Photophysical properties of Re(I)(CO)3(phen) pendants grafted to a poly-4-vinylpyridine backbone. A correlation between photophysical properties and morphological changes of the backbone

Abstract

Photochemical and photophysical properties of a polymer, Re-P4VP, consisting of -Re(I)(CO)3(phen) pendants grafted to a poly-4-vinylpyridine backbone, P4VP, were interpreted on the bases of morphological transformations. These transformations are responsible of a significant increase of the MLCTRe(I) → phen excited state luminescence lifetime when the polymer concentration is increased. Also a nearly 8-fold increase in the luminescence quantum yield resulted from the protonation of Re-P4VP with consequent changes of the excited state decay kinetics. Results of TEM and AFM morphological studies on P4VP and Re-P4VP in the presence of HClO4 acid, i.e., to form Re-P4VPHn n+ , revealed that they have concentration dependent morphologies. From low to large concentrations of the Re-P4VP polymer, the morphology of Re-P4VP varies from a nonhomogeneous distribution of spherical nanoaggregates coexisting with micrometer size fibers to an homogeneous distribution of spherical nanoaggregates with diameters around 25 nm. The Re-P4VP morphology is also altered when the polymer pyridines are protonated. Protonation of diluted solutions of Re-P4VP polymers decrease the sizes of the nanoaggregates and small objects with diameters smaller than 10 nm appear.

Morphology-dependent Photophysical Properties of Poly-4-vinylpyridine Polymers Containing –Re(CO)3(N^N)+ Pendants

“…When a deaerated solution of poly-I in CH 3 CN is irradiated at λ exc = 350 nm, the characteristic luminescence of pendants -Re(CO) 3 phen + chromophores showing a broad unstructured band centered at λ max = 550 nm is observed. In this work, 45 a complementary study to the previous one in the literature, 42 it has been established that the luminescence lifetime of excited -Re(CO) 3 phen + pendant chromophores in poly-I is dependent on the polymer concentration. Luminescence lifetimes were calculated from traces obtained with polymer concentrations corresponding to a total chromophore concentration varying from [Re] = 2 x 10 -5 M to 4 x 10 -4 M. In the range of [Re] = 2 x 10 -5 M to 1 x 10 -4 M, a sum of two exponential functions was needed, with lifetimes τ em,1 and τ em,2 to fit the luminescence decay profiles.…”

“…The shorter lifetime, τ em,1 = 55 ± 7 ns, remains essentially constant between 2 x 10 -5 M and 1 x 10 -4 M, while the longer lifetime, τ em,2 , increased monotonically from 240 to 490 ns. When [Re] > 1 x 10 -4 M, the luminescence decay was fitted without deviation to a single exponential with a lifetime τ em = 581 ± 10 ns, which is independent of polymer concentration in the concentration range 1 x 10 -4 M < [Re] < 4 x 10 -4 M. TEM and AFM studies 45 on poly-I and its protonated form, poly-IH n n+ , have shown that (i) the morphology of Re-P4VP polymers is concentration-dependent and (ii) protonation of poly-I polymers alters strongly their morphology. Hereafter, the polymer concentration will be expressed in chromophore units, i.e.…”

“…After protonation of poly-I, its morphology is strongly affected -at low concentration of the Re(I) polymers, small objects at polymer scales are clearly observed and the fiber-structure is evident; at higher concentration of the Re(I) polymers, polymer morphology shifts after protonation from a homogeneous distribution of spherical nanodomains to a bicontinuous bilayer with attached small objects at polymer scales sizes. 45 Figure 9 shows an example of the morphological changes experienced by poly-I after protonation observed by TEM.…”

“…34 However, little attention was paid to Re(I) polymeric complexes, and only a few examples can be found in the literature up to the beginning of the new century. 35 After 2000, however, there has been a huge development in the field, mainly due to our research, 19,[36][37][38][39][40][41][42][43][44][45][46] and the work of the research group led by Chan. 47,48…”

Energy Transfer between CNT Surface and −Re(CO)3(phen)+* Pendants Grafted to P4VP in Nanohybrid Shish-Kebob-like Structures

“…In the last two decades, we have focused our research interests on the study of the photochemical and morphological properties of Re­(I) polymeric complexes. The polymers used in our works have been derived from the P4VP backbone, and they contain fac -XRe­(CO) 3 L pendants in their structure. − The Re­(I) polymers are polyelectrolytes where Re­(I) center coordinates one of every three pyridines present in the P4VP. They display interesting as well as intriguing features both in photochemistry and in material science.…”