Convert strings to json in php

You need to use json_decode ("Decodes a JSON string") instead of json_encode ("Returns the JSON representation of a value").

Assuming your input is correct (and the example presented by you is), the return value will be an object representing the JSON data. You can also get the result as an array (see the docs for parameter reference).

EDIT: There must be another problem with your code, please post your complete code.
(My guess would be that you are not checking the returned value but expect json_decode to modify the parameter by reference and only check the parameter variable - that would explain why "nothing happens")

The following works:

(Ideone snippet)

PHP code:

<?php

$json = <<<JSON
[{"target_detail_id":"66351031","first_name":"Dorothy","last_name":"Smith","company":"Active Money Now","sic_code":"","position":"","target":"1300572544","website":"","email":"[email protected]","email_status":"","country":"Australia","city":"Broken Hill","postal_code":"2880","address":"Po Box 41","note":""}]
JSON;

$object = json_decode($json);
$array = json_decode($json, true);

var_dump($object);
var_dump($array);

output:

array(1) {
  [0]=>
  object(stdClass)#1 (15) {
    ["target_detail_id"]=>
    string(8) "66351031"
    ["first_name"]=>
    string(7) "Dorothy"
    ["last_name"]=>
    string(5) "Smith"
    ["company"]=>
    string(16) "Active Money Now"
    ["sic_code"]=>
    string(0) ""
    ["position"]=>
    string(0) ""
    ["target"]=>
    string(10) "1300572544"
    ["website"]=>
    string(0) ""
    ["email"]=>
    string(26) "[email protected]"
    ["email_status"]=>
    string(0) ""
    ["country"]=>
    string(9) "Australia"
    ["city"]=>
    string(11) "Broken Hill"
    ["postal_code"]=>
    string(4) "2880"
    ["address"]=>
    string(9) "Po Box 41"
    ["note"]=>
    string(0) ""
  }
}
array(1) {
  [0]=>
  array(15) {
    ["target_detail_id"]=>
    string(8) "66351031"
    ["first_name"]=>
    string(7) "Dorothy"
    ["last_name"]=>
    string(5) "Smith"
    ["company"]=>
    string(16) "Active Money Now"
    ["sic_code"]=>
    string(0) ""
    ["position"]=>
    string(0) ""
    ["target"]=>
    string(10) "1300572544"
    ["website"]=>
    string(0) ""
    ["email"]=>
    string(26) "[email protected]"
    ["email_status"]=>
    string(0) ""
    ["country"]=>
    string(9) "Australia"
    ["city"]=>
    string(11) "Broken Hill"
    ["postal_code"]=>
    string(4) "2880"
    ["address"]=>
    string(9) "Po Box 41"
    ["note"]=>
    string(0) ""
  }
}

EDIT2:

1. You don't need quotes around the json_decode parameter, just use

   json_decode($_REQUEST['derulo'], true);
   

   But this is not what is causing problems (it's just inefficient, php has to parse another variable in a string).

2. Your php snippet works, so you must be getting wrong data from the query. You can easily check for that with

   var_dump($_REQUEST['derulo']);
   

   You shouldn't be mixing sending data in both the url and over data, when using a GET request or switch to POST. I'd recommend letting jQuery take care of the serialization of the data, e.g.

   $.ajax({
       type: 'GET',
       url: 'index.php',
       data: {
         'task':'search',
         'wtd':'ul',
         'derulo':JSON.stringify($('#getdbresult').val())
       },
       beforeSend: function(){
           $('.the-modal').html('Updating...');
       }, 
       success: function(d){
           $('.the-modal').html(d);
           console.log(d);
       }
     });