From Figure 9, it is evident that the annealing of TPP leads to an absorption peak reduction. As in the previous case, the combination of TPP with Au results in the appearance of the Soret band. Figure 9B shows the luminescence spectra excited at 440 nm. A principally different result was obtained in the case of the sandwich Au/TPP/Au structure in comparison with Au/TPP. In the former case, the luminescence peak at 720 nm is almost completely suppressed but another peak at 660 nm

increased significantly. After annealing, a luminescence quenching was observed. Figure 9 Absorption (A) and luminescence (B) spectra of Au/TPP/Au and TPP films annealed (T) at 160°C for 24 h. Discussion Au/TPP structure The Soret band increases several times after TPP deposition onto the gold surface. The phenomenon cannot be explained by only the presence of Au and TPP components. Similar phenomena, i.e., a luminescence increase, were reported earlier AMG510 datasheet for a mixture of dyes with colloid metal nanoparticles [30]. In this case, the luminescence intensity

increased twice. The absorption and luminescence increase can be explained in terms of photon-plasmon conversion. Excitation of plasmons leads to a sufficient light energy concentration near the gold surface, where TPP molecules www.selleckchem.com/products/anlotinib-al3818.html are located. As a result, more energy is absorbed and re-emitted. On the other hand, absorption increases several times, but luminescence is only doubled. The missing part of the absorbed energy is probably expended through nonradiative relaxation of the excited state. This luminescence quenching becomes notable due Interleukin-2 receptor to the proximity of the Au surface. The quenching is a result of a very strong nonradiative energy transfer from chromophores to the metal substrates. This effect is typical for a dye deposited primarily onto a metal surface and can be overcome by addition of a thick

intermediate layer [31]. Assembled molecular layers of porphyrin derivatives are often created by the Langmuir-Blodgett (LB) method [32]. Another method consists in covalently binding of porphyrins to a gold surface through Au-S interactions [33, 34]. Highly ordered adlayers of porphyrin molecules were found to form on a sulfur-modified Au (111) surface in [35]. Different orientations were achieved depending on the number of thiol groups per porphyrin molecule: porphyrin molecules having a single chain are somewhat tilted against surface normal, and porphyrins with four chains are oriented coplanar. Spacer length also affects the orientation of porphyrins onto the gold surface – as the length of spacers increases, porphyrin molecules tend to form highly ordered structures on the gold surface [36]. The obtained results check details indicate the dependence of porphyrin orientation and degree of gold surface covering on the crystal orientation of gold, quality of gold surface, and type of porphyrin used.