect of the solution environment [26] and absorption on solid surface [27,28] have been well studied, most of the work have been based only on experiments, and does not discuss the effect of change of linker molecules in case of covalent attachment of dyes. In this work we have combined theoretical calculations and experimental observations to understand the effects of immobilization on spectral properties of dyes and the shifts due to formation of aggregates.…”

Panchromatic Sensitizer for Dye-Sensitized Solar Cells: Unsymmetrical Squaraine Dyes Incorporating Benzodithiophene π-Spacer with Alkyl Chains to Extend Conjugation, Control the Dye Assembly on TiO2, and Retard Charge Recombination

“…The initial results of the squaraine based DSSCs were poor compared to organometallic dyes because of strong aggregation on metal oxide surface, which hampered the IPCE, leading to low PCEs in the absence of coadsorbents (like 3α,7α-dihydroxy-5β-cholanic acid, CDCA). − Aggregation of dyes on TiO 2 is common phenomenon and has variable effect on the performance of DSSCs. ,,− These aggregates can be studied by UV–vis spectroscopy as blue-shifted (H-type aggregates) or red-shifted (J-type aggregates) absorption with respect to monomer absorption. In some cases aggregation helped in broadening the absorption spectra, which increased the light harvesting efficiency − whereas in many instances it reduced the photocurrent through self-quenching processes where significant portion of absorbed photons was wasted due to deactivation of the excited state. ,, Efforts have been made to increase the absorption of squaraine into the far-red region as well as to avoid aggregation by tuning the structural design. Yum et al reported the first unsymmetrical squaraine dye (SQ1) where carboxylic group was attached to the indolium group.…”