Research
Focus
Anti-Dissipative Energy Conversion
We engineer kinetic barriers to trap high-energy excited states and to exploit them in productive chemistry.
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Excited-State Mixed-Valence Systems
We translate decades of ground-state research into the excited state to model the products of primary charge separation in natural photosynthesis.
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Carbon Dots for Solar-to-Fuel Catalysis
We develop sustainable catalysts for hydrogen evolution and other reactions based upon structural and mechanistic insights.
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Other Projects & Collaborations
We also work on other projects and enjoy collaborations on different topics.
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Anti-Dissipative Energy Conversion
In most chromophores, after light absorption, a fast cascade of exergonic processes drives excited-state population to the lowest-energy excited state. Implicitly, significant amounts of energy are dissipated and therefore lost in the energy conversion process. Our aim is to identify dissipative pathways and to block them with large kinetic barriers. The resulting long-lived excited states are high-energy species able to engage in energy-demanding reactions.
Anti-Kasha MLCT Chromophores from an Orbital Perspective
In this comprehensive review, we surveyed metal complexes where observations of anti-Kasha behavior were made, and proposed an orbital view of their photophysics.
“Harnessing High-Energy MLCT Excited States for Artificial Photosynthesis”
Substituent Effects on Hole Reconfiguration
Using 4-substituted pyridines with different electron donating character, we derived design guidelines for impeding hole reconfiguration.
“Influence of Donor-Acceptor Interactions on MLCT Hole Reconfiguration in {Ru(bpy)} Chromophores”
Anti-Dissipative Proof-of-Concept
We avoided the dissipation of 140 meV in photoinduced electron transfer models.
“Anti-Dissipative Strategies toward More Efficient Solar Energy Conversion”
Hole Reconfiguration Barriers in Transition-Metal Complexes
We quantified hole reconfiguration barriers, dove into their physical origin and identified the conical intersections in simple charge-transfer chromophores.
"Unusually high energy barriers for internal conversion in a {Ru(bpy)} chromophore"
Symmetry-Differentiated Energy-Transfer Reactivity
Ultrafast optical transient absorption studies on bimetallic Ru-Cr and trimetallic Ru-Ru-Cr complexes revealed that, while {Ru(tpy)} MLCT states with proper symmetry engage in energy transfer to Cr(III), those with mismatching symmetry remain inert.
“Bifurcation of Excited State Trajectories Toward Energy Transfer or Electron Transfer Directed by Wave Function Symmetry”
Symmetry-Differentiated Electron-Transfer Reactivity
Ultrafast optical transient absorption studies on bimetallic Ru-Os and Ru-Co complexes revealed that, while {Ru(tpy)} MLCT states with proper symmetry engage in electron transfer to Os(III), those with mismatching symmetry remain inert.
“Wave-Function Symmetry Control of Electron-Transfer Pathways within a Charge-Transfer Chromophore”
Different MLCT Populations Coexist in Peace
We investigated a bimetallic ruthenium polypyridine and discovered that, contrary to Kasha's rule, MLCT excited states with different electronic configurations for the excited hole can coexist in the nanosecond timescale.
“Coexistence of MLCT Excited States of Different Symmetry upon Photoexcitation of a Single Molecular Species”
Where is the MLCT-Excited Hole?
We observed for the first time a hole-reconfiguration process within the t2g orbital set of a ruthenium polypyridine. This has huge potential for energy applications.
“Trapping Intermediate MLCT States in Low-Symmetry {Ru(bpy)} Complexes”
Excited-State Mixed-Valence Systems
Mixed-valence systems are the simplest models of electron transfer, and we study them in the excited state as models for excited-state electron transfer. We work with different types of systems, like IVCT excited states, locally-excited mixed valence systems, and photoinduced mixed-valence systems. We are interested in their dynamics, electronic structure, and reactivity, and in their inherent differences with their ground-state analogs.
