Graphene Oxide With Covalently Linked Porphyrin Antennae

Graphene Oxide With Covalently Linked Porphyrin Antennae Swetanshu Tandon Paper Title: Graphene oxide with covalently linked porphyrin antennae: Synthesis,characterization and photophysical properties. Relevant spectroscopic Techniques UV-visible spectroscopy ATR-IR spectroscopy Raman spectroscopy Fluorescence spectroscopy Transient absorption spectroscopy Introduction In this paper, the authors describe the synthesis, characterisation and properties of a hybrid material, GO-H2P, obtained by treating graphene oxide (GO) with 5-(4-aminophenyl)-10, 15, 20-triphenyl-21, 23H-porphyrin (H2P). The characterisation has been done by UV–visible, ATR-IR (Attenuated Total Reflection Infrared) and Raman spectroscopy. Steady state and time resolved fluorescence studies and transient absorption measurements were also conducted to study the electron transfer process from H2P to graphene oxide by photoexcitation. Morphological characterisation has been carried out with the help of transmission electron microscopy (TEM) and atomic force microscopy (AFM). Cyclic voltametry and differential pulsed voltametry were conducted to study the electrochemical characteristics like redox potentials. Choice of techniques Spectroscopic techniques have been carried out on the GO-H2P material dispersed in dimethylformamide at concentration not exceeding 1 mg/mL. UV-visible spectroscopy has been employed in this study due to the presence of porphyrin group which have a characteristic absorption around 420 nm (Soret band) corresponding to a1u(π)–eg*(π) transitions and a weak absorption near 550 nm (Q band).The Soret band involves transition from ground state to second excited state while Q band involves transition from ground state to first excited state. Graphene oxide also shows a characteristic transition at 230 nm again corresponding to π-π* transitions. The nature of linkage can be investigated with the help of this technique. ATR-IR spectroscopy has been used in the study in order to characterise the O–H, C=O, and C–OH bands present in graphene oxide which have characteristic vibrations. Also, in order to confirm the formation of GO-H2P hybrid by the formation of amide units between carboxylic group of graphene oxide and amine group of the porphyrin derivative, ATR-IR spectroscopy can be used. Raman spectroscopy has been used to follow the transformation of graphite to graphene oxide and further to GO-H2P. The sp2 hybridisation in all the three materials, i.e. graphite, graphene and graphene oxide, leads to the formation of different peaks due to first and higher order scattering process. The presence of π-electrons make the scattering process resonant thus making the response stronger. The fluorescence properties of porphyrin derivatives due to π- π* transitions between the two highest occupied molecular orbitals and the two lowest occupied molecular orbitals within the ring justifies the use fluorescence spectroscopy in the study. Fluorescence spectroscopy has been used to examine the nature of electronic interaction between graphene oxide and H2P. The photoexcitability of GO-H2P leads to the application of transient absorption spectroscopy. Transient absorption spectroscopy has allowed the examination of the phenomenon of quenching of luminescence in further detail. Information Obtained A broad monotonically decreasing signal on moving from ultraviolet to visible region was obtained in the UV-visible spectrum of GO-H2P which is characteristic of graphene oxide. The spectrum was obtained in a solution of dimethylformamide at concentration not exceeding 1 mg/mL as mentioned before. Broadening and shortening of the band at 420 nm, characteristic of H2P (Soret-band), is also observed besides its bathochromic shift (by ca. 2 nm) while the Q bands were flattened to the base line. Bathochromic shift signifies increased conjugation. So, it can be concluded that not only there is a linkage between GO and H2P units but also electronic interactions between the two. The ATR-IR spectra provided in the supporting information reveals a peak at 1715 cm-1 corresponding to C=O vibration. The fingerprints are at 3616 cm-1 and 3490 cm-1due to O–H stretching due to their high bond strength. The covalent linkage between GO and H2P moieties is supported by the presence of a peak at 1630 cm-1 which is characteristic of carbonyl group of amide units. The signal due to graphene layer appears in the region ~1650 – 1550 nm. In the Raman spectrum for graphite the G-band, characteristic of all sp2 hybridised carbons, is present at 1580 cm-1. The G/ (or 2D)-band – the first overtone of the D peak which is also a characteristic of all sp2 hybridised carbons – is located at 2725 cm-1 as a sharp and symmetric band. For GO, the Raman spectrum shows a D band, which is a characteristic of disorder for sp2 hybridised carbons, at 1345 cm-1. This accounts for the defects produced due to the oxidation of graphite. Also, the G/-band in GO appears broader and hypsochromically shifted thereby implying the presence of single and bilayers of GO sheets which is further supported by AFM analysis. The Raman spectrum of GO-H2P is almost identical to that of GO. This means that treatment with H2P perturbs the graphene layer of GO to a very small extent. IR as well as Raman spectroscopic techniques have been used in this study to follow the formation of GO-H2P from graphite. Both these techniques complement each other as one (infrared spectroscopy) is applicable to vibrational modes in which the dipole moment of the molecule is altered while the other (Raman spectroscopy) is applicable to modes involving change in the electric polarizability. ATR-IR spectroscopy