Herein, we report a homoleptic iron complex bearing tridentate bis‐carbene (CNC) ligands designed for sensitization of TiO2 photoanodes. Its excited state has been characterized by ultra‐fast transient spectroscopy and time‐dependent density functional theory (TD‐DFT) computations, which reveal a record triplet metal‐to‐ligand charge‐transfer (3MLCT) excited‐state lifetime (16 ps). The new dye was efficiently chemisorbed on TiO2 and promoted electron injection and photocurrent generation in a dye‐sensitized solar cell upon solar irradiation.

Herein we report the synthesis and time-resolved spectroscopic characterization of a homoleptic Fe(ii) complex exhibiting a record (3)MLCT lifetime of 26 ps promoted by benzimidazolylidene-based ligands. Time dependent density functional molecular modeling of the triplet excited state manifold clearly reveals that, at equilibrium geometries, the lowest (3)MC state lies higher in energy than the lowest (3)MLCT one. This unprecedented energetic reversal in a series of iron complexes, with the stabilization of the charge-transfer state, opens up new perspectives towards iron-made excitonic and photonic devices, hampering the deactivation of the excitation via metal centered channels.

The first combined theoretical and photovoltaic characterization of both homoleptic and heteroleptic Fe(ii)-carbene sensitized photoanodes in working dye sensitized solar cells (DSSCs) has been performed. Three new heteroleptic Fe(ii)-NHC dye sensitizers have been synthesized, characterized and tested. Despite an improved interfacial charge separation in comparison to the homoleptic compounds, the heteroleptic complexes did not show boosted photovoltaic performances. The ab initio quantitative analysis of the interfacial electron and hole transfers and the measured photovoltaic data clearly evidenced fast recombination reactions for heteroleptics, even associated with un unfavorable directional electron flow, and hence slower injection rates, in the case of homoleptics. Notably, quantum mechanics calculations revealed that deprotonation of the not anchored carboxylic function in the homoleptic complex can effectively accelerate the electron injection rate and completely suppress the electron recombination to the oxidized dye. This result suggests that introduction of strong electron-donating substituents on the not-anchored carbene ligand in heteroleptic complexes, in such a way of mimicking the electronic effects of the carboxylate functionality, should yield markedly improved interfacial charge generation properties. The present results, providing for the first time a detailed understanding of the interfacial electron transfers and photovoltaic characterization in Fe(ii)-carbene sensitized solar cells, open the way to a rational molecular engineering of efficient iron-based dyes for photoelectrochemical applications.

Conjugated donor-acceptor block co-oligomers that self-organize into D-A mesomorphic arrays have raised increasing interest due to their potential applications in organic solar cells. We report here a combined experimental and computational study of charge transfer (CT) state formation and recombination in isolated donor-spacer-acceptor oligomers based on bisthiophene-fluorene (D) and perylene diimide (A), which have recently shown to self-organize to give a mesomorphic lamellar structure at room temperature. Using femtosecond transient absorption spectroscopy and Time-Dependent Density Functional Theory in combination with the Marcus-Jortner formalism, the observed increase of the CT lifetimes is rationalized in terms of a reduced electronic coupling between D and A brought about by the chemical design of the donor moiety. A marked dependence of the CT lifetime on solvent polarity is observed, underscoring the importance of electrostatic effects and those of the environment at large. The present investigation therefore calls for a more comprehensive design approach including the effects of molecular packing.

Characterization data of selected compounds 2) Complementary steady-state spectra DPP 3) Spectra of differential ε 's 4) Singular Value Decomposition 5) 290fs DADS 6) References 1) Characterization data of selected compounds TPA-DPP-TPA λ max abs (THF) = 623 nm (ε = 83 500 M-1 cm-1); λ max emis (THF) = 660 nm, Φ = 0.32 in THF (the reference used was a reported BODIPY dye (Φ = 0.49 in CH 2 Cl 2 , excitation @650 nm). 1

Constructing heterogeneous interfaces on a nanoscale that can prominently improve the gas-sensing properties has been comprehensively reported. However, the effect of parallel heterostructures formed by unique synthetic means on nitrogen dioxide room-temperature sensing properties still needs to be clarified, which hinders the development of heterostructured hybrid materials in the field of gas sensing. In this study, large-sized MoS2 was parallel-wrapped on the surface of nanoscale Bi2S3 rods, and then, the Bi2S3/MoS2 nanocomposite aerogels were formed by freeze drying and calcination. The NO2 sensing performance of the hybrids and possible surface processes at room temperature have been investigated and deduced. The as-prepared nanocomposite aerogels (Bi2S3/MoS2-2) exhibited a larger specific surface area, a mass of active defect sites, and a higher charge density, thus possessing 15- and 20-times higher response than that of pristine MoS2 nanosheets and Bi2S3 nanorods, respectively. This study provides an efficient way to synthesize large-area parallel heterostructures between two bis-sulfides (Bi2S3 and MoS2), leading to excellent NO2 gas sensing performance.

A detailed spectro-temporal analysis of the ultrafast transient absorption and fluorescence signals allows deciphering multiple energy and charge transfer processes in a lightharvesting molecular triad designed as photo-sensitizing unit featuring a novel BODIPY compound.

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