Red-light sensitized hole-conducting polymer for energy conversion

We report a novel hole conductive polymer with photoactive Os(ii) complexes in the side chains. This PPV derivative can be activated upon absorption of red visible light and delivers notable photocurrents when used as photocathode material. Thus, the polymer presents as a stepping stone towards developing soft matter alternatives to NiO photocathodes, which function under visible light irradiation. To show the concept we combine electrical impedance spectroscopy with steady state spectroscopy. As light-driven hole injection from Os complex to the PPV polymer is thermodynamically feasible both based on reductive quenching of photoexcited PPV and based on oxidative quenching of the photoexcited Os chromophores we investigate the impact of illumination wavelengths on the photocathode behavior and photochemical stability of the material. While both blue and red light excitation, i.e., excitation of the chromophoric units PPV and excitation of the metal-to-ligand charge transfer transitions in the side-chain pendant Os chromophores yield cathodic photocurrents, the photochemical stability is drastically enhanced upon red-light excitation. Hence, the results of the investigations discussed show the validity of the concept developing red-light sensitized hole-conducting polymers for energy conversion.

It Is Good to Be Flexible: Energy Transport Facilitated by Conformational Fluctuations in Light-Harvesting Polymers

We investigate the mechanism of energy transfer between ruthenium(II) (Ru) and osmium(II) (Os) polypyridyl complexes affixed to a polyfluorene backbone (PF-RuOs) using a combination of time-resolved emission spectroscopy and coarse-grained molecular dynamics (CG MD). Photoexcitation of a Ru chromophore initiates Dexter-style energy hopping along isoenergetic complexes followed by sensitization of a lower-energy Os trap. While we can determine the total energy transfer rate within an ensemble of solvated PF-RuOs from time-dependent Os* emission spectra, heterogeneity of the system and inherent polymer flexibility give rise to highly multiexponential kinetics. We developed a three-part computational kinetic model to supplement our spectroscopic results: (1) CG MD model of PF-RuOs that simulates molecular motions out to 700 ns, (2) energy transfer kinetic simulations in CG MD PF-RuOs that produce time-resolved Ru and Os excited-state populations, and (3) computational experiments that interrogate the mechanisms by which motion aids energy transfer. Good agreement between simulated and experimental emission transients reveals that our kinetic model accurately simulates the molecular motion of PF-RuOs during energy transfer. Simulated results indicate that pendant flexibility allows 81% of the excited state to sensitize an Os trap compared to a 48% occupation when we treat pendants statically. Our computational experiments show how static pendants are only able to engage in local energy transfer. The excited state equilibrates across a domain of complexes proximal to the initial excitation and becomes trapped within that unique, frozen locality. Side-chain flexibility enables pendants to swing in and out of the original domain spreading the excited state out to ±30 pendant complexes away from the initial excitation.

A 3D electropolymerized thin film based on a thiophene-functionalized Ru(ii) complex: electrochemical and photoelectrochemical insights

A 3D electropolymerized Ru(ii) complex film exhibited a rapid redox reaction and an oxygen reduction enhanced photocurrent which increased by 1.5 fold to 2.3 μA cm⁻².

A multidonor-photosensitizer-multiacceptor triad for long-lived directional charge separation

The modular assembly of a directional photoredox-active multidonor-photosensitizer-multiacceptor (D_n-P-A_m) architecture is presented. The triad assembly features a central Ru(ii) sensitizer equipped with pendant polymer chains consisting of multiple triarylamine (pTARA) and naphthalene diimide (pNDI) units, respectively. Upon excitation, the efficient formation (>96%) of charge separation (CS) was observed featuring similar CS lifetimes (400 ns) as related molecular triads. In contrast, a significant additional longer-lived CS component (2400 ns, 30%) is observed indicating multiple contributing pathways.

Covalently assembled polymer nanocapsules: a novel scaffold for light-harvesting

A light-harvesting system was firstly established on the basis of a covalently assembled nanocapsule.

Direct Observation of an Efficient Triplet Exciton Diffusion Process in a Platinum-Containing Conjugated Polymer

We report the synthesis and characterization of a conjugated polymer incorporated with cyclometalated platinum complexes on the main chain. The polymer may serve as an efficient triplet sensitizer in light-harvesting systems. The photophysical properties of the polymer were studied by nanosecond and femtosecond time-resolved transient absorption spectroscopies. After excitation, an energy-transfer process from the thiophene units on the conjugated main chain to the singlet excited state of the Pt complex moieties occurred in less than 150 fs. The subsequent intersystem crossing process resulted in the formation of a triplet excited state at the Pt complex moieties in ∼3.2 ps, which was then followed by an efficient triplet diffusion process that led to the formation of triplet excitons on the polymer main chain in ∼283 ps. This proposed efficient triplet sensitized polymer system not only enhances the exciton diffusion length but also reduces energy loss in the process, which displays remarkable implications in the design of novel materials for triplet sensitized solar cells.

