Theoretical study on photophysical properties of novel bis(BF2)-2,2′-bidipyrrins dyes: Effect of variation in monomer structure

In this work, monomeric molecules (BODIPY) 4,4-difluoro-1,2,3,5,7-pentamethyl-6-ethyl-4-bora-3a,4a-diaza-s-indacene (1), 4,4-difluoro-1,7-dimethyl-2,3,6-terethyl-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene (Ph1), dimeric monomers (bisBODIPY) 2, Ph2, and their packing systems were taken as calculation models to investigate the relationship between monomeric structures and spectral properties of packing systems. Their spectra and carrier transport properties were systemically investigated by density functional theory and time-dependent DFT methods. The results reveal that dimeric monomers bisBODIPY 2 and Ph2 show significantly bathochromic shift and exhibit a clear exciton splitting in the absorption spectrum compared with those of 1 and Ph1. Monomeric and dimeric molecules have different monomer conformations (nearly flat and corniform, respectively) and thus diverse packing styles. The intermolecular aggregation affects the excitation energy and oscillator strength of monomers 1 and Ph1 more than those of the corniform monomers 2 and Ph2. The unique corniform structure of molecules 2 and Ph2 can greatly reduce self-quenching effect induced by the formation of excimers. This means that suitable modification of molecular arrangement is an effective way to reduce self-quenching. From the calculation results for molecules Ph1 and 1, the aryl group at the 8-position of BODIPY core can hardly affect the optical properties. According to our calculations, BODIPY 1 is a better hole transporter than electron transporter with the internal reorganization energy for hole (lambda(+)) even lower than that of 4,4'-bis(phenyl-mtolylamino)biphenyl (TPD), a well-known hole-transporting material. Molecules Ph1, BisBODIPYs 2, and Ph2 are promising candidate to be excellent ambipolar materials for electroluminescent devices, owing to their quite small and nearly identical reorganization energies for both carriers. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012