Heteroleptic Cu(I) bis-diimine complexes as sensitizers in dye-sensitized solar cells (DSSCs): on some factors affecting intramolecular charge transfer.

A set of eight heteroleptic bis-diimine copper dye complexes with two different ancillary ligands (functionalised 2,9-dimethyl-1,10-phenanthroline (dmp) and functionalised 6,6'-diphenyl-2,2'-bipyridine (dpbpy)) are investigated for their potential use as sensitizers in dye-sensitized solar cells (DSSCs), using first principles density functional theory (DFT) and time dependent DFT (TDDFT). A detailed analysis of the structural properties, projected density of electronic states and Kohn-Sham energy levels, and optical absorption spectra in the UV-visible region reveals that substituting the thiophene group in the ancillary ligand, and enhancing conjugation in the anchoring ligand, lead to increase in the light harvesting efficiency (LHE). However, a natural transition orbital (NTO) analysis, shows that the nature of charge transfer depends mainly on the nature of the parent ancillary group and is not significantly affected by the structural modifications. Importantly, the lower energy excitations lead to favourable mixed metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT), as well as good electron injection. The best charge transfer directionality is found in the dmp-based dyes, particularly thiophene substituted dyes, thus making these the more effective sensitizers in DSSCs.

Quantum dots as an electron or hole acceptor: on some factors affecting charge transfer in dye-quantum dot composites.

We report a density functional theory (DFT)/time dependent DFT (TDDFT) computational investigation on some factors affecting the nature of charge transfer in CdS quantum dots (QDs) of two different sizes attached to one or two units of dyes among three species viz., coumarine (C343), fluorescein (FLU) and NKX-2388 (NKX). The direction and nature of charge transfers have been ascertained from natural transition orbital analysis. Factors affecting the charge transfer mechanism include the interaction of dyes with QDs, the interaction of a dye with another dye and the effect of solvation. The strength of interaction of the dye and QD depends on the orientation of the dye unit(s) and the type of anchoring group of the dyes and even the direction of charge transfer reverses for different orientation of the dye with respect to the QD in some systems. In addition, hybridized energy levels of the dye-QD composites are formed which leads to direct charge transfer. We observe both direct and indirect charge transfers for different excited states, which is indeed an interesting feature. Interestingly, when two dye molecules are attached to a QD, the direct charge transfer exists between dyes of the same species only. The energy levels, as well as corresponding absorption peaks, exhibit pronounced energy shifts in implicit solvation models.

Density functional investigation and some optical experiments on dye-sensitized quantum dots.

Dye-sensitized quantum dots (QDs) are promising candidates for dye-sensitized solar cells (DSSCs). Here, we report steady state (absorption and photoluminescence) optical measurements on several sizes of CdS QDs ligated with Coumarin 343 dye (C-343) and two different solvents, viz., chloroform and toluene. We further report detailed first principles density functional theory and time-dependent density functional theory studies of the geometric, electronic and optical (absorption and emission) properties of three different sized capped QDs, ligated with C-343 dye. The absorption spectrum shows a QD-size-independent peak, and another peak which shifts to blue with decrease in QD size. The first peak is found to arise from the dye molecule and the second one from the QD. Charge transfer using natural transition orbitals (NTOs) is found to occur from dye-to-QDs and is solvent-dependent. In the emission spectra, the luminescence intensity of the dye is quenched by the addition of the QD indicating a strong interaction between the QD and the dye.

Efficacy and safety of topical 2% rebamipide ophthalmic suspension in dry eye disease at tertiary care centre.

Purpose: To evaluate the effect and side effects of topical 2% rebamipide ophthalmic suspension in dry eye disease. Method: This prospective randomized case control study included total 80 patients (40 cases and 40 controls) of dry eye. Symptoms were graded according to OSDI scoring system and specific tests for dry eye included Tear film breakup time (TBUT), Schirmer's test, Fluorescein corneal staining (FCS), Rose Bengal staining) were performed. Case group received 2% rebamipide ophthalmic suspension four times daily and control group given carboxymethylcellulose 0.5% four times daily. The follow ups had done at two, six and twelve weeks. Results: The maximum numbers of patients were between 45-60 years. Patient with mild moderate and severe OSDI Score shows marked improvement. Mild TBUT score showed improvement but statistically not significant (P value-0.34). In moderate and severe TBUT Score statistically significant improvement (P value- 0.0001, 0.0001). In all grade FCS shows statistically significant improvement with p value-0.0001, 0.0001, and 0.028 respectively. Schirmer's test score in all cases had shown improvement but statistically not significant and P value were 0.09, 0.07, and 0.07 respectively. In mild, moderate and severe Rose Bengal staining statistically significant improvement (P value -0.027, 0.0001, and 0.04) .The only side effect was dysgeusia (10% patients). Conclusion: Rebamipide 2% ophthalmic suspension showed significant improvement in symptoms and signs of dry eye. It able to modify epithelial cell function, improve tear stability, and suppress inflammation suggests that it may be a first drug of choice for severe dry eye disease.

Evaluation of changes in corneal endothelium in chronic kidney disease.

Purpose: Chronic kidney disease (CKD) is an emerging health problem worldwide. In CKD corneal endothelial changes also occur probably due to accumulation of inflammatory cytokines and increased multiple toxic products. The aim of this study was to analyze the effect of CKD on corneal endothelium and correlate the findings with severity of disease with help of noninvasive technique. Methods: The study comprised 75 eyes of 75 cases divided into three groups with group A comprising of CKD cases on dialysis, group B of nondialysis CKD cases, and group C of controls. Each group had 25 cases each of either sex and between 15-80 age groups. All patients were investigated for blood urea, serum creatinine, and blood sugar and underwent complete ophthalmic examination of both eyes along with wide-field specular microscopy examination. Results: The majority of patients (33.3%) belonged to age range of 61-70 years with male predominance and the most common cause of CKD was found to be diabetes with 17 (34%) cases. We found normal corneal endothelial cell density (ECD) with the mean ECD of 2364.52 ± 397.72 mm2 in the dialysis group, 2467.8 ± 352.88 mm2 in nondialysis group, and 2521.68 ± 250.26 mm2 in the control group of patients. However, we found significant increase in coefficient of variation (CV) with 36 ± 5.8% in dialysis group, 37 ± 4.5% in nondialysis group and 32 ± 0.8% in controls (P = 0.001) and decreased hexagonality (Hx) with 47 ± 7.3% in dialysis group, 46 ± 4.7% in nondialysis group and 51 ± 6.7% in the controls (P = 0.031). This showed increased tendency of pleomorphism and polymegathism in corneal endothelial cells in CKD cases. No correlation was found between blood urea or serum creatinine levels with endothelial parameters in any group. Conclusion: CKD causes morphological changes like polymegathism and pleomorphism in corneal endothelium and hence these cases are more vulnerable and special care should be taken before any intraocular surgical procedure.