Efficient light harvesting through titania inverse opal nanostructures (TiO2 IOs) can be achieved by strategically engineering binary and ternary heterojunctions with various metal oxides. In this study, we developed two distinct binary heterojunctions involving titanium dioxide paired with tin oxide (TiO2-SnO2 IOs) and bismuth oxide (TiO2-Bi2O3 IOs), alongside a ternary heterojunction combining titanium dioxide, tin oxide, and bismuth oxide (TiO2-SnO2-Bi2O3 IOs). These IOs were synthesized using a soft template method. We employed transient absorption spectroscopy to assess the lifetime of photogenerated carriers in the IO systems, revealing a notably long lifetime exceeding 5 ns for all samples. Our investigation into photocatalytic activity demonstrated that both TiO2-Bi2O3 IOs and TiO2-SnO2 IOs binary heterojunctions exhibited enhanced performance, displaying 20 % and 5 % greater photocatalytic activity for acetylene degradation, respectively, compared to pure TiO2 IOs. Notably, the TiO2-SnO2-Bi2O3 IOs ternary heterojunction showcased a remarkable increase in photocatalytic activity, with a 53 % improvement over TiO2 IOs.

Although long-range intramolecular electron transfer has been extensively demonstrated in covalently linked donor-acceptor conjugates, intramolecular singlet fission (ISF) over linker lengths significantly exceeding 15 Å has not yet been observed. Moreover, no studies have shown linker-length-dependent control of the singlet correlated triplet pair (TT) dynamics, where singlet TT undergoes spin conversion to quintet TT or dissociation into two individual triplet states (T1 + T1) via quintet TT. Here, we report pentacene dimers bridged by two different polyyne-based molecular wires, in which long-range ISF is successfully observed over linker lengths of up to ∼35 Å. As the linker length increases, we further demonstrate tunable singlet TT dynamics, achieving systematic control over pathways: spin conversion to quintet TT, and dissociation of quintet TT into T1 + T1. Transient absorption measurements reveal that the individual triplet yields increase with increasing linker length, while the nearly quantitative formation of the 1TT is maintained. The small attenuation factors for ISF and for recombination of singlet TT to the ground state indicate that the polyyne linker functions as an efficient molecular wire. Thermodynamic analysis and time-resolved electron paramagnetic resonance measurements clearly reveal that vibration-driven structural modulation of the polyyne-based molecular wire in the singlet TT directly controls the branching between (i) spin conversion from singlet TT to quintet TT and (ii) dissociation into T1 + T1 via quintet TT following spin conversion. These findings establish molecular wires as effective platforms for long-range ISF and provide a mechanistic foundation for engineering singlet TT dynamics across extended molecular distances.

Visible-light responsive, stable, and abundant absorbers are required for the rapid integration of green, clean, and renewable technologies in a circular economy. Photoactive solid-solid heterojunctions enable multiple charge pathways, inhibiting recombination through efficient charge transfer across the interface. This study spotlights the physico-chemical synergy between titanium dioxide (TiO2) anatase and carbon nitride (CN) to form a hybrid material. The CN(10%)-TiO2(90%) hybrid outperforms TiO2 and CN references and literature homologs in four photo and photoelectrocatalytic reactions. CN-TiO2 achieved a four-fold increase in benzylamine conversion, with photooxidation conversion rates of 51, 97, and 100 % at 625, 535, and 465 nm, respectively. The associated energy transfer mechanism was elucidated. In photoelectrochemistry, CN-TiO2 exhibited 23 % photoactivity of the full-spectrum measurement when using a 410 nm filter. Our findings demonstrate that CN-TiO2 displayed a band gap of 2.9 eV, evidencing TiO2 photosensitization attributed to enhanced charge transfer at the heterointerface boundaries via staggered heterojunction type II.

