Applications of conjugated organic compounds in the field of electronics and optoelectronics and of pyrene derivatives as fluorescent probes are well established. The synthesis of the novel pyrene-based 2,11-di-tert-butyl-6,7,15,16-tetrakis(alkoxy/alkythio)quinoxaline[2',3':9,10]phenanthro[4,5-abc]phenazine, TQPP-[t-Bu](2)-[XR](4) (X = O, S; R = C(n)H(2n+1)), is reported along with an in-depth spectroscopic characterization and evaluation of their photophysical properties. Despite their larger core size, the reported TQPP materials showed similar fluorescence behavior to that of pyrene itself, with no significant shift in their fluorescence peak. The fluorescence spectra showed peaks corresponding to the monomer and to the excimer. Even though these TQPP compounds showed poor solubility in various solvents, their solvatochromism could be investigated in different solvents ranging from polar solvents such as methanol to nonpolar solvents such as cyclohexane; Stokes shifts, fluorescence lifetimes, fluorescence quantum yields, as well as radiative and nonradiative rate constants are determined for four of these TQPP materials in various solvents. Quantum yields were found to be low for these TQPP compounds in solvents such as tetrahydrofuran (THF), whereas they were relatively higher in cyclohexane and dioxane. Monomer to excimer intensity ratio versus gross solvent scale (E(T)30) and orientation polarizabilty (Delta f) were correlated. Although TQPP-[t-Bu](2)-[XR](4) displayed similar fluorescent emission and excitation behavior as that of pyrene, a relatively smaller lifetime was observed for these compounds compared to that of pyrene.

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The important role played by organic conjugated compounds in the fields of electronics and optoelectronics has led to a vast field of research concerned with synthesizing various complex structures where pi-pi stacking plays a vital role. Pyrene-based molecules are examples of compounds which allow efficient charge transfer through pi-pi molecular stacking. Photophysical studies of such compounds have shown similar behavior as that of pyrene, even though they bear two additional conjugated rings and four long alkyl chains. Chain length may have played an effective role in influencing the pi-pi molecular stacking of such molecules. In continuation of our earlier work (Moustafa, R. M.; Degheili, J. A.; Patra, D.; Kaafarani, B. R. J. Phys. Chem. A 2008, 113, 1235-1243), we hereby synthesize and investigate the role of the chain lengths on the photophysical aspects of 2,11-di-tert-butyl-6,7,15,16-tetrakis(alkoxy/alkythio)quinoxaline-[2',3':9,10]phenanthro[4,5-abc]phenazine, TQPP-[t-Bu](2)-[XR](4) (X = O, S; R = C(n)H(2n+1)). Various photophysical parameters such as Stokes shift, fluorescence lifetime, fluorescence quantum yield, and radiative and nonradiative rate constants are evaluated for TQPP-[t-Bu](2)-[OR](4) and TQPP-[t-Bu](2)-[SR](4) in tetrahydrofuran. The variation of the Stokes shift, fluorescence quantum yield, and lifetime are also correlated with the number of carbons in the alkyl chain R for TQPP-[t-Bu](2)-[OR](4) and TQPP-[t-Bu](2)-[SR](4).

The morphological and electrical properties of 2,11-di-tert-butyl-6,7,15,16-tetrakis(hexylthio)quinoxalino[2′,3′: 9,10]phenanthro[4,5-abc]phenazine (TQPP) organic molecule combined with butylamine (BAM)-modified graphene sheets (GSs) are described. The grafting of the amine onto the graphene sheet plane promotes its compatibility with this BAM soluble molecule, leading to the preparation of homogeneous films containing exfoliated graphene sheets, as demonstrated by infrared spectroscopy, field emission electron microscopy, and Raman spectroscopy. The film deposited from the BAM-modified GSs/TQPP blend showed a photoelectrical response higher than those prepared with neat molecule and GSs/TQPP blend, respectively.