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The optical spectra of transition metal dichalcogenide monolayers are dominated by excitons and trions. Here, we establish the dependence of these optical transitions on the disorder from hyperspectral imaging of h-BN encapsulated monolayer MoSe2. While both exciton and trion energies vary spatially, these two quantities are almost perfectly correlated, with spatial variation in the trion binding energy of only ∼0.18 meV. In contrast, variation in the energy splitting between the two lowest energy exciton states is one order of magnitude larger at ∼1.7 meV. Statistical analysis and theoretical modeling reveal that disorder results from dielectric and bandgap fluctuations, not electrostatic fluctuations. Our results shed light on disorder in high quality TMDC monolayers, its impact on optical transitions, and the many-body nature of excitons and trions. [ABSTRACT FROM AUTHOR]

The trion, a three-body charge-exciton bound state, offers unique opportunities to simultaneously manipulate charge, spin, and excitation in one-dimensional single-walled carbon nanotubes (SWNTs) at room temperature. Effective exploitation of trion quasi-particles requires fundamental insight into their creation and decay dynamics. Such knowledge, however, remains elusive for SWNT trion states, due to the electronic and morphological heterogeneity of commonly interrogated SWNT samples, and the fact that transient spectroscopic signals uniquely associated with the trion state have not been identified. Here, we prepare lengthsorted SWNTs and precisely control charge-carrier-doping densities to determine trion dynamics using femtosecond pump-probe spectroscopy. Identification of the trion transient absorptive hallmark enables us to demonstrate that trions (i) derive from a precursor excitonic state, (ii) are produced via migration of excitons to stationary hole-polaron sites, and (iii) decay in a first-order manner. Importantly, under appropriate carrier-doping densities, exciton-to-trion conversion in SWNTs can approach 100% at ambient temperature. Our findings open up possibilities for exploiting trions in SWNT optoelectronics, ranging from photovoltaics and photodetectors to spintronics. [ABSTRACT FROM AUTHOR]

Realizing chromophores that simultaneously possess substantial near-infrared (NIR) absorptivity and long-lived, high-yield triplet excited states is vital for many optoelectronic applications, such as optical power limiting and triplet-triplet annihilation photon upconversion (TTA-UC). However, the energy gap law ensures such chromophores are rare, and molecular engineering of absorbers having such properties has proven challenging. Here, we present a versatile methodology to tackle this design issue by exploiting the ethyne-bridged (polypyridyl)metal(II) (M; M = Ru, Os)-(porphinato)metal(II) (PM'; M' = Zn, Pt, Pd) molecular architecture (M-(PM')n-M), wherein high-oscillator-strength NIR absorptivity up to 850 nm, near-unity intersystem crossing (ISC) quantum yields (ΦISC), and triplet excited-state (T1) lifetimes on the microseconds time scale are simultaneously realized. By varying the extent to which the atomic coefficients of heavy metal d orbitals contribute to the one-electron excitation configurations describing the initially prepared singlet and triplet excited-state wave functions, we (i) show that the relative magnitudes of fluorescence (k[sup 0]F), S1 → S0 nonradiative decay (knr), S1 → T1 ISC (kISC), and T1 → S0 relaxation (kT[sub 1]→S0) rate constants can be finely tuned in M-(PM')n-M compounds and (ii) demonstrate designs in which the kISC magnitude dominates singlet manifold relaxation dynamics but does not give rise to T1 → S0 conversion dynamics that short-circuit a microseconds time scale triplet lifetime. Notably, the NIR spectral domain absorptivities of M-(PM')n-M chromophores far exceed those of classic coordination complexes and organic materials possessing similarly high yields of triplet-state formation: in contrast to these benchmark materials, this work demonstrates that these M-(PM')n-M systems realize near unit ΦISC at extraordinarily modest S1-T1 energy gaps (~0.25 eV). This study underscores the photophysical diversity of the M-(PM')n-M platform and presents a new library of long-wavelength absorbers that efficiently populate long-lived T1 states. [ABSTRACT FROM AUTHOR]

