Partha Maity

The synergistic effect of elongated exciton transport and strong exciton-CT state coupling facilitates the generation of long-lived reactive charges in NIR organic photocatalysts.

A single organic semiconductor typically struggles with inefficient intrinsic charge generation due to large binding energy ( E _B ≈ 0.5 electron volts) of Frenkel excitons, particularly in narrow-bandgap organic semiconductors that exhibit near-infrared (NIR) absorption. Here, we develop double-cable polymer–based nanoparticles (NPs), enabling single-component organic photocatalysts to achieve NIR photon absorption and generate long-lived free charges simultaneously. as -DCPIC, a double-cable polymer with donor polymer (PBDB-T) as electron-donating conjugated backbones and pendent NIR acceptor (TPDIC) as the electron-deficient side chains, offers potential for self-sustained photoelectric conversion. Consequently, as -DCPIC NPs exhibit significantly enhanced hydrogen evolution performance (11.88 mmol per hour per gram) compared to pristine PBDB-T or TPDIC NPs. Transient absorption spectroscopy elucidates the effective electron-hole separation inside as -DCPIC NPs, whereas decay kinetics monitor the long-lived free carriers (109 nanoseconds) in as -DCPIC NPs. Our findings demonstrate that double-cable polymers provide a powerful platform for establishing efficient single-component organic photocatalysts to generate long-lived reactive charges.

We studied the intersystem crossing (ISC) property of red-light absorbing heavy atom-free dihydronaphtho[b]-fused Bodipy derivatives (with phenyl group attached at the lower rim via ethylene bridge, taking constrained geometry, i.e., BDP-1 and the half-oxidized product BDP-2) and dispiroflourene[b]-fused Bodipy (BDP-3) that have a twisted π-conjugated framework. BDP-1 and BDP-3 show strong and sharp absorption bands (i.e., ε = 2.0 × 10⁵ M^-1 cm^-1 at 639 nm, fwhm ∼491 cm^-1 for BDP-3). BDP-1 is significantly twisted (φ = 21.6°), while upon mono-oxidation, BDP-2 becomes nearly planar on the oxidized side (φ = 3.5°). Interestingly, BDP-2 showed efficient ISC (triplet state quantum yield, Φ_T = 40%) due to S₁/T₂ state energy matching. Long-lived triplet excited state was observed (τ_T = 212 μs in solution and 2.4 ms in polymer matrix), and ISC takes 4.0 ns. Differently, twisted BDP-1 gives weak ISC only 5%, ISC takes 7.7 ns, and the triplet state is populated only with addition of ethyl iodide. Time-resolved electron paramagnetic resonance spectra of BDP-1 revealed the coexistence of two triplet states, with drastically different zero-field splitting D parameters of -2047 MHz and -1370 MHz, respectively, along with varying sublevel population ratios. We demonstrate that the ISC is not necessarily enhanced by torsion of the π-conjugation framework; instead, S₁/T_n state energy matching is more efficient to induce ISC even in compounds that have planar molecular structures.

Copper nanoclusters (Cu NCs) characterized by their well-defined electronic and optical properties are an ideal platform for organic photocatalysis and exploring atomic-level behaviors. However, their potential as greener, efficient catalysts for challenging reactions like decarboxylative oxygenation under mild conditions remains unexplored. Herein, we present Cu₁₃(Nap)₃(PPh₃)₇H₁₀ (hereafter Cu₁₃Nap), protected by 1-naphthalene thiolate (Nap), which performs well in decarboxylative oxidation (90% yield) under photochemical conditions. In comparison, the isostructural Cu₁₃(DCBT)₃(PPh₃)₇H₁₀ (hereafter Cu₁₃DCBT), stabilized by 2,4-dichlorobenzenethiolate (DCBT), yields only 28%, and other previously reported Cu NCs (Cu₂₈, Cu₂₉, Cu₄₅, Cu₅₇, and Cu₆₁) yield in the range of 6-18%. The introduction of naphthalene thiolate to the surface of Cu₁₃ NCs influences their electronic structure and charge transfer in the ligand shell, enhancing visible light absorption and catalytic performance. Density functional theory (DFT) and experimental evidence suggest that the reaction proceeds primarily through an energy transfer mechanism. The energy transfer pathway is uncommon in the context of previous reports for decarboxylative oxidation reactions. Our findings suggest that strategically manipulating ligands holds significant potential for creating composite active sites on atomically precise copper NCs, resulting in enhanced catalytic efficacy and selectivity across various challenging reactions.