provides information of the functional groups and thus helps in following and confirming the formation of GO-H2P from graphene oxide and the porphyrin derivative. Raman spectroscopy, on the other hand, supports the observations obtained by infrared spectroscopy. Also, it provides an insight of the extent of disorder of the graphene layer which keeps vibrating. The D band gives information about the extent of disorder in graphene layers. UV-visible spectroscopy provides information about the nature of interaction between GO and H2P units. It, in addition to the data provided b y IR and Raman spectroscopy, points out that transfer of electrons might be possible between the porphyrin units and graphene oxide layers. The nature of electronic interactions of the H2P units with the graphene oxide sheets has been further investigated by fluorescence spectroscopy. On excitation with 418 nm radiation, characteristic fluorescence emission H2P, in dimethylformamide, at 660 nm and 716 nm are observed. In GO-H2P, these emissions are significantly quenched. The emission at 660 nm is also shifted by 10 nm hypsochromically. Quantifying the quenching of the porphyrin emission in this hybrid material tends to be a little difficult because of interference from the absorption of graphene oxide at the excitation wavelength. However, the effective emission quenching of porphyrin in the GO-H2P hybrid indicates that electronic interactions between the singlet excited state of the porphyrin and graphene oxide are dominant. The fluorescence lifetime of photoexcited porphyrin in GO-H2P hybrid have been calculated to be 675 ps (50%) and 1600 ps (50%) which is significantly lower than that of the intact porphyrin, H2P (2900 ps (100%)). This further supports the efficient emission quenching by the graphene sheets. The effective quenching of the fluorescence emission due to H2P in GO-H2P implies electronic interaction between the singlet excited state of H2P with GO. So, H2P acts as an energy absorber unit and GO unit acts as an electron transporting unit. Transient absorption spectrum complements the information obtained from fluorescence spectroscopy using Nd-YAG laser. The Q band can be photoexcited by using a laser light source of 532 nm which led to the population of the singlet excited state of H2P. The band absorption, in the transient absorption spectrum, due to oxidised porphyrin species (H2P+) lies in the visible region at 610 nm. The band observed at 450 nm is the characteristic feature of porphyrin and is almost identical to the one observed in the transient absorption spectroscopy of intact H2P. It occurs due to triplet-triplet absorption of the porphyrin. The bands in the near infrared region are due to the electrons trapped within the reduced graphene sheets (GO) in which absorption is observed in the near infrared region due to the presence of GO species. This is further supported by the absorption spectrum of electrochemically reduced graphene oxide. Thus, transient absorption spectrum provides evidence in support of t he formation of charge separated radical ion pair GO H2P+. The depletion observed near 1100 nm is due to the fundamental YAG laser. The decline of transient absorption with time is a proof of the development of charge recombination which de-excites the radical ion pair back to its ground state. The decay profile for these transient species gave a charge-recombination rate constant (kCR) of 1.8 X 107 s1. This allows the evaluation of the lifetime of the radical ion pair GO H2P+ which comes out to be 56 ns in dimethylformamide. This further confirms that the charge separation is the cause of fluorescence quenching. The emission and transient absorption spectroscopy give information about the conductive nature of GO-H2P hybrid. As pointed out in the observations of UV-visible spectroscopy, the nature of bond in between graphene oxide and H2P if not purely covalent but involves electronic interaction too. Fluorescence spectroscopy helps in further examining the nature of interaction of the GO-H2P linkage. It confirms the observations of UV-visible spectroscopy and indicates the presence of charged species as inferred by the short fluorescence lifetime profile. Transient absorption spectroscopy further confirms this. Also, it confirms that the observations of cyclic voltammetry and differential pulsed voltametry which indicate the presence of radical ion pairs GO H2P+. It also indicates the development of charge recombination which drives the radical ion pair back to its ground state. Overall, it gets confirmed that H2P can easily get photoexcited and transfer electron to graphene oxide which is able to capture these electrons effectively. Additional spectroscopic information that may provide useful information The presence of porphyrin moiety makes this substance particularly interesting. This is because of the characteristic Soret band which is used for its identification. Also, the molar extinction coefficient for porphyrins is pretty high. 5-(4-aminophenyl)-10, 15, 20-triphenyl-21, 23H-porphyrin, which has been used in the analysis, is chiral in nature. So, circular dichroic spectroscopy can be conducted. The high value of the molar extinction coefficient would be helpful as it increases the sensitivity of the technique in this study carried out over this porphyrin derivative covalently linked to graphene oxide. The chiral nature would not only help in supporting the data obtained by various characterisation techniques (infrared, UV-visible, Raman spectroscopy) but would prove helpful in the conformational and configurational analysis of the porphyrin as well. It might also help in exploring the chiral nature of the GO-H2P hybrid. Spectra and Tables

