We have used short laser pulses to generate transient vapor nanobubbles around plasmonic nanoparticles. The photothermal, mechanical and optical properties of such bubbles were found to be different from those of plasmonic nanoparticle and vapor bubbles as well. This phenomena was considered as a new complex nanosystem -plasmonic nanobubble (PNB). Mechanical and optical scattering properties of PNB depended upon the nanoparticle surface and heat capacity, clusterization state, and the optical pulse length. The generation of the PNB required much higher laser pulse fluence thresholds than the explosive boiling level, and was characterized by the relatively high lower threshold of the minimal size (lifetime) of PNB. Optical scattering by PNB and its diameter (measured as the lifetime) has been varied with the fluence of laser pulse and this has demonstrated the tunable nature of PNB.Keywords vapor nanobubble; photothermal; scattering; pulsed laser; gold nanoparticle; plasmon resonance; vapor bubble Plasmonic nanoparticles (NP) are known for their outstanding photothermal [1][2][3][4][5][6] and optical scattering 1,[7][8][9][10][11][12] properties. These properties result from the interaction of NPs with optical radiation and the surrounding environment, and are characterized through their absorption and scattering cross-sections, respectively, which are well studied as a function of the parameters of NP, environment and optical radiation. [13][14][15][16][17][18][19] Since such interaction usually occurs in some medium (environment) the secondary thermal and hydrodynamic phenomena in such medium may significantly influence the properties of NPs as optical probes and heat sources. Short optical pulses and high-energy excitation of plasmonic NPs create transient and non-stationary thermal fields with vapor-liquid interfaces that significantly influence heat transfer from NP to its environment and create a strong gradient of the refractive index. In addition, vapor layers around NP cause blue shifts and attenuation of the extinction spectrum. 20 The multi-factor and non-stationary nature of the radiation-NP-vapor-liquid system complicates its experimental study and theoretical modeling. Available thermal models 6,17,[21][22][23][24] are applicable mainly for continuous excitation and stationary heat transfer at low temperatures or for very short laser pulses (femto-second range), for a limited number of shapes of NP, and for temperatures that assume constant plasmonic cross-sections and are *Rice University, Physics and Astronomy -MS 61, 6100 Main Street, Houston, TX 77005, dmitri.lapotko@rice.edu . NIH Public AccessAuthor Manuscript ACS Nano. Author manuscript; available in PMC 2011 April 27. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript below the boiling threshold for the environment. Measuring a high transient temperature around individual NPs in a two-phase medium can be quite difficult if not impossible. Experimental methods 8,[21][22][23][24][25] for monitoring the transien...

Ensemble and single molecule spectroscopic measurements on a bichromophoric dendrimer system were performed. Although Fo ¨rster type energy processes such as energy hopping and singlet-singlet annihilation can be observed at the ensemble and single molecule level, only single molecule measurements can visualize the presence of singlet-triplet annihilation. The flux dependent population of the triplet state suggests facilitated formation of the triplet through a higher singlet excited state. The presence of synthesis inherent structural isomers, not to be distinguished at the ensemble level, could be demonstrated by analyzing modulated fluorescence intensity trajectories. These data show the complementarity of both the ensemble and single molecule approaches in the study of detailed photophysics of a multichromophoric system.