syntax to use binding expression inside href - angularjs

Question

I have created a nested accordian bootstrap panel. On clicking the parent(top most) panel heading - dropdown works fine but on clicking the child(sub panel heading) panel heading-dropdown wont work. I am retriving panel contents(sub panel heading and body) using angular $http.get rest api.
In this case, i think i did a mistake in syntax while linking the panel heading and panel body with its href and id attribute values( ng-href="{{productline_name}}" and id="{{productline_name}}" ).
Below code is placed inside top most panel body to create nested panel
<div class="panel-group col-lg-3" style="background-color:#505054;height:450px" id="accordion">
<div class="panel" style="background-color:#505054;color:#C1C1C1;border-bottom: 1px solid #eee;">
<h6>Clear Filter</h6>
</div>
<div class="panel" style="background-color:#505054;color:white;border-bottom: 1px solid white;">
<div class="panel-heading">
<h6>
<div class="accordion-toggle" data-toggle="collapse" data-parent="#accordion" href="#collapse1">PRODUCT</div>
</h6>
</div>
<div id="collapse1" class="panel-collapse collapse in">
<div class="panel-body">
<ul>
<li class="panel-title"><a ng-click="cfilter('all')"><h5>All Records</h5></a></li>
<li ng-repeat="pline in detpline" class="panel-group" id="accordion2">
<div class="panel" style="background-color:#505054;color:white;border-bottom: 1px solid white;">
<div class="panel-heading" ng-click="plinefunc(pline.productline_name)">
<h6>
<div class="accordion-toggle" data-toggle="collapse" data-parent="#accordion2" ng-href="{{productline_name}}">{{pline.productline_name}}</div>
</h6>
</div>
<div id="{{productline_name}}" class="panel-collapse collapse">
<div class="panel-body">
<ul>
<li class="panel-title" ng-repeat="prd in detp"><a ng-click="cfilter(prd.product_name)"><h5>{{prd.product_name}}</h5></a></li>
</ul>
</div>
</div>
</div>
</li>
</ul>
</div>
</div>
</div>
</div>
Can any one help in this? what is the correct syntax to use to link panel heading and panel body via binding expresion?
Note: I am using binding expression for linking only to avoid opening all other sub panel heading contents on-clicking one of the sub panel heading.