Compare racial and cultural struggles in Alice Walker’s The Color Essay

Compare racial and cultural struggles in Alice Walker’s The Color Purple as well as Toni Morrison’s The Bluest Eye. In African-American texts, blacks are seen as struggling with the patriarchal worlds they live in order to achieve a sense of Self and Identity. The texts I have chosen illustrate the hazards of Western religion, Rape, Patriarchal Dominance and Colonial notions of white supremacy; an intend to show how the protagonists of Alice Walker’s The Color Purple as well as Toni Morrison’s The Bluest Eye, cope with or crumble due to these issues in their struggle to find their identities. The search for self-identity and self-knowledge is not an easy task, even more so when you are a black woman and considered a mule and a piece of property. Providing an in depth analysis of these texts, this essay attempts to illustrate how both of these Afro-American writers depict and resolve their respective protagonists’ struggles. Religion is believed by many to serve as a means to achieving or finding self or identity. However, in the Euro-influenced Christian religion especially, directly after ‘finding one’s self’, one is called to deny one’s self in the name of a white ‘God’. ‘Humble yourself and cast your burdens to God’ they say, for ‘He will make all wrongs right’. Logically however, one must ask†¦what interest does the white God (who is especially portrayed in Afro-American writings such as The Color Purple and The Bluest Eye as a further extension of Patriarchal values) have in black people? Moreso, if the Christian bible is so heavily influenced by white man, what interest does the God it portrays have in black women? In The Color Purple, Celie’s original intended audience is a white, male God w... ... the voiceless, to overcome the patriarchal oppression and gradually find her ‘Self’. Bibliography Cutter, Martha. Philomela Speaks: Alice Walker's Revisioning of Rape Archetypes in The Color Purple - Critical Essay. MELUS, Fall – Winter, 2000. Davis, Thadious M. Walker’s Celebration of Self in Southern Generations. Hooks, Bell, ‘Writing the Subject: Reading The Color Purple’, in Bloom, H., ed. Modern Critical Views: Alice Walker, New York, 1989. Katz, Tamar. â€Å"Show Me How to Do Like You.† Didacticism and Epistolary Form in The Color Purple. 1988. Morrison, Toni The Bluest Eye, London: Picador, 1990. Peach, Linden Toni Morrison London: MacMillan, 1995. Shakhovtseva, Elena.  «The Heart of Darkness » in a Multicolored World: The Color Purple by Alice Walker as a womanist text. Walker, Alice The Color Purple London: The Women’s Press, 1986.