Vibrational Proof of Full Delocalization in the Excited State
Using femtosecond IR spectroscopy to monitor CN stretching signals, we discovered that a bimetallic complex belongs to Robin & Day's Class III.
“Barrierless Electron Transfer in a Photosynthetic Reaction Center Model”
Modulation of Positive Charge Density in the Excited State
Ligand substitution in bimetallic ruthenium polypyridines allowed us to tune charge density distribution between both Ru ions, ranging from more localized to essentially delocalized MLCT excited states.
“Tuning Electron-Transfer Driving Force in Photosynthetic Special Pair Models”
Tutorial Review on Excited-State Mixed Valency
We reviewed the differences between IVCT excited states, locally-excited mixed-valence systems, and photoinduced mixed-valence systems.
“An Introduction to the Chemistry and Properties of Excited-State Mixed-Valence Systems”
Photoinduced Mixed Valence Interactions Extend Excited-State Lifetimes in Pyrazine-Bridged Systems
Pyrazine-based MLCT states live only few picoseconds. However, upon coordination of a second Ru ion, lifetime was extended to the nanosecond regime. Furthermore, we provide design guidelines related to cis and trans substitutions.
“Ru Monoimines with Extended Excited-State Lifetimes and Geometrical Modulation of Photoinduced Mixed-Valence Interactions”
The Excited-State Creutz-Taube Ion
We created the excited-state analog of the famous mixed-valence system, quantified excited-state electronic coupling and exploited its nanosecond lifetime in bimolecular photoinduced electron transfer.
“The Excited-State Creutz-Taube Ion”
Concept Review on Photoinduced IVCT Bands
We analyzed recent contributions on the utilization of PI-IVCT bands, detected via ultrafast optical transient absorption spectroscopy, as key tools to study donor-acceptor inversion, hole delocalization, coexistence of excited states and excited-state nature.
“Photoinduced Intervalence Charge Transfers: Spectroscopic Tools to Study Fundamental Phenomena and Applications”
Photoinduced Mixed Valence Photoswitch
Photoexcitation triggers drastic conformational changes in the bridge, switching electronic communication in the ground and excited states.
“A Photoinduced Mixed-Valence Photoswitch”
Ligand-Based Photoinduced Mixed Valency
We exploited PI-IVCT bands in the NIR to differentiate between LMCT and MC states in the decay cascades of Fe(III) and Fe(IV) complexes.
“Intense Photoinduced Intervalence Charge Transfer in High-Valent Iron Mixed Phenolate/Carbene Complexes”
Photoinduced Mixed Valence Interactions Extend Excited-State Lifetimes in Cyanide-Bridged Systems
A two-fold increase of MLCT lifetimes was achieved in bimetallic ruthenium polypyridines, relative to their monometallic references.
“A Hole-Delocalization Strategy: Photoinduced Mixed-Valence MLCT States Featureing Extended Lifetimes”
The Donor is the Acceptor, and the Acceptor is the Donor
Upon MLCT photoexcitation, {(tpy)Ru} becomes the electron acceptor and {M(CN)6} become the donor in the photoinduced mixed valence system, reversing their roles in the ground-state mixed valence analogue. This is due to the tpy•–, present in the MLCT state.
“Inversion of Donor-Acceptor Roles in Photoinduced Intervalence Charge Transfers”
Locally-Excited Mixed Valency and Splitting of IVCT Bands
Using optical transient absorption spectroscopy, we monitored the excited-state dynamics in Cr-Ru-Cr trimetallic complexes. Ru→Cr energy transfer is as fast as 600 fs. In the Cr-centered MC state, two IVCT bands are spin-allowed.
“Electronic Energy Transduction from {Ru(py)4} Chromophores to Cr(III) Luminophores”
Carbon Dots for Solar-to-Fuel Catalysis
Carbon Dots prepared from biomolecules contain molecular fragments associated to the carbonaceous nanoparticle, preserved thanks to the pre-carbonization conditions employed in the synthesis. These molecular fragments play the lead role in both key functions of solar-to-hydrogen conversion: visible-light absorption and catalytic activity. We investigate different biomolecular precursors, the mechanisms behind the formation of molecular fluorophores/catalysts, their catalytic activity and mechanisms.
