Strong quantization effects and tuneable near‐infrared photoluminescence emission are reported in mechanically exfoliated crystals of γ‐rhombohedral semiconducting InSe. The optical properties of InSe nanosheets differ qualitatively from those reported recently for exfoliated transition metal dichalcogenides and indicate a crossover from a direct to an indirect band gap semiconductor when the InSe flake thickness is reduced to a few nanometers.

High broad‐band photoresponsivity of mechanically formed InSe–graphene van der Waals heterostructures is achieved by exploiting the broad‐band transparency of graphene, the direct bandgap of InSe, and the favorable band line up of InSe with graphene. The photoresponsivity exceeds that for other van der Waals heterostructures and the spectral response extends from the near‐infrared to the visible spectrum.

Dedicated to Professor Fraser Stoddart on the occasion of his 70th birthdayIngenious new template-directed strategies make it possible to synthesize an increasingly wide range of molecular architectures, which would otherwise be inaccessible. [1][2][3][4][5][6][7][8][9][10][11][12] Recently, we developed the concept of Vernier templating-the use of noncommensurate combinations of templates and building blocks to direct the formation of cyclic oligomers, such that the number of binding sites in the product is the lowest common multiple of the numbers of sites in the template and the starting material. [12d] This principle allows a small template to direct the formation of a much larger macrocycle. Previously, we illustrated this idea with the synthesis of a 12-porphyrin nanoring, c-P12, from a linear zinc porphyrin tetramer, l-P4, and a hexapyridyl template, T6.Here we report the synthesis of a 24-porphyrin ring, c-P24, by two Vernier-templated routes: a) coupling the linear porphyrin octamer l-P8 in the presence of hexapyridyl template T6, and b) coupling the linear porphyrin hexamer l-P6 in the presence of the octapyridyl template T8 (Scheme 1). The 24porphyrin nanoring can be prepared in yields of up to 25 %. It has a diameter of 10 nm, as confirmed by scanning tunneling microscopy (STM), and a molecular weight of 26 kDa, thus placing it in the size range of a typical protein. This flexible macrocycle can be locked into a planar p-conjugated conformation by the cooperative self-assembly of a 2:24 doublestrand complex with the linear diamine ligand 1,4diazabicyclo[2.2.2]octane (DABCO).The representation of the two routes to c-P24 in Scheme 1 overlooks the fact that complexes such as (l-P8) 3 ·(T6) 4 and c-P24·(T6) 4 have many possible isomers, as illustrated in Figure 1. However, the formation of these isomeric intermediates should not detract from the efficiency of the Vernier-templated synthesis, because removal of the template will convert all these isomers into the same c-P24 open ring (except for knotted structures, for example, Figure 1 d [13] ).Palladium-catalyzed oxidative coupling of the linear porphyrin octamer l-P8 [12a] in the presence of the hexapyridyl template T6 [12b,c] gave the expected product c-P24, together with the 16-porphyrin ring c-P16 [14] and linear polymers, all as complexes with T6. The polymeric by-products were removed Scheme 1. a) Vernier-templated synthesis of the nanoring c-P24. Reagents: 1) [PdCl 2 (PPh 3 ) 2 ], CuI, benzoquinone, iPr 2 NH; 2) pyridine. b) Structures of T6, T8, and c-P24; Ar = 3,5-bis(octyloxy)phenyl. Figure 1. Four examples of possible isomers of c-P24·(T6) 4 . [13]

concentration can be modifi ed, and photoresponsivity of SLG can be signifi cantly enhanced by the choice of ligands. By reducing the length of capping ligands, hence the thickness of the dielectric barrier between the QDs and the SLG, and by preserving the integrity of the ligand layer, we achieve the efficient transfer of photogenerated carriers from the QDs to the graphene before recombining, resulting in enhanced photoresponsivities of up to ≈10 9 A W −1 .Single layer graphene grown by low-pressure chemical vapor deposition (LP-CVD) [ 14,15 ] was processed into a planar transistor and deposited onto a SiO 2 /n-Si substrate with oxide layer thickness t = 300 nm, as shown schematically in Figure 1 a (see also the Supporting Information, Figure S1). The length, L , and width, w , of the graphene channel are 6 and 10 µm, respectively. The n-Si layer serves as a gate electrode. Colloidal quantum dots with an average PbS core diameter of d = 4.5nm QD (Figure 1 b) were stabilized using the following capping ligands of different length, l , which determines the effective separation between the PbS nanocrystals and graphene: polyethylene glycol H (O CH 2 CH 2 ) n OH with n = 2000 for QD p2000 and n = 500 for QD p500 [ 16 ] and corresponding length of l ≈ 10 nm and l ≈ 5 nm, respectively; [ 17 ] a mixture of thioglycerol (TGL) and 2,3-dimercapto-1-propanol (DTG), l ≈ 0.5 nm for QD TGL , [ 18 ] see Table 1 . We note that the ligand size is estimated for extended molecules and does not include any effects that could arise from compression of the ligand layer upon drying under vacuum. The interparticle distances observed on TEM images are comparable with the theoretical estimate of the ligand length (see the Supporting Information, Figure S2). The QDs were dropcast from aqueous solution (5 mg mL −1 ) to produce continuous thick (>100 nm) coverage of the graphene layer, followed by drying for 12 h in vacuum at room temperature. The size of the QDs and their room temperature photoluminescence spectra (with a peak at photon energy ≈1.1eV) are similar in all three structures, i.e., they are not affected by the ligand. All measured devices demonstrate stable and reproducible behavior during the measurement period of at least 14 days. All samples were stored in dry nitrogen cabinet and all electrical measurements were performed at room temperature T = 300 K in vacuum (≈10 −6 mbar). The I V ( ) g characteristics were measured using slow sweeping rate, r , of the gate voltage, i.e., r ≤ 0.02 V s −1 .The pristine monolayer graphene devices show a linear dependence of current, I , on bias voltage, V s , and a minimum conductance at a gate voltage, V ≈ +30V g min corresponding to p-type doping with hole concentration, p ≈ 2 × 10 12 cm −2

The fluorescence of a two-dimensional supramolecular network of 5,10,15,20-tetrakis(4-carboxylphenyl)porphyrin (TCPP) adsorbed on hexagonal boron nitride (hBN) is red-shifted due to, primarily, adsorbate-substrate van der Waals interactions. TCPP is deposited from solution on hBN and forms faceted islands with typical dimensions of 100 nm and either square or hexagonal symmetry. The molecular arrangement is stabilized by in-plane hydrogen bonding as determined by a combination of molecular-resolution atomic force microscopy performed under ambient conditions and density functional theory; a similar structure is observed on MoS2 and graphite. The fluorescence spectra of submonolayers of TCPP on hBN are red-shifted by ∼30 nm due to the distortion of the molecule arising from van der Waals interactions, in agreement with time-dependent density functional theory calculations. Fluorescence intensity variations are observed due to coherent partial reflections at the hBN interface, implying that such hybrid structures have potential in photonic applications.