M. V. George

Fluorescence enhancement of bis(2,4,6-trihydroxyphenyl)squaraine anion by 2 : 1 host–guest complexation with β-cyclodextrin

β-Cyclodextrin (β-CD) forms a 2: 1 inclusion complex with the anion of bis(2,4,6-trihydroxyphenyl)squaraine dye (Sq), in aqueous solutions, bringing about a significant enhancement in the fluorescence yield (ca. 90-fold) and the stability of the dye anion. Apart from the effect of the hydrophobic environment and the decrease in rotational freedom brought about by β-CD encapsulation, intramolecular hydrogen bonding between the OH groups on the phenyl rings and the oxygen atoms in the central cyclobutane ring in the anion guest molecule can significantly contribute to the stiffening of the molecule in the excited state. In the absence of β-CD, intermolecular hydrogen bonding with solvent molecules disrupts the intramolecular hydrogen-bonding processes, bringing about a decrease in the fluorescence yield of the anion.

Interaction of semiconductor colloids with J-aggregates of a squaraine dye and its role in sensitizing nanocrystalline semiconductor films

The role of bis(2,4,6-trihydroxyphenyl)squaraine, Sq, in sensitizing large bandgap semiconductors has been investigated in the present study. The dye in its aggregate form readily interacts with the TiO2 colloids giving rise to a new charge transfer band in the red region. The apparent association constant for the dye aggregate and TiO2 colloid as determined from a Benesi-Hildebrand plot is 1600 M-1. Nanocrystalline semiconductor films prepared from TiO2, ZnO, and SnO2 colloids have been modified with Sq to probe the photosensitization effects. Both dye monomers and aggregates were found to participate in the charge injection process. An incident photon-to-photocurrent efficiency up to 0.7% has been observed.The role of bis(2,4,6-trihydroxyphenyl)squaraine, Sq, in sensitizing large bandgap semiconductors has been investigated in the present study. The dye in its aggregate form readily interacts with the TiO2 colloids giving rise to a new charge transfer band in the red region. The apparent association constant for the dye aggregate and TiO2 colloid as determined from a Benesi-Hildebrand plot is 1600 M-1. Nanocrystalline semiconductor films prepared from TiO2, ZnO, and SnO2 colloids have been modified with Sq to probe the photosensitization effects. Both dye monomers and aggregates were found to participate in the charge injection process. An incident photon-to-photocurrent efficiency up to 0.7% has been observed.

PICOSECOND DYNAMICS OF AN IR SENSITIVE SQUARAINE DYE. ROLE OF SINGLET AND TRIPLET EXCITED STATES IN THE PHOTOSENSITIZATION OF TIO2 NANOCLUSTERS

The photosensitization properties of a novel squaraine dye is probed using picosecond laser flash photolysis. The dye which exists in a protonation equilibrium with a pKa of 4.9 has a strong absorption in the IR region. The protonated form of the dye is highly fluorescent and is readily quenched in colloidal TiO2 suspensions. The association constant as determined from the quenching studies is 1.25×103 M−1. The singlet excited state of the protonated form of the dye participates in the charge injection process with a heterogeneous electron transfer rate constant of 8.3×109 s−1. The unprotonated form of the dye injects electrons from both the singlet and triplet excited state with electron transfer rate constants of 1×1010 s−1 and 1.25×109 s−1, respectively.

A squaraine-based near-infrared absorbing sensor for the selective detection of transition and other metal ions in aqueous media

A near infrared absorbing cationic squaraine dye 1 is shown to be capable of detecting trace amounts of transition and lanthanide metal ions in aqueous media, even in the presence of alkali and alkaline earth metal ions.

Photochemistry of squaraine dyes. Part 10.—Excited-state properties and photosensitization behaviour of an IR sensitive cationic squaraine dye

The singlet and triplet excited-state behaviour of a cationic squaraine dye, (Sq) in acetonitrile is investigated using pico- and nano-second laser flash photolysis. The dye in its protonated form has absorption and emission maxima at 780 and 812 nm, respectively. The singlet excited state exhibits a difference absorption maximum at 640 nm and a lifetime of 1.1 ± 0.1 ns. The triplet excited state, generated by T–T sensitization method exhibited a difference absorption maximum at 620 nm and a lifetime of 45 ± 5 µs. At higher laser excitation intensities, the dye underwent photoionization to yield a cation radical (abs. max. 630 nm). Photosensitization properties of the IR sensitive squaraine dye are demonstrated by modifying a nanocrystalline SnO2 electrode and exciting it with visible–IR light.

Anthraquinone-photocatalysed addition of amines to α,β-unsaturated esters: a novel route to indolizidone, pyrrolizidone and related ring systems

The indolizidone 9, the pyrrolizidone 14, a mixture of heliotridone 15a and pseudoheliotridone 15b and the lactam 19 have been synthesized in a one-step anthraquinone-photocatalysed reaction of the corresponding amines, piperidine 1, pyrrolidine 10 and morpholine 16, with α,β-unsaturated esters.

Splenic pathology in traumatic rupture of the spleen: a five year study.

OBJECTIVES To Study the histopathology of spleens with a history of traumatic rupture with a view to establish possible predisposing factors to the rupture METHODS This study examined the gross and microscopic features of consecutive cases of splenectomies done for traumatic rupture during a five year period in order to evaluate the presence or absence of any pathology prior to rupture. RESULTS Of the 17 cases of splenectomy during this period, 14 were normal and 3 cases showed pathology other than rupture. CONCLUSION In the five year period of studying splenic pathology in traumatic rupture, 82% of the spleens showed normal histology except for the rupture. 18% of the cases showed different pathological findings on histopathology which could have contributed to the rupture.

An uncommon presentation of giant cell tumor.

Giant Cell Tumors commonly occur at the ends of long bones. However in rare cases, they can occur in the bones of the hands and feet. Tumors in these locations occur in younger patients; in addition, these tumors are more commonly multifocal and are associated with a higher risk for local recurrence than tumors at the ends of long bones. Since lesions in the small bones may be multifocal, a patient with a giant cell tumor of the small bones should undergo a skeletal survey to exclude similar lesions elsewhere. Primary surgical treatment ranges from curettage or excision with or without bone grafting to amputation. The success of surgical treatment depends on the completeness with which the tumor was removed. We are presenting a case report of a 34 year old female, who presented with a swelling in the right hand, following trauma. X-ray of the hand showed an osteolytic expansile lesion at the base of the 1(st) metacarpal bone. The lesion was initially curetted and then treated by local resection with bone grafting. Histological examination revealed a typical benign giant cell tumor composed of closely packed stromal cells with a variable admixture of giant cells. Follow up at the end of one year did not reveal any recurrence of the tumor.

Crown ether derivatives of squaraine: new near-infrared-absorbing, redox-active fluoroionophores for alkali metal recognition

Three monoaza crown ether bisphenylsquaraine dyes, 1–3, with excellent solubilities in both polar and non-polar solvents, have been synthesised. The fluorescence yields of these red-sensitive dyes are dependent on the solvent polarity. They are capable of binding quantitatively with alkali metal ions, Li–, Na+, K+, as is seen from their fluorescence quenching and shift in the oxidation potentials. The fluorimetric and electrochemical experiments indicate the potential application of these dyes for cation recognition.