Spectral and Thermal Spectral Stability Study for Fluorene-Based Conjugated Polymers

Abstract

We have studied the spectral (UV−vis absorption and fluorescence) and thermally spectral stability of seven fluorene-based blue-light-emitting polymers in film states. These polymers have different side chain and backbone structure. Spiro-functionalization at the C-9 bridge position of fluorene unit could significantly improve the emission spectral quality (narrower spectrum and shorter tail extended to longer wavelength direction) and thermally spectral stability of 9,9-disubstituted polyfluorene derivatives. A glass transition temperature dependence for excimer emission in the polymers was demonstrated, and the improvement of thermally spectral stability by the spiro-functionalization is attributed to the increase of glass transition temperature. The backbone structural modification for 9,9-disubstituted polyfluorenes by alternatively inserting substituted phenylene units could provide blue emission with the spectral quality and thermally spectral stability even better than spiro-functionalized polyfluorenes, and no glass transition temperature dependence for excimer formation was observed in the backbone-modified polymers. The spectral properties of the polymers are dependent on the substitution on the phenylene ring. Thermotropic liquid crystallization was observed in the polymers bearing long alkoxy substituents. The good thermally spectral stability of the polymers is attributed to the poor planar configuration of the backbone and the efficient separation of the side chains on phenylene units for backbones.

Dispositivos poliméricos eletroluminescentes

“…Ele e seus derivados, normalmente com substituição na posição 9 do anel central, formam uma classe de polímeros conjugados que emitem na região azul do espectro da radiação eletromagnéti-ca. Essa classe de polímeros, alguns dos quais estão mostrados na Figura 2, tem despertado o interesse dos estudiosos por suas propriedades elétricas e ópticas com potencial aplicação para fabricação de dispositivos emissores de luz (LEDs) [22][23][24][25][26][27][28][29][30][31][32][33] . Estes polímeros apresentam algumas propriedades interessantes para essa finalidade destacando-se, entre elas, grande estabilidade química, térmica e oxidativa 18,[34][35][36][37][38] ; alto rendimento quântico de fluorescência tanto em solução quanto no estado sólido 37,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] ; possibilidade de formarem materiais líquido-cristalinos 46,58-68 com altos parâmetros de ordem e temperaturas de transição termotrópica na faixa entre 100 a 170 o C, ocorrendo entre as temperaturas de amolecimento e de decomposição térmica [69][70][71]…”

The Effect of Controlled Dopant Concentration on the Performance of Blue Polymer Light‐emitting Diodes

“…As the NPB concentration increased to 3% NPB, molecular disorder became dominant and carrier mobility decreased. Researchers [25][26][27] have shown the appearance of a shoulder on the main emission peak results mainly from an enhanced molecular order structure that is induced by molecular aggregation of the emitting polymers such as BP105. As the concentration of NPB in BP105 was increased, as shown in Fig.…”

A convenient one-pot preparation of spiro[fluorene-9,9’-xanthene]-3’,6’-diol derivatives

“…Two explanations have been given for the green emission: one was the keto defect, [14][15][16][17] and the other was the formation of interchain excimers. [18][19][20] The introduction of spiro structures is thought as one of the most promising solutions to the problem. [21][22][23] In recent years, spiro compounds as organic molecular materials have become promising candidates for optoelectronic devices.…”