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

Abstract

ae Nonlinear optical response in organic semiconductors has been an attractive property for many practical applications. For frequency up-converted lasers, to date, conjugated polymers, fluorescent dyes and small organic molecules have been proposed but their performances have been severely limited due to the difficulty in simultaneously achieving strong nonlinear optical response and high performance optical gain. In this work, we show that structurally designed truxene-based star-shaped oligofluorenes exhibit strong structure-property relationships enabling enhanced nonlinear optical response with favorable optical gain performance. As the number of fluorene repeat units in each arm is increased from 3 to 6, these molecules demonstrate a two-photon absorption cross-section as high as 2200 GM, which is comparable to that of linear conjugated polymers. Tailored truxene oligomers with six fluorene units in each arm (T6) show two-photon absorption pumped amplified spontaneous emission with a threshold as low as 2.43 mJ cm À2, which is better than that of the lowest reported threshold in organic semiconductors. Furthermore, we show a frequency up-converted laser using the newly designed and synthesized star-shaped oligomer T6 with a threshold as low as 3.1 mJ cm À2 , which is more than an order of magnitude lower than that of any conjugated polymer. Thus, these oligomers with enhanced nonlinear optical properties are highly attractive for bio-integrated applications such as photodynamic therapy and in vivo bio-sensing.

Highly Efficient Multiphoton‐Pumped Frequency‐Upconversion Stimulated Blue Emission with Ultralow Threshold from Highly Extended Ladder‐Type Oligo(p‐phenylene)s

“…2.0 mJ) in DMSO, [3c] PhN-OF(5)-NPh (ca. 267 mJ) in solid state, [16] and even better than that of colloidal nanoplatelets (ca. 267 mJ) in solid state, [16] and even better than that of colloidal nanoplatelets (ca.…”

“…1.5 mJ) in toluene, [17] tailored truxene oligomer (T6) (ca. 267 mJ) in solid state, [16] and even better than that of colloidal nanoplatelets (ca. 1.2 mJ) in solution.…”

“…Remarkably,t he highly extended (L)-Ph(10)-NPh exhibits exceptionally large 2PAc ross-sections with am aximum s 2 of 3643 GM at 740 nm, further affirming the significance of lateral substitution of alkylphenyl moieties [11a] and highly extended effective conjugation length [15] for alarge enhancement of MPAresponses,offering an effective strategy to achieve an excellent nonlinearity-transparencyt rade-off. Not only such ar ecord high intrinsic s 2 but also the scaled 2PAm erit are much greater than those of (Ph)-OF(5)-NPh (2559 GM and 0.62 GM), [11a] 4FL (2357 GM and 0.61 GM) [10a] and the tailored truxene oligomer T6 (2183 GM and 0.038 GM) [16] and comparable to that of high molecular weight linear conjugated polymer film (ca. 4000 GM estimated from the nonlinear absorption coefficient), [15] highlighting the promise of this class of oligomers to function as ag ain material for 2PP ASE/lasing applications.…”

Pyridazine‐Containing Diazatwistanthracene and Tetraazatwisttetracene: Synthesis, Crystal Structures and Third Order Non‐linear Optical Properties

“…Two‐photon absorption (TPA) exhibits the process in which substance simultaneously absorbs two photons to an excited state under the excitation of a strong laser ,. Recently, organic materials with excellent two‐photon absorption properties have been widely investigated and applicated in different aspects, including optical limiting, up‐converted lasing, 3D optical data storage, micro‐fabrication, photodynamic therapy, and two‐photon laser scanning fluorescence imaging, etc . Actually, the molecular structures strongly affect the TPA properties.…”

“…[29,30] Recently, organic materials with excellent two-photon absorption properties have been widely investigated and applicated in different aspects, including optical limiting, up-converted lasing, 3D optical data storage, micro-fabrication, photodynamic therapy, and two-photon laser scanning fluorescence imaging, etc. [31][32][33][34][35][36] Actually, the molecular structures strongly affect the TPA properties. Studies showed that the appropriate choices of donor, acceptors and π-bridges [37,38] inducing appropriate intraor inter-molecular dipola moments are important for the TPA properties.…”