186259-63-2

Basic information

• Product Name: 2,7-Dibromo-9,9-diphenylfluororene
• Synonyms: 2,7-Dibromo-9,9-diphenyl-fluororene;2,7-Dibromo-9,9-diphenyl-9H-fluorene;2,7-Dibromo-9,9-diphenylfluorene;9,9-Diphenyl-2,7-dibromofluorene;2,7-Dibromo-9,9-diph;2,7-broMo-9,9-diphenyl-9HFluorene;2,7-DibroMo-9,9-diphenylfluorene,9,9-diphenyl-2,7-dibroMofluorene;9H-Fluorene,2,7-dibroMo-9,9-diphenyl-
• CAS NO: 186259-63-2
• Molecular Formula: C₂₅H₁₆Br₂
• Molecular Weight: 476.20254
• EINECS: 1533716-785-6
• Product Categories: Fluorene Derivatives;Electronic Chemicals;Fluorene Series;OLED materials,pharm chemical,electronic
• Mol File: 186259-63-2.mol
• Article Data: 13

Chemical Properties

• Melting Point: 279-281 °C
• Boiling Point: 520.3 °C at 760 mmHg
• Flash Point: 311.1 °C
• Appearance: /
• Density: 1.548 g/cm³
• Vapor Pressure: 2.08E-10mmHg at 25°C
• Refractive Index: 1.693
• Storage Temp.: Sealed in dry,Room Temperature
• CAS DataBase Reference: 2,7-Dibromo-9,9-diphenylfluororene(CAS DataBase Reference)
• NIST Chemistry Reference: 2,7-Dibromo-9,9-diphenylfluororene(186259-63-2)
• EPA Substance Registry System: 2,7-Dibromo-9,9-diphenylfluororene(186259-63-2)

Safety Data

• Hazardous Substances Data: 186259-63-2(Hazardous Substances Data)

Usage

General Description

2,7-Dibromo-9,9-diphenylfluororene is a chemical compound with the molecular formula C26H16Br2. It belongs to the class of polyaromatic hydrocarbons and is characterized by its two bromine substituents and two phenyl groups attached to the central fluororene core. 2,7-Dibromo-9,9-diphenylfluororene is commonly used as a building block in the synthesis of organic semiconductors and materials for optoelectronic devices. Its unique structure and properties make it a valuable tool in the development of advanced electronic and photonic technologies. Additionally, 2,7-Dibromo-9,9-diphenylfluororene has been studied for its potential application in organic light-emitting diodes (OLEDs) and organic solar cells due to its promising optoelectronic properties.

InChI:InChI=1/C25H16Br2/c26-19-11-13-21-22-14-12-20(27)16-24(22)25(23(21)15-19,17-7-3-1-4-8-17)18-9-5-2-6-10-18/h1-16H

Synthetic route

iodobenzene (591-50-4) + 2,7-dibromo-9H-fluorene (16433-88-8) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
With tetrabutylammomium bromide; sodium hydroxide In dimethyl sulfoxide for 5h; Sonication;	98%

2,7-dibromo-(9-phenyl-9H-fluoren-9-ol) (132717-37-4) + benzene (71-43-2) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
With trifluorormethanesulfonic acid at 80℃; for 6h; Reflux;	93%
With trifluorormethanesulfonic acid at 80℃; for 6h; Friedel-Crafts reaction;	88%
With trifluorormethanesulfonic acid at 50 - 80℃; for 6h; Inert atmosphere; Schlenk technique;	70%

9,9-diphenylfluorene (20302-14-1) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
With bromine; acetic acid In chloroform for 1h; Inert atmosphere; Reflux;	90%

(4,4'-dibromo-biphenyl-2-yl)-diphenyl-methanol → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
With sulfuric acid; acetic acid at 100℃; for 1h;	89%

