1,4-bis[β-(2-benzoxazoly1) vinyl] benzene (BBVB) laser dye and sodium salt of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS); spectroscopic investigation and DFT, NBO and TD-DFT calculations

Abstract

Excitation energy transfer (ET) from 1,4-bis[β-(2-benzoxazoly1) vinyl] benzene as a donor to sodium salt of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) as an acceptor was investigated in the absence and presence of metallic silver nanoparticles (Ag NPs). The emission intensities and Stern –Volmer constants (KSV) of the ET processes were calculated in methanol (MeOH) and 40% ethylene glycol (EG) as 5.87 × 104 M−1 and 6.27 × 104 M−1, respectively. KSV value in the presence of Ag NPs was 1.028 × 105 M−1 in methanol, much higher than in absence of NPs. This is attributed to the role of Ag NPs in increasing the strength of the donor–acceptor interactions. These results denote the use of Ag NPs for measuring the proximity of large biomolecules and ET-based assays. Also, the critical ET distance Ro was calculated as 36 Å. This magnitude is higher than the common value of 10 Å for the collisional ET mechanism. This high Ro value indicates the underlying mechanism as long-range dipole–dipole interaction. The BBVB, TPPS, and BBVB/TPPS molecular structures (MSs) were optimized using the DFT/ B3LYP/6-311G (d) method for the quantum calculations. The calculated electronic UV–Vis absorption spectra for BBVB and BBVB/TPPS MSs in MeOH were examined by the time-dependent density functional theory (TD-DFT) at CAM-B3LYP/6-311G++(3d,3p) level. Interestingly, all theoretical results of BBVB and BBVB/TPPS molecules were highly matched with the experimental results. Furthermore, the Natural Bond Orbital (NBO) analyses for BBVB and BBVB/TPPS MSs were obtained using the B3LYP/6-311G(d) level of theory.