Evolutionism :: Science, Theories, Darwinism

What is Evolution? Evolution is the theory that all living things in the world have come into being through a non-guided, natural process starting from a primeval mass of subatomic particles and radiation, over 20 billion years ago (History). This theory says that all living things have increased intelligence or have changed in other ways over many, many years.   Ã‚  Ã‚  Ã‚  Ã‚  The theory of evolution hasn’t been around for ever. Before the 20th century, people wanted to understand the world around them, but many of them believed that God created everything. A small number of scientists believed that living things had evolved from each other and there was no God. The theory was sort of a dream or manifestation without any original grounds for belief. Over time more and more people looked into evolutionism and they developed possibilities of how it occurred. Many theories were developed, but someone always disproved them. Recently with the discovery of genetic mutation and a new understanding of genes and DNA, the evidence supporting evolution has greatly increased.   Ã‚  Ã‚  Ã‚  Ã‚  Charles Darwin was one scientist who helped to increase the evidence supporting evolution. Darwin developed the idea of â€Å"natural selection† where living things that reproduced in large numbers and survived became dominant and other living things adapted to survive, or they died. Francis Crick, a scientist, co-discovered DNA which opened new doors to the idea of evolutionism (History). DNA is the pattern by which people are created as individuals. Now Evolutionism is the only origin of life that can be taught in public schools. However, in private

Dinner with Father :: Example Personal Narratives

Dinner with Father I wonder what it would be like to go to dinner with my father. One of the chief words my uncle uses to describe my father is "classy," so I'm sure that he would take me to a fancy restaurant. We would sit across the table from each other, both decked out in dark suits. My hair would fall into my eyes and I would brush it out of the way, looking to see the expression on his face. He was a large man, both in my memories and in photographs I've seen. I'm sure that he would dominate the conversation, both physically and mentally. His absence from my life has resulted in my sort of revering him, and so I think that the evening would be unevenly balanced toward my listening to him speak. And what better questions to ask than his opinions of me and my habits? It would be strange, seeking acceptance from someone who has had such a powerful effect on my life, influencing me more through his absence than through his presence. My early years with my father have become harder and harder to recall. From what I can remember, and what I have gleaned from my brother and mother, I was on the verge of spending "quality time" with my father. My brother, who is four years older than I, spent the last few years with Dad talking and reading and walking, all things I yearn to have done with him. The dinner would be a chance for me to bond with my father, and to get a sense of the man he was. This is what my brother and my mother know, but cannot convey to me. I would show him some of the poems I've written about him and me. I would question him to see whether or not the image of him I had forged in my mind, in my writing, is true. In my philosophy class this year, we are reading Plato's Republic, which my mother has told me was my father's favourite book. I am fortunate enough to have his copy of the Republic, a tattered, red-leather bound copy from long ago. I want to know what he gleaned from this book that made it so important to him. I would use the dinner (which I know would be too short) to fill in the gaps in my perception of my father.