An exciton–polariton condensate is a hybrid light–matter state in the quantum fluid phase. The photonic component endows it with characters of spin, as represented by circular polarization. Spin-polarization can form stochastically for quasi-equilibrium exciton–polariton condensates at parallel momentum vector k|| ∼ 0 from bifurcation or deterministically for propagating condensates at k|| > 0 from the optical spin-Hall effect (OSHE). Here, we report deterministic spin-polarization in exciton–polariton condensates at k|| ∼ 0 in microcavities containing methylammonium lead bromide perovskite (CH3NH3PbBr3) single crystals under non-resonant and linearly polarized excitation. We observe two energetically split condensates with opposite circular polarizations and attribute this observation to the presence of strong birefringence, which introduces a large OSHE at k|| ∼ 0 and pins the condensates in a particular spin state. Such spin-polarized exciton–polariton condensates may serve not only as circularly polarized laser sources but also as effective alternatives to ultracold atom Bose–Einstein condensates in quantum simulators of many-body spin–orbit coupling processes. [ABSTRACT FROM AUTHOR]

We report four supermolecular chromophoresbased on (porphinato)zinc(II) (PZn) and (polypyridyl)metal units bridgedvia ethyne connectivity (Pyr1RuPZn2, Pyr1RuPZnRuPyr1, Pyr1RuPZn2RuPyr1,and OsPZn2Os) thatfulfill critical sensitizer requirements for NIR-to-vis triplet–tripletannihilation upconversion (TTA-UC) photochemistry. These NIR sensitizersfeature: (i) broad, high oscillator strength NIR absorptivity (700nm < λmax(NIR)< 770 nm; 6 × 104M–1cm–1< extinction coefficient(λmax(NIR)) < 1.6 × 105M–1cm–1; 820 cm–1< fwhm < 1700 cm–1); (ii) substantial intersystemcrossing quantum yields; (iii) long, microsecond time scale T1state lifetimes; and (iv) triplet states that are energeticallypoised for exergonic energy transfer to the molecular annihilator(rubrene). Using low-power noncoherent illumination at power densities(1–10 mW cm–2) similar to that of terrestrialsolar photon illumination conditions, we demonstrate that Pyr1RuPZn2, Pyr1RuPZn2RuPyr1,and Pyr1RuPZnRuPyr1sensitizers can be used in combinationwith the rubrene acceptor/annihilator to achieve TTA-UC: these studiesrepresent the first examples whereby a low-power noncoherent NIR lightsource drives NIR-to-visible upconverted fluorescence centered ina spectral window within the bandgap of amorphous silicon. [ABSTRACT FROM AUTHOR]

We report the first-order hyperpolarizabilities (βHRS values) of individualized, length-sorted (700 ± 50 nm long) (6,5) SWNTs and corresponding polymer-wrapped (6,5) SWNT superstructures. These SWNT-based nanohybrids feature semiconducting polymers that wrap the SWNT surface in an exclusive left-handed helical fashion. Manipulation of the polymer electronic structures in these well-defined nanoscale objects provides a new avenue to modulate the magnitude of βHRS at long wavelength (1280 nm). [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotube (SWNT)-based nanohybrid compositions based on (6,5) chirality-enriched SWNTs ([(6,5) SWNTs]) and a chiral n-type polymer (SPBN( b)-Ph4PDI) that exploits a perylenediimide (PDI)-containing repeat unit are reported; S-PBN(b)-Ph4PDI-[(6,5) SWNT] superstructures feature a PDI electron acceptor unit positioned at 3 nm intervals along the nanotube surface, thus controlling rigorously SWNT-electron acceptor stoichiometry and organization. Potentiometric studies and redox-titration experiments determine driving forces for photoinduced charge separation (CS) and thermal charge recombination (CR) reactions, as well as spectroscopic signatures of SWNT hole polaron and PDI radical anion (PDI-•) states. Time-resolved pump-probe spectroscopic studies demonstrate that SPBN( b)-Ph4PDI-[(6,5) SWNT] electronic excitation generates PDI-• via a photoinduced CS reaction (ΤCS.0.4 ps, ΦCS ≈0.97). These experiments highlight the concomitant rise and decay of transient absorption spectroscopic signatures characteristic of the SWNT hole polaron and PDI-• states. Multiwavelength global analysis of these data provide two charge-recombination time constants (ΤCR≈31.8 and 250 ps) that likely reflect CR dynamics involving both an intimately associated SWNT hole polaron and PDI-• charge-separated state, and a related charge-separated state involving PDI-• and a hole polaron site produced via hole migration along the SWNT backbone that occurs over this timescale. [ABSTRACT FROM AUTHOR]