Dimerization effect of fluorene-based semiconductors on conformational planarization for microcrystal lasing

Abstract

Efficient ultraviolet organic microcrystal lasers were demonstrated based on bulky diarylfluorene dimers with a fully coplanar conformation.

Diastereoisomer‐Induced Morphology Tunable Self‐Assembled Organic Microcrystals of Conjugated Molecules for Ultraviolet Laser

“…DPFOH was synthesized via coupling 2‐bromo‐9‐phenylfluorene‐9‐ol with 9‐phenylfluorene‐9‐ol boric acid ester according to our previous works. [ 35,37 ] As depicted in Figure 1B and Figure S1, Supporting Information, there are two ultraviolet spots (DPFOH‐1 and DPFOH‐2) on thin‐layer chromatography (TLC) plate with the retention factor ( R f ) of 0.19 and 0.13 (under 365 nm), respectively. These two compounds were facilely separated by silica gel chromatography, and the molecular structures were determined by matrix‐assisted laser desorption/ionization time of flight mass (MALDI‐TOF‐MS), 1 H and 13 C NMR spectra, and single crystal X‐ray analysis (Figures S2–S7 and Table S1, Supporting Information).…”

“…Apparently, these different intermolecular interactions for rac ‐ and meso ‐DPFOH are expected to result in unique self‐assembly behaviors and intermolecular arrangement in the condensed structure for optoelectronic applications. [ 24,25,37,38 ]…”

“…Two isomers show similar maximum absorption peaks at 330 nm in both solution and film states due to the similar conjugated backbone structures. [ 28 ] In diluted solution, both stereoisomers exhibit three identical well‐resolved emission peaks at around 368, 387, and 406 nm corresponding to 0–0, 0–1, and 0–2 vibronic transition, [ 28,35,37 ] respectively (Figure 4A,B). Similarly, the emission spectra of them in film state present two emission bands at about 400 and 416 nm.…”

“…The microrods of rac ‐DPFOH present well‐structured emission peaks at about 404 and 420 nm, similar to planar conformation of fluorene‐based dimer. [ 37 ] However, the microplates of meso ‐DPFOH exhibited a broad emission band at 420 nm with a long tail to 600 nm and red‐shifted to about 20 nm. Meanwhile, from the fluorescence excitation–emission contour plot (Figure 4D), it is easy to observe that emission peak of the rac ‐DPFOH microcrystal presented exceptionally well‐resolved structure with narrower and sharper emission peaks than those of meso ‐DPFOH microcrystals, similar to single molecular chain of polyfluorenes, such as octafluorenes.…”

Enhanced Energy Transfer in Doped Bifluorene Single Crystals: Prospects for Organic Lasers

“…Long‐range molecular order in organic SCs ensures enhanced ambipolar carrier transport . Moreover, improved light outcoupling is facilitated in crystals with highly defined smooth facets that act as Fabry–Perot cavities providing feedback for stimulated emission and thus allowing to achieve lasing thresholds down to hundreds of nJ cm −2 …”