Effect of Chain Length on the Photophysical Properties of Pyrene-Based Molecules Substituted with Extended Chains

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-ab-c]phenazine, TQPP-[t-Bu](2)-[XR](4) (X=O, S;R = CnH2n+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).