Green-and-red photoluminescence from Si–Si and Ge–Ge bonded network homopolymers and copolymers

Abstract

Recently, we found pure green photoluminescence (PL) at 540 nm (2.34 eV) in a vacuum, which is characteristic of a Si-Si bonded network polymer bearing n-butyl groups (organopolysilyne, SNP). SNP was carefully isolated as an orange-yellow solid by avoidance of contact with air and water in the polymer synthesis and PL measurement. This was in contrast with previous reports that SNPs carrying alkyl groups have a blue PL band around 450-480 nm. By applying the modified technique to a soluble Ge-Ge bonded network polymer carrying n-butyl groups (organopolygermyne, GNP), with much care in synthesising the polymer and measuring the PL, we found that GNP reveals a very brilliant red-coloured PL band at 690 nm (1.80 eV) in a vacuum at 77 K. This was in contrast with a previous report that GNP carrying n-hexyl groups has a green PL band at 560 nm (2.21 eV). On the other hand, soluble Si-Ge network copolymers (SGNPs) prepared in a similar way to SNP and GNP syntheses showed green-and-red dual PL bands at 540 nm and 690 nm. Based on analyses with IR, Raman, HR-TEM, XPS, EELS, UV-Vis and PL data, the dual emission was assumed to originate from the coexistence of Si and Ge domains (1-2 nm in diameter), possibly, in the same skeleton of SGNP.

Synthesis, Properties, and Derivatization of Poly(dihydrogermane): A Germanium-Based Polyethylene Analogue

“…For the present (GeH 2 ) n samples, optical band gap depends upon mode of preparation and is a reflection of their morphology; optical band gaps of 2.70 and 2.31 eV were obtained for (GeH 2 ) n prepared using Methods 1 and 2, respectively. We also note that while Urbach tails were observed for both samples, it is more prevalent for (GeH 2 ) n prepared using Method 1 and reflects a lack of long-range ordering. , …”

“…We also note that while Urbach tails were observed for both samples, it is more prevalent for (GeH2)n prepared using Method 1 and reflects a lack of long range order in the material. 30,43 The experimental values reported here agree well with first principles calculations reported by Zeng et al 11 who predicted a (GeH2)n band gap of 3.03 eV. These authors indicated that bandedge states in (GeH2)n arise primarily from the atomic orbital delocalized over the Ge backbone; in these systems the lowest unoccupied molecular orbital (i.e., LUMO; conduction band edge) arises from Ge 4s and 4px orbitals while the highest occupied molecular orbital (i.e., HOMO; valence band edge) is dominated by the Ge 4pz (along the Ge-Ge chain).…”

“…We also note that while Urbach tails were observed for both samples, it is more prevalent for (GeH 2 ) n prepared using Method 1 and reflects a lack of long-range ordering. 30,45 Although chain length is known to impact band gap of polymers, its impact is primarily manifested when the chains are short. 10,46,47 While the impact of chain length cannot be completely discounted, given the high M w of the present systems, alternative explanations must be invoked.…”

Inorganic and organometallic polymers

“…49 The controlled electropolymerisation of diorganodichlorosilanes R 2 SiCl 2 enabled the synthesis of well-defined polysilane block copolymers such as [PhSiMe] m -b-[BuSiMe] n to be prepared. 50 A series of network polygermasilanes with tunable Si/Ge ratios in 0.25 increments were synthesised via Wurtz coupling of BuECl 3 co-monomers (E = Ge and Si) in the presence of alkali metal reductants; upon increasing incorporation of Ge into the 1-2 nm sized network domains, the observed PL became red-shifted and particles with pure Ge cores exhibited intense red-coloured photoluminescence at 690 nm at 77 K. 51 Highly promising photovoltaic dithienylgermole polymers such as 13 52 have been reported by a number of groups in 2011 with solar cell power conversion efficiencies (PCEs) as high as 4%. [52][53][54][55] An inverted BHJ solar cell featuring dithienylgermoles yielded an impressive PCE of 7.3%.…”

Air-stable poly(3,3,3-trifluoropropylsilyne) homo- and copolymers

“…45 This result indicates that these SNPs possess either an a-Si skeleton or a skeleton with no long-range ordering. 29,46 Fig. 2 Fluoroalkyl fractions characterized by 1 H NMR and XPS as a function of the nominal mole feed fraction of 1 used during the preparation of F x B 1Àx SNP (x ¼ 0.25, 0.50 and 0.75).…”