Several hexaazatrinaphthylene derivatives and a tris(thieno)hexaazatriphenylene derivative have been synthesised by reaction of the appropriate diamines with hexaketocyclohexane. The crystal structure of 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene has been determined by X-ray diffraction; this reveals a molecular structure in good agreement with that predicted by density functional theory (DFT) calculations and pi-stacking with an average spacing between adjacent molecular planes of 3.18 A. Solid-state ionisation potentials have been measured by using UV photoelectron spectroscopy and fall in the range of 5.99 to 7.76 eV, whereas solid-state electron affinities, measured using inverse photoelectron spectroscopy, vary in the range -2.65 to -4.59 eV. The most easily reduced example is a tris(thieno)hexaazatriphenylene substituted with bis(trifluoromethyl)phenyl groups; DFT calculations suggest that the highly exothermic electron affinity is due both to the replacement of the outermost phenylene rings of hexaazatrinaphthylene with thieno groups and to the presence of electron-withdrawing bis(trifluoromethyl)phenyl groups. The rather exothermic electron affinities, the potential for adopting pi-stacked structures and the low intramolecular reorganisation energies obtained by DFT calculations suggest that some of these molecules may be useful electron-transport materials.

Electron-phonon coupling plays a key role in a variety of elemental excitations and their interactions in semiconductor nanostructures. Here we demonstrate that the relaxation rate of free excitons in a single ZnTe nanobelt (NB) is considerably enhanced via a nonthermalized hot-exciton emission process as a result of an ultrastrong electron-phonon coupling. Using time-resolved photoluminescence (PL) spectroscopy and resonant Raman spectroscopy (RRS), we present a comprehensive study on the identification and the dynamics of free/bound exciton recombination and the electron-phonon interactions in crystalline ZnTe NBs. Up to tenth-order longitudinal optical (LO) phonons are observed in Raman spectroscopy, indicating an ultrastrong electron-phonon coupling strength. Temperature-dependent PL and RRS spectra suggest that electron-phonon coupling is mainly contributed from Light hole (LH) free excitons. With the presence of hot-exciton emission, two time constants (∼80 and ∼18 ps) are found in photoluminescence decay curves, which are much faster than those in many typical semiconductor nanostructures. Finally we prove that under high excitation power amplified spontaneous emission (ASE) originating from the electron-hole plasma occurs, thereby opening another radiative decay channel with an ultrashort lifetime of few picoseconds.

Many squaraines have been observed to exhibit two-photon absorption at transition energies close to those of the lowest energy one-photon electronic transitions. Here, the electronic and vibronic contributions to these low-energy two-photon absorptions are elucidated by performing correlated quantum-chemical calculations on model chromophores that differ in their terminal donor groups (diarylaminothienyl, indolenylidenemethyl, dimethylaminopolyenyl, or 4-(dimethylamino)phenylpolyenyl). For squaraines with diarylaminothienyl and dimethylaminopolyenyl donors and for the longer examples of 4-(dimethylamino)phenylpolyenyl donors, the calculated energies of the lowest two-photon active states approach those of the lowest energy one-photon active (1B(u)) states. This is consistent with the existence of purely electronic channels for low-energy two-photon absorption (TPA) in these types of chromophores. On the other hand, for all squaraines containing indolinylidenemethyl donors, the calculations indicate that there are no low-lying electronic states of appropriate symmetry for TPA. Actually, we find that the lowest energy TPA transitions can be explained through coupling of the one-photon absorption (OPA) active 1B(u) state with b(u) vibrational modes. Through implementation of Herzberg-Teller theory, we are able to identify the vibrational modes responsible for the low-energy TPA peak and to reproduce, at least qualitatively, the experimental TPA spectra of several squaraines of this type.

Dielectric relaxation spectroscopy is used to quantify molecular motion in alkylsilane SAMs coated on porous glass over a broad temperature range, -30 to -150 degrees C. Systematic measurements using SAMs with variable coating densities allow us to determine the effect of monolayer disorder on molecular mobility in thin molecular films. A relaxation process with an activation energy of approximately 25 kJ/mol is found to dominate dynamics of SAM-chain segments near the substrate. By introducing polar CN groups at the ends of the chain, we show that the relaxation process in the monolayer canopy can be isolated and studied. This approach can be generalized to other substituent polar groups to probe localized relaxation dynamics in surface-grafted monolayer films.

Lead halide perovskites exhibit good performance in room-temperature exciton–polariton lasers and efficient flow of polariton condensates. Shaping and directing polariton condensates by confining the potential is essential for polariton-based optoelectronic devices, which have seldom been explored based on perovskite materials. Here, we investigate the trapping of polaritons in micron-sized CsPbBr3 flakes embedded in a microcavity by varying the negative detuning energy (from −36 to −172 meV) at room temperature. The confinement by the crystal edge results in quantized polariton states both below and above the condensed threshold. As the cavity is more negatively detuned (Δ ≤ −118 meV), the condensed polaritons undergo a transition from the ground state to metastable states with a finite group velocity (∼50 μm/ps at Δ = −118 meV). The metastable polariton condensates can be optically and stably driven between different polariton states by simply changing the pump fluence. The manipulations of the polariton states reveal the effective control of polariton relaxation in quantized polariton states by the underlying exciton–polariton and polariton–polariton scattering. Our findings pave the way for novel polaritonic light sources and integrated polariton devices through the trap engineering of perovskite microcavities.