2,7-dibromofluorene-9-one (14348-75-5) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Multi-step reaction with 2 steps 1: diethyl ether / 3 h / Heating 2: conc. H2SO4 / 3 h View Scheme
Multi-step reaction with 2 steps 1: 90 percent / diethyl ether / Heating 2: 88 percent / CF3SO3H / 6 h / 80 °C View Scheme
Multi-step reaction with 2 steps 1.1: magnesium / diethyl ether / 4 h / Reflux 1.2: 12 h / Reflux 2.1: trifluorormethanesulfonic acid / Heating View Scheme

phenylmagnesium bromide + [(4-methoxy-1,3-η3-cyclohexenyl)PdCl]2 → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Multi-step reaction with 2 steps 1: diethyl ether / 3 h / Heating 2: conc. H2SO4 / 3 h View Scheme

methyl 4,4'-dibromo-[1,1'-biphenyl]-2-carboxylate → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Multi-step reaction with 2 steps 1: 94 percent / tetrahydrofuran; hexane / 17 h / -78 - 20 °C 2: 89 percent / H2SO4; AcOH / 1 h / 100 °C View Scheme

phenyllithium (591-51-5) + [Ru(η3-CH2CHCH2)(η5-C5Me5)(η2-t-BuNC(Ph)=Nt-Bu)](1+)*PF6(1-) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Multi-step reaction with 2 steps 1: 94 percent / tetrahydrofuran; hexane / 17 h / -78 - 20 °C 2: 89 percent / H2SO4; AcOH / 1 h / 100 °C View Scheme

phenylmagnesium bromide + antimony trichloride → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Multi-step reaction with 2 steps 1: 90 percent / diethyl ether / Heating 2: 88 percent / CF3SO3H / 6 h / 80 °C View Scheme

bromobenzene (108-86-1) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Multi-step reaction with 2 steps 1.1: magnesium / diethyl ether / 4 h / Reflux 1.2: 12 h / Reflux 2.1: trifluorormethanesulfonic acid / Heating View Scheme

9H-fluorene (86-73-7) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Multi-step reaction with 4 steps 1: N-Bromosuccinimide / 1,2-propylene cyclic carbonate / 3 h / Reflux 2: chromium(VI) oxide; acetic acid / 1 h / 120 °C 3: iodine; magnesium / diethyl ether 4: trifluorormethanesulfonic acid View Scheme
Multi-step reaction with 4 steps 1.1: bromine / chloroform / 20 h / 0 - 20 °C / Darkness; Inert atmosphere; Schlenk technique 2.1: potassium dichromate; acetic acid / 6 h / 120 °C / Inert atmosphere; Schlenk technique 3.1: magnesium; iodine / tetrahydrofuran / Schlenk technique; Inert atmosphere 3.2: Reflux; Inert atmosphere; Schlenk technique 4.1: trifluorormethanesulfonic acid / 6 h / 50 - 80 °C / Inert atmosphere; Schlenk technique View Scheme

2,7-dibromo-9H-fluorene (16433-88-8) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Multi-step reaction with 3 steps 1: chromium(VI) oxide; acetic acid / 1 h / 120 °C 2: iodine; magnesium / diethyl ether 3: trifluorormethanesulfonic acid View Scheme
Multi-step reaction with 3 steps 1.1: potassium dichromate; acetic acid / 6 h / 120 °C / Inert atmosphere; Schlenk technique 2.1: magnesium; iodine / tetrahydrofuran / Schlenk technique; Inert atmosphere 2.2: Reflux; Inert atmosphere; Schlenk technique 3.1: trifluorormethanesulfonic acid / 6 h / 50 - 80 °C / Inert atmosphere; Schlenk technique View Scheme
Multi-step reaction with 3 steps 1: potassium permanganate / 3 h / 20 °C / Inert atmosphere 2: tetrahydrofuran / 1 h / Inert atmosphere; Reflux 3: sulfuric acid / 16 h / Inert atmosphere; Reflux View Scheme

bromobenzene (108-86-1) + 2,7-dibromofluorene-9-one (14348-75-5) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Multi-step reaction with 2 steps 1.1: n-butyllithium / tetrahydrofuran; hexane / 0.67 h / -78 °C 1.2: 4 h / -78 °C 2.1: trifluorormethanesulfonic acid / 6 h / 80 °C / Reflux View Scheme

9-fluorenone (486-25-9) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Multi-step reaction with 2 steps 1: N-Bromosuccinimide; methanesulfonic acid / chloroform 2: sulfuric acid / tetrahydrofuran; benzene View Scheme

2,7-dibromofluorene-9-one (14348-75-5) + phenylmagnesium bromide (100-58-3) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
With sulfuric acid In tetrahydrofuran; benzene

2,7-dibromofluorene-9-one (14348-75-5) + phenyllithium (591-51-5) → 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2)

