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Fluorescent molecular probes based on phospho-nate-functionalized porphyrin derivatives have been designed for selective detection of nitroaromatics. It is shown that molecular recognition is based on cooperative hydrogen bonding and π-π stacking interactions with electron-deficient molecules (nitro-aromatic compounds, NACs), displaying superior detection toward trinitrotoluene (TNT). The P=0 functional groups decrease the lowest unoccupied molecular orbital (l.UMO) energy level of the porphyrins and, consequently, facilitate the electron inoculation to TNT through a photoinduced electron transfer (PET) process. The hydroxyl groups of the phosphonates and pyrrole -NH protons are further engaged in donor-acceptor interactions with TNT by strong intermolecular hydrogen bonding interactions (as evidenced by single crystal X-ray, NMR, and density functional theory (DFT) showing turn off fluorescence behavior. The nonplanarity of the porphyrins induced by protonation at the central core of the porphyrin H4TPPA2+ undergoes additional interactions, furnishing an anomalous increase in the selectivity of TNT at nanomolar levels in solution (limit of detection, LOD ~ 5 nM) Porphyrin-doped hybrid PMMA [poly(methyl methacrylate)] polymer films demonstrate the reversibility of the fluorescence behavior and exhibit high photostability. The formation of discrete molecular aggregates on the surface of hybrid films and efficient diffusion of TNT vapors (10 ppb) displayed high selectivity in the solid state. The hybrid films are further used to demonstrate the detection of NACs in the aqueous medium, ultimately providing a platform for a practical strategy and implementation for the detection of toxic NACs. [ABSTRACT FROM AUTHOR]

Nonlinear optical transmission of graphene oxide–(Cu, Zn, Sn, H2) porphyrin composites was investigated using the Z-scan technique at 532 nm with picosecond (ps) and 800 nm with femtosecond laser pulses. Pure porphyrins show saturable absorption (SA) in reverse saturable absorption (RSA) behaviour and graphene oxide shows complete RSA behaviour, observed in an open aperture Z-scan curve. Interestingly, composites have shown a switch-over from reverse RSA to SA and back to RSA behaviour, observed with variation of intensity towards the focus, due to strong two-photon absorption as well as excited state absorption in the ps regime. This switching behaviour was interpreted as due to long lifetimes and saturation of the excited states. This may find application in optical switching. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid borate glasses containing a series of Al(III)Porphyrins were prepared by rapid melt quench technique at 230°C. The hybrid glass samples were characterized by X-ray diffraction, optical absorption, steady state and time resolved fluorescence emission. Upon exposure to UV light at 260nm, the glass samples exhibit strong blue emission and red emission at 365nm. The appearance of large stokes shift (Δυ) and enhanced S 2 → S 0 emission at ∼495nm indicates that structure of Al(III)Porphyrins were inherently modified in glass matrix. Time resolved fluorescence of the hybrid glasses shows three exponential decay with τ 1 =0.11–0.59ns, τ 2 =3.13–3.95ns and τ 3 =8.13–9.56ns. In the present study, we investigate the influence of glassy environment on the photophysical properties and the structure of Al(III)Porphyrins in borate glass was modeled through DFT calculations. [Copyright &y& Elsevier]

Abstract: Hybrid borate glasses containing various hydroxy phenyl derivatives of porphyrin were prepared by melt quenching technique. The effect of hydroxy functional groups on the photophysical properties was investigated by means of optical absorption, steady-state fluorescence and time resolved fluorescence spectroscopy. The optical absorption spectra show red shift in Soret and Q-band with increase in the number of –OH groups on the phenyl ring of the porphyrin. The steady-state emission spectrum shows strong S2→S0 emission around 498–540nm and red shifted S1→S0 emission around 669–803nm. Time resolved fluorescence shows three exponential decay with τ 1 =11±2ps (64.56%), τ 2 =0.16±0.1ns (24.54%), and τ 3 =2.94±0.1ns (10.9%) for 2mg of H2OHP doped glass. The appearance of strong S2→S0 emission indicates that the structure of porphyrin inherently modified in the glass matrix. The boron ions of the borate network interact at the central core of the porphyrin and also form oxy bridge at the periphery. The effect of porphyrin concentration on photophysical properties and the possible structures of porphyrin in the borate glass matrix were investigated. [Copyright &y& Elsevier]

