How temperature and hydrostatic pressure impact organic room temperature phosphorescence from H-aggregation of planar triarylboranes and the application in bioimaging

Highly efficient persistent organic room temperature phosphorescence(RTP) has attracted increasing attention because of promising applications in fields of chemical sensors, optoelectronic devices, information security, and bioimaging, etc. Wherein,the crystal engineering of H-aggregation offers stabilization for long-lived triplet exciton for RTP, but the related research is rare because of the scarcity of ideal phosphorescent H-aggregate. Herein, we designed planar tricoordinate organoboron derivatives with molecular arrangement in ideal H-aggregation. The integration of Br atom can largely enhance RTP efficiency through increasing SOC effect, while the antiparallel molecular arrangement causes annihilation of triplet exciton. Thanks to good selfassembly property, their RTP can even be observed in PMMA matrix with doping ratio of merely 1 wt%. We further found that the cryogenic temperature contributes to stabilizing triplet exciton in H-aggregation, leading to red-shifted phosphorescence. By applying high hydrostatic pressure, the phosphorescence was largely enhanced and redshifted, demonstrating the crucial role of H-aggregation on RTP property. In phosphorescent tissue imaging of live mouse, nanoparticles of BrBA exhibited high contrast image via eliminating the interference of autofluorescence.

Surface-state triggered solvatochromism of carbonized polymer dot and its two-photon luminescence

This study reports a new nitrogen-doped carbonized polymer dot(CPD)-based solvatochromic probe.Its color-changing for different solvents was explored in detail by the measurements of photophysical parameters(involving Stokes shifts,fluorescence quantum yield,fluorescence lifetime,radiative decay rate constant,and non-radiative decay rate constant)and the following analyses according to Lippert–Mataga equation and Kamlet–Taft model.The hydrogen bonding effect of the CPD in protonic solvents was semi-quantitatively assessed.It takes charge of the solvatochromic phenomenon,especially in proton solvents.Interestingly,this CPD exhibits two-photon solvatochromism.Moreover,the relations between the photophysical parameters and the surface states of CPD in aprotic and proton solvents were depicted.The results reveal the nitrogen doping in the CPD impacts the up-and down-conversion solvatochromic features from the comparison between N-free and N-doped CPDs in many characterizations.In addition,this N-doped CPD was dispersed into polymer matrices to fabricate tunable solid-state luminescent films,which is another model for evidencing the interactions of the CPD with surroundings.This study is of significance in understanding the surface-state controlled luminescence in the CPDs,and will be beneficial for developing new smart,responsive carbon-based nanoprobes.

Modulation of hot regions in waveguide-based evanescent-field-coupled localized surface plasmons for plasmon-enhanced spectroscopy

Coupling efficiency between the localized surface plasmons(LSPs) of metal nanoparticles(NPs) and incident light dominates the sensitivities of plasmon-based sensing spectroscopies and imaging techniques, e.g., surfaceenhanced Raman scattering(SERS) spectroscopy. Many endogenous features of metal NPs(e.g., size, shape,aggregation form, etc.) that have strong impacts on their LSPs have been discussed in detail in previous studies.Here, the polarization-tuned electromagnetic(EM) field that facilitates the LSP coupling is fully discussed.Numerical analyses on waveguide-based evanescent fields(WEFs) coupled with the LSPs of dispersed silver nanospheres and silver nano-hemispheres are presented and the applicability of the WEF-LSPs to plasmon-enhanced spectroscopy is discussed. Compared with LSPs under direct light excitation that only provide 3–4 times enhancement of the incidence field, the WEF-LSPs can amplify the electric field intensity about 30–90 times(equaling the enhancement factor of 10~6–10~8 in SERS intensity), which is comparable to the EM amplification of the SERS"hot spot" effect. Importantly, the strongest region of EM enhancement around silver nanospheres can be modulated from the gap region to the side surface simply by switching the incident polarization from TM to TE, which widely extends its sensing applications in surface analysis of monolayer of molecule and macromolecule detections. This technique provides us a unique way to achieve remarkable signal gains in many plasmon-enhanced spectroscopic systems in which LSPs are involved.

Boosting a sub-10 nm nanogap array by plasmon-triggered waveguide resonance

Gap-type metallic nanostructures are widely used in catalytic reactions,sensors,and photonics because the hotspot effect on these nanostructures supports giant local electromagnetic field enhancement.To achieve hotspots,researchers devote themselves to reducing gap distances,even to 1 nm.However,current techniques to fabricate such narrow gaps in large areas are still challenging.Herein,a new coupling way to boost the sub-10 nm plasmonic nanogap array is developed,based on the plasmon-triggered optical waveguide resonance via near-field coupling.This effect leads to an amplified local electromagnetic field within the gap regions equivalent to narrower gaps,which is evidenced experimentally by the surface-enhanced Raman scattering intensity of probed molecules located in the gap and the finite-difference time-domain numerical simulation results.This study provides a universal strategy to promote the performance of the existing hotspot configurations without changing their geometries.

Surface-enhanced Raman scattering(SERS)based on surface plasmon resonance coupling techniques

Surface plasmon resonance(SPR)can provide a remarkably enhanced electromagetic field around metal surface.It is one of the enhancement models for explaining surface-enhanced Raman scattering(SERS)phonomenon.With the development of SERS theories and techniques,more and more studies referred to the configurations of the optical devices for coupling the excitation and radiation of SERS,including the prism-coupling,waveguide-coupling,and grating-coupling modes.In this review,we will summarize the recent experimental improvements on the surface plasmoncoupled SERS.