A novel fluoranthene based fluorescent chemosensor for the detection of picric acid (PA) at the parts per billion (ppb) level was evaluated. Static fluorescence quenching was the dominant process by intercalative π–π interaction between fluoranthene (S₁) and nitroaromatics.

In this paper we present the structure and spectroscopic, photophysical and nonlinear optical studies of covalently functionalized novel graphene oxide–[Cu, Zn, Sn, H₂ (metal free), VO] porphyrin composites. The composites were characterized by Field Enhanced Scanning Electron Microscopy (FE-SEM), micro-Raman, optical absorption, Fourier transform infrared (FT-IR), steady state and time resolved fluorescence spectroscopic techniques. The composites exhibit strong fluorescence quenching, suggesting strong electronic interactions between the porphyrin and graphene oxide molecules. Nonlinear optical absorption (NLA) studies of graphene oxide–porphyrin composites were investigated using the Z-scan technique at 532 and 800 nm with nanosecond (ns) and femtosecond (fs) laser pulses. Composites show strong two-photon absorption (TPA) as well as excited state absorption (ESA) leading to reverse saturable absorption (RSA) behaviour in the ns regime and saturable absorption (SA) behaviour was observed in fs regime. The metal free porphyrin–graphene oxide (GO) composite shows significant nonlinear absorption behaviour as well as highest fluorescence quenching behaviour compared to other GO–porphyrin composites. We further observed the enhanced figure of merit (FOM) values for composites in comparison with individual molecules.

Diketopyrrolopyrrole (DPP) based molecular semiconductors have emerged as promising materials for high performance active layers in organic solar cells. It is imperative to comprehend the origin of such a property by investigating the fundamental structure property correlation. In this report we have investigated the role of the donor group in DPP based donor–acceptor–donor (D–A–D) structure to govern the solid state, photophysical and electrochemical properties. We have prepared three derivatives of DPP with varying strengths of the donor groups, such as phenyl (PDPP-Hex), thiophene (TDPP-Hex) and selenophene (SeDPP-Hex). The influence of the donor units on the solid state packing was studied by single crystal X-ray diffraction. The photophysical, electrochemical and density functional theory (DFT) results were combined to elucidate the structural and electronic properties of three DPP derivatives. We found that these DPP derivatives crystallized in the monoclinic space group P2₁/c and show herringbone packing in the crystal lattice. The derivatives exhibit weak π–π stacking interactions as two neighboring molecules slip away from each other with varied torsional angles at the donor units. The high torsional angle of 32° (PDPP-Hex) between the phenyl and lactam ring results in weak intramolecular interactions between the donor and acceptor, while TDPP-Hex and SeDPP-Hex show lower torsional angles of 9° and 12° with a strong overlap between the donor and acceptor units. The photophysical properties reveal that PDPP-Hex exhibits a high Stokes shift of 0.32 eV and SeDPP-Hex shows a high molar absorption co-efficient of 33 600 L mol⁻¹ cm⁻¹ with a low band gap of ∼2.2 eV. The electrochemical studies of SeDPP-Hex indicate the pronounced effect of selenium in stabilizing the LUMO energy levels and this further emphasizes the importance of chalcogens in developing new n-type organic semiconductors for optoelectronic devices.

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 $\chi \left(3\right)$ of graphene and graphene-porphyrin composites were, in the order of ${10}^{-12}\text{esu}$ , 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.