Silent Features of the British Constitution

The English Constitution has made a great circuit of the globe & has become a common possession of civilized man. (G. B Adams) A Constitution means certain principles on which the Government of the State is organized & which determines the relations between the people & the Government the Constitution of British is unique in nature & has provided inspiration for a number of other constitutions in the world.Following are the salient features of the British Constitution.Unwritten:The British Constitution is unwritten in nature but it does not imply that all of its parts are unwritten. It means that it has not been reduced to writing in a single document. Some of the components are found in written from. Such as the Reform Act, 1832, the Parliament Act of 1911 etc.Evolution Growth:British Constitution is a result of an evolutionary growth. Constitution efforts as well as needs of time shaped its spontaneous growth.Flexible Constitution:British Constitution is a flexible Constitution & p arliament can amend it like alterations in the statutory laws by a simple majority.Unitary:British have unitary constitution. All powers of the state are concentrated in the hands of a single government for the whole country. There are no units or states in British.Bicameralism:The Parliament consists of two chambers House of Lords & House of Commons. The House of commons is a popular chamber whose member directly elected by the people while the House of Lords is basically a hereditary chamber & its member are nominated by the Queen.Supremacy of the Parliament:In U.K, Parliament has complete Supremacy or sovereignty. No law enacted by the parliament can be challenged in the court on the plea that is against the constitution.According To De Loeme:â€Å"British Parliament can do everything except to make a man into a woman†.Constitution Monarchy:From Constitution point of view, the crown is the repository of the entire Government of authority in British.Contrast In Theory & Pra ctice:There is sharp contrast between theory & practice in British As of points out that â€Å"theoretically, British Government is absolute monarchy, its government from signifies constitution monarchy while in practice, the Government structure is closer to republican from.Collective Responsibility:of Commons & the crown.Limited Separation Of Power:In British, there is limited Separation of power. There is concentration of political powers in the parliament while the cabinet which exercises executive power is just a committee of the parliament. Nevertheless many safeguards have been provided especially under Act of Settlement of 1701 to secure the independence of judiciary from under influence on the part of other two branches on the Government.Independence of Judiciary:Necessary safeguards have been provided against all sorts of interference in judicial process. Judges are paid liberal salaries & ensured security of service.Rule of Law:U.K Constitution provides rule of law. The principle of rule of law may be defined as that none of the person in above or below the law. All the persons are equal in the eyes of law. F any person violates the law, he should face the trial of the case in the Government & no person is given imprisonment until his offence is proved in the court.Fundamental Rights:Fundamental rights of the citizens have not been incorporated in the form of a list in the English Constitution. Constitution law is not the creator but a product of fundamental rights, which have been recognized from time to time by the Courts.ConventionsConventions play a vital role in the British political system. A government is formed & removed on the basis of convention. As Prof. Smith says that the conventions are main living source behind the Constitution.Two Party System:Two party system is flourished in British right from the beginning of the parliamentary period. Before the emergence of the present labor party in the second decay of the present century, the fight was between the conservatives & the Liberal party, but now the liberal party has lost its political significance.XVI: Universal Adult Suffrage:Every individual of the age of 18 has the right to vote.Mixed Constitution:The British Constitution is a mixture of the monarchical, aristocratic & democratic principal.Conservativeness:The British Constitution is a symbol of Conservativeness. The trend of the people of U.K is absolutely n favor of old institutions & this concept is existence of conservatism.Establishment of Local Government Institutions:The existence of local Government in U.K. Constitution is another comprehensive feature of the Constitution. Local Government institution is symbols of the civil liberties & freedom of the people.Unreality:Another characteristic of the English Constitution is its unreality. It has righty been pointed out that nothing in it is what seems or seems what it.Conclusion:  To conclude, I can say, that British Constitution in neither absolute ly unwritten nor absolutely written. It is a combination of both & has made a circuit for the globe & has become the common possession of civilized man.