Synthetic approaches towards structurally-defined electrochemically and (photo)redox-active polymer architectures

This review details synthetic strategies leading to structurally-defined electrochemically and (photo)redox-active polymer architectures,e.g.block, graft and end functionalized (co)polymers.

Pharmacophore based virtual screening for identification of marine bioactive compounds as inhibitors against macrophage infectivity potentiator (Mip) protein of Chlamydia trachomatis

Macrophage infectivity potentiator (Mip) is the virulence factor fromChlamydia trachomatisthat is primarily responsible for causing sexually transmitted diseases (STDs) and blindness.

Ultrafast dynamics in multifunctional Ru(II)-loaded polymers for solar energy conversion

The use of sunlight to make chemical fuels (i.e., solar fuels) is an attractive approach in the quest to develop sustainable energy sources. Using nature as a guide, assemblies for artificial photosynthesis will need to perform multiple functions. They will need to be able to harvest light across a broad region of the solar spectrum, transport excited-state energy to charge-separation sites, and then transport and store redox equivalents for use in the catalytic reactions that produce chemical fuels. This multifunctional behavior will require the assimilation of multiple components into a single macromolecular system. A wide variety of different architectures including porphyrin arrays, peptides, dendrimers, and polymers have been explored, with each design posing unique challenges. Polymer assemblies are attractive due to their relative ease of production and facile synthetic modification. However, their disordered nature gives rise to stochastic dynamics not present in more ordered assemblies. The rational design of assemblies requires a detailed understanding of the energy and electron transfer events that follow light absorption, which can occur on time scales ranging from femtoseconds to hundreds of microseconds, necessitating the use of sophisticated techniques. We have used a combination of time-resolved absorption and emission spectroscopies with observation times that span 9 orders of magnitude to follow the excited-state evolution within polymer-based molecular assemblies. We complement experimental observations with molecular dynamics simulations to develop a microscopic view of these dynamics. This Account provides an overview of our work on polymers decorated with pendant Ru(II) chromophores, both in solution and on surfaces. We have examined site-to-site energy transport among the Ru(II) complexes, and in systems incorporating π-conjugated polymers, we have observed ultrafast formation of a long-lived charge-separated state. When attached to TiO2, these assemblies exhibit multifunctional behavior in which photon absorption is followed by energy transport to the surface and electron injection to produce an oxidized metal complex. The oxidizing equivalent is then transferred to the conjugated polymer, giving rise to a long-lived charge-separated state.

Electronic and optical properties of polypyridylruthenium derivatized polystyrenes: multi-level computational analysis of metallo-polymeric chromophore assemblies

Great effort is geared toward investigation of new materials for solar energy conversion in recent years. Polymeric chromophore assemblies consisting of [Ru(bpy)3](2+) complexes attached to a polystyrene backbone have gained considerable interest in recent years because of their structural flexibility combined with their ability to efficiently capture solar energy and transport the captured energy in the form of exciton or charges. We employ a combination of computational methods to examine how opto-electronic properties of [Ru(bpy)3](2+) complexes are influenced by the polymer dynamics in these polymeric chromophore assemblies. The covalent linker between the polymer and the light-absorbing Ru complex is thought to play an important role in optimizing the assemblies for solar energy conversion and transport. We find that the presence of -CH2- groups in the linker has a significant impact on the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energies of the pendants. Generally speaking, a longer linker leads to higher HOMO energies. Without the presence of -CH2- groups, a mixture of cis and trans amide bond in the covalent linker leads to a bimodal distribution for both HOMO and LUMO energies. Importantly, we find that distributions of orbital energies from individual [Ru(bpy)3](2+) pendants have the maximum overlap when there is only one -CH2- group in the linker. Such an isotropic energy distribution is likely to be important for charge transport within the assemblies. We also find that in contrast to the isolated [Ru(bpy)3](2+) complex, the HOMO is generally found on the linker rather than on Ru atom. This does not change the character of the metal-to-ligand charge transfer (MLCT) excited states, as these excitations in the pendants do not derive from HOMO/LUMO transitions but rather from HOMO - 2/LUMO transition since HOMO - 2 is located on the Ru atom.

Ru(bpy)32+ derivatized polystyrenes constructed by nitroxide-mediated radical polymerization. Relationship between polymer chain length, structure and photophysical properties

A series of polystyrene-based light harvesting polymers featuring pendant polypyridyl ruthenium complexes has been synthesized.

Novel metallo-dendrimers containing various Ru core ligands and dendritic thiophene arms for photovoltaic applications

A polymer solar cell device containing an active layer of BTRu2G3 : PC70BM = 1 : 3 (by wt), i.e., the third generation of the bis-Ru-based dendritic complex BTRu2G3 showed the highest PCE value of 0.77%.