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A new organic hybrid material, 2,4-dichlorobenzyl triphenylphosphinium picrate, [2Cl4ClBzTPP][PIC](1), has been grown by slow evaporation solution growth technique, and characterized by elemental analysis, spectroscopy, thermal analysis, powder and single crystal XRD. The composite belongs to monoclinic system with space group P2(1)/c, and consists of a pair of [2Cl4ClBzTPP]+ cations and picrate anions. The experimental vibrational bands (IR and Raman) have been discussed and assigned based on DFT calculations. The HOMO-LUMO energy gap explains the charge transfer interactions in the molecule. TG-TDA technique reveals that the title crystal was stable up to 168 °C. The fluorescence spectra reveal that the compound shows violet and green fluorescence emissions at 377 and 509 nm upon excitation at 250 nm in solid state at room temperature. The energy of weak interactions in the molecule and nonlinear optical properties were studied using DFT calculations.

The electronic structures, absorption and emission spectra of selected 6-substituted coumarins were investigated and compared with unsubstituted coumarin by using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods with Gaussian 09 software package. Results revealed that the presented absorption and emission spectra were affected by the substituent groups apparently. The maximum absorption wavelength of a coumarin molecule can be shifted to a longer one by introducing a large conjugated substituent, an electron donating group or a group which can form a rigid structure with the parent moiety at 6-position. The lowest energy emission of a 6-substituted coumarin can be greatly red-shifted by modifying the substituent to one which can be strongly conjugated with the phenyl ring. A group which has a strongly electron-withdrawing effect may cause a large excitation intensity and a short wavelength in emission. Most selected molecules are predicted to give the lowest-energy emissions in the purple or blue light region, which are supposed to be selected and modified as purple or blue luminescent materials. 6-nitrocoumarin is predicted as an invisible fluorescent material. 6,7-benzocoumarin, which forms a rigid conjugated ring with the parent moiety, is expected to be modified as a green luminescent material. Many of these 6-substituted coumarins are expected to be potential candidates as large Stokes shift dyes for multicolor labeling and fluorescence-activated cell sorting (FACS), especially those molecules, which bear CONH2, CN, and CH3 respectively.