Excited State Torsional Processes in Chalcogenopyrylium Monomethine Dyes.

Chalcogenopyrylium monomethine (CGPM) dyes represent a class of environmentally activated singlet oxygen generators with applications in photodynamic therapy (PDT) and photoassisted chemotherapy (PACT). Upon binding to genomic material, the dyes are presumed to rigidify, allowing for intersystem crossing to outcompete excited state deactivation by internal conversion. This results in large triplet yields and hence large singlet oxygen yields. To understand the nature of the internal conversion process that controls the activity of the dyes, femtosecond transient absorption experiments were performed on a series of S-, Se-, and Te-substituted CGPM dyes. For S- and Se-substituted species in methanol, rapid internal conversion from the singlet excited state, S1, occurs in ∼5 ps, deactivating the optically active excited state. The internal conversion produces a distorted ground-state species that returns to its equilibrium structure in ∼20 ps. For Te-substituted species, the internal conversion competes with rapid intersystem crossing to the lowest triplet state, T1, which occurs with a ∼ 100 ps time constant in methanol. In more viscous methanol/glycerol mixtures, the internal conversion to the ground state slows by 2 orders of magnitude, occurring in 500-600 ps. For Se- and Te-substituted species in viscous environments, the slower internal conversion rate allows a larger triplet yield. Using femtosecond stimulated Raman spectroscopy (FSRS) and time-dependent density functional theory (TD-DFT), the internal conversion is determined to occur by twisting of the pyrylium rings about the monomethine bridge. Evolution from the distorted ground state occurs by twisting back to the S0 equilibrium structure. The environmentally dependent photoactivity of CGPM dyes is discussed in the context of PDT and PACT applications.

Sensitive SERS nanotags for use with a hand-held 1064 nm Raman spectrometer.

This is the first report of the use of a hand-held 1064 nm Raman spectrometer combined with red-shifted surface-enhanced Raman scattering (SERS) nanotags to provide an unprecedented performance in the short-wave infrared (SWIR) region. A library consisting of 17 chalcogenopyrylium nanotags produce extraordinary SERS responses with femtomolar detection limits being obtained using the portable instrument. This is well beyond previous SERS detection limits at this far red-shifted wavelength and opens up new options for SERS sensors in the SWIR region of the electromagnetic spectrum (between 950 and 1700 nm).

Sensitive SERS nanotags for use with 1550 nm (retina-safe) laser excitation.

Chalcogenopyrylium nanotags demonstrate an unprecedented SERS performance with a retina safe, 1550 nm laser excitation. These unique nanotags consisting of chalcogenopyrylium dyes and 100 nm gold nanoparticles produce exceptional SERS signals with picomolar detection limits obtained at this extremely red-shifted and eye-safe laser excitation.

Rational design of a chalcogenopyrylium-based surface-enhanced resonance Raman scattering nanoprobe with attomolar sensitivity.

High sensitivity and specificity are two desirable features in biomedical imaging. Raman imaging has surfaced as a promising optical modality that offers both. Here we report the design and synthesis of a group of near-infrared absorbing 2-thienyl-substituted chalcogenopyrylium dyes tailored to have high affinity for gold. When adsorbed onto gold nanoparticles, these dyes produce biocompatible SERRS nanoprobes with attomolar limits of detection amenable to ultrasensitive in vivo multiplexed tumour and disease marker detection.

Functionalisation of hollow gold nanospheres for use as stable, red-shifted SERS nanotags.

Hollow Gold Nanospheres (HGNs) exhibit a unique combination of properties which provide great scope for their use in many biomedical applications. However, they are highly unstable to changes in their surrounding environment and have a tendency to aggregate, particularly when exposed to high salt concentrations or changes in pH which is not ideal for applications such as cell imaging and drug delivery where stable solutions are required for efficient cellular uptake. Therefore there is a significant need to find a suitable stabilising agent for HGNs, however potential stabilising agents for these nanostructures have not previously been compared. Within this work we present an improved method for stabilising HGNs which simultaneously shifts the SPR from around 700 nm to 800 nm or greater. Herein, we compare three different materials which are commonly used as stabilising agents; polymers, sugars and silica in order to determine the optimum stabilising agent for HGNs. Analysis was performed using extinction spectroscopy and dynamic light scattering, supported with SEM imaging. Results showed PEG to be the most suitable stabilising agent for HGNs displaying both an increased stability to changes in salt concentration and pH as well as increased long term stability in solution. Furthermore, we demonstrate that in addition to increased stability, SERS detection can be achieved at both 1064 nm and 785 nm excitation. This combination of improved stability with a SPR in the NIR region along with SERS detection demonstrates the great potential for these nanostructures to be used in applications such as biological SERS imaging and drug delivery.

Extreme red shifted SERS nanotags.

Surfaced enhanced Raman scattering (SERS) nanotags operating with 1280 nm excitation were constructed from reporter molecules selected from a library of 14 chalcogenopyrylium dyes containing phenyl, 2-thienyl, and 2-selenophenyl substituents and a surface of hollow gold nanoshells (HGNs). These 1280 SERS nanotags are unique as they have multiple chalcogen atoms available which allow them to adsorb strongly onto the gold surface of the HGN thus producing exceptional SERS signals at this long excitation wavelength. Picomolar limits of detection (LOD) were observed and individual reporters of the library were identified by principal component analysis and classified according to their unique structure and SERS spectra.

Synthesis and photoelectrochemical performance of chalcogenopyrylium monomethine dyes bearing phosphonate/phosphonic acid substituents.

Chalcogenopyrylium monomethine dyes were prepared via condensation of a 4-methylchalcogenopyrylium compound with a chalcogenopyran-4-one bearing a 4-(diethoxyphosphoryl)phenyl substituent (or the phosphonic acid derivative). The dyes have absorbance maxima of 603-697 nm in the window where the solar spectrum is most intense. The dyes formed H-aggregates on TiO2, increasing the light-harvesting efficiency of the dyes. Shortcircuit photocurrent action spectra were acquired to evaluate the influence of dye structure on the photoelectrochemical performance.