A trichromophore has been synthesized comprising a perylene diimide sandwiched between two perylene monoimide diester (PMIDE) units and held in place by xanthene spacers. The DFT computed structure indicates π-stacking of the three polycycles, with a mean interplanar separation of 4.2Ă, but with the central unit displaced sideways. Phenyl groups inserted between xanthene and perylene help to rigidify the structure. Electronic interactions between perylene polycycles splits the absorption spectrum, which is dominated by transitions to the upper-lying H-state. Excimer-like emission is observed in solution at room temperature, for which the lifetime is ≈22 ns in toluene and ≈8 ns in CH2Cl2. Transient absorption spectroscopy indicates the instantaneous formation of a Franck-Condon state, which undergoes rapid vibrational cooling to populate the low-lying J-state. This species transforms over 40-60 ps into an excimer-like state wherein the exciton is delocalized over all three perylenes. A slower structural re-arrangement, complete within 1 ns, minimizes electronic interactions with one of the PMIDE units and stabilizes the resultant bipartite excimer-like state.

Nonlinear optical interactions in nanostructures are crucial for both fundamental research and practical applications. The optical Kerr effect, a third-order nonlinear phenomenon, causes anisotropic changes in the refractive index of materials under intense laser illumination. However, this effect is intrinsically weak, limiting its utility in free-space nanophotonics. This work demonstrates an enhancement of the optical Kerr effect by over three orders of magnitude through guided-mode resonance in a dielectric diffraction grating with a thickness of less than 300 nm. The study includes the design, fabrication, and transmittance measurements of a resonant silicon nitride crossed grating, illuminated with short light pulses. Spectral resonance shifts with increasing pulse power are observed, resulting in over 50% modulation of the resonance magnitude and enabling dynamic transitions between "Off " and "On" transmission states of the grating. Additionally, the potential of the grating for dynamic pulse shaping is demonstrated. These findings offer promising avenues for developing advanced all-optical devices in free-space nanophotonics.

Singlet fission (SF) is a spin-allowed multiexciton generation (MEG) process, where one singlet exciton (S1) splits into two triplet excitons (2T1) in two nearby molecules (theoretical maximum triplet quantum yield: 2). In contrast, bi- and multiexciton states of quantum dots (QDs) have been generated by exciting them at high excitation density (multiple-photon excitation). Here, we propose combining these materials for the integrated MEG (iMEG) process using 6,13-bis(triisopropylsilylethynyl)pentacene (TP) dimer [(TP)2]-modified CdSe QD (CdSeQD) hybrids. Upon photoexcitation of CdSeQD with multiple-photon excitation, a sequential photoinduced process from the multiexciton state (CdSeQD) to SF [(TP)2] occurred through singlet-singlet energy transfer (EnT) from CdSeQD to TP. The number of triplet excitons generated per CdSeQD (N T) increased up to similar to 4.9 +/- 0.7 at higher excitation intensities. Our proposed inorganic-organic hybrid system demonstrates a novel exciton amplification process for various future uses, such as solar energy conversion, optoelectronics, and biological applications.

The instability and broad optical features of perovskites limit the full realization of their unique optoelectronic potential. In this study, a novel MAPbBr3@SWCNTs hybrid material is presented, in which methylammonium lead bromide perovskite (MAPbBr3) is successfully encapsulated in single-walled carbon nanotubes (SWCNTs), fabricated in the form of thin films. Encapsulation enables the formation of 1D perovskite structures with narrowband light-emission, confined within a protective carbon nanoshell. A thorough investigation is conducted into the hybrid material's structure, linear optical properties, ultrafast carrier dynamics, and THz conductivity. The encapsulation preserves the distinct characteristics of both MAPbBr3 and SWCNTs while introducing novel optoelectronic effects, including the tuning and spectral unification of perovskite photoluminescence (PL), as well as doping-induced modifications to SWCNT carrier relaxation dynamics. Furthermore, the observation of negative photoconductivity (NPC) response of MAPbBr3@SWCNTs thin films highlights the potential of this innovative material as a strong candidate for future energy-efficient photodetectors, optoelectronic switches, neuromorphic computing devices, photovoltaic enhancers, and flexible electronics.