Abstract: Freebase tetra phenyl porphyrin (H2TPP) and its derivatives in different concentration ranges (0.5–2.0mg per 12g of boric acid) were incorporated into borate glass matrix by melt quenching technique at 230°C. The formed glasses were stable and in green colour. The optical absorption and emission properties are different from that observed in solutions. The absorption spectrum shows a two line pattern Soret band at 435–454nm and Q-band at 665–701nm. The emission spectrum shows strong S2 →S0 emission at 490–520nm region and S1 →S0 emission at 725–810nm. The time resolved fluorescence decay of S1 →S0 emission shows three exponential decay. For example, in the case of 2mg of H2THP doped glass the lifetimes were found to be τ 1 =0.511ns (26.7%), τ 2 =10ps (64.68%) and τ 3 =3.965ns (8.62%). These unusual photophysical properties were found to arise from different structural motifs of porphyrin in the glass. These structures were further modeled through reactions of porphyrin with BF3O(C2H5) in solution and DFT calculations. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid borate glasses containing different concentrations of meso-tetrakis(p-sulfonatophenyl) porphyrin sodium salt (TPPS4) were prepared. The obtained glass samples were found to be transparent and homogeneous. Formation of TPPS4-J-aggregates in borate glass was investigated by means of optical absorption, steady state and time resolved fluorescence spectroscopy. The hybrid glasses exhibit a strong S2→S0 emission at ∼473nm and J-aggregates show emission at ∼733nm. Time resolved fluorescence show two exponential decay with lifetime of τ 1 =65±10ps (∼80%) and τ 2 =3.87±0.1ns (∼20%) respectively. Dielectric properties such as dielectric constant (ɛ′), dielectric loss (tan δ) and ac conductivity (σ ac) over a range of frequency and temperature of these glasses were studied. The ac conductivity was found to be proportional to ω s (where s <1). The observed change in dielectric parameters due to different concentrations of TPPS4 has been analyzed in light of different polarization mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid borate glasses containing different concentrations (0.5–2.0mg in 12g of boric acid) of Mesoporphyrin(IX)dimethylester, Protoporphyrin(IX)dimethylester and Hematoporphyrin(IX)dimethylester were prepared by rapid melt quench technique at 230°C. The hybrid glass samples were characterized by X-ray diffraction, optical absorption, steady state and time-resolved fluorescence emission. The optical absorption spectrum shows red-shift in Soret band along with change in Q-band pattern. The intensity of Q-band was found to increase with increase in the concentration of porphyrin in the glass. Steady state emission spectrum shows strong S2→S0 emission in the range 462–495nm and blue shift in S1→S0 emission. Time-resolved fluorescence emission and fluorescence excitation spectra showed that different structures of porphyrins were exist in the glass samples. The variation in the spectral behaviour in the glass was correlated with those in solution medium and possible structures of porphyrin in borate glass were explored. [ABSTRACT FROM AUTHOR]

The nonlinear optical (NLO) and optical limiting (OL) properties of covalently linked graphene-porphyrin composite materials were investigated using Z-scan technique in nanosecond regime. We observed enhanced NLO and OL properties of graphene-porphyrin composites in comparison to the individual graphene and porphyrins. The improved OL property of composites is attributed to energy transfer between porphyrin and graphene, which improved excited state absorption and nonlinear scattering. Nonlinear optical susceptibilities χ(3) of graphene and graphene-porphyrin composites were, in the order of 10-12 esu, measured using degenerate four wave mixing technique in nanosecond regime. High values of excited state absorption and two-photon absorption were observed for the composites. [ABSTRACT FROM AUTHOR]