Excimer Formation by Poly(N-vinylcarbazole) in Solution

AB-alternating copolymers via chain-growth polymerization: synthesis, characterization, self-assembly, and functions

In this review, four topics on alternating copolymers synthesized via chain-growth polymerization are reviewed: (1) how to control the alternating sequence; (2) sequence analysis; (3) self-assembly; and (4) functions.

Photophysics of Carbazole-Containing Systems. 2. Fluorescence Behaviour of Poly(N-Vinyl Carbazole) and N -Vinyl Carbazole/Methyl Acrylate Copolymer Films

The fluorescence behaviour of thin films of poly( N-vinyl carbazole), PNVCz, and a series of N-vinyl carbazole/methyl acrylate, NVCz/MA, copolymers has been investigated using both steady-state and time-resolved emission techniques. The fluorescence of PNVCz at 298 K is dominated by emission from two excimeric traps. Trap I has the conventional ‘sandwich’ structure formed from two fully overlapped aromatic rings. The other (trap II) is a species involving two partially overlapped carbazole substituents. The fluorescences of the NVCz/MA copolymers contain contributions from unassociated or monomeric carbazoyl excited states which increase in prominence as the aromatic content of the system is reduced. The influence of intermolecular interactions in creating excimer traps is apparent: even at a carbazole content of 8.3 mol%, excimer emission is evident. In PNVCz and copolymers of higher aromatic contents, the microtacticity of the macromolecule exerts a dominant influence upon the photophysical behaviour of the bulk polymer despite the moderating effects of intermolecular interactions between chromophores.

As the temperature of the system is reduced, the contribution from trap II to the overall fluorescence from the polymer films increases relative to that made by emission from trap I. At 77 K, the fluorescence of PNVCz contains a significant contribution from trap II emission. At 298 K, fluorescence from the conventional excimer, trap I, dominates the steady-state emission spectrum. On the basis of observations upon time-resolved fluorescence data, it is proposed that restrictions to the reorientation of carbazole substituents which occur at low temperature serve to inhibit the conversion of a proportion of the trap II sites into fully overlapped excimers, thereby reducing depletion of the trap II population. Implicit to this explanation of the photophysical characteristics of PNVCz and the higher content NVCz/MA copolymers, is the belief that the high concentration of excimer-forming trap sites mitigates against significant energy migration between carbazole substituents which might otherwise populate the excimer traps. These observations are of importance to considerations of the photoconductivity displayed by polymers derived from NVCz.

Broadband spectra with fluorescence and phosphorescence dual emission from bichromophoric platinum metallomesogens containing a 6,12-dihydro-indeno[1,2-b]fluorene linkage

Two bichromophoric platinum metallomesogens, FJ-1 and FJ-2, exhibited fluorescence (¹π,π*) and phosphorescence (³π,π*) dual emissions in solution. Their photophysical properties were detailedly investigated by experiment and theory calculation.

Orderly ultrathin films based on perylene/poly(N-vinyl carbazole) assembled with layered double hydroxide nanosheets: 2D fluorescence resonance energy transfer and reversible fluorescence response for volatile organic compounds

Neutral poly(N-vinyl carbazole) (PVK) and perylene are coassembled within the interlayers of layered double hydroxide (LDH) nanosheets to form (perylene@PVK/LDH)(n) ultrathin films by the hydrogen-bond layer-by-layer assembly method. An efficient 2D fluorescence resonance energy transfer (FRET) process from PVK to perylene is demonstrated, and this FRET process can be inhibited/recovered reversibly by the adsorption/desorption of common volatile organic compounds (VOCs).

Effects of lipid structure on energy transfer from carbazolyl to anthryl groups in a lipid bilayer

Two types of chromophoric amphiphiles were synthesized: one of them possesses a molecular structure of N,N-dialkyl aromatic amino acid (5X18 type, where X is A or Cz), and the other alpha,gamma-dialkylglutamate connected to aromatic amino acid (mXG12 type, where m is an integer). 5-N-Ethylcarbazolyl and 9-anthryl groups were chosen as the chromophore, and introduced to each amino acid derivative. All the amphiphiles formed assembly showing gel-liquid crystalline phase transition. The phase-transition temperature of the assembly composed of mXG12-type amphiphile was higher than that of 5X18-type amphiphile. Absorption and CD spectra of 6-(trimethylammonium)hexanoyl-L-3-(5-N-ethylcarbazolyl) alanine N,N-dioctadecylamide bromide (5Cz18) in the assembly indicated the absence of strong ground-state interactions between the carbazolyl groups, while those of 6-(trimethylammonium)hexanoyl-L-3-(5-N-ethylcarbazolyl)alanyl-L-gl utamic acid alpha,gamma-didodecyl ester (5CzG12) or 11-(trimethylammonium)undecanoyl-L-3-(5-N-ethylcarbazolyl)al anyl-L-glutamic acid alpha,gamma-didodecyl ester (10CzG12) indicated the ground-state interactions based on dimer or higher aggregates. Fluorescence spectra of 5Cz18 showed very weak excimer emission, while excimer and/or excited dimer or higher aggregates were observed in the assembly of 5CzG12 or 10CzG12. Similar results were obtained for amphiphiles (mAG12) with anthryl and hydroxyethyldimethylammonium groups in places respectively of carbazolyl and trimethylammonium groups of 5CzG12 and 10CzG12. Taking these results together into consideration, the molecular packing of mXG12 in the assembly should be tighter than that of 5X18. In the binary assembly of 6-(trimethylammonium)hexanoyl-L-3-(9-anthryl) alanine N,N-dioctadecylamide bromide (5A18)/5Cz18 (1/99 mol/mol), about 60% of photoenergy absorbed by the carbazolyl groups was transferred to the anthryl groups, indicating an efficient energy migration along the two-dimensional array of carbazolyl chromophores of 5Cz18. On the other hand, in the mCzG12/mAG12 binary assembly, the energy-transfer efficiency was much lower due to the formation of dimer or the higher aggregates acting as energy-dissipating sites.