Conditions	Yield
Friedel-Crafts Alkylation;

2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → 2,7-diiodo-9,9-diphenylfluorene

Conditions	Yield
Stage #1: 2,7-dibromo-9,9-diphenyl-9H-fluorene With n-butyllithium In tetrahydrofuran at -78℃; for 1h; Stage #2: With iodine In tetrahydrofuran at 20℃; for 2h;	92%

2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) + trimethylsilylacetylene (1066-54-2) → C35H34Si2

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; copper(l) iodide In triethylamine at 20 - 70℃; Sonogashira Cross-Coupling; Inert atmosphere; Schlenk technique;	92%

9,9-diphenyl-7-trimethylsilylfluorenyl-2-boronic acid (885665-22-5) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → 7,7'-bis(trimethylsilyl)-ter(9,9-diphenylfluorene) (885665-24-7)

Conditions	Yield
With potassium carbonate; triphenylphosphine; palladium diacetate In methanol; toluene at 75℃; Suzuki cross-coupling;	86%

(4-aminophenyl)boronic acid (89415-43-0) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → 4,4'-(9,9-diphenyl-9H-fluorene-2,7-diyl)dianiline

Conditions	Yield
With tetrakis(triphenylphosphine) palladium(0); Aliquat 336; potassium carbonate In tetrahydrofuran at 80℃; for 24h; Suzuki-Miyaura Coupling; Inert atmosphere;	86%

N-phenyl-1-naphthylamine (90-30-2) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → N,N'-di-naphthalen-1-yl-9,9,N,N'-tetraphenyl-9H-fluorene-2,7-diamine

Conditions	Yield
With palladium diacetate; tri-tert-butyl phosphine; sodium t-butanolate In toluene at 100℃; for 4h;	85%

2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) + {4-[bis(2,4,6-trimethylphenyl)boranyl]phenyl}boronic acid (684243-16-1) → 2,7-bis(4-(dimesitylboryl)phenyl)-9,9-diphenylfluorene (1498411-24-7)

Conditions	Yield
With tetrakis(triphenylphosphine) palladium(0); potassium carbonate In ethanol; water; toluene for 12h; Reflux; Inert atmosphere;	83%

C20H13N3 (866181-29-5) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → C65H40N6

Conditions	Yield
With tri-tert-butyl phosphine; sodium t-butanolate; tris(dibenzylideneacetone)dipalladium (0) In toluene for 8h; Heating;	82%

chloro-trimethyl-silane (75-77-4) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → 2-bromo-9,9-diphenyl-7-trimethylsilylfluorene (885665-21-4)

Conditions	Yield
Stage #1: 2,7-dibromo-9,9-diphenyl-9H-fluorene With n-butyllithium In tetrahydrofuran at -78℃; for 1h; Stage #2: chloro-trimethyl-silane In tetrahydrofuran at 20℃; for 2h;	81%

C20H13NS2 + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → C65H40N2S4

Conditions	Yield
With tris-(dibenzylideneacetone)dipalladium(0); sodium t-butanolate; tri tert-butylphosphoniumtetrafluoroborate In toluene for 1h; Inert atmosphere;	78.9%

2‐{[1,1'‐biphenyl]‐2‐yl}‐4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → 2,7-di(biphenyl-2-yl)-9,9-diphenyl-9H-fluorene

Conditions	Yield
With tetrakis(triphenylphosphine) palladium(0); potassium carbonate In ethanol; water; toluene at 90℃; for 24h; Suzuki Coupling; Inert atmosphere; Schlenk technique;	75%

benzo[c]carbazole (205-25-4) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → C41H26BrN

Conditions	Yield
With tris-(dibenzylideneacetone)dipalladium(0); tri-tert-butyl phosphine; sodium t-butanolate In toluene at 80℃; Inert atmosphere;	74%

3-Methyldiphenylamine (1205-64-7) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → 9,9,N,N'-tetraphenyl-N,N'-di-m-tolyl-9H-fluorene-2,7-diamine

Conditions	Yield
With palladium diacetate; tri-tert-butyl phosphine; sodium t-butanolate In toluene at 100℃; for 6h;	69%

C24H23NO + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → C73H60N2O2

Conditions	Yield
With tris-(dibenzylideneacetone)dipalladium(0); tri-tert-butyl phosphine; sodium t-butanolate In toluene at 105℃; for 24h; Inert atmosphere;	66.8%

