Fluorescence Decay Study of Anisotropic Rotations of Substituted Pyrenes Physisorbed and Chemically Attached to a Fumed Silica Surface

Abstract

Optical polarization spectroscopy has been used to investigate molecular dynamics of the fluorescent probes 1-pyrenebutanol and 1-pyrenebutyric acid at the solid/air interface of cab-o-sil (fumed silica nanoparticles). Pyrenebutanol was chemically attached to the surface of cab-o-sil through a silyl ether bond, while pyrenebutyric acid was physisorbed on the surface. Dynamics of fluorescence depolarization for both molecules was studied under steady-state and time-resolved conditions. Low and high loadings of the probe molecules were used in our studies to examine the dynamics of the probes motion and excimer formation. Our data indicate that excimer formation is mostly static in nature for the adsorbed probe, but shows more dynamic character for the chemically attached probe with spacer molecules present. Fluorescence lifetimes were dependent on the concentration of the probe molecule and became shorter at higher surface loadings for both the chemically attached and physisorbed probes. For the chemically attached probe, the presence of excess co-attached biphenyl molecules was found to provide a 2-D solvent-like environment.

Multi-mode humidity sensing with water-soluble copper phthalocyanine for increased sensitivity and dynamic range

“…The CuPcTs optical thickness change also exhibits slight (~10 nm) hysteresis in the 50–80% RH range between adsorption and desorption processes. The rapid thickness change at RH > 70% is consistent with formation of a mixed H 2 O-CuPcTs phase facilitated by hydrogen bonding between H 2 O adsorbates and gas-phase water molecules 16 , 17 , 38 . Upon formation of H 2 O multilayers and merging of adjacent adsorbed H 2 O clusters, interactions between mobile Na + ions, CuPc(SO 3 − ) 4 15 , and hydrogen-bonded water can facilitate fracture and displacement of solid-phase domains which increases intermolecular spacing and leads to significant film swelling 18 , 39 – 41 .…”

“…The presence of H 2 O at SO 3 Na groups induces salt dissociation, leading to formation of Na + and CuPc(SO 3 − ) 4 ions 15 , 16 which contribute to charge transport in CuPcTs at RH > 45% 12 . Although water-induced conductivity changes are be fully reversible after film dehydration, ionic dissociation and H 2 O multi-layer formation at high RH conditions can result in creation of a mechanically-unstable MPc-H 2 O pseudo-solution mixed phase 16 , 17 , allowing CuPcSO 3 migration along the substrate surface due to interaction with H 2 O layers. Mobility of CuPc(SO 3 − ) 4 ions can result in morphological changes including domain displacement and fracture 11 , 18 .…”

Interactions of functionalized carbon nanotubes with tethered pyrenes in solution

“…For pyrene derivatives on various surfaces ͑such as silica͒, there is typically strong static pyrene excimer emission due to significant aggregation ͑pre-association͒ of pyrene structures in the ground state. 28,29 For I Py -SWNT, the absorption and emission results suggest that the pyrene structures in neighboring I Py units ͑attached to the same piece of SWNT͒ are apparently not stacked together on the nanotube surface. This might be a result of steric hindrance in I Py , due to the presence of a long alkyl chain and the relatively short tether linking the pyrene moiety.…”

In Situ Formation of Ag Nanoparticles Capped by Photoactivable Ligands for Optical Sensing of Hypochlorite

“…It is notable that the excimer emission of pyrene located at 420–520 nm increased by 13‐fold after about 90 min exposure (Figure b). Depending upon the origin of the pyrene dimer, there are two kinds of excimers: a dynamic excimer and a static excimer . The examination of the excitation spectrum is considered to be a useful method to differentiate a dynamic excimer from a static one .…”