Critical Review on Photocatalytic Carbon Dots
We critically analysed the structural complexity of Carbon Dots and their different roles in photocatalytic hydrogen evolution, as photosensitizers, co-catalysts and catalysts. We also focused on the fine-tuning of optical properties and charge management, outlining both experimental and theoretical methods.
“Designing Carbon Dots for Enhanced Photo-Catalysis: Challenges and Opportunities”
Taming Visible-Light Absorption in Carbon Dots
We uncovered the molecular origins of visible-light absorption in Carbon Dots.
“Understanding the Visible Absorption of Electron Accepting and Donating CNDs”
All-in-one Carbon Nanodots for Hydrogen Evolution from Seawater
We obtained record hydrogen evolution activity in the absence of co-catalysts, and identified the molecular moieties associated to the carbon nanoparticles that determine their photocatalytic behavior.
“Carbon Nanodots for All-in-One Photocatalytic Hydrogen Generation”
Review on Different Types of Carbon Nanocolloids
We embraced the inherent diversity of excited states in carbon-based particles, enabling us to focus on the engineering of their optical properties based on their structural variability.
“Optical processes in carbon nanocolloids”
Other Projects & Collaborations
Photocatalysis with Iron, Iridium & Bismuth Chromophores, MC excited-state dynamics, Carbon Dots & (nano)graphene, Perovskite & 2D TMD nanohybrids.
Photocatalysis with Transition-Metal and Main Block-Metal Chromophores
Intra-Ion-Pair Charge Transfer and Charge Transfer to the Solvent in a Pentacationic Iridium Chromophore
Led by the teams of Ludovic Troian-Gautier (UCLouvain) and Ke Hu (Fudan University).
“Outcompeting Thermodynamics: Ion-Pairing and Coulombic Interactions to Trigger Perfluoroacetate Intra-Ionic Photooxidation for Perfluoroalkylation Reactions”
MLCT States in a Bi(I) Complex
Led by the team of Josep Cornellà (MPI Mülhlheim).
Iron vs. Ruthenium vs. Iridium
Led by the teams of Gerald Meyer (UNC Chapel Hill), Renato Sampaio (Brookhaven National Lab), Benjamin Elias and Ludovic Troain-Gautier (UCLouvain).
“Mechanistic investigation of a visible light mediated dehalogenation/cyclisation reaction using iron(III), iridium(III) and ruthenium(II) photosensitizers”
Green-Light Photocatalysis using a Fe(III) LMCT Chromophore
Led by the teams of Gerald Meyer (UNC Chapel Hill), Renato Sampaio (Brookhaven National Lab), Benjamin Elias and Ludovic Troain-Gautier (UCLouvain).
“Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light”
Metal-Centered Excited States in Ruthenium Chromophores
MC States Dominate Excited-State Decay in {Ru(R-py)4Cl2}
Using ultrafast optical TA, we investigated the role of ligand-field dd states for a series of ruthenium tetrapyridine-dichloro compounds.
“Ligand field states dominate excited state decay in trans-[Ru(py)4Cl2] MLCT chromophores”
Direct Observation of MC States in Ruthenium Pyridine Complexes
Ligand-field dd states are usually hard to directly detect due to a slow population rate relative to a fast decay. Thanks to ligand design, we performed one of the first direct spectroscopic observations.
“Spectroscopic signatures of ligand field states in {RuII(imine)} complexes”
MC Excited States Mediate the Photorelease of CO
Led by the team of Leonardo Slep (UBA).
“Time-Resolved Exploration of a photoCORM {Ru(bpy)} Model Compound”
Carbon Dots, Molecular Nanographenes & Graphene Oxide
Molecular Nanographene with Pentagons and Heptagons
Led by the teams of Dirk Guldi (FAU), Ji Ma (UCAS) and Xiliang Feng (TU-Dresden).