The instability and broad optical features of perovskites limit the full realization of their unique optoelectronic potential. In this study, a novel MAPbBr 3 @SWCNTs hybrid material is presented, in which methylammonium lead bromide perovskite (MAPbBr 3 ) is successfully encapsulated in single‐walled carbon nanotubes (SWCNTs), fabricated in the form of thin films. Encapsulation enables the formation of 1D perovskite structures with narrowband light‐emission, confined within a protective carbon nanoshell. A thorough investigation is conducted into the hybrid material's structure, linear optical properties, ultrafast carrier dynamics, and THz conductivity. The encapsulation preserves the distinct characteristics of both MAPbBr 3 and SWCNTs while introducing novel optoelectronic effects, including the tuning and spectral unification of perovskite photoluminescence (PL), as well as doping‐induced modifications to SWCNT carrier relaxation dynamics. Furthermore, the observation of negative photoconductivity (NPC) response of MAPbBr 3 @SWCNTs thin films highlights the potential of this innovative material as a strong candidate for future energy‐efficient photodetectors, optoelectronic switches, neuromorphic computing devices, photovoltaic enhancers, and flexible electronics.

Transition metal oxides are pivotal in enhancing surface passivation and facilitating charge transfer (CT) in silicon based photonic devices, improving their efficacy and affordability through interfacial engineering. This study investigates TiO2/Si heterojunctions prepared by atomic layer deposition (ALD) with different pre-ALD chemical and post-ALD thermal treatments, exploring their influence on the surface passivation and the correlation with the CT at the TiO2-Si interface. Surface passivation quality is evaluated by the photoconductance decay method to study the effective carrier lifetime, while CT from Si to TiO2 is examined by transient reflectance spectroscopy. Surprisingly, the as-deposited TiO2 on HF-treated n-Si (without interfacial SiOx) demonstrates superior surface passivation with an effective lifetime of 1.23 ms, twice that of TiO2/SiOx/n-Si, and a short characteristic CT time of 200 ps, tenfold faster than that of TiO2/SiOx/n-Si. Post-ALD annealing at temperatures approaching the TiO2 crystallization onset re-introduces the SiOx layers in HF-treated samples and induces chemical and structural changes in all the samples which decrease passivation and prolong the CT time and are hence detrimental to the photonic device performance.

A series of ferrocene(Fc)-bridged pentacene(Pc)-dimers [Fc−Ph(2, n )−(Pc) 2 : n =number of phenylene spacers] were synthesized to examine the tortional motion effect of Fc-terminated phenylene linkers on strongly coupled quintet multiexciton ( 5 TT) formation through intramolecular singlet fission (ISF). Fc−Ph(2,4)−(Pc) 2 has a relatively small electronic coupling and large conformational flexibility according to spectroscopic and theoretical analyses. Fc−Ph(2,4)−(Pc) 2 exhibits a high-yield 5 TT together with quantitative singlet TT ( 1 TT) generation through ISF. This demonstrates a much more efficient ISF than those of other less flexible Pc dimers. The activation entropy in 1 TT spin conversion of Fc−Ph(2,4)−(Pc) 2 is larger than those of the other systems due to the larger conformational flexibility associated with the torsional motion of the linkers. The torsional motion of linkers in 1 TT is attributable to weakened metal-ligand bonding in the Fc due to hybridization of the hole level of Pc to Fc in 1 TT unpaired orbitals.

Complexes of quantum dots with molecular catalysts are promising building blocks for photo-catalytic applications. Herein, we report the formation of stable complexes between colloidal CdTe quantum dots (CQDs) and two synthesized structurally different cobalt porphyrin derivatives (CoPp and CoPm, with phenyl and mesityl groups attached at the meso positions, respectively) through a sulfur bridge. Using both spectroscopy and computational methods, we found that the porphyrin adopts a "flat" binding mode on the CQD surface. We observed the coordination of the Co center on the CQD surface. This coordination is stronger for CoPp than for CoPm, resulting in a larger red shift in the absorption band. In addition, we measured a four fold increase in the electron transfer (ET) rate from the CQD to CoPp compared to that with CoPm by a transient absorption study and the charge recombination extended to tens of nanoseconds or longer depending on the structure of the porphyrin periphery. A spectrum measured after the ET points to a loss of coordination between the Co and CQD in a CoP/CQD complex. The experimental results are in agreement with density functional theory calculation results on the CoP complexes on CdTe surfaces, pointing to the porphyrin preferring to align along the CQD surface in the ground state. The change of porphyrin alignment from flat alignment before the excitation to upright alignment after the ET is a likely cause for the extended lifetime of the charge-separated (CS) state, due to an increase in the CS distance. Furthermore, the spectrum of the CS state can be assigned to catalytically active CoIP, proposing the applicability of the complexes in CO2 reduction. Complexes of quantum dots with molecular catalysts are promising building blocks for photo-catalytic applications.

