The low embodied energy and high power-conversion efficiency (h) over disparate light intensities renders the dyesensitized solar cell (DSSC) [1,2] a promising alternative to conventional photovoltaic technologies.[3] Significant penetration of the DSSC into the photovoltaic market, however, is hindered predominantly by the long-term stability of dyes and electrolytes under practical conditions. [4][5][6] The instability of champion (i.e., h > 10 %) dyes (which, until recently, [7] all were derivatives of [Ru(dcbpy) 2 (NCS) 2 ] (N3; dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) [2] ) in the DSSC is caused primarily by desorption of the dyes from the surface and/or liberation of the NCS À ligands from the metal centre. [5,6] While the rate of dye desorption from TiO 2 can be manipulated by replacing the À CO 2 H moiety with other anchoring groups, this strategy typically compromises electron injection into the TiO 2 .[8] An alternative approach is to replace the dcbpy ligands that comprise N3 with bidentate ligands bearing aliphatic substituents (e.g., Scheme 1 a), which serve to hinder water from reaching the surface to hydrolytically cleave the TiO 2 -dye ester linkage.[9] These groups provide the additional benefit of suppressing recombination between the electrolyte and the electrons in TiO 2 , thus leading to higher efficiencies (Scheme 1 a). [2] Chemical strategies for avoiding the labile RuÀNCS bond have been realized recently; [10,11] indeed, we [12] and others [13,14] have 1+ (ppy = 2-phenylpyridine) provide a versatile platform in this respect because: 1) the highest occupied molecular orbital (HOMO) is extended over the metal and anionic ring thus enabling its modulation through judicious installation of substituents at the À R 2 site in Scheme 1 b; [15] and 2) the low-lying excited states, which contain orbital character that resides on the p* framework of the dcbpy ligand(s), are poised for electron injection into the TiO 2 . [10,11,[15][16][17][18] This scenario leaves open the opportunity to replace one dcbpy with a bidentate ligand capable of suppressing recombination and enhancing the optical properties as per the aforementioned protocol (Scheme 1). [2,19] While we recently demonstrated synthetic access to trisheteroleptic Ru sensitizers (e.g., 1 and 2; Scheme 2), [20] we learned that removing the acid linkers raises the HOMO level of the sensitizer to potentially compromise dye regeneration. (The HOMO level of the sensitizer must lie lower in energy than the I À /I 3 À redox couple that resides at approximately + 0.5 V vs. normal hydrogen electrode (NHE).[21] Although the HOMO of 1 lies at + 0.70 V vs. NHE and therefore meets this criterion, [20] champion Ru-based sensitizers all have oxidation potentials higher than ca. + 0.9 V.[2] ) We therefore set out to overcome this potential shortcoming by introducing strongly electronwithdrawing ÀCF 3 substituents to the cyclometalating ligand to accommodate efficient dye regeneration. These design elements led to the preparation of 3-a Ru II complex devoid Sch...

Examination of the aqueous electrochemistry of a Co(II) complex bearing a pentadentate ligand suggests that the catalytic current corresponding to water oxidation is molecular in origin, and does not emanate exclusively from Co-oxide phases formed in situ.

On the basis of a time-dependent self-consistent density functional tight-binding (TD-DFTB) approach, we present a novel method able to capture the differences between direct and indirect photoinjection mechanisms in a fully atomistic picture. A model anatase TiO2 nanoparticle (NP) functionalized with different dyes has been chosen as the object of study. We show that a linear dependence of the rate of electron injection with respect to the square of the applied field intensity can be viewed as a signature of a direct electron injection mechanism. In addition, we show that the nature of the photoabsorption process can be understood in terms of orbital population dynamics occurring during photoabsorption. Dyes involved in both direct (type-I) and indirect (type-II) mechanisms were studied to test the predictive power of this method.

Characterization of the redox properties of TiO2 interfaces sensitized to visible light by a series of cyclometalated ruthenium polypyridyl compounds containing both a terpyridyl ligand with three carboxylic acid/carboxylate or methyl ester groups for surface binding and a tridentate cyclometalated ligand with a conjugated triarylamine (NAr3) donor group is described. Spectroelectrochemical studies revealed non-Nernstian behavior with nonideality factors of 1.37 ± 0.08 for the Ru(III/II) couple and 1.15 ± 0.09 for the NAr3(•+/0) couple. Pulsed light excitation of the sensitized thin films resulted in rapid excited-state injection (k(inj) > 10(8) s(-1)) and in some cases hole transfer to NAr3 [TiO2(e(-))/Ru(III)-NAr3 → TiO2(e(-))/Ru(II)-NAr3(•+)]. The rate constants for charge recombination [TiO2(e(-))/Ru(III)-NAr3 → TiO2/Ru(II)-NAr3 or TiO2(e(-))/Ru(II)-NAr3(•+) → TiO2/Ru(II)-NAr3] were insensitive to the identity of the cyclometalated compound, while the open-circuit photovoltage was significantly larger for the compound with the highest quantum yield for hole transfer, behavior attributed to a larger dipole moment change (Δμ = 7.7 D). Visible-light excitation under conditions where the Ru(III) centers were oxidized resulted in injection into TiO2 [TiO2/Ru(III)-NAr3 + hν → TiO2(e(-))/Ru(III)-NAr3(•+)] followed by rapid back interfacial electron transfer to another oxidized compound that had not undergone excited-state injection [TiO2(e(-))/Ru(III)-NAr3 → TiO2/Ru(II)-NAr3]. The net effect was the photogeneration of equal numbers of fully reduced and fully oxidized compounds. Lateral intermolecular hole hopping (TiO2/Ru(II)-NAr3 + TiO2/Ru(III)-NAr3(•+) → 2TiO2/Ru(III)-NAr3) was observed spectroscopically and was modeled by Monte Carlo simulations that revealed an effective hole hopping rate of (130 ns)(-1).