Critique on Happiness and Analysis Essay

In Karl Giberson’s article â€Å"The Ends of Happiness† (2006), from the Science & Spirit magazine, he raises the topic of happiness, where he claims that people are now pursuing the means to happiness as an end to itself and have missed the point of life. Although Giberson(2006) has made some valid arguments in claiming that people pursue wealth as a means to happiness, his arguments are largely undermined due to a lack of reliable evidences. Giberson’s (2006) claims are not unfounded, as human beings tend to set their goals on material success. For them, monetary success is their definition of happiness. This idea is illustrated by the statement â€Å"The means have become an end for many of us†¦Ã¢â‚¬ (para. 11). He goes on to say that many others â€Å"can’t seek happiness directly† (para. 7). His thoughts align well with society’s widely accepted view that â€Å"without family and friends it is hard to find happiness, for these are essential partners in living and doing well†(para. 9). As such, Giberson (2006) implies that happiness comes from the various experiences and journeys which we go through in life, such as quality time spent with people around us. However, Giberson (2006) makes an unsuccessful attempt in persuading his readers to adopt his beliefs by merely referencing to Aristotle’s philosophy of â€Å"living well and doing well† (para. 8). Throughout the article, Giberson (2006) constantly refers to his own opinions and experiences. For example, he reminisces that â€Å"in reflecting on the accumulated memories of happy times †¦ [he finds himself] agreeing with Aristotle† (para. 12). Thereafter, he mentions that he â€Å"coached [his] children’s sports teams †¦ and lov(ed) it† (para. 13). This demonstrates that his views are greatly influenced by emotions rather than facts. Although the use of anecdotes sparks interest and engages his readers effectively, his excessive usage of this communication technique makes his arguments seem unsupported and weak. As a result of his heavy reliance on his own opinions, it has led to a hasty generalisation in his argument as seen through his claim that â€Å"America †¦ is not a nation pursuing happiness† (para. 11). Due to a lack of expert opinion and statistical data, his claim remains unpersuasive and has little credibility. Hence, Giberson’s(2006) article lacks concrete support and fails to make a compelling argument. Although Giberson (2006) provides a good point of view on how people are becoming too focused on wealth in the pursuit of happiness, he makes sweeping statements that lacks credibility. He can provide a more concrete argument by using a wider range of reliable sources. This will greatly strengthen Giberson’s (2006) argument and lend credibility to his claim. It would help greatly if he had supporting opinions of other academic writers who follow his train of thought. In essence, his article did indeed establish his thesis that people are pursuing the means to happiness as an end to itself, but had unfortunately failed to compellingly persuade his audience. Reference: Giberson, K. (2006, March/April). The Ends of Happiness. Retrieved on 21 Jan 2013 from http://ehis.ebscohost.com/eds/pdfviewer/pdfviewer?sid=4e0e6d4c-0091-45b9-be30-fd892a301bf9%40sessionmgr10&vid=3&hid=2

Lucy v. Zehmer Case Brief Essay

I. Statement of the Facts Zehmer owned a Farm that Lucy had made several offers to purchase, all of which Zehmer rejected. Lucy met Zehmer in the latter’s restaurant one evening. After drinking, they had a substantial discussion about the sale of the farm. Lucy made an offer of $50,000. Zehmer drafted up Lucy a contract specifying the land, the amount, title satisfactory to buyer. Lucy took the written agreement and offered $50,000 to Zehmer who refused to abide to the written agreement. Lucy filed a lawsuit against Zehmer to compel him to transfer the title of the farm to him for $50,000. Zehmer supported that the writing was prepared as a bluff, the whole matter was a joke, no binding contract was made, and at the time he made the offer he was â€Å"was as high as Georgia pine†. The trial court ruled in favor of Zehmer. Lucy appealed to the Supreme Court of Appeals of Virginia. II. Issue Does the offer made by Zehmer – supposedly as a joke – constitute a valid contract? III. Rule of Law â€Å"The first requirement for effective offer is a serious intent. Not determined by subjective intentions, beliefs and assumptions of the offeror. Rather it is determined by what a reasonable person in the offeree’s position would conclude that the offreror’s words and actions meant.† Offers made in jest, obvious anger, or undue excitement do not count and the acceptance of them does not create an agreement. IV. Analysis In his defense, Zehmer claimed that the offer to sell his farm to Lucy was made as a joke and at the time he made it they were both drinking and he was not in a state of sobriety. The court judged Zehmer’s argument about his mental state inconsistent due to the fact he was able to provide great detail what was said and done that night in his testimony. The court found that the contract was discussed for forty minutes, rewritten to include Mrs. Zehnmer, and she did sign it. The discussion of what to be included in the sale and the provisions of it made a serious transaction. The delivery of the written contract shows a good faith offer and a good faith acceptance.