This paper describes the influence of the donor group on the solid state packing and electronic properties of diketopyrrolopyrrole based small molecules.

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 (S(1)) and nitroaromatics.

In this work, we have synthesized a series of TDPP derivatives with different alkyl groups such as n-hexyl (−C 6 H 13 ) 3a, 2-ethylhexyl (-(2-C 2 H 5 )C 6 H 12 ) 3b, triethylene glycol mono methyl ether (-(CH 2 CH 2 O) 3c H 3 , TEG) 3c, and octadodecyl (-(8-C 8 H 17 )C 12 H 22 ) 3d. N,N dialkylation of thiophene-diketopyrrolopyrrole (TDPP, 1) strongly influences its solubility, solid state packing, and structural order. These materials allow us to explicitly study the influence of alkyl chain on solid state packing and photophysical properties. TDPP moiety containing two different alkyl groups 3e (TEG and 2-ethylhexyl) and 3f (TEG and n-hexyl) were synthesized for the first time. The absorption spectra of all derivatives exhibited a red shift in solid state when compared to their solution spectra. The type of alkyl chains leads to change in the optical band gaps in solid state. The fluorescence study reveals that TDPP derivatives have strong π−π interaction in the solid state and the extent of bathochromic shift is due to combination of intramolecular interaction and formation of aggregates in solid state. This behavior strongly depends on the nature of alkyl chain. The presence of strong C−H•••O inter chain interactions and CH−π interactions in solid state exhibits strong influence on the photophysical properties of TDPP chromophore.

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.