Molecular assemblies featuring two-dimensionality have attracted increasing attention, whereas such structures are difficult to construct simply relying on spontaneous molecular assembly. Here we present two-dimensional assemblies of acene chromophores achieved using a tripodal triptycene supramolecular scaffold, which have been shown to exhibit a strong ability to assemble molecular and polymer motifs two-dimensionally. We designed pentacene and anthracene derivatives sandwiched by two tripodal triptycene units. These compounds assemble into expected two-dimensional structures, with the pentacene chromophores having both sufficient overlap to cause singlet fission and space for conformational change to facilitate the dissociation of a triplet pair into two free triplets, which is not the case for the anthracene analogue. Detailed spectroscopic analysis revealed that the pentacene chromophore in the assembly undergoes singlet fission with a high quantum yield (ΦSF = 88±5%), giving rise to triplet pairs, from which free triplets are efficiently generated (ΦT = 130±8.8%). This demonstrates the utility of the triptycene-based scaffold to design functional π-electronic molecular assemblies.

Innovative research on metal-oxide gas sensors involves nanostructuring and surface modification as key elements to tailor sensitivity and selectivity. This work addresses a ZnO nanowire-based sensing device obtained by coupling a lithographically prepared substrate with hydrothermal ZnO growth, to align and interconnect the nanowires between two electrical contacts. Furthermore, conformal coating by atomic layer deposition technique allows functionalization of the surface of the nanowires with sub-monolayers of Al2O3 and TiO2. A detailed analysis is carried out from a morphological and structural point of view with photoluminescence and Raman spectroscopy and electron microscopy. The material characterization results are analyzed in comparison with the functional characterization in gases toward reducing (NO2) and oxidizing (H2S) gases. Unparalleled sensing enhancement with Atomic Layer Deposition functionalization is obtained for NO2 detection. The passivation role of surface states is discussed combining information from experimental techniques with a proposed model. Nanowires (NWs) growing from selected areas connect each other in the middle of the contact. Conformal coating by atomic layer deposition technique with sub-monolayers of Al2O3 and TiO2 is investigated to modify the surface of the NWs allowing tailoring the selectivity and sensitivity of the nanostructures. image

Transient absorption spectroscopy is a powerful technique to study the photoinduced phenomena in a wide range of states from solutions to solid film samples. It was designed and developed based on photoinduced absorption changes or that photoexcitation triggers a chain of reactions with intermediate states or reaction steps with presumably different absorption spectra. However, according to general electromagnetic theory, any change in the absorption properties of a medium is accompanied by a change in the refractive properties. Although this photoinduced change in refractive index has a negligible effect on solution measurements, it may significantly affect the measured response of thin films. In this Perspective paper, we examine why and how the measured responses of films differ from their expected "pure" absorption responses. The effect of photoinduced refractive index change can be concluded and studied by comparing the transmitted and reflected probe light responses. Another discussed aspect is the effect of light interference on thin films. Finally, new opportunities of monitoring the photocarrier migration in films and studying nontransparent samples using the reflected probe light response are discussed. Most of the examples provided in this article focus on studies involving perovskite, TiO2, and graphene-based films, but the general discussion and conclusions can be applicable to a wide range of semiconductor and thin metallic films.

For the first time, we have prepared non-aggregating phthalocyanine cobalt complexes as a set of resolved positional isomers. These compounds comprise a unique test bed for the structure-properties studies, as their optical and electrochemical properties are influenced by the planarity of the phthalocyanine macrocycle, which can be controlled by the positional isomerism of the bulky aromatic substituents at the α-phthalo sites. We support our conclusions with molecular modelling studies, which show a perfect match between the calculated and experimentally determined spectral/electrochemical values. We challenge a common perception that the NMR spectra of cobalt phthalocyanines cannot be measured due to the paramagnetic nature of Co(II). We suggest instead that the key factors affecting the NMR spectral resolution are molecular aggregation and π-π stacking. These interactions are suppressed by the bulky peripheral substituents on the cobalt phthalocyanines prepared, making these isomeric compounds an excellent tool for paramagnetic NMR studies.

