We review the present status of experiments and calculations for circularly polarized luminescence (CPL) of simple organic molecules and of stimuli-responsive organic molecules. Together with the historical report of the main instrumental approaches, a few crucial points about experiments are tackled, with the aim of defining measurement protocols, in view of the wide availability of commercial apparatuses in the near future. The calculations aimed at interpreting the CPL spectra, mostly based on time-dependent Density Functional Theory (TD-DFT) calculations, which started around 2010, are reviewed, limiting the discussion to small to mid-sized molecules. Some applications of CPL spectra of organic molecules-based systems are presented, with a focus especially on two fields: material science and biology. Chirality 28:696-707, 2016. © 2016 Wiley Periodicals, Inc.

Four different hexahelicenes, 5-aza-hexahelicene (1), hexahelicene (2), 2-methyl-hexahelicene (3), and 2-bromo-hexahelicene (4), were prepared and their enantiomers, which are stable at r.t., were separated. Vibrational circular dichroism (VCD) spectra were measured for compound 1; for all the compounds, electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) spectra were recorded. Each type of experimental spectrum was compared with the corresponding theoretical spectrum, determined via Density Functional Theory (DFT). Following the recent papers by Nakai et al., this comparison allowed to identify some features related to the helicity and some other features typical of the substituent groups on the helical backbone. The Raman spectrum of compound 1 is also examined from this point of view

UV, circular dichroism (CD), fluorescence and circularly polarized luminescence (CPL) spectra were recorded for a set of four related [2.2.1] bicyclic compounds ((1S,4S)-and (1R,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one, namely (1S)- and (1R)-camphor (), (1S,4R)-4,7,7-trimethylbicyclo[2.2.1]hept-5-en-2-one, (1S)-dehydro-epicamphor (), (1S,4S)-1,7,7-trimethylbicyclo[2.2.1]heptane-2,5-dione, (1S)-5-oxocamphor (), (1S,4R)- and (1R,4S)-1,7,7-trimethylbicyclo[2.2.1]heptane-2,3-dione, (1S)- and (1R)-camphorquinone ()) and a set of three related [2.2.2] bicyclic compounds (1S,4S)-bicyclo[2.2.2]octan-2,5-dione (saturated diketone ()), (1R,4R)-bicyclo[2.2.2]oct-7-en-2,5-dione (unsaturated diketone ()), ((1S,4S)-bicyclo[2.2.2]oct-7-en-5(S)-ol-2-one (which we refer to as unsaturated hydroxy-ketone ()). For the latter three compounds also mid-IR vibrational circular dichroism (VCD) spectra were recorded and are presented. Time-Dependent Density Functional (TD-DFT) calculations provide a satisfactory interpretation of both absorption and emission chiroptical spectra and permit insight into ground and excited state electronic properties. We discuss the applicability of the octant rule or of other approximated models to rationalize the observed sign of the CPL.

The interest of circular dichroism in the solid state is stimulated by several needs, such as the desire to get solvent free spectra, the insolubility of the sample or the intrinsic process in which the sample itself is prepared or manipulated. We approach the argument on the basis of the sampling technique, since each different case calls for specific care in getting proper results.

Near infrared vibrational circular dichroism spectra in the region of 1300 to 800 nm were recorded for 12 enantiomeric pairs of molecules with a home-made dispersive apparatus. With respect to earlier measurements, a better signal-to-noise ratio was obtained, thus allowing a more precise determination of molecular parameters. A detailed examination of the spectra between 1300 and 1100 nm allowed us to correlate the data of the different molecules, based on local properties of given molecular moieties. The relevance of this correlation in configurational and/or conformational studies is discussed.

Linear conjugated oligothiophenes of variable length and different substitution pattern are ubiquitous in technologically advanced optoelectronic devices, though limitations in application derive from insolubility, scarce processability and chain-end effects. This study describes an easy access to chiral cyclic oligothiophenes constituted by 12 and 18 fully conjugated thiophene units. Chemical oxidation of an “inherently chiral” sexithiophene monomer, synthesized in two steps from commercially available materials, induces the formation of an elliptical dimer and a triangular trimer endowed with electrosensitive cavities of different tunable sizes. Combination of chirality with electroactivity makes these molecules unique in the current oligothiophenes literature. These macrocycles, which are stable and soluble in most organic solvents, show outstanding chiroptical properties, high circularly polarized luminescence effects and an exceptional enantiorecognition ability.

Among the various chiroptical spectroscopic techniques available today, circularly polarized luminescence (CPL) plays a minor role and is still used by a limited number of specialists. The cost of the few commercial instruments available and the complexity of homemade apparatuses have strongly limited the widespread application of this technique. New technological approaches, such as the use of light-emitting diode (LED) sources, may significantly simplify the required instrumentation and encourage new potential users. Calibration procedure and the quantitative determination of CPL and total luminescence intensity as well as the corresponding g ratio are described.

The electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectra of both enantiomers of naringenin (4',5,7-trihydroxyflavanone) in acetonitrile solution have been measured. The enantiomers were obtained by chiral HPLC separation of the racemic sample. DFT calculations have been performed for relevant conformers and subsequent evaluations of VCD spectra are compared with VCD experiments: safe assignment of the absolute configuration is provided, based in particular on the VCD data. The relevance of the rotational conformers of the hydroxyl groups and of the mobility of phenol moiety is studied: based on this, we provide a first interpretation of the observed intense and broad couplet at 1325/1350 cm(-1). Four conformers contribute to this pattern with different sign and amplitude as shown by DFT calculations. Time dependent DFT calculations have been performed and compared with ECD experimental data, under the same assumption of conformational properties and mobilities investigated by VCD.