“Deep-Saddle-Shaped Nanographene Induced by Four Heptagons: Efficient Synthesis and Properties”
Nanographene-Ru Porphyrin Dyads and Triads
Led by the teams of Norbert Jux and Dirk Guldi (FAU).
“Laterally π‐Extensed Nitrogen‐Doped Molecular Nanographenes–From Anti‐Kasha Emission to Ping‐Pong Energy Transfer Events”
Optical Communication between Different Carbon Dots
Led by the teams of Dirk Guldi (FAU) and Maurizio Prato (U Trieste).
“Synthetic strategies for the selective functionalization of carbon nanodots allow optically communicating suprastructures”
Citrazinic Acid Carbon Dots for Mercury Detection
Led by the team of Radek Zbořil (U Olomouc).
“Carbon Dots Enabling Parts‐Per‐Billion Sensitive and Ultraselective Photoluminescence Lifetime‐Based Sensing of Inorganic Mercury”
Graphene-Oxide-BODIPY Conjugates
Led by the teams of Barbara Richichi (U Firenze), Dirk Guldi (FAU) and Alberto Bianco (U Strasbourg).
“Graphene Oxide‐BODIPY Conjugates as Highly Fluorescent Materials”
Review on 0D, 1D and 2D Nanocarbons
Led by the team of Dirk Guldi (FAU).
“Photon- and Charge-Management in Advanced Energy Materials: Combining 0D, 1D, and 2D Nanocarbons as well as Bulk Semiconductors with Organic Chromophores”
Charge Separation when Carbon Dots Meet TCAQ
Led by the teams of María Ángeles Herranz and Nazario Martín (UCM) and Dirk Guldi (FAU).
“Assessing the Photoinduced Electron-Donating Behavior of Carbon Nanodots in Nanoconjugates”
Carbon Dots Meet Rylen Diimides
Led by the teams of Luka Đorđević and Maurizio Prato (U Trieste) and Dirk Guldi (FAU).
“Synthesis And Excited State Processes of Arrays Containing Amine-Rich Carbon Dots and Unsymmetrical Rylene Diimides”
Symmetry-Breaking Charge Separation when Carbon Dots Meet Phthalocyanines
Led by the teams of Luka Đorđević and Maurizio Prato (U Trieste) and Dirk Guldi (FAU).
“Symmetry-Breaking Charge Transfer Chromophore Interactions Supported by Carbon Nanodots”
Review on Charge Management with Carbon Dots
“Carbon Nanodots for Charge-Transfer Processes”
Charge Separation when Carbon Dots Meet exTTF
Led by the teams of María Ángeles Herranz and Nazario Martín (UCM) and Dirk Guldi (FAU).
“Exploring Tetrathiafulvalene–Carbon Nanodot Conjugates in Charge Transfer Reactions”
Perovskites & Transition-Metal Dichalcogenide Nanohybrids and Nanoconjugates
Singlet Energy Transfer from Pervoskite Nanocrystals to Covalently-Anchored Phthalocyanines
Led by the teams of Tomás Torres (UAM), Julia Pérez-Prieto and Raquel Galián (UV) and Dirk Guldi (FAU).
“Deciphering the Energy Transfer Mechanism Across Metal Halide Perovskite-Phthalocyanine Interfaces”
Long-Lived Charge Separation in {2H-WS2·PDI}
Led by the teams of Andreas Hirsch and Dirk Guldi (FAU).
“Noncovalent Liquid Phase Functionalization of 2H-WS2 with PDI: An Energy Conversion Platform with Long-Lived Charge Separation”
Electronic Energy Bounces between MoS2 and Porphyrin
Led by the teams of Raúl Arenal (U. Zaragoza), Dirk Guldi (FAU) and Nikos Tagmatarchis (NHRF).
“Ping-Pong Energy Transfer in Covalently Linked Porphyrin-MoS2 Architectures”