The kinetics of electron extraction at the electron transfer layer/perovskite interface strongly affects the efficiency of a perovskite solar cell. By combining transient absorption and time-resolved photoluminescence spectroscopy, the electron extraction process between FA0.83Cs0.17Pb(I0.83Br0.17)3 and TiO2 single crystals with different orientations of (100), (110), and (111) were probed from subpicosecond to several hundred nanoseconds. It was revealed that the band alignment between the constituents influenced the relative electron extraction process. TiO2(100) showed the fastest overall and hot electron transfer, owing to the largest conduction band and Fermi level offset compared to FA0.83Cs0.17Pb(I0.83Br0.17)3. It was found that an early electron accumulation in these systems can have an influence on the following electron extraction on the several nanosecond time scale. Furthermore, the existence of a potential barrier at the TiO2/perovskite interface was also revealed by performing excitation fluence-dependent measurements.

Hydrogen peroxide (H2O2) is a crucial chemical used in numerous industrial applications, yet its manufacturing relies on the energy-demanding anthraquinone process. Solar-driven synthesis of H2O2 is gaining traction as a promising research area, providing a sustainable method for its production. Herein, a controllable activation of n → π* electronic transition is presented to boost the photocatalytic H2O2 evolution in ionic carbon nitrides. This enhancement is achieved through the simultaneous introduction of structural distortions and defect sites (─C ≡ N groups and N vacancies) into the KPHI framework. The optimal catalyst (2%Ox-KPHI) reached an apparent quantum yield of 41% at 410 nm without the need for any cocatalysts, outperforming most previously reported carbon nitride-based photocatalysts. Extensive experimental characterizations and theoretical calculations confirm that a corrugated configuration and the presence of defects significantly broaden the light absorption profile, improve carrier separation and migration, promote O2 adsorption, and lower the energy barriers for H2O2 desorption. Transient absorption spectroscopy indicates that the enhanced photocatalytic performance of 2%Ox-KPHI is largely attributed to the preferential migration of electrons at defect sites over extended timescales, following the diffusion of geminate carriers across the PHI sheets.

Developing bioinspired materials to convert sunlight into electricity efficiently is paramount for sustainable energy production. Fluorescent proteins are promising candidates as photoactive materials due to their high fluorescence quantum yield and absorption extinction coefficients in aqueous media. However, developing artificial bioinspired photosynthetic systems requires a detailed understanding of molecular interactions and energy transfer mechanisms in the required operating conditions. Here, the supramolecular self-assembly and photophysical properties of fluorescent proteins complexed with organic dyes are investigated in aqueous media. Supercharged mGreenLantern protein, mutated to have a charge of +22, is complexed together with anionic zinc phthalocyanines having 4 or 16 carboxylate groups. The structural characterization reveals a strong electrostatic interaction between the moieties, accompanied by partial conformational distortion of the protein structure, yet without compromising the mGreenLantern chromophore integrity as suggested by the lack of emission features related to the neutral form of the chromophore. The self-assembled biohybrid shows a total quenching of protein fluorescence, in favor of an energy transfer process from the protein to the phthalocyanine, as demonstrated by fluorescence lifetime and ultrafast transient absorption measurements. These results provide insight into the rich photophysics of fluorescent protein-dye complexes, anticipating their applicability as water-based photoactive materials.

The kinetics of electron extraction at the electron transfer layer/perovskite interface strongly affects the efficiency of a perovskite solar cell. By combining transient absorption and time-resolved photoluminescence spectroscopy, the electron extraction process between FA0.83Cs0.17Pb(I0.83Br0.17)3 and TiO2 single crystals with different orientations of (100), (110), and (111) were probed from subpicosecond to several hundred nanoseconds. It was revealed that the band alignment between the constituents influenced the relative electron extraction process. TiO2(100) showed the fastest overall and hot electron transfer, owing to the largest conduction band and Fermi level offset compared to FA0.83Cs0.17Pb(I0.83Br0.17)3. It was found that an early electron accumulation in these systems can have an influence on the following electron extraction on the several nanosecond time scale. Furthermore, the existence of a potential barrier at the TiO2/perovskite interface was also revealed by performing excitation fluence-dependent measurements.