I am looking for a score that could measure non linear association between a categorical response variable or dependent variable (Y) and a continous explanatory or independent variable (X).
For your categorical dependent variable, how many levels (categories) are there? If there are more than 2, you can consider using an ordinal or multinomial logistic regression model.
Ok, this is actually a little better. You can use a standard logistic regression model with your continuous variable as the predictor. Since your categorical outcome has two levels, you'll just need to specify which is the outcome of interest and which is the reference. Some programs require you to re-code your categorical variables as a 0/1 binary variable with 1 as the outcome and 0 as the reference.