The syntheses and physicochemical properties of nine bis-tridentate ruthenium(II) complexes containing one cyclometalating ligand furnished with terminal triphenylamine (TPA) substituents are reported. The structure of each complex conforms to a molecular scaffold formulated as [Ru(II)(TPA-2,5-thiophene-pbpy)(Me(3)tctpy)] (pbpy = 6-phenyl-2,2'-bipyridine; Me(3)tctpy = trimethyl-4,4',4''-tricarboxylate-2,2':6',2''-terpyridine), where various electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) are installed about the TPA unit and the anionic ring of the pbpy ligand. It is found that the redox chemistry of the Ru center and the TPA unit can be independently modulated by (i) placing EWGs (e.g., -CF(3)) or EDGs (e.g., -OMe) on the anionic ring of the pbpy ligand (substituted sites denoted as R(2) or R(3)) and/or (ii) installing electron-donating substituents (e.g., -H, -Me, -OMe) para to the amine of the TPA group (i.e., R(1)). The first oxidation potential is localized to the TPA unit when, for example, EDGs are placed at R(1) with EWGs at R(2) (e.g., the TPA(•+)/TPA(0) and Ru(III)/Ru(II) redox couples appear at +0.98 and +1.27 V vs NHE, respectively, when R(1) = -OMe and R(2) = -CF(3)). This situation is reversed when R(3) = EDG and R(1) = -H: TPA-based and metal-centered oxidation waves occur at +1.20 and +1.11 V vs NHE, respectively. The UV-vis spectrum for each complex is broad (e.g., absorption bands are extended from the UV region to beyond 800 nm in all cases) and intense (e.g., ε ∼ 10(4) M(-1)·cm(-1)) because of the overlapping intraligand charge-transfer and metal-to-ligand charge-transfer transitions. The information derived from this study offers guiding principles for modulating the physicochemical properties of bichromic cyclometalated ruthenium(II) complexes.

The fac-[Re(CO) 3 (deeb)L] + complex (C2) where L is the (E)-2-((3-amino-pyridin-4-ylimino)-methyl)-4,6di-tert-butylphenol ancillary ligand, which presents an intramolecular hydrogen bond, has been synthesized and characterized using UV-vis, 1 H-NMR, FT-IR, cyclic voltammetry and DFT calculations.The UV-vis absorption and emission properties have been studied at room temperature and the results were compared with TDDFT calculations including spin-orbit effects. We report an alternative synthesis route for the fac-Re(CO) 3 (deeb)Br (C1) complex where deeb = (4,4 0 -diethanoate)-2,2 0 -bpy. Besides, wehave found that the C1 shows a red shift in the emission spectrum due to the nature of the ancillary electron donating ligand, while the C2 complex shows a blue shift in the emission spectrum suggesting that the ancillary ligand L has electron withdrawing ability and the importance of the intramolecular hydrogen bond. The calculations suggest that an experimental mixed absorption band at 361 nm could be assigned to MLCT and LLCT transitions. The electron withdrawing nature of the ancillary ligand in C2 explains the electrochemical behavior, which shows the oxidation of Re I at 1.83 V and the reduction of deeb at À0.77 V. 1.44 [s, 6H, (-CH 3 )], 4.49 [m, 4H], 5.92 [s, 2H, -NH 2 ], 6.45 [d; J = 5.5 Hz; 1H], 7.28 [d; J = 1.5 Hz; 1H], 7.47 [s, 1H], 7.51 [s, 1H], 7.53 [s, 1H], 8.11 [s, 1H], 8.20 [d; J = 5.5 Hz; 2H], 8.91 [s, 2H], Scheme 1 Structures of deeb and L ligands used in this work.

A theoretical procedure, via quantum chemical computations, to elucidate the detection principle of the turn‐off luminescence mechanism of an Eu‐based Metal‐Organic Framework sensor (Eu‐MOF) selective to aniline, is accomplished. The energy transfer channels that take place in the Eu‐MOF, as well as understanding the luminescence quenching by aniline, were investigated using the well‐known and accurate multiconfigurational ab initio methods along with sTD‐DFT. Based on multireference calculations, the sensitization pathway from the ligand (antenna) to the lanthanide was assessed in detail, that is, intersystem crossing (ISC) from the S1 to the T1 state of the ligand, with subsequent energy transfer to the 5D0 state of Eu3+. Finally, emission from the 5D0 state to the 7FJ state is clearly evidenced. Otherwise, the interaction of Eu‐MOF with aniline produces a mixture of the electronic states of both systems, where molecular orbitals on aniline now appear in the active space. Consequently, a stabilization of the T1 state of the antenna is observed, blocking the energy transfer to the 5D0 state of Eu3+, leading to a non‐emissive deactivation. Finally, in this paper, it was demonstrated that the host‐guest interactions, which are not taken frequently into account by previous reports, and the employment of high‐level theoretical approaches are imperative to raise new concepts that explain the sensing mechanism associated to chemical sensors.

Aminopyridin-3-yl)imino]-methyl}-4,6-di-tert-butyl-phenol (3), a ligand containing an intramolecular hydrogen bond, was prepared according to a previous literature report, with modifications, and was characterized by UV-vis, FTIR, 1 H-NMR, 13 C-NMR, HHCOSY, TOCSY and cyclic voltammetry. Computational analyses at the level of DFT and TD-DFT were performed to study its electronic and molecular structures. The results of these analyses elucidated the behaviors of the UV-vis and electrochemical data. Analysis of the transitions in the computed spectrum showed that the most important band is primarily composed of a HOMO→LUMO transition, designated as an intraligand (IL) charge transfer.