7-N,N-diphenylamino-9,9-diphenylfluorenyl-2-boronic acid + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → 2,7''-bis(diphenylamino)-7,2',7',2''-ter(9,9-diphenylfluorene)

Conditions	Yield
With potassium carbonate; triphenylphosphine; palladium diacetate In methanol; toluene at 75℃; Suzuki cross-coupling;	65%

C28H26BN3O3 + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → C81H64N6O2

Conditions	Yield
With tetrakis(triphenylphosphine) palladium(0); sodium carbonate In toluene at 105℃; for 24h; Inert atmosphere;	63.3%

4-butyl-N-(4-butylphenyl)aniline (227003-50-1) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → 7-bromo-N,N-bis(4-butylphenyl)-9,9-diphenyl-9H-fluoren-2-amine (1564287-40-6)

Conditions	Yield
With 1,1'-bis-(diphenylphosphino)ferrocene; bis(dibenzylideneacetone)-palladium(0); sodium t-butanolate In toluene at 110℃; for 24h; Buchwald-Hartwig Coupling; Inert atmosphere;	63%

N,N-dimethyl-formamide (68-12-2, 33513-42-7) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → C27H18O2

Conditions	Yield
Stage #1: 2,7-dibromo-9,9-diphenyl-9H-fluorene With n-butyllithium In tetrahydrofuran at -78℃; for 1h; Stage #2: N,N-dimethyl-formamide In tetrahydrofuran at 20℃; for 3h;	63%
Stage #1: 2,7-dibromo-9,9-diphenyl-9H-fluorene With n-butyllithium In tetrahydrofuran at -78℃; for 1h; Stage #2: N,N-dimethyl-formamide In tetrahydrofuran at 20℃; for 3h;	60%

2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) + phenylboronic acid (98-80-6) → C31H21Br

Conditions	Yield
With potassium phosphate; tetrakis(triphenylphosphine) palladium(0) In ethanol; water; toluene at 80℃; for 2h; Inert atmosphere; Reflux;	62%

2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) + 9,9-dihexylfluorene-2-boronic acid (371193-08-7) → TFP (1106670-17-0)

Conditions	Yield
With potassium hydroxide; tetrakis(triphenylphosphine) palladium(0) In tetrahydrofuran; water at 75℃; for 24h; Suzuki coupling;	59%

4-(1,2,2-triphenylvinyl)phenylboronic acid (1227040-87-0) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → 9,9-diphenyl-2,7-bis(4-(1,2,2-triphenylvinyl)phenyl)fluorene

Conditions	Yield
With tetrakis(triphenylphosphine) palladium(0); potassium carbonate In ethanol; water; toluene for 12h; Suzuki Coupling; Reflux; Inert atmosphere;	56%

N-[1,1"-biphenyl]-4-yl-N-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]-[1,1-biphenyl]-4-amine (952431-30-0) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → C85H60N2

Conditions	Yield
With tetrakis(triphenylphosphine) palladium(0); potassium carbonate In toluene at 115℃; for 14h; Inert atmosphere;	52%

diphenylamine (122-39-4) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → 2-bromo-7-diphenylamino-9,9-diphenylfluorene + C49H36N2

Conditions	Yield
With tris-(o-tolyl)phosphine; sodium t-butanolate; palladium diacetate In toluene at 110℃; for 24h;	A 45% B 25%

9H-carbazole (86-74-8) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → C37H24BrN

Conditions	Yield
With tris-(dibenzylideneacetone)dipalladium(0); tri-tert-butyl phosphine; sodium t-butanolate In toluene at 100℃; for 33h; Inert atmosphere;	41%

2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) + 3,6-bis(3,6-di-tert-butylcarbazol-N-yl)carbazole (551951-04-3) → C129H124N6 (1610059-35-2)

Conditions	Yield
With 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone; copper(l) iodide; 18-crown-6 ether; potassium carbonate at 180℃; for 48h;	35%

4-aminotriphenylamine (2350-01-8) + 1-Bromonaphthalene (90-11-9) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → C81H58N4

