Hot carrier dynamics in metalated porphyrin-naphthalimide thin films

This study employs femtosecond transient absorption spectroscopy to investigate the rapid dynamics of excited state carriers in three metalated porphyrin-naphthalimide (PN) molecules and one free-base molecule. The dynamics of electron injection, from PN to mesoporous titania (TiO2), in PN adsorbed TiO2 films (Ti-PN), were carefully investigated and compared to PN adsorbed ZrO2 films (Zr-PN). In addition, we examined the self-assembled PN films and found that, in their self-assembled state, these molecules exhibited a longer relaxation time than Zr-PN monomeric films, where the charge injection channel was insignificant. The ground-state bleach band in the Ti-PN films gradually shifted to longer wavelengths, indicating the occurrence of the Stark effect. Faster electron injection was observed for the metalated PN systems and the electron injection times from the various excited states to the conduction band of TiO2 (CB-TiO2) were obtained from the target model analysis of the transient absorption spectra data matrix. In these metal-organic complexes, hot electron injection from PN to CB-TiO2 occurred on a time scale of <360 fs. Importantly, Cu(II)-based PN complexes exhibited faster injection and longer recombination times. The injection times have been estimated to result from a locally excited state at ≈280 fs, a hot singlet excited state at 4.95 ps, and a vibrationally relaxed singlet excited state at 97.88 ps. The critical photophysical and charge injection processes seen here provide the potential for exploring the underlying factors involved and how they correlate with photocatalytic performance.

Self-Assembled Monolayers of Push-Pull Chromophores as Active Layers and Their Applications

In recent decades, considerable attention has been focused on the design and development of surfaces with defined or tunable properties for a wide range of applications and fields. To this end, self-assembled monolayers (SAMs) of organic compounds offer a unique and straightforward route of modifying and engineering the surface properties of any substrate. Thus, alkane-based self-assembled monolayers constitute one of the most extensively studied organic thin-film nanomaterials, which have found wide applications in antifouling surfaces, the control of wettability or cell adhesion, sensors, optical devices, corrosion protection, and organic electronics, among many other applications, some of which have led to their technological transfer to industry. Nevertheless, recently, aromatic-based SAMs have gained importance as functional components, particularly in molecular electronics, bioelectronics, sensors, etc., due to their intrinsic electrical conductivity and optical properties, opening up new perspectives in these fields. However, some key issues affecting device performance still need to be resolved to ensure their full use and access to novel functionalities such as memory, sensors, or active layers in optoelectronic devices. In this context, we will present herein recent advances in π-conjugated systems-based self-assembled monolayers (e.g., push-pull chromophores) as active layers and their applications.

Cycloisomerization of π-Coupled Heteroatom Nucleophiles by Gold Catalysis: En Route to Regiochemically Defined Heterocycles

Since the dawn of millennium, catalytic gold chemistry is at the forefront to set off diverse organic reactions via unique activation of π-bonded molecules. Within this purview, cycloisomerization of heteroatom nucleophiles linked to a π-system is one of the well recognized chemistry for the construction of numerous heterocyclic cores. Though the rudimentary aspects of this transformation are reviewed by several groups in different timeline, a holistic view on regiochemistry of such reactions went largely overlooked. Hence, this account emphasizes the gold catalyzed regioselective cycloisomerization of structurally distinctive π-connected hetero-nucleophiles leading to different heterocycles documented in the last two decades. From an application perspective, this account also highlights those methodologies which find a role in the total synthesis of natural products. Wherever appropriate, mechanistic details and contributing factors for selectivity are also discussed.

Photocatalytic hydrogen production of porphyrin nanostructures: spheres vs. fibrils, a case study

Herein, we illustrate the preparation of a covalent connected peptide-porphyrin hybrid (Fmoc-FF-(Zn)Por). The thorough investigation of its self-organization features demonstrated that Fmoc-FF-(Zn)Por self-assembles into either spheres or fibrils by altering the solvent mixture. Interestingly, photocatalytic hydrogen (H2) evolution experiments revealed that fibrils were more efficient towards H2 production compared to spheres.

Thermodynamic Phase-like Transition Effect of Molecular Self-assembly

The technique of self-assembled monolayers (SAMs) is frequently applied for grafting functional groups or area-selective deposition of thin films on a material surface. The formation and quality of SAMs are fundamentally determined by thermodynamic data, which are difficult to measure with available experimental methods. This work quantitatively extracted thermodynamic parameters including ΔH°, ΔG°, and ΔS° during the SAMs construction process with an ultrasensitive resonant microcantilever as molecule-surface interactions real-time recording tool. By correlating the thermodynamic parameters with self-assembling temperatures, a new thermodynamic phase-like transition effect of molecular self-assembly has been first revealed. The sharp transition of the thermodynamic parameters defines the critical condition for SAMs formation. The thermodynamic data further provide optimized reaction conditions for constructing high-quality SAMs. The explored quantitative thermodynamic analysis method not only plays as criterion for SAM growth but also helps to fundamentally elucidate physicochemical mechanism of spontaneous self-assembly.