Location, Location, Location ‐ Strategic Positioning of 2,1,3‐Benzothiadiazole Units within Trigonal Quaterfluorene‐Truxene Star‐Shaped Structures

Abstract

The fused, bicyclic molecule, 2,1,3‐Benzothiadiazole (BT), has become a key ingredient in the design of new organic semiconductors for light emission and energy harvesting applications. Here, the synthesis is reported of a series of trigonal, star‐shaped compounds comprising a truxene core and three quater‐dialkylfluorene arms into each of which a BT unit is inserted sequentially at each possible position (T4BT‐A to T4BT‐E). Analysis of the resulting electronic properties shows that as a consequence of conjugative coupling to the core and the resulting symmetry there are three distinct locations for the BT unit and the influence that these locations have on light emission and other spectroscopic characteristics is discussed. The systematic variation in photophysical properties for the different structural isomers helps to clarify the influence of BT unit addition to 9,9‐dialkylfluorene chains. It also helps to establish a design template for the construction of donor‐acceptor conjugated materials with targeted properties. For T4BT‐E with a BT unit at the terminal position of each arm, the photoluminescence quantum efficiency is significantly reduced and no amplified spontaneous emission is observed under typical pumping conditions. Theoretical calculations assist in understanding the variation in behaviors among the T4BT‐X family of compounds, especially in relation to their photoluminescence decay times and the Raman scattering intensities of their dominant BT‐unit‐centred molecular vibrations.

Ultralow-threshold up-converted lasing in oligofluorenes with tailored strong nonlinear absorption

“…The T3 and T4 compounds were synthesized according to our previous reports. 6,38 The synthesis of T6 oligofluorene is presented in Scheme 1 and described in the Experimental section (also see Fig. S1 and S2, ESI †).…”

Host Exciton Confinement for Enhanced Förster‐Transfer‐Blend Gain Media Yielding Highly Efficient Yellow‐Green Lasers

“…[27,29,38,39] The short DBPhFCz conjugation length together with its bulky, nonplanar shape introduces a large degree of confinement, countering geminatepair sepa ration and reducing substantially charge generation rate (k p ) . Polaronpairs will still form via diffusioncontrolled processes that lead to dissociation at randomly encountered sites with suitable (structurederived) offsets in HOMO/LUMO energy [40] and/or via exciton-exciton annihilation [41] but on significantly longer timescales. Such sites are also expected to be less numerous for the more glasslike DBPhFCz host.…”

Incorporation of perfluorohexyl-functionalised thiophenes into oligofluorene-truxenes: synthesis and physical properties

“…The regioselectivity of this reaction was poor, and the product was obtained as a mixture with its isomer, 2-iodo-4-perfluorohexylthiophene, which was separated by column chromatography. Compound 4 then underwent Suzuki–Miyaura coupling with compound 5 , which was synthesised according to our previously published method [17], and the product obtained, 6 , was deprotected by bromination to give compound 7 and then reacted with bis(pinacolato)diboron to afford boronic ester 8 .…”