Conditions	Yield
Stage #1: 4-aminotriphenylamine; 2,7-dibromo-9,9-diphenyl-9H-fluorene With potassium carbonate; copper In nitrobenzene at 180℃; for 6h; Stage #2: 1-Bromonaphthalene In nitrobenzene for 18h;	32%

naphthalene-2-boronic acid (32316-92-0) + 2,7-dibromo-9,9-diphenyl-9H-fluorene (186259-63-2) → C45H30

Conditions	Yield
With bis-triphenylphosphine-palladium(II) chloride; tetrabutylammomium bromide; potassium carbonate In water; toluene for 2h; Inert atmosphere; Reflux;	16%

Upstream product

• 20302-14-1 9,9-diphenylfluorene 
• 14348-75-5 2,7-dibromofluorene-9-one 
• 591-51-5 phenyllithium 
• 100-58-3 phenylmagnesium bromide 
• 486-25-9 9-fluorenone 
• 16433-88-8 2,7-dibromo-9H-fluorene 
• 86-73-7 9H-fluorene 
• 108-86-1 bromobenzene 
• 132717-37-4 2,7-dibromo-(9-phenyl-9H-fluoren-9-ol) 
• 71-43-2 benzene 
• 591-50-4 iodobenzene 

Downstream Products

• 1158844-82-6 C₃₇H₂₆ 
• 1158844-83-7 C₃₇H₂₄Br₂ 
• 1158844-84-8 C₄₉H₄₈B₂O₄ 
• 1158844-49-5 C₇₇H₅₀ 
• 1610059-35-2 C₁₂₉H₁₂₄N₆ 
• 1207176-74-6 C₄₃H₂₈BrN 

Relevant articles and documents

Photophysical properties and optical power limiting ability of Pt(II) polyynes bearing fluorene-type ligands with ethynyl units at different positions

Two series of Pt(II) polyynes bearing fluorene-type ligands with ethynyl units at different positions have been synthesized. In the absorption spectra, the Pt(II) polyynes bearing fluorene-type ligands with ethynyl units at 3,6-position have blue-shift with respect to the corresponding analogs bearing fluorene-type ligands with ethynyl units at 2,7-position, showing better transparency in the visible light region. Moreover, the Pt(II) polyynes bearing fluorene-type ligands with ethynyl units at 3,6-position show stronger triplet emission than corresponding analogs bearing fluorene-type ligands with ethynyl units at 2,7-position in the photoluminescent (PL) spectra. Furthermore, these Pt(II) polyynes were applied to optical power limiting (OPL) field. The Pt(II) polyynes bearing fluorene-type ligands with ethynyl units at 2,7-position show better OPL performance than the corresponding analogs with fluorene-type ligands of ethynyl units at 3,6-position. Therefore, changing the position of the ethynyl units in fluorene-type ligands can not only effectively control the photophysical properties of the Pt(II) polyynes, but also has an important effect on their OPL ability.

Fluorene derivative and organic light-emitting device prepared by same

The invention provides a fluorene derivative and an organic light-emitting device prepared by the same and relates to the technical field of organic photoelectric materials. The fluorene derivative and the organic light-emitting device prepared by the same have the advantages that the fluorene derivative is prepared by connecting substituted or unsubstituted condensed imidazole and condensed oxazole derivatives to a fluorene host, the prepared fluorene derivative has certain electron transport ability, the composition of holes and electrons on a light-emitting layer is benefited, and the fluorene derivative is good in stability and luminous efficiency, simple to synthesize, easy in synthesizing operation, capable of being used in the organic light-emitting device to serve as the light-emitting layer doping material and capable of effectively solving the problems that the blue light-emitting material in the organic light-emitting device is low in luminous efficiency and short in servicelife; the organic light-emitting device is high in luminous efficiency and long in service life.

Photochemical Degradation of Various Bridge-Substituted Fluorene-Based Materials

Photochemical degradation is an important issue to be overcome in advancing the lifetime of fluorene-containing conjugated polymers. In order to optimize the inertness of the materials, a quantitative measure for the efficiency of degradation is needed. Here, we introduce a method to measure a relative quantum yield of the photochemical degradation by monitoring the kinetics of the process by means of UV/vis spectroscopy and liquid chromatography (LC) techniques. This method is employed to a set of differently substituted 2,7-diphenylfluorenes, serving as model compounds for polyfluorene materials. Our measurements show that the quantum yield changes by orders of magnitude upon varying the bridge substituents and that altered kinetics indicate changing degradation mechanisms.