Colloidal quantum dots (CQDs) are emerging materials for short‐wave infrared (SWIR, ≈1100–3000 nm) photodetectors, which are technologically important for a broad array of applications. Unfortunately, the most developed SWIR CQD systems are Pb and Hg chalcogenides; their toxicity and regulated compositions limit their applications. InSb CQD system is a potential environmentally friendly alternative, whose bandgap in theory, is tunable via quantum confinement across the SWIR spectrum. However, InSb CQDs are difficult to exploit, due to their complex syntheses and uncommon reactive precursors, which greatly hinder their application and study. Here, a one‐pot synthesis strategy is reported using commercially available precursors to synthesize—under standard colloidal synthesis conditions—high‐quality, size‐tunable InSb CQDs. With this strategy, the large Bohr exciton radius of InSb can be exploited for tuning the bandgap of the CQDs over a wide range of wavelengths (≈1250–1860 nm) across the SWIR region. Furthermore, by changing the surface ligands of the CQDs from oleic acid (OA) to 1‐dodecanthiol (DDT), a ≈20‐fold lengthening in the excited‐state lifetime, efficient carrier multiplication, and slower carrier annihilation are observed. The work opens a wide range of SWIR applications to a promising class of Pb‐ and Hg‐free CQDs.

InAs colloidal quantum dots (CQDs) have emerged as candidate lead- and mercury-free solution-processed semiconductors for infrared technology due to their appropriate bulk bandgap, which can be tuned by quantum confinement, and promising charge-carrier transport properties. However, the lack of suitable arsenic precursors and readily accessible synthesis conditions have limited InAs CQDs to smaller sizes (in situ precursor complexation, we isolate the reaction mechanism, producing InAs nanorod CQDs that display narrow excitonic features and efficient carrier multiplication. Our work enables InAs CQDs for a wider range of SWIR applications.

Bodipy (BDP)‐perylenebisimide (PBI) donor–acceptor dyads/triad were prepared to study the spin–orbit charge‐transfer intersystem crossing (SOCT‐ISC). For BDP‐PBI‐3, in which BDP was attached at the imide position of PBI, higher singlet oxygen quantum yield (Φ_Δ=85 %) was observed than the bay‐substituted derivative BDP‐PBI‐1 (Φ_Δ=30 %). Femtosecond transient absorption spectra indicate slow Förster resonance energy transfer (FRET; 40.4 ps) and charge separation (CS; 1.55 ns) in BDP‐PBI‐3, while for BDP‐PBI‐1, CS takes 2.8 ps. For triad BDP‐PBI‐2, ultrafast FRET (149 fs) and CS (4.7 ps) process were observed, the subsequent charge recombination (CR) takes 5.8 ns and long‐lived ³PBI* (179.8 μs) state is populated. Nanosecond transient absorption spectra of BDP‐PBI‐3 show that the CR gives upper triplet excited state (³BDP*) and subsequently, via a slow intramolecular triplet energy transfer (14.5 μs), the ³PBI* state is finally populated, indicating that upper triplet state is involved in SOCT‐ISC. Time‐resolved electron paramagnetic resonance spectroscopy revealed that both radical pair ISC (RP ISC) and SOCT‐ISC contribute to the ISC. A rare electron spin polarization of (e, e, e, e, e, e) was observed for the triplet state formed via the RP ISC mechanism, due to the S−T₊₁/T₀ states mixing.