Strong Two‐Photon Excited Fluorescence and Stimulated Emission from an Organic Single Crystal of an Oligo(Phenylene Vinylene)

Abstract

In this Communication Figure 5 and Figure S5 in the Supporting Information were misinterpreted as a result of an experimental artifact. While we wrote on page 734, that two-photon excited fluorescence of TOPV in the solid state can be unambiguously recorded even on a standard spectrofluorimeter with a Xe lamp as excitation source, a critical reader noticed that a high-intensity laser is still needed to promote a material in the excited state by a two-photon absorption process. In additional experiments we found that the observed emission applying an excitation at 800 nm was a result of the higher order of the diffraction light in the monochromator of the spectrofluorimeter used. Thus, there are also photons available at 400 nm for one-photon excitation, although 800 nm was set as the excitation in the equipment. Diffraction light of a higher order in the monochromator caused the observed emission. This mistake happened as a result of relying on the specifications of the commercial equipment used for the experiments, which suggests that higher-order diffraction light from the monochro-mator is completely filtered out. This assumption led us to draw an incorrect conclusion because we believed our material has such a strong two-photon absorption that just a Xe lamp could be sufficient to promote the material by a two-photon absorption process. As the content that refers to Figure 5 and Figure S5 is based on a wrong assumption this part of the article is incorrect. A high-intensity laser source is still needed for two-photon excitation, as described elsewhere. [1] Soon after the publication of our Communication, we noticed a new article by Spano [2] which revealed that some organic dyes that were formerly thought to form J-aggregates based on spectral shifts are actually H-like aggregates. Further investigation suggested that the TOPV molecules may exhibit similar behavior. Although comparison between the molecular and powder absorption (Figure S3 in the Supporting Information) suggests a red-shift of the absorption in the solid state versus in solution, TOPV molecules might form weakly coupled H-aggregate rather than J-aggregate as we had ascribed in our Communication. The small bump at 467 nm in the powder emission spectrum (Figure S3 in the Supporting Information) become apparent in nanoparticles with increasing molecular disorder, and therefore can be assigned to the 0-0 band of H-aggregates. [2,3] The table of contents entry may also confuse some readers. The meaning of "Low in, high out" used in the Communication refers to the nature of TPA phenomenon. The TOPV molecule emits one higher-energy photon after absorbing two low-energy photons. No quantitative two-photon absorptivity of the crystal is meant in this context.

Intermolecular Charge‐Transfer Interactions Facilitate Two‐Photon Absorption in Styrylpyridine–Tetracyanobenzene Cocrystals

“…[1][2][3][4][5] To date,t here have been extensive studies on synthesizing single-component chromophores with large TPAcross-sections (s TPA ). [6,7] During the structural optimization process,p arameters such as 1) strength of the electrondonor and -acceptor groups,2)the coplanarity of conjugated systems,a nd 3) the length and path of conjugated chains should be considered. [8][9][10] Organic molecules are explored with these considerations in mind (ranging from simple dipolar (D-p-A chromophores), quadrupolar (D-p-A-p-D and A-p-D-p-A chromophores) and octupolar dyes (branched-like chromophores comprised of dipolar units), to dendrimers), with the aim of increasing the extent of electron delocalization necessary to achieve high s TPA .…”

“…Upon excitation by 780 nm laser light, the upconversion PL spectra of STC cocrystals exhibited the same shape as the steady-state measurement (Figure 3a), which illustrates that the emission processes from the one-and two-photon excited states to the ground state are same.W hent he power of the excitation source was increased, the two-photon-excited fluorescence intensity showed as quare dependence with the incident energy,i mplying that the upconverted emission stems from at wo-photon absorption process (Figure 3b). [6] Moreover, STC cocrystals present ab road two-photon excitation window ranging between 720 and 880 nm (Figure 3c). In our previous work, 4-styrylpyridine exhibited second harmonic generation (SHG) without showing TPA.…”

Ultrasound‐Assisted Construction of Halogen‐Bonded Nanosized Cocrystals That Exhibit Thermosensitive Luminescence

“…Such behavior is consistent with the fact that the relative amount of molecules of compound A, which lack strong p À p interactions, on the outer surface of the cocrystal further increase upon decreasing the particle size. Moreover, noting the up-conversion phenomenon of the stilbene compounds, the prepared nano-cocrystals were also excited at 700 and 800 nm by using a Xe lamp as an excitation source [15] on a standard spectrofluorimeter (Figure 3 B). Compared with the microsized sample of cocrystal A·B, which was prepared by using the grinding method, the emission spectra for the nano-cocrystal exhibit a sharp main band with a blue-shift of 3 nm.…”

Crystal structure of 2,5-diethoxy-1,4-bis[2-(quinoline)ethenyl]benzene, C32H28N2O2

“…The oligo(phenylene vinylene) and its derivatives (OPVs) are one kind of highly conjugated linear molecules, attracting increasing interest in the elds of nonliear optic [1], solid state opto-electronics [2] and molecular devices [3]. A large number of OPVs with large two-photon absorption sections (nonliear optical properties) were synthesized and investigated by changing the donor/acceptor(D/A) strength, conjugation length [4], for their potential applications in two-photon uorescence imaging, optical power limiting, two-photon up-conversion lasing, three-dimensional optical data storage, 3D microfabrication, and